search.xml

<?xml version="1.0" encoding="utf-8"?>
<search>
  <entry>
    <title>消息通知系统</title>
    <url>/2026/03/07/notification-system/</url>
    <content><![CDATA[<link rel="stylesheet" class="aplayer-secondary-style-marker" href="\assets\css\APlayer.min.css"><script src="\assets\js\APlayer.min.js" class="aplayer-secondary-script-marker"></script><p>最近在给自己的博客系统补一些互动功能，比如点赞、收藏、关注之类的。<br>做着做着就发现一个问题：用户其实不知道别人对他做了什么。</p>
<p>比如：</p>
<ul>
<li>有人点赞了你的文章</li>
<li>有人收藏了你的文章</li>
<li>有人关注了你</li>
<li>或者有人给你发了私信</li>
</ul>
<p>如果没有通知系统，这些行为基本就是“悄悄发生”，用户完全感知不到。</p>
<p>所以就顺手把消息通知模块也做了一遍。这篇文章主要记录一下整个实现过程，以及中间踩的一些坑。</p>
<h2 id="一、先想清楚通知是什么"><a href="#一、先想清楚通知是什么" class="headerlink" title="一、先想清楚通知是什么"></a>一、先想清楚通知是什么</h2><p>一开始我其实想过几种设计，比如：</p>
<ul>
<li>点赞通知一张表</li>
<li>评论通知一张表</li>
<li>关注通知一张表</li>
</ul>
<p>但很快发现这样会非常麻烦。</p>
<p>更简单的方式其实是把通知抽象成一条行为记录：</p>
<p>某个用户对另一个用户做了一件事情。</p>
<p>于是通知结构其实只需要几个关键字段：</p>
<ul>
<li>通知接收者</li>
<li>操作发起者</li>
<li>操作类型</li>
<li>是否已读</li>
<li>创建时间</li>
<li>（如果涉及文章）文章 ID</li>
</ul>
<p>于是最后设计了一张 <code>notifications</code> 表。</p>
<figure class="highlight sql"><table><tr><td class="code"><pre><span class="line"><span class="keyword">CREATE TABLE</span> notifications (</span><br><span class="line">    id <span class="type">BIGINT</span> <span class="keyword">PRIMARY KEY</span> AUTO_INCREMENT,</span><br><span class="line">    user_id <span class="type">BIGINT</span> <span class="keyword">NOT NULL</span>,</span><br><span class="line">    actor_id <span class="type">BIGINT</span> <span class="keyword">NOT NULL</span>,</span><br><span class="line">    type <span class="type">VARCHAR</span>(<span class="number">50</span>) <span class="keyword">NOT NULL</span>,</span><br><span class="line">    article_id <span class="type">BIGINT</span>,</span><br><span class="line">    message_content <span class="type">VARCHAR</span>(<span class="number">1000</span>),</span><br><span class="line">    is_read <span class="type">BOOLEAN</span> <span class="keyword">DEFAULT</span> <span class="literal">FALSE</span>,</span><br><span class="line">    created_at <span class="type">TIMESTAMP</span> <span class="keyword">DEFAULT</span> <span class="built_in">CURRENT_TIMESTAMP</span></span><br><span class="line">);</span><br></pre></td></tr></table></figure>

<p>这里有两个字段比较关键。</p>
<p><code>user_id</code><br>表示通知接收者。</p>
<p>比如：</p>
<p>“A 给 B 点赞”</p>
<p>这里 <code>user_id = B</code>。</p>
<p><code>actor_id</code><br>表示触发行为的人。</p>
<p>同样这个例子里：</p>
<p><code>actor_id = A</code>。</p>
<p><code>type</code><br>通知类型，用来区分不同通知。</p>
<p>目前我的系统里大概有几种：</p>
<ul>
<li><code>like</code></li>
<li><code>favorite</code></li>
<li><code>comment</code></li>
<li><code>follow</code></li>
<li><code>private_message</code></li>
</ul>
<p>这种设计的好处是以后扩展会很方便，比如以后想加：</p>
<ul>
<li>系统通知</li>
<li>管理员警告</li>
<li>评论回复提醒</li>
</ul>
<p>都可以直接扩展 <code>type</code>。</p>
<h2 id="二、通知是在哪生成的"><a href="#二、通知是在哪生成的" class="headerlink" title="二、通知是在哪生成的"></a>二、通知是在哪生成的</h2><p>通知本身其实只是一个附属功能，它一定是伴随着其他业务产生的。</p>
<p>比如：</p>
<ul>
<li>点赞成功</li>
<li>评论成功</li>
<li>关注成功</li>
</ul>
<p>所以我的做法是把通知逻辑统一封装在一个 <code>NotificationService</code> 里。</p>
<p>各个业务模块只需要在操作成功之后调用它。</p>
<p>比如点赞文章的时候：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line">notificationService.createNotification(</span><br><span class="line">    article.getAuthor().getId(),</span><br><span class="line">    userId,</span><br><span class="line">    <span class="string">&quot;like&quot;</span>,</span><br><span class="line">    articleId</span><br><span class="line">);</span><br></pre></td></tr></table></figure>

<p>收藏、关注基本也是同样的逻辑。</p>
<p>这样做的好处是：</p>
<ul>
<li>通知逻辑和业务逻辑是解耦的</li>
<li>以后如果要改通知系统，只需要改一个地方</li>
</ul>
<h2 id="三、未读通知计数"><a href="#三、未读通知计数" class="headerlink" title="三、未读通知计数"></a>三、未读通知计数</h2><p>通知列表其实很好做，分页查数据库就行。</p>
<p>真正麻烦的是未读通知数。</p>
<p>因为很多地方都会显示它，比如：</p>
<ul>
<li>页面右上角的小红点</li>
<li>消息中心</li>
<li>移动端提示</li>
</ul>
<p>如果每次都查数据库：</p>
<p><code>countByUserIdAndIsReadFalse(userId)</code></p>
<p>在用户量大的情况下其实挺浪费资源的。</p>
<p>所以我给未读计数加了一层 Redis 缓存。</p>
<p>逻辑很简单：</p>
<ul>
<li>先查 Redis</li>
<li>没命中再查数据库</li>
<li>查到结果写回 Redis</li>
</ul>
<p>代码大概是这样：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="type">long</span> <span class="title function_">getUnreadCount</span><span class="params">(Long userId)</span> &#123;</span><br><span class="line"></span><br><span class="line">    <span class="type">String</span> <span class="variable">key</span> <span class="operator">=</span> <span class="string">&quot;notification:unread:count:&quot;</span> + userId;</span><br><span class="line"></span><br><span class="line">    <span class="type">Object</span> <span class="variable">cached</span> <span class="operator">=</span> redisUtil.get(key);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">if</span> (cached != <span class="literal">null</span>) &#123;</span><br><span class="line">        <span class="keyword">return</span> Long.parseLong(cached.toString());</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="type">long</span> <span class="variable">count</span> <span class="operator">=</span> notificationRepository</span><br><span class="line">            .countByUserIdAndIsReadFalse(userId);</span><br><span class="line"></span><br><span class="line">    redisUtil.set(key, count, <span class="number">1800</span>);</span><br><span class="line"></span><br><span class="line">    <span class="keyword">return</span> count;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>这样大部分请求都会直接命中缓存。</p>
<h2 id="四、缓存更新策略"><a href="#四、缓存更新策略" class="headerlink" title="四、缓存更新策略"></a>四、缓存更新策略</h2><p>缓存加上去之后，还要解决一个问题：什么时候更新 Redis？</p>
<p>我的策略是：</p>
<p>新通知产生的时候：</p>
<p>Redis <code>count +1</code>，但前提是缓存已经存在。</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">if</span> (redisUtil.hasKey(countKey)) &#123;</span><br><span class="line">    redisUtil.incr(countKey, <span class="number">1</span>);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>如果缓存不存在就不管，因为下次查询会重新建立缓存。</p>
<p>而当通知被标记为已读时，我一开始的想法是：</p>
<p><code>count -1</code></p>
<p>但后来发现这个方案在并发情况下其实容易出问题。</p>
<p>比如：</p>
<ul>
<li>用户同时标记多条通知</li>
<li>或者新通知和标记已读同时发生</li>
</ul>
<p>最后可能导致计数不准确。</p>
<p>所以最后我选择了一个更简单的方法：</p>
<p>直接删除缓存。</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line">redisUtil.delete(countKey);</span><br></pre></td></tr></table></figure>

<p>这样下次查询时会重新统计数据库。</p>
<p>虽然多查了一次数据库，但逻辑会简单很多，也更安全。</p>
<h2 id="五、数据库索引"><a href="#五、数据库索引" class="headerlink" title="五、数据库索引"></a>五、数据库索引</h2><p>通知列表是一个比较典型的查询：</p>
<figure class="highlight sql"><table><tr><td class="code"><pre><span class="line"><span class="keyword">WHERE</span> user_id <span class="operator">=</span> ?</span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span> created_at <span class="keyword">DESC</span></span><br></pre></td></tr></table></figure>

<p>另外一个高频查询是：</p>
<figure class="highlight sql"><table><tr><td class="code"><pre><span class="line"><span class="keyword">WHERE</span> user_id <span class="operator">=</span> ?</span><br><span class="line"><span class="keyword">AND</span> is_read <span class="operator">=</span> <span class="literal">false</span></span><br></pre></td></tr></table></figure>

<p>所以我给表加了一个联合索引：</p>
<figure class="highlight sql"><table><tr><td class="code"><pre><span class="line">INDEX idx_user_read (user_id, is_read, created_at <span class="keyword">DESC</span>)</span><br></pre></td></tr></table></figure>

<p>这个索引基本可以覆盖：</p>
<ul>
<li>通知列表查询</li>
<li>未读通知查询</li>
<li>未读数量统计</li>
</ul>
<p>效果还是挺明显的。</p>
<h2 id="六、一个小坑"><a href="#六、一个小坑" class="headerlink" title="六、一个小坑"></a>六、一个小坑</h2><p>功能写完之后测试的时候，我发现一个很奇怪的现象：</p>
<p>我给自己的文章点赞，系统也给我发了一条通知。</p>
<p>技术上没问题，但体验非常奇怪。</p>
<p>后来就在创建通知的时候加了一句判断：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">if</span> (userId.equals(actorId)) &#123;</span><br><span class="line">    <span class="keyword">return</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>这样就不会出现自己通知自己的情况了。</p>
<h2 id="七、如果以后要升级"><a href="#七、如果以后要升级" class="headerlink" title="七、如果以后要升级"></a>七、如果以后要升级</h2><p>现在这个通知系统其实是一个比较基础的实现，如果继续完善的话还有不少可以做的。</p>
<p>比如：</p>
<h3 id="1-实时通知"><a href="#1-实时通知" class="headerlink" title="1. 实时通知"></a>1. 实时通知</h3><p>现在前端是每隔一段时间轮询接口。</p>
<p>如果用 WebSocket，其实可以做到真正的实时推送。</p>
<h3 id="2-消息队列"><a href="#2-消息队列" class="headerlink" title="2. 消息队列"></a>2. 消息队列</h3><p>现在通知是同步创建的。</p>
<p>如果以后并发比较高，可以把通知放到 MQ 里异步处理。</p>
<p>流程会变成：</p>
<p>用户操作<br>↓<br>发送通知事件<br>↓<br>消息队列<br>↓<br>通知服务消费<br>↓<br>写入数据库</p>
<p>这样可以减少主业务的延迟。</p>
]]></content>
      <categories>
        <category>项目总结</category>
      </categories>
      <tags>
        <tag>Spring Boot</tag>
        <tag>Redis</tag>
        <tag>数据库设计</tag>
        <tag>系统设计</tag>
        <tag>通知系统</tag>
      </tags>
  </entry>
  <entry>
    <title>设计模式面试复习笔记</title>
    <url>/2026/03/16/design-pattern-interview-notes/</url>
    <content><![CDATA[<link rel="stylesheet" class="aplayer-secondary-style-marker" href="\assets\css\APlayer.min.css"><script src="\assets\js\APlayer.min.js" class="aplayer-secondary-script-marker"></script><p>在准备后端面试时，设计模式几乎是绕不开的话题。<br>很多框架（例如 Spring）内部大量使用了设计模式，因此理解这些模式不仅有助于写业务代码，也能更好地理解框架源码。</p>
<p>设计模式本质上是：</p>
<blockquote>
<p>针对常见软件设计问题的通用解决方案。</p>
</blockquote>
<p>经典设计模式共有 23 种，通常分为三大类：</p>
<table>
<thead>
<tr>
<th>类型</th>
<th>作用</th>
</tr>
</thead>
<tbody><tr>
<td>创建型模式</td>
<td>解决对象创建问题</td>
</tr>
<tr>
<td>结构型模式</td>
<td>解决类或对象组合问题</td>
</tr>
<tr>
<td>行为型模式</td>
<td>解决对象之间交互问题</td>
</tr>
</tbody></table>
<p>面试中最常问的其实只有几种，下面整理几个高频模式。</p>
<h2 id="一、单例模式（Singleton）"><a href="#一、单例模式（Singleton）" class="headerlink" title="一、单例模式（Singleton）"></a>一、单例模式（Singleton）</h2><h3 id="1-解决的问题"><a href="#1-解决的问题" class="headerlink" title="1. 解决的问题"></a>1. 解决的问题</h3><p>确保某个类在系统中只有一个实例，并提供全局访问方式。</p>
<p>典型场景：</p>
<ul>
<li>配置管理</li>
<li>日志对象</li>
<li>数据库连接池</li>
<li>Spring Bean 默认单例</li>
</ul>
<h3 id="2-基本实现（线程不安全）"><a href="#2-基本实现（线程不安全）" class="headerlink" title="2. 基本实现（线程不安全）"></a>2. 基本实现（线程不安全）</h3><figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">Singleton</span> &#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> Singleton instance;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="title function_">Singleton</span><span class="params">()</span> &#123;&#125;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">static</span> Singleton <span class="title function_">getInstance</span><span class="params">()</span> &#123;</span><br><span class="line">        <span class="keyword">if</span> (instance == <span class="literal">null</span>) &#123;</span><br><span class="line">            instance = <span class="keyword">new</span> <span class="title class_">Singleton</span>();</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">return</span> instance;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>这个版本在多线程环境下不安全。</p>
<h3 id="3-面试常问：线程安全实现（DCL）"><a href="#3-面试常问：线程安全实现（DCL）" class="headerlink" title="3. 面试常问：线程安全实现（DCL）"></a>3. 面试常问：线程安全实现（DCL）</h3><figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">Singleton</span> &#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">volatile</span> Singleton instance;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="title function_">Singleton</span><span class="params">()</span> &#123;&#125;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">static</span> Singleton <span class="title function_">getInstance</span><span class="params">()</span> &#123;</span><br><span class="line">        <span class="keyword">if</span> (instance == <span class="literal">null</span>) &#123;</span><br><span class="line">            <span class="keyword">synchronized</span> (Singleton.class) &#123;</span><br><span class="line">                <span class="keyword">if</span> (instance == <span class="literal">null</span>) &#123;</span><br><span class="line">                    instance = <span class="keyword">new</span> <span class="title class_">Singleton</span>();</span><br><span class="line">                &#125;</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">return</span> instance;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>关键点：</p>
<ul>
<li><code>volatile</code> 防止指令重排</li>
<li>双重检查减少锁开销</li>
</ul>
<h3 id="4-更简单写法（推荐）"><a href="#4-更简单写法（推荐）" class="headerlink" title="4. 更简单写法（推荐）"></a>4. 更简单写法（推荐）</h3><figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">Singleton</span> &#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="type">Singleton</span> <span class="variable">INSTANCE</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">Singleton</span>();</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="title function_">Singleton</span><span class="params">()</span> &#123;&#125;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">static</span> Singleton <span class="title function_">getInstance</span><span class="params">()</span> &#123;</span><br><span class="line">        <span class="keyword">return</span> INSTANCE;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>利用类加载机制保证线程安全，写法也更简洁。</p>
<h2 id="二、工厂模式（Factory）"><a href="#二、工厂模式（Factory）" class="headerlink" title="二、工厂模式（Factory）"></a>二、工厂模式（Factory）</h2><h3 id="1-解决的问题-1"><a href="#1-解决的问题-1" class="headerlink" title="1. 解决的问题"></a>1. 解决的问题</h3><p>当对象创建逻辑复杂时，将对象创建过程封装起来。</p>
<p>核心思想：</p>
<blockquote>
<p>让对象的创建和使用分离。</p>
</blockquote>
<h3 id="2-简单工厂示例"><a href="#2-简单工厂示例" class="headerlink" title="2. 简单工厂示例"></a>2. 简单工厂示例</h3><p>假设系统支持多种消息发送方式：邮件、短信、推送。</p>
<p>统一接口：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">interface</span> <span class="title class_">MessageSender</span> &#123;</span><br><span class="line">    <span class="keyword">void</span> <span class="title function_">send</span><span class="params">(String message)</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>实现类：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">EmailSender</span> <span class="keyword">implements</span> <span class="title class_">MessageSender</span> &#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">send</span><span class="params">(String message)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;发送邮件：&quot;</span> + message);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">SmsSender</span> <span class="keyword">implements</span> <span class="title class_">MessageSender</span> &#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">send</span><span class="params">(String message)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;发送短信：&quot;</span> + message);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>工厂类：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">MessageFactory</span> &#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">static</span> MessageSender <span class="title function_">create</span><span class="params">(String type)</span> &#123;</span><br><span class="line">        <span class="keyword">if</span> (<span class="string">&quot;email&quot;</span>.equals(type)) &#123;</span><br><span class="line">            <span class="keyword">return</span> <span class="keyword">new</span> <span class="title class_">EmailSender</span>();</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">if</span> (<span class="string">&quot;sms&quot;</span>.equals(type)) &#123;</span><br><span class="line">            <span class="keyword">return</span> <span class="keyword">new</span> <span class="title class_">SmsSender</span>();</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">throw</span> <span class="keyword">new</span> <span class="title class_">IllegalArgumentException</span>(<span class="string">&quot;unsupported type: &quot;</span> + type);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>使用方式：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="type">MessageSender</span> <span class="variable">sender</span> <span class="operator">=</span> MessageFactory.create(<span class="string">&quot;email&quot;</span>);</span><br><span class="line">sender.send(<span class="string">&quot;hello&quot;</span>);</span><br></pre></td></tr></table></figure>

<h3 id="3-面试常问"><a href="#3-面试常问" class="headerlink" title="3. 面试常问"></a>3. 面试常问</h3><p>简单工厂 vs 工厂方法：</p>
<table>
<thead>
<tr>
<th>模式</th>
<th>特点</th>
</tr>
</thead>
<tbody><tr>
<td>简单工厂</td>
<td>一个工厂类创建所有对象</td>
</tr>
<tr>
<td>工厂方法</td>
<td>每种产品对应一个工厂</td>
</tr>
</tbody></table>
<p>工厂方法接口示例：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">interface</span> <span class="title class_">Factory</span> &#123;</span><br><span class="line">    MessageSender <span class="title function_">create</span><span class="params">()</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h2 id="三、策略模式（Strategy）"><a href="#三、策略模式（Strategy）" class="headerlink" title="三、策略模式（Strategy）"></a>三、策略模式（Strategy）</h2><h3 id="1-解决的问题-2"><a href="#1-解决的问题-2" class="headerlink" title="1. 解决的问题"></a>1. 解决的问题</h3><p>当一个功能有多种实现方式时，可以在运行时动态选择算法。</p>
<p>核心思想：</p>
<blockquote>
<p>将不同算法封装为独立策略。</p>
</blockquote>
<h3 id="2-示例：支付系统"><a href="#2-示例：支付系统" class="headerlink" title="2. 示例：支付系统"></a>2. 示例：支付系统</h3><p>支付策略接口：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">interface</span> <span class="title class_">PayStrategy</span> &#123;</span><br><span class="line">    <span class="keyword">void</span> <span class="title function_">pay</span><span class="params">(<span class="type">int</span> amount)</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>支付宝策略：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">AlipayStrategy</span> <span class="keyword">implements</span> <span class="title class_">PayStrategy</span> &#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">pay</span><span class="params">(<span class="type">int</span> amount)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;支付宝支付：&quot;</span> + amount);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>微信策略：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">WechatPayStrategy</span> <span class="keyword">implements</span> <span class="title class_">PayStrategy</span> &#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">pay</span><span class="params">(<span class="type">int</span> amount)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;微信支付：&quot;</span> + amount);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>使用方式：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="type">PayStrategy</span> <span class="variable">strategy</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">AlipayStrategy</span>();</span><br><span class="line">strategy.pay(<span class="number">100</span>);</span><br></pre></td></tr></table></figure>

<h3 id="3-面试延伸"><a href="#3-面试延伸" class="headerlink" title="3. 面试延伸"></a>3. 面试延伸</h3><p>Spring 中大量使用策略模式，例如：</p>
<ul>
<li><code>HandlerMapping</code></li>
<li><code>HandlerAdapter</code></li>
<li><code>ViewResolver</code></li>
</ul>
<p>通过接口定义统一行为，不同实现类提供不同策略。</p>
<h2 id="四、观察者模式（Observer）"><a href="#四、观察者模式（Observer）" class="headerlink" title="四、观察者模式（Observer）"></a>四、观察者模式（Observer）</h2><h3 id="1-解决的问题-3"><a href="#1-解决的问题-3" class="headerlink" title="1. 解决的问题"></a>1. 解决的问题</h3><p>当一个对象状态变化时，自动通知其他对象。</p>
<p>核心思想：</p>
<blockquote>
<p>发布-订阅机制。</p>
</blockquote>
<h3 id="2-示例"><a href="#2-示例" class="headerlink" title="2. 示例"></a>2. 示例</h3><p>观察者接口：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">interface</span> <span class="title class_">Observer</span> &#123;</span><br><span class="line">    <span class="keyword">void</span> <span class="title function_">update</span><span class="params">(String message)</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>具体观察者：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">UserObserver</span> <span class="keyword">implements</span> <span class="title class_">Observer</span> &#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">final</span> String name;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">public</span> <span class="title function_">UserObserver</span><span class="params">(String name)</span> &#123;</span><br><span class="line">        <span class="built_in">this</span>.name = name;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">update</span><span class="params">(String message)</span> &#123;</span><br><span class="line">        System.out.println(name + <span class="string">&quot; 收到通知：&quot;</span> + message);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>被观察对象：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">import</span> java.util.ArrayList;</span><br><span class="line"><span class="keyword">import</span> java.util.List;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">NotificationService</span> &#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">final</span> List&lt;Observer&gt; observers = <span class="keyword">new</span> <span class="title class_">ArrayList</span>&lt;&gt;();</span><br><span class="line"></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">addObserver</span><span class="params">(Observer observer)</span> &#123;</span><br><span class="line">        observers.add(observer);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">notifyObservers</span><span class="params">(String message)</span> &#123;</span><br><span class="line">        <span class="keyword">for</span> (Observer observer : observers) &#123;</span><br><span class="line">            observer.update(message);</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h3 id="3-实际应用"><a href="#3-实际应用" class="headerlink" title="3. 实际应用"></a>3. 实际应用</h3><p>典型场景：</p>
<ul>
<li>Spring 事件机制</li>
<li>消息订阅</li>
<li>GUI 事件监听</li>
<li>MQ 消费者模型</li>
</ul>
<h2 id="五、代理模式（Proxy）"><a href="#五、代理模式（Proxy）" class="headerlink" title="五、代理模式（Proxy）"></a>五、代理模式（Proxy）</h2><h3 id="1-解决的问题-4"><a href="#1-解决的问题-4" class="headerlink" title="1. 解决的问题"></a>1. 解决的问题</h3><p>为对象提供一个代理对象，控制对原对象的访问。</p>
<p>常见用途：</p>
<ul>
<li>权限控制</li>
<li>日志记录</li>
<li>延迟加载</li>
<li>AOP</li>
</ul>
<h3 id="2-示例-1"><a href="#2-示例-1" class="headerlink" title="2. 示例"></a>2. 示例</h3><p>接口：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">interface</span> <span class="title class_">Service</span> &#123;</span><br><span class="line">    <span class="keyword">void</span> <span class="title function_">execute</span><span class="params">()</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>真实对象：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">RealService</span> <span class="keyword">implements</span> <span class="title class_">Service</span> &#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">execute</span><span class="params">()</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;执行真实业务&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>代理对象：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">ServiceProxy</span> <span class="keyword">implements</span> <span class="title class_">Service</span> &#123;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">final</span> Service realService;</span><br><span class="line"></span><br><span class="line">    <span class="keyword">public</span> <span class="title function_">ServiceProxy</span><span class="params">(Service realService)</span> &#123;</span><br><span class="line">        <span class="built_in">this</span>.realService = realService;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">execute</span><span class="params">()</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;权限检查&quot;</span>);</span><br><span class="line">        realService.execute();</span><br><span class="line">        System.out.println(<span class="string">&quot;记录日志&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h3 id="3-面试重点"><a href="#3-面试重点" class="headerlink" title="3. 面试重点"></a>3. 面试重点</h3><p>Spring AOP 本质就是代理模式：</p>
<ul>
<li>JDK 动态代理</li>
<li>CGLIB 动态代理</li>
</ul>
<h2 id="六、面试中常见问题"><a href="#六、面试中常见问题" class="headerlink" title="六、面试中常见问题"></a>六、面试中常见问题</h2><h3 id="1-Spring-用到了哪些设计模式？"><a href="#1-Spring-用到了哪些设计模式？" class="headerlink" title="1. Spring 用到了哪些设计模式？"></a>1. Spring 用到了哪些设计模式？</h3><p>常见答案：</p>
<ul>
<li>单例模式（Bean 默认单例）</li>
<li>工厂模式（<code>BeanFactory</code>）</li>
<li>策略模式（<code>HandlerMapping</code>）</li>
<li>代理模式（AOP）</li>
<li>模板方法模式（<code>JdbcTemplate</code>）</li>
<li>观察者模式（Spring Event）</li>
</ul>
<h3 id="2-单例模式为什么需要-volatile？"><a href="#2-单例模式为什么需要-volatile？" class="headerlink" title="2. 单例模式为什么需要 volatile？"></a>2. 单例模式为什么需要 <code>volatile</code>？</h3><p>因为 JVM 可能发生指令重排。</p>
<p>对象创建步骤本应是：</p>
<ol>
<li>分配内存</li>
<li>初始化对象</li>
<li>指向对象</li>
</ol>
<p>但可能重排为：</p>
<ol>
<li>分配内存</li>
<li>指向对象</li>
<li>初始化对象</li>
</ol>
<p>这样会导致其他线程拿到“未初始化完成”的对象。</p>
<p><code>volatile</code> 可以禁止这类重排。</p>
<h3 id="3-策略模式和工厂模式区别"><a href="#3-策略模式和工厂模式区别" class="headerlink" title="3. 策略模式和工厂模式区别"></a>3. 策略模式和工厂模式区别</h3><table>
<thead>
<tr>
<th>模式</th>
<th>关注点</th>
</tr>
</thead>
<tbody><tr>
<td>工厂模式</td>
<td>对象创建</td>
</tr>
<tr>
<td>策略模式</td>
<td>算法选择</td>
</tr>
</tbody></table>
<p>很多时候这两个模式会结合使用：先由工厂创建策略对象，再在运行时切换策略。</p>
<h2 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h2><p>面试中复习设计模式，不需要死记 23 种模式的所有细节。<br>更重要的是把握这三点：</p>
<ul>
<li>这个模式解决了什么问题</li>
<li>在项目中哪里能用</li>
<li>在 Spring 或常见框架中有什么对应落地</li>
</ul>
<p>如果你能结合业务场景讲清楚“为什么用、怎么用、有哪些权衡”，通常会比只背定义更有说服力。</p>
]]></content>
      <categories>
        <category>项目总结</category>
      </categories>
      <tags>
        <tag>Java</tag>
        <tag>设计模式</tag>
        <tag>Spring</tag>
        <tag>面试复习</tag>
      </tags>
  </entry>
  <entry>
    <title>为 Hexo 博客添加 Giscus 评论系统</title>
    <url>/2026/02/08/add-giscus-comments/</url>
    <content><![CDATA[<link rel="stylesheet" class="aplayer-secondary-style-marker" href="\assets\css\APlayer.min.css"><script src="\assets\js\APlayer.min.js" class="aplayer-secondary-script-marker"></script><p>为博客添加评论功能是增强互动性的重要一步。这篇文章记录我为 Hexo + Butterfly 博客集成 Giscus 评论系统的完整过程。</p>
<h2 id="为什么选择-Giscus？"><a href="#为什么选择-Giscus？" class="headerlink" title="为什么选择 Giscus？"></a>为什么选择 Giscus？</h2><p>在众多评论系统中（Disqus、Gitalk、Valine 等），我选择 Giscus 的原因：</p>
<ul>
<li><strong>无需数据库</strong>：不需要额外的后端服务</li>
<li><strong>支持 Markdown</strong>：评论可以使用完整的 Markdown 语法</li>
<li><strong>主题适配</strong>：自动适配网站的明暗主题</li>
<li><strong>完全免费</strong>：无任何使用限制</li>
<li><strong>隐私友好</strong>：不会追踪用户数据</li>
</ul>
<h2 id="准备工作"><a href="#准备工作" class="headerlink" title="准备工作"></a>准备工作</h2><h3 id="1-创建评论存储仓库"><a href="#1-创建评论存储仓库" class="headerlink" title="1. 创建评论存储仓库"></a>1. 创建评论存储仓库</h3><p>在 GitHub 上创建一个公开仓库用于存储评论数据。</p>
<p><strong>关键设置：</strong></p>
<ul>
<li>仓库必须是 <strong>public</strong>（公开）</li>
<li>启用 <strong>Discussions</strong> 功能：进入仓库 Settings → Features → 勾选 Discussions</li>
</ul>
<h3 id="2-安装-Giscus-App"><a href="#2-安装-Giscus-App" class="headerlink" title="2. 安装 Giscus App"></a>2. 安装 Giscus App</h3><p>访问 <a href="https://github.com/apps/giscus">Giscus App</a> 并安装到你的评论仓库：</p>
<ol>
<li>点击 “Install”</li>
<li>选择 “Only select repositories”</li>
<li>选中刚才创建的仓库</li>
<li>授权安装</li>
</ol>
<h2 id="配置-Giscus"><a href="#配置-Giscus" class="headerlink" title="配置 Giscus"></a>配置 Giscus</h2><h3 id="3-获取配置参数"><a href="#3-获取配置参数" class="headerlink" title="3. 获取配置参数"></a>3. 获取配置参数</h3><p>访问 <a href="https://giscus.app/zh-CN">Giscus 官网</a> 进行配置：</p>
<p><strong>① 仓库信息</strong></p>
<figure class="highlight plaintext"><table><tr><td class="code"><pre><span class="line">仓库：用户名/仓库名</span><br></pre></td></tr></table></figure>

<p><strong>② Discussion 分类</strong></p>
<p>选择 “Announcements” 类型（推荐），这样只有仓库维护者可以创建新讨论，但所有人都能评论。</p>
<p><strong>③ 映射方式</strong></p>
<p>选择 “pathname”（路径名），这样每篇文章会根据 URL 路径自动创建对应的 Discussion。</p>
<p><strong>④ 主题</strong></p>
<p>选择 “preferred_color_scheme”（跟随系统），自动适配明暗模式。</p>
<p><strong>⑤ 获取关键 ID</strong></p>
<p>配置完成后，Giscus 会生成一段代码，从中提取两个关键参数：</p>
<figure class="highlight html"><table><tr><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">script</span> <span class="attr">src</span>=<span class="string">&quot;https://giscus.app/client.js&quot;</span></span></span><br><span class="line"><span class="tag">        <span class="attr">data-repo</span>=<span class="string">&quot;用户名/仓库名&quot;</span></span></span><br><span class="line"><span class="tag">        <span class="attr">data-repo-id</span>=<span class="string">&quot;XXXXXXXXXXX&quot;</span>          &lt;!<span class="attr">--</span> <span class="attr">这是</span> <span class="attr">repo_id</span> <span class="attr">--</span>&gt;</span><span class="language-handlebars"><span class="language-xml"></span></span></span><br><span class="line"><span class="language-xml"><span class="language-handlebars">        data-category=&quot;Announcements&quot;</span></span></span><br><span class="line"><span class="language-xml"><span class="language-handlebars">        data-category-id=&quot;XXXXXXXXXXXX&quot; <span class="comment">&lt;!-- 这是 category_id --&gt;</span></span></span></span><br><span class="line"><span class="language-xml"><span class="language-handlebars">        ...&gt;</span></span></span><br><span class="line"><span class="language-xml"><span class="language-handlebars"></span></span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br></pre></td></tr></table></figure>

<p>记下 <code>data-repo-id</code> 和 <code>data-category-id</code> 的值。</p>
<h2 id="在-Butterfly-主题中配置"><a href="#在-Butterfly-主题中配置" class="headerlink" title="在 Butterfly 主题中配置"></a>在 Butterfly 主题中配置</h2><h3 id="4-修改主题配置文件"><a href="#4-修改主题配置文件" class="headerlink" title="4. 修改主题配置文件"></a>4. 修改主题配置文件</h3><p>打开 <code>themes/butterfly/_config.yml</code>，找到 <code>comments</code> 部分：</p>
<figure class="highlight yaml"><table><tr><td class="code"><pre><span class="line"><span class="attr">comments:</span></span><br><span class="line">  <span class="comment"># 选择评论系统</span></span><br><span class="line">  <span class="attr">use:</span> <span class="string">giscus</span></span><br><span class="line">  <span class="attr">text:</span> <span class="literal">true</span></span><br><span class="line">  <span class="comment"># lazyload: 懒加载评论</span></span><br><span class="line">  <span class="attr">lazyload:</span> <span class="literal">false</span></span><br><span class="line">  <span class="comment"># count: 显示评论数</span></span><br><span class="line">  <span class="attr">count:</span> <span class="literal">true</span></span><br><span class="line">  <span class="comment"># card_post_count: 在卡片上显示评论数</span></span><br><span class="line">  <span class="attr">card_post_count:</span> <span class="literal">true</span></span><br></pre></td></tr></table></figure>

<p>然后找到 <code>giscus</code> 配置段，填入参数：</p>
<figure class="highlight yaml"><table><tr><td class="code"><pre><span class="line"><span class="attr">giscus:</span></span><br><span class="line">  <span class="attr">repo:</span> <span class="string">用户名/仓库名</span></span><br><span class="line">  <span class="attr">repo_id:</span> <span class="string">XXXXXXXXXXXXXXXXXX</span></span><br><span class="line">  <span class="attr">category_id:</span> <span class="string">XXXXXXXXXXXXXXXXXX</span></span><br><span class="line">  <span class="attr">theme:</span></span><br><span class="line">    <span class="attr">light:</span> <span class="string">light</span></span><br><span class="line">    <span class="attr">dark:</span> <span class="string">dark</span></span><br><span class="line">  <span class="attr">option:</span></span><br><span class="line">    <span class="attr">data-mapping:</span> <span class="string">pathname</span></span><br><span class="line">    <span class="attr">data-strict:</span> <span class="number">0</span></span><br><span class="line">    <span class="attr">data-reactions-enabled:</span> <span class="number">1</span></span><br><span class="line">    <span class="attr">data-emit-metadata:</span> <span class="number">0</span></span><br><span class="line">    <span class="attr">data-input-position:</span> <span class="string">bottom</span></span><br><span class="line">    <span class="attr">data-lang:</span> <span class="string">zh-CN</span></span><br><span class="line">    <span class="attr">data-loading:</span> <span class="string">lazy</span></span><br></pre></td></tr></table></figure>

<p><strong>参数说明：</strong></p>
<ul>
<li><code>repo</code>: 你的评论仓库（格式：用户名&#x2F;仓库名）</li>
<li><code>repo_id</code>: 从 Giscus 获取的仓库 ID</li>
<li><code>category_id</code>: 从 Giscus 获取的分类 ID</li>
<li><code>data-mapping: pathname</code>: 使用文章路径作为映射</li>
<li><code>data-lang: zh-CN</code>: 界面语言设为中文</li>
<li><code>data-reactions-enabled: 1</code>: 启用表情回应功能</li>
</ul>
<h3 id="5-重新生成并部署"><a href="#5-重新生成并部署" class="headerlink" title="5. 重新生成并部署"></a>5. 重新生成并部署</h3><figure class="highlight bash"><table><tr><td class="code"><pre><span class="line">hexo clean</span><br><span class="line">hexo generate</span><br><span class="line">hexo deploy</span><br></pre></td></tr></table></figure>

<h2 id="效果验证"><a href="#效果验证" class="headerlink" title="效果验证"></a>效果验证</h2><p>部署完成后，访问任意文章页面，应该能看到：</p>
<ul>
<li>文章底部出现 Giscus 评论框</li>
<li>需要登录 GitHub 才能评论</li>
<li>评论会自动同步到仓库的 Discussions 中</li>
<li>支持 Markdown 格式、代码高亮、表情回应</li>
</ul>
<h2 id="注意事项"><a href="#注意事项" class="headerlink" title="注意事项"></a>注意事项</h2><ol>
<li><strong>仓库必须公开</strong>：私有仓库无法使用 Giscus</li>
<li><strong>确保安装了 Giscus App</strong>：否则评论无法加载</li>
<li><strong>Discussions 必须启用</strong>：在仓库设置中开启</li>
<li><strong>首次评论会自动创建 Discussion</strong>：按文章路径命名</li>
<li><strong>可以在 GitHub 仓库中管理评论</strong>：删除、编辑、置顶等</li>
</ol>
]]></content>
      <categories>
        <category>博客搭建</category>
      </categories>
      <tags>
        <tag>Hexo</tag>
        <tag>Giscus</tag>
        <tag>评论系统</tag>
      </tags>
  </entry>
  <entry>
    <title>评论系统设计与实现</title>
    <url>/2026/02/11/comment-system/</url>
    <content><![CDATA[<link rel="stylesheet" class="aplayer-secondary-style-marker" href="\assets\css\APlayer.min.css"><script src="\assets\js\APlayer.min.js" class="aplayer-secondary-script-marker"></script><p>本文记录我在博客项目中实现评论功能时，涉及的一些细节。</p>
<hr>
<h2 id="一、后端实现"><a href="#一、后端实现" class="headerlink" title="一、后端实现"></a>一、后端实现</h2><h3 id="1-评论实体设计（Comment）"><a href="#1-评论实体设计（Comment）" class="headerlink" title="1. 评论实体设计（Comment）"></a>1. 评论实体设计（Comment）</h3><p>评论表的核心在于<strong>自引用关系</strong>：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="meta">@Entity</span></span><br><span class="line"><span class="keyword">public</span> <span class="keyword">class</span> <span class="title class_">Comment</span> &#123;</span><br><span class="line">    <span class="meta">@Id</span></span><br><span class="line">    <span class="keyword">private</span> Long id;</span><br><span class="line">    </span><br><span class="line">    <span class="keyword">private</span> String content;  <span class="comment">// VARCHAR(1000)</span></span><br><span class="line">    </span><br><span class="line">    <span class="meta">@ManyToOne(fetch = FetchType.EAGER)</span></span><br><span class="line">    <span class="keyword">private</span> Article article;  <span class="comment">// 所属文章</span></span><br><span class="line">    </span><br><span class="line">    <span class="meta">@ManyToOne(fetch = FetchType.EAGER)</span></span><br><span class="line">    <span class="keyword">private</span> User author;  <span class="comment">// 评论作者</span></span><br><span class="line">    </span><br><span class="line">    <span class="meta">@ManyToOne(fetch = FetchType.LAZY)</span></span><br><span class="line">    <span class="keyword">private</span> Comment parentComment;  <span class="comment">// 父评论（自引用关系）</span></span><br><span class="line">    </span><br><span class="line">    <span class="meta">@CreationTimestamp</span></span><br><span class="line">    <span class="keyword">private</span> LocalDateTime createdAt;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h4 id="设计要点"><a href="#设计要点" class="headerlink" title="设计要点"></a>设计要点</h4><ul>
<li><code>parentComment</code> 指向自身，实现评论嵌套</li>
<li>父评论使用 <code>LAZY</code>，避免循环加载</li>
<li>作者、文章使用 <code>EAGER</code>，避免访问时频繁触发延迟加载</li>
<li>不在实体中直接维护 children，避免 ORM 复杂度失控</li>
</ul>
<blockquote>
<p>高并发场景应使用join fetch 或DTO投影来精确控制查询行为。</p>
</blockquote>
<hr>
<h3 id="2-数据访问层（Repository）"><a href="#2-数据访问层（Repository）" class="headerlink" title="2. 数据访问层（Repository）"></a>2. 数据访问层（Repository）</h3><figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">interface</span> <span class="title class_">CommentRepository</span> <span class="keyword">extends</span> <span class="title class_">JpaRepository</span>&lt;Comment, Long&gt; &#123;</span><br><span class="line">    <span class="comment">// 按文章ID查询，升序排列（老评论在前）</span></span><br><span class="line">    Page&lt;Comment&gt; <span class="title function_">findByArticleIdOrderByCreatedAtAsc</span><span class="params">(Long articleId, Pageable pageable)</span>;</span><br><span class="line">    </span><br><span class="line">    <span class="comment">// 按作者ID查询（用于个人主页）</span></span><br><span class="line">    Page&lt;Comment&gt; <span class="title function_">findByAuthorId</span><span class="params">(Long authorId, Pageable pageable)</span>;</span><br><span class="line">    </span><br><span class="line">    <span class="comment">// 查找子评论（用于级联删除）</span></span><br><span class="line">    List&lt;Comment&gt; <span class="title function_">findByParentCommentId</span><span class="params">(Long parentId)</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p> 👉 <strong>递归删除时依赖 <code>findByParentCommentId</code> 查找子节点</strong></p>
<blockquote>
<p>评论属于高频读写表，后续应在数据库层添加必要索引。</p>
</blockquote>
<hr>
<h3 id="3-评论创建逻辑（Service）"><a href="#3-评论创建逻辑（Service）" class="headerlink" title="3. 评论创建逻辑（Service）"></a>3. 评论创建逻辑（Service）</h3><figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">public</span> CommentDTO <span class="title function_">createComment</span><span class="params">(Long articleId, Long userId, String content, Long parentId)</span> &#123;</span><br><span class="line">    <span class="comment">// 验证文章和用户存在</span></span><br><span class="line">    <span class="type">Article</span> <span class="variable">article</span> <span class="operator">=</span> articleRepository.findById(articleId)...</span><br><span class="line">    <span class="type">User</span> <span class="variable">author</span> <span class="operator">=</span> userRepository.findById(userId)...</span><br><span class="line">    </span><br><span class="line">    <span class="comment">// 验证内容非空</span></span><br><span class="line">    <span class="keyword">if</span> (content == <span class="literal">null</span> || content.trim().isEmpty()) &#123;</span><br><span class="line">        <span class="keyword">throw</span> <span class="keyword">new</span> <span class="title class_">RuntimeException</span>(<span class="string">&quot;评论内容不能为空&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    </span><br><span class="line">    <span class="comment">// 如果是回复，验证父评论</span></span><br><span class="line">    <span class="keyword">if</span> (parentId != <span class="literal">null</span>) &#123;</span><br><span class="line">        <span class="type">Comment</span> <span class="variable">parent</span> <span class="operator">=</span> commentRepository.findById(parentId)...</span><br><span class="line">        <span class="comment">// 确保父评论属于同一篇文章</span></span><br><span class="line">        <span class="keyword">if</span> (!parent.getArticle().getId().equals(articleId)) &#123;</span><br><span class="line">            <span class="keyword">throw</span> <span class="keyword">new</span> <span class="title class_">RuntimeException</span>(<span class="string">&quot;父评论与文章不匹配&quot;</span>);</span><br><span class="line">        &#125;</span><br><span class="line">        comment.setParentComment(parent);<span class="comment">// 设置parentcomment</span></span><br><span class="line">    &#125;</span><br><span class="line">    </span><br><span class="line">    <span class="comment">// 保存并转换为DTO</span></span><br><span class="line">    comment = commentRepository.save(comment);</span><br><span class="line">    <span class="keyword">return</span> convertToDTO(comment, userId);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h4 id="核心约束点"><a href="#核心约束点" class="headerlink" title="核心约束点"></a>核心约束点</h4><ul>
<li>回复的父评论必须属于同一篇文章</li>
<li>所有评论统一通过 DTO 返回，避免实体泄露</li>
<li>创建逻辑不做层级限制，展示逻辑交给前端</li>
</ul>
<hr>
<h3 id="4-递归级联删除"><a href="#4-递归级联删除" class="headerlink" title="4. 递归级联删除"></a>4. 递归级联删除</h3><p>删除一条评论时，必须同时删除：</p>
<ol>
<li>所有子评论（递归）</li>
<li>所有关联的点赞记录</li>
<li>保证外键约束不报错</li>
<li>保证操作原子性</li>
</ol>
<h4 id="实现方案"><a href="#实现方案" class="headerlink" title="实现方案"></a>实现方案</h4><figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="meta">@Transactional</span></span><br><span class="line"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">deleteComment</span><span class="params">(Long commentId, Long userId)</span> &#123;</span><br><span class="line">    <span class="type">Comment</span> <span class="variable">comment</span> <span class="operator">=</span> commentRepository.findById(commentId)...</span><br><span class="line">    </span><br><span class="line">    <span class="comment">// 权限检查：只能删除自己的评论</span></span><br><span class="line">    <span class="keyword">if</span> (!comment.getAuthor().getId().equals(userId)) &#123;</span><br><span class="line">        <span class="keyword">throw</span> <span class="keyword">new</span> <span class="title class_">RuntimeException</span>(<span class="string">&quot;只能删除自己的评论&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    </span><br><span class="line">    deleteCommentWithChildren(comment);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">// 递归删除子评论</span></span><br><span class="line"><span class="keyword">private</span> <span class="keyword">void</span> <span class="title function_">deleteCommentWithChildren</span><span class="params">(Comment comment)</span> &#123;</span><br><span class="line">    <span class="comment">// 递归删除所有子评论</span></span><br><span class="line">    List&lt;Comment&gt; children = commentRepository.findByParentCommentId(comment.getId());</span><br><span class="line">    <span class="keyword">for</span> (Comment child : children) &#123;</span><br><span class="line">        deleteCommentWithChildren(child);  <span class="comment">// 递归调用</span></span><br><span class="line">    &#125;</span><br><span class="line">    </span><br><span class="line">    <span class="comment">// 先删除该评论的所有点赞（解决FK约束）</span></span><br><span class="line">    commentLikeRepository.deleteByCommentId(comment.getId());</span><br><span class="line">    </span><br><span class="line">    <span class="comment">// 最后删除评论本身</span></span><br><span class="line">    commentRepository.deleteById(comment.getId());</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h4 id="设计要点-1"><a href="#设计要点-1" class="headerlink" title="设计要点"></a>设计要点</h4><ul>
<li>深度优先遍历（DFS）</li>
<li>时间复杂度 O(n)</li>
<li>使用事务保证一致性</li>
<li>显式控制删除顺序，避免外键（FK）约束问题</li>
</ul>
<blockquote>
<p>为避免复杂递归以及保留上下文，可考虑采用逻辑删除<code>private boolean deleted;</code>。</p>
</blockquote>
<hr>
<h2 id="二、前端实现"><a href="#二、前端实现" class="headerlink" title="二、前端实现"></a>二、前端实现</h2><h3 id="1-数据结构设计"><a href="#1-数据结构设计" class="headerlink" title="1. 数据结构设计"></a>1. 数据结构设计</h3><p>前端接收的是<strong>平铺数组</strong>，自行构建树结构：</p>
<figure class="highlight javascript"><table><tr><td class="code"><pre><span class="line"><span class="title function_">data</span>(<span class="params"></span>) &#123;</span><br><span class="line">    <span class="keyword">return</span> &#123;</span><br><span class="line">        <span class="attr">comments</span>: [],        <span class="comment">// 平铺的评论列表（从API获取）</span></span><br><span class="line">        <span class="attr">commentTree</span>: [],     <span class="comment">// 树型结构（用于渲染）</span></span><br><span class="line">        <span class="attr">newCommentContent</span>: <span class="string">&#x27;&#x27;</span>,  <span class="comment">// 新评论内容</span></span><br><span class="line">        <span class="attr">replyingTo</span>: <span class="literal">null</span>,    <span class="comment">// 当前回复的评论对象</span></span><br><span class="line">        <span class="attr">replyContent</span>: <span class="string">&#x27;&#x27;</span>     <span class="comment">// 回复内容</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<blockquote>
<p>选择前端构建树结构而不是后端直接递归组装，是为了保持接口简单、避免后端递归查询带来的复杂度，同时让前端掌控展示策略。</p>
</blockquote>
<hr>
<h3 id="2-评论树构建与展平"><a href="#2-评论树构建与展平" class="headerlink" title="2. 评论树构建与展平"></a>2. 评论树构建与展平</h3><figure class="highlight javascript"><table><tr><td class="code"><pre><span class="line"><span class="title function_">buildCommentTree</span>(<span class="params">comments</span>) &#123;</span><br><span class="line">    <span class="keyword">const</span> map = <span class="keyword">new</span> <span class="title class_">Map</span>();</span><br><span class="line">    <span class="keyword">const</span> roots = [];</span><br><span class="line">    </span><br><span class="line">    <span class="comment">// 1. 创建映射表，每个评论作为一个节点</span></span><br><span class="line">    comments.<span class="title function_">forEach</span>(<span class="function"><span class="params">comment</span> =&gt;</span> &#123;</span><br><span class="line">        map.<span class="title function_">set</span>(comment.<span class="property">id</span>, &#123; ...comment, <span class="attr">children</span>: [] &#125;);</span><br><span class="line">    &#125;);</span><br><span class="line">    </span><br><span class="line">    <span class="comment">// 2. 构建父子关系</span></span><br><span class="line">    comments.<span class="title function_">forEach</span>(<span class="function"><span class="params">comment</span> =&gt;</span> &#123;</span><br><span class="line">        <span class="keyword">const</span> node = map.<span class="title function_">get</span>(comment.<span class="property">id</span>);</span><br><span class="line">        </span><br><span class="line">        <span class="comment">// 顶级评论（没有父评论）</span></span><br><span class="line">        <span class="keyword">if</span> (!comment.<span class="property">parentId</span>) &#123;</span><br><span class="line">            roots.<span class="title function_">push</span>(node);</span><br><span class="line">            <span class="keyword">return</span>;</span><br><span class="line">        &#125;</span><br><span class="line">        </span><br><span class="line">        <span class="comment">// 找到最顶层的父评论（展平多层嵌套）</span></span><br><span class="line">        <span class="keyword">let</span> parent = map.<span class="title function_">get</span>(comment.<span class="property">parentId</span>);</span><br><span class="line">        <span class="keyword">while</span> (parent &amp;&amp; parent.<span class="property">parentId</span>) &#123;</span><br><span class="line">            parent = map.<span class="title function_">get</span>(parent.<span class="property">parentId</span>);</span><br><span class="line">        &#125;</span><br><span class="line">        </span><br><span class="line">        <span class="comment">// 将当前评论添加到顶层父评论的children中</span></span><br><span class="line">        <span class="keyword">if</span> (parent) &#123;</span><br><span class="line">            parent.<span class="property">children</span>.<span class="title function_">push</span>(node);</span><br><span class="line">        &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">            roots.<span class="title function_">push</span>(node);  <span class="comment">// 孤儿节点作为顶级评论</span></span><br><span class="line">        &#125;</span><br><span class="line">    &#125;);</span><br><span class="line">    </span><br><span class="line">    <span class="keyword">return</span> roots;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h4 id="设计要点-2"><a href="#设计要点-2" class="headerlink" title="设计要点"></a>设计要点</h4><ul>
<li>支持任意层级回复</li>
<li>UI 只展示两层</li>
<li>不需要后端额外接口</li>
<li>构建复杂度 O(n)</li>
</ul>
<blockquote>
<p>前端只展示两层结构，避免前端无限递归渲染</p>
</blockquote>
]]></content>
      <categories>
        <category>项目总结</category>
      </categories>
      <tags>
        <tag>Spring Boot</tag>
        <tag>数据库设计</tag>
        <tag>评论系统</tag>
      </tags>
  </entry>
  <entry>
    <title>使用 Hexo + Butterfly 搭建我的个人博客</title>
    <url>/2026/02/05/hexo-butterfly-blog-setup/</url>
    <content><![CDATA[<link rel="stylesheet" class="aplayer-secondary-style-marker" href="\assets\css\APlayer.min.css"><script src="\assets\js\APlayer.min.js" class="aplayer-secondary-script-marker"></script><h2 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h2><p>很早之前就想搭一个属于自己的博客，但一直停留在“想做”的阶段。  </p>
<p>这篇文章主要记录我使用 <strong>Hexo + Butterfly</strong> 搭建博客的过程，一方面作为备忘，另一方面也算是这个博客的起点。</p>
<hr>
<h2 id="关于技术选型"><a href="#关于技术选型" class="headerlink" title="关于技术选型"></a>关于技术选型</h2><p>一开始我也考虑过很多方案，比如 WordPress，或者干脆用前端框架自己写一套。<br>但综合考虑之后，还是选择了 Hexo。</p>
<p>原因其实很简单：<br>Hexo 是静态博客，结构清晰，写文章就是写 Markdown，不需要关心数据库和后端服务。对目前的我来说，这种“专注写作本身”的方式更合适。</p>
<p>在主题方面，我选择了 Butterfly。这个主题整体风格简洁，配置项比较全，文档也比较完善，适合长期维护。</p>
<hr>
<h2 id="Hexo-的安装与初始化"><a href="#Hexo-的安装与初始化" class="headerlink" title="Hexo 的安装与初始化"></a>Hexo 的安装与初始化</h2><p>本地环境准备好 Node.js 和 Git 之后，就可以直接安装 Hexo CLI。</p>
<figure class="highlight bash"><table><tr><td class="code"><pre><span class="line">npm install -g hexo-cli</span><br></pre></td></tr></table></figure>

<p>接着初始化博客目录：</p>
<figure class="highlight bash"><table><tr><td class="code"><pre><span class="line">hexo init blog</span><br><span class="line"><span class="built_in">cd</span> blog</span><br><span class="line">npm install</span><br></pre></td></tr></table></figure>

<p>随后在 themes 目录下克隆主题仓库：</p>
<figure class="highlight bash"><table><tr><td class="code"><pre><span class="line">git <span class="built_in">clone</span> https://github.com/jerryc127/hexo-theme-butterfly.git</span><br></pre></td></tr></table></figure>

<p>然后在站点配置文件 _config.yml 中，把主题改成：</p>
<figure class="highlight yml"><table><tr><td class="code"><pre><span class="line"><span class="attr">theme:</span> <span class="string">butterfly</span></span><br></pre></td></tr></table></figure>

<p>接下来便是完善一些基础配置和页面。</p>
<hr>
<h2 id="添加-Live2D-小人"><a href="#添加-Live2D-小人" class="headerlink" title="添加 Live2D 小人"></a>添加 Live2D 小人</h2><p>为了让博客更有趣一些，我在右下角添加了一个 Live2D 小人。Butterfly 主题支持通过代码注入的方式快速集成。</p>
<h3 id="配置方法"><a href="#配置方法" class="headerlink" title="配置方法"></a>配置方法</h3><p>打开 <code>themes/butterfly/_config.yml</code>，找到 <code>inject</code> 配置段，在 <code>bottom</code> 部分添加以下代码：</p>
<figure class="highlight yaml"><table><tr><td class="code"><pre><span class="line"><span class="attr">inject:</span></span><br><span class="line">  <span class="attr">head:</span></span><br><span class="line">    <span class="comment"># ... 其他配置</span></span><br><span class="line">  <span class="attr">bottom:</span></span><br><span class="line">    <span class="bullet">-</span> <span class="string">&#x27;&lt;script src=&quot;https://cdn.jsdelivr.net/npm/live2d-widget@3.1.4/lib/L2Dwidget.min.js&quot;&gt;&lt;/script&gt;&#x27;</span></span><br><span class="line">    <span class="bullet">-</span> <span class="string">&#x27;&lt;script&gt;L2Dwidget.init(&#123; model: &#123; jsonPath: &quot;https://cdn.jsdelivr.net/npm/live2d-widget-model-shizuku@1.0.5/assets/shizuku.model.json&quot; &#125;, display: &#123; position: &quot;right&quot;, width: 150, height: 300, hOffset: 30, vOffset: -10 &#125;, mobile: &#123; show: true, scale: 0.6 &#125;, react: &#123; opacityDefault: 0.8, opacityOnHover: 0.2 &#125; &#125;);&lt;/script&gt;&#x27;</span></span><br></pre></td></tr></table></figure>

<h3 id="参数说明"><a href="#参数说明" class="headerlink" title="参数说明"></a>参数说明</h3><ul>
<li><strong>model.jsonPath</strong>：角色模型的 CDN 地址，这里使用的是 Shizuku（时雨）模型</li>
<li><strong>display.position</strong>：显示位置（left&#x2F;right），这里设为右下角</li>
<li><strong>display.width&#x2F;height</strong>：模型宽高（像素）</li>
<li><strong>display.hOffset&#x2F;vOffset</strong>：水平和垂直偏移量</li>
<li><strong>mobile.show</strong>：是否在移动端显示</li>
<li><strong>mobile.scale</strong>：移动端缩放比例</li>
<li><strong>react.opacityDefault</strong>：默认透明度</li>
<li><strong>react.opacityOnHover</strong>：鼠标悬停时的透明度（0.2 表示鼠标移上去会变淡）</li>
</ul>
<h3 id="可选模型"><a href="#可选模型" class="headerlink" title="可选模型"></a>可选模型</h3><p>除了 Shizuku，还可以选择其他模型：</p>
<figure class="highlight javascript"><table><tr><td class="code"><pre><span class="line"><span class="comment">// Koharu（小春）</span></span><br><span class="line"><span class="string">&quot;https://cdn.jsdelivr.net/npm/live2d-widget-model-koharu@1.0.5/assets/koharu.model.json&quot;</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// Hibiki（响）</span></span><br><span class="line"><span class="string">&quot;https://cdn.jsdelivr.net/npm/live2d-widget-model-hibiki@1.0.5/assets/hibiki.model.json&quot;</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// Miku（初音未来）</span></span><br><span class="line"><span class="string">&quot;https://cdn.jsdelivr.net/npm/live2d-widget-model-miku@1.0.5/assets/miku.model.json&quot;</span></span><br></pre></td></tr></table></figure>

<p>只需要替换 <code>jsonPath</code> 的值即可切换角色。</p>
]]></content>
      <categories>
        <category>博客搭建</category>
      </categories>
      <tags>
        <tag>Hexo</tag>
        <tag>Butterfly</tag>
        <tag>博客</tag>
      </tags>
  </entry>
  <entry>
    <title>一次理解访问者模式</title>
    <url>/2026/03/15/visitor-pattern-when-operations-change/</url>
    <content><![CDATA[<link rel="stylesheet" class="aplayer-secondary-style-marker" href="\assets\css\APlayer.min.css"><script src="\assets\js\APlayer.min.js" class="aplayer-secondary-script-marker"></script><p>在学习设计模式时，访问者模式经常被认为是比较难理解的一种模式。</p>
<p>原因也很简单：它不像单例、工厂那样直观，而且在日常项目里也不是最高频出现的模式。</p>
<p>不过如果你接触过编译器、AST、复杂数据结构遍历，你很可能已经见过它的影子。</p>
<p>简单来说，访问者模式解决的问题是：</p>
<blockquote>
<p>当对象结构稳定，但对对象的操作经常变化时，如何避免频繁修改类结构。</p>
</blockquote>
<h2 id="一、先看一个直观例子"><a href="#一、先看一个直观例子" class="headerlink" title="一、先看一个直观例子"></a>一、先看一个直观例子</h2><p>假设我们有一个系统，表示不同类型的文件：</p>
<ul>
<li>Word 文档</li>
<li>PDF 文件</li>
<li>Excel 表格</li>
</ul>
<p>先定义统一接口：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">interface</span> <span class="title class_">File</span> &#123;</span><br><span class="line">    <span class="keyword">void</span> <span class="title function_">accept</span><span class="params">(Visitor visitor)</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>不同文件类型只负责“接待”访问者：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">WordFile</span> <span class="keyword">implements</span> <span class="title class_">File</span> &#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">accept</span><span class="params">(Visitor visitor)</span> &#123;</span><br><span class="line">        visitor.visit(<span class="built_in">this</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">class</span> <span class="title class_">PdfFile</span> <span class="keyword">implements</span> <span class="title class_">File</span> &#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">accept</span><span class="params">(Visitor visitor)</span> &#123;</span><br><span class="line">        visitor.visit(<span class="built_in">this</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="keyword">class</span> <span class="title class_">ExcelFile</span> <span class="keyword">implements</span> <span class="title class_">File</span> &#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">accept</span><span class="params">(Visitor visitor)</span> &#123;</span><br><span class="line">        visitor.visit(<span class="built_in">this</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>这些类本质上是对象结构（数据&#x2F;类型）的表达。</p>
<h2 id="二、不用访问者会发生什么"><a href="#二、不用访问者会发生什么" class="headerlink" title="二、不用访问者会发生什么"></a>二、不用访问者会发生什么</h2><p>假设系统现在要支持这些操作：</p>
<ul>
<li>打开文件</li>
<li>导出文件</li>
<li>统计文件信息</li>
</ul>
<p>最直接的写法通常是把行为塞进每个类：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">WordFile</span> &#123;</span><br><span class="line">    <span class="keyword">void</span> <span class="title function_">open</span><span class="params">()</span> &#123;&#125;</span><br><span class="line">    <span class="keyword">void</span> <span class="title function_">export</span><span class="params">()</span> &#123;&#125;</span><br><span class="line">    <span class="keyword">void</span> <span class="title function_">statistics</span><span class="params">()</span> &#123;&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>问题很快出现：如果以后要新增一个功能，比如“打印文件”，就必须改动：</p>
<ul>
<li><code>WordFile</code></li>
<li><code>PdfFile</code></li>
<li><code>ExcelFile</code></li>
</ul>
<p>每个类都得加 <code>print()</code> 方法。</p>
<p>这显然违背了开闭原则：</p>
<blockquote>
<p>对扩展开放，对修改关闭。</p>
</blockquote>
<h2 id="三、引入访问者模式"><a href="#三、引入访问者模式" class="headerlink" title="三、引入访问者模式"></a>三、引入访问者模式</h2><p>访问者模式的核心思想是：</p>
<blockquote>
<p>把“操作”从对象结构中抽离出来。</p>
</blockquote>
<p>对象只负责提供结构，操作交给访问者。</p>
<p>先定义访问者接口：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">interface</span> <span class="title class_">Visitor</span> &#123;</span><br><span class="line">    <span class="keyword">void</span> <span class="title function_">visit</span><span class="params">(WordFile file)</span>;</span><br><span class="line">    <span class="keyword">void</span> <span class="title function_">visit</span><span class="params">(PdfFile file)</span>;</span><br><span class="line">    <span class="keyword">void</span> <span class="title function_">visit</span><span class="params">(ExcelFile file)</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>实现一个“打开文件”访问者：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">OpenVisitor</span> <span class="keyword">implements</span> <span class="title class_">Visitor</span> &#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">visit</span><span class="params">(WordFile file)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;打开 Word 文件&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">visit</span><span class="params">(PdfFile file)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;打开 PDF 文件&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">visit</span><span class="params">(ExcelFile file)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;打开 Excel 文件&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>再实现一个“导出文件”访问者：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">ExportVisitor</span> <span class="keyword">implements</span> <span class="title class_">Visitor</span> &#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">visit</span><span class="params">(WordFile file)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;导出 Word 文件&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">visit</span><span class="params">(PdfFile file)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;导出 PDF 文件&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">visit</span><span class="params">(ExcelFile file)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;导出 Excel 文件&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h2 id="四、怎么使用"><a href="#四、怎么使用" class="headerlink" title="四、怎么使用"></a>四、怎么使用</h2><figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="type">File</span> <span class="variable">file</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">WordFile</span>();</span><br><span class="line"><span class="type">Visitor</span> <span class="variable">visitor</span> <span class="operator">=</span> <span class="keyword">new</span> <span class="title class_">OpenVisitor</span>();</span><br><span class="line"></span><br><span class="line">file.accept(visitor);</span><br></pre></td></tr></table></figure>

<p>执行流程是：</p>
<figure class="highlight text"><table><tr><td class="code"><pre><span class="line">file.accept(visitor)</span><br><span class="line">      ↓</span><br><span class="line">visitor.visit(file)</span><br></pre></td></tr></table></figure>

<p>这个过程本质上就是双重分派（double dispatch）。</p>
<h2 id="五、为什么这样设计"><a href="#五、为什么这样设计" class="headerlink" title="五、为什么这样设计"></a>五、为什么这样设计</h2><p>访问者模式最大的优势是：</p>
<blockquote>
<p>新增操作非常容易。</p>
</blockquote>
<p>比如现在想增加“统计文件大小”，只需要新增一个访问者：</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">SizeVisitor</span> <span class="keyword">implements</span> <span class="title class_">Visitor</span> &#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">visit</span><span class="params">(WordFile file)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;统计 Word 文件大小&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">visit</span><span class="params">(PdfFile file)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;统计 PDF 文件大小&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">void</span> <span class="title function_">visit</span><span class="params">(ExcelFile file)</span> &#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;统计 Excel 文件大小&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>原来的文件类完全不用动。</p>
<h2 id="六、典型适用场景"><a href="#六、典型适用场景" class="headerlink" title="六、典型适用场景"></a>六、典型适用场景</h2><p>访问者模式不是每个项目都会用，但在下面场景非常合适：</p>
<h3 id="1-编译器-AST"><a href="#1-编译器-AST" class="headerlink" title="1. 编译器 AST"></a>1. 编译器 AST</h3><p>抽象语法树节点（如 <code>Expression</code>、<code>Statement</code>、<code>IfStatement</code>）结构相对稳定，<br>但操作很多：</p>
<ul>
<li>代码生成</li>
<li>语义分析</li>
<li>优化</li>
</ul>
<h3 id="2-复杂对象结构遍历"><a href="#2-复杂对象结构遍历" class="headerlink" title="2. 复杂对象结构遍历"></a>2. 复杂对象结构遍历</h3><p>例如：</p>
<ul>
<li>文件系统</li>
<li>UI 组件树</li>
<li>文档结构</li>
</ul>
<p>针对同一结构，可以有不同访问者：</p>
<ul>
<li>渲染</li>
<li>统计</li>
<li>导出</li>
</ul>
<h3 id="3-报表-数据分析"><a href="#3-报表-数据分析" class="headerlink" title="3. 报表 &#x2F; 数据分析"></a>3. 报表 &#x2F; 数据分析</h3><p>同一组数据不断增加新输出方式：</p>
<ul>
<li>生成 PDF</li>
<li>生成 Excel</li>
<li>生成图表</li>
</ul>
<h2 id="七、缺点"><a href="#七、缺点" class="headerlink" title="七、缺点"></a>七、缺点</h2><p>访问者模式最大缺点是：</p>
<blockquote>
<p>一旦对象结构变化，改动成本很高。</p>
</blockquote>
<p>例如新增一个文件类型 <code>ImageFile</code>，那所有访问者都要补对应方法：</p>
<ul>
<li><code>OpenVisitor</code></li>
<li><code>ExportVisitor</code></li>
<li><code>SizeVisitor</code></li>
<li>以及其他所有 <code>Visitor</code> 实现</li>
</ul>
<p>所以它更适合：</p>
<blockquote>
<p>对象结构稳定，但操作经常变化的系统。</p>
</blockquote>
<h2 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h2><p>访问者模式可以用一句话概括：</p>
<blockquote>
<p>对象负责结构，访问者负责行为。</p>
</blockquote>
<p>它的核心价值是把操作和数据结构分离。</p>
<p>当系统满足以下条件时，访问者模式通常很合适：</p>
<ul>
<li>数据结构稳定</li>
<li>操作经常增加</li>
<li>需要对同一组对象执行多种不同操作</li>
</ul>
]]></content>
      <categories>
        <category>项目总结</category>
      </categories>
      <tags>
        <tag>系统设计</tag>
        <tag>Java</tag>
        <tag>设计模式</tag>
      </tags>
  </entry>
  <entry>
    <title>页面刷新时的 Load 动画是如何实现的</title>
    <url>/2026/04/23/refresh-load-animation-implementation/</url>
    <content><![CDATA[<link rel="stylesheet" class="aplayer-secondary-style-marker" href="\assets\css\APlayer.min.css"><script src="\assets\js\APlayer.min.js" class="aplayer-secondary-script-marker"></script><h2 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h2><p>之前在看自己博客刷新的时候，发现页面总会先出来一个短暂的 Load 动画：有时是全屏遮罩，有时是进度条，有时只是中间一个在转的小图标。</p>
<p>一开始我以为这是浏览器或者 Hexo 默认带的效果，后来翻了一下 Butterfly 的源码，才发现它其实是主题自己加的一层“过渡界面”。这篇文章就顺着这条线，记录一下它到底是怎么实现的。</p>
<h2 id="它从哪里进入页面"><a href="#它从哪里进入页面" class="headerlink" title="它从哪里进入页面"></a>它从哪里进入页面</h2><p>Butterfly 会在全局布局里直接注入加载层。换句话说，页面刚开始渲染的时候，<code>body</code> 里面就已经先放进去了这层结构。</p>
<p>关键入口在布局文件里：</p>
<figure class="highlight plaintext"><table><tr><td class="code"><pre><span class="line">body</span><br><span class="line">  !=partial(&#x27;includes/loading/index&#x27;, &#123;&#125;, &#123;cache: true&#125;)</span><br></pre></td></tr></table></figure>

<p>这个 <code>index</code> 入口会再根据配置选择不同的加载方案：</p>
<figure class="highlight plaintext"><table><tr><td class="code"><pre><span class="line">if theme.preloader.enable</span><br><span class="line">  if theme.preloader.source === 1</span><br><span class="line">    include ./fullpage-loading.pug</span><br><span class="line">  else</span><br><span class="line">    include ./pace.pug</span><br></pre></td></tr></table></figure>

<p>所以我现在看到的刷新动画，其实就两种形态：</p>
<ul>
<li><code>source: 1</code> 时是全屏 preloader</li>
<li><code>source: 2</code> 时是 pace.js 进度条</li>
</ul>
<h2 id="全屏-Load-动画怎么工作"><a href="#全屏-Load-动画怎么工作" class="headerlink" title="全屏 Load 动画怎么工作"></a>全屏 Load 动画怎么工作</h2><p>如果用的是全屏 preloader，页面会先渲染出一个固定定位的遮罩层：左右两块背景，加中间那个 spinner。效果很简单，但第一眼挺有存在感。</p>
<p>对应的核心结构如下：</p>
<figure class="highlight plaintext"><table><tr><td class="code"><pre><span class="line">#loading-box</span><br><span class="line">  .loading-left-bg</span><br><span class="line">  .loading-right-bg</span><br><span class="line">  .spinner-box</span><br><span class="line">    .configure-border-1</span><br><span class="line">      .configure-core</span><br><span class="line">    .configure-border-2</span><br><span class="line">      .configure-core</span><br><span class="line">    .loading-word= _p(&#x27;loading&#x27;)</span><br></pre></td></tr></table></figure>

<p>这层样式通过固定定位把整个视口盖住，保证页面还没准备好之前，用户看到的不是半成品内容，而是一个完整的加载状态。</p>
<p>CSS 的关键点有三个：</p>
<ul>
<li><code>#loading-box</code> 以及左右背景块都是 <code>position: fixed</code></li>
<li><code>spinner-box</code> 覆盖在正中央，展示旋转动画</li>
<li>当加上 <code>.loaded</code> 类后，左右背景会向两侧平移并退出视口，spinner 也会被隐藏</li>
</ul>
<p>看到这里我就基本明白了：它并不是靠复杂的 JS 一帧一帧去画动画，而是切换 class，让 CSS 的 transition 和 keyframes 自己跑起来。</p>
<h2 id="什么时候结束加载"><a href="#什么时候结束加载" class="headerlink" title="什么时候结束加载"></a>什么时候结束加载</h2><p>真正决定动画什么时候消失的，是一段内联脚本。</p>
<p>它做了两件事：</p>
<h3 id="1-先进入加载状态"><a href="#1-先进入加载状态" class="headerlink" title="1. 先进入加载状态"></a>1. 先进入加载状态</h3><p>脚本一开始会执行 <code>initLoading()</code>：</p>
<figure class="highlight js"><table><tr><td class="code"><pre><span class="line"><span class="attr">initLoading</span>: <span class="function">() =&gt;</span> &#123;</span><br><span class="line">  $body.<span class="property">style</span>.<span class="property">overflow</span> = <span class="string">&#x27;hidden&#x27;</span></span><br><span class="line">  $loadingBox.<span class="property">classList</span>.<span class="title function_">remove</span>(<span class="string">&#x27;loaded&#x27;</span>)</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>这里会先把 <code>body</code> 的滚动锁住，避免页面还没加载完的时候，用户就已经开始乱滚导致视觉闪动。</p>
<h3 id="2-再在合适时机结束加载"><a href="#2-再在合适时机结束加载" class="headerlink" title="2. 再在合适时机结束加载"></a>2. 再在合适时机结束加载</h3><p>随后它会根据页面状态决定什么时候移除加载层：</p>
<figure class="highlight js"><table><tr><td class="code"><pre><span class="line"><span class="keyword">if</span> (<span class="variable language_">document</span>.<span class="property">readyState</span> === <span class="string">&#x27;complete&#x27;</span>) &#123;</span><br><span class="line">  preloader.<span class="title function_">endLoading</span>()</span><br><span class="line">&#125; <span class="keyword">else</span> &#123;</span><br><span class="line">  <span class="variable language_">window</span>.<span class="title function_">addEventListener</span>(<span class="string">&#x27;load&#x27;</span>, preloader.<span class="property">endLoading</span>)</span><br><span class="line">  <span class="variable language_">document</span>.<span class="title function_">addEventListener</span>(<span class="string">&#x27;DOMContentLoaded&#x27;</span>, preloader.<span class="property">endLoading</span>)</span><br><span class="line">  <span class="built_in">setTimeout</span>(preloader.<span class="property">endLoading</span>, <span class="number">7000</span>)</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>这段逻辑其实挺典型，我自己看下来就是：</p>
<ul>
<li><code>DOMContentLoaded</code> 负责在 DOM 结构可用时尽快结束</li>
<li><code>load</code> 负责等图片、样式、脚本这些资源真正加载完</li>
<li><code>setTimeout</code> 是兜底，防止某些资源出问题后加载层一直挂着不消失</li>
</ul>
<p>最终执行 <code>endLoading()</code> 时，会恢复滚动并给加载层加上 <code>.loaded</code>：</p>
<figure class="highlight js"><table><tr><td class="code"><pre><span class="line"><span class="attr">endLoading</span>: <span class="function">() =&gt;</span> &#123;</span><br><span class="line">  <span class="keyword">if</span> ($loadingBox.<span class="property">classList</span>.<span class="title function_">contains</span>(<span class="string">&#x27;loaded&#x27;</span>)) <span class="keyword">return</span></span><br><span class="line">  $body.<span class="property">style</span>.<span class="property">overflow</span> = <span class="string">&#x27;&#x27;</span></span><br><span class="line">  $loadingBox.<span class="property">classList</span>.<span class="title function_">add</span>(<span class="string">&#x27;loaded&#x27;</span>)</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>等 <code>loaded</code> 类加上去之后，CSS 动画开始生效，左右背景滑出，整个 Load 动画也就结束了。这个过程很干脆，没有多余的逻辑。</p>
<h2 id="为什么刷新时特别明显"><a href="#为什么刷新时特别明显" class="headerlink" title="为什么刷新时特别明显"></a>为什么刷新时特别明显</h2><p>“刷新页面”这个场景和“站内切页”不太一样。</p>
<p>刷新时浏览器会重新请求整页，主题的加载层也会从最初就出现在 HTML 里，所以用户通常会先看到一个完整的过渡界面，等页面就绪后再被移除。</p>
<p>如果主题启用了 PJAX，站内跳转又会多一层处理：</p>
<figure class="highlight js"><table><tr><td class="code"><pre><span class="line">btf.<span class="title function_">addGlobalFn</span>(<span class="string">&#x27;pjaxSend&#x27;</span>, preloader.<span class="property">initLoading</span>, <span class="string">&#x27;preloader_init&#x27;</span>)</span><br><span class="line">btf.<span class="title function_">addGlobalFn</span>(<span class="string">&#x27;pjaxComplete&#x27;</span>, preloader.<span class="property">endLoading</span>, <span class="string">&#x27;preloader_end&#x27;</span>)</span><br></pre></td></tr></table></figure>

<p>这也意味着，不只是首次刷新会出现动画，后续的局部切页同样会沿用这一套加载逻辑。</p>
<h2 id="如果想改成进度条"><a href="#如果想改成进度条" class="headerlink" title="如果想改成进度条"></a>如果想改成进度条</h2><p>Butterfly 还预留了 pace.js 方案。它不会显示全屏遮罩，而是显示一条页面顶部的进度条。</p>
<p>对应逻辑更简单：</p>
<figure class="highlight plaintext"><table><tr><td class="code"><pre><span class="line">script.</span><br><span class="line">  window.paceOptions = &#123;</span><br><span class="line">    restartOnPushState: false</span><br><span class="line">  &#125;</span><br><span class="line"></span><br><span class="line">  btf.addGlobalFn(&#x27;pjaxSend&#x27;, () =&gt; &#123;</span><br><span class="line">    Pace.restart()</span><br><span class="line">  &#125;, &#x27;pace_restart&#x27;)</span><br><span class="line"></span><br><span class="line">link(rel=&quot;stylesheet&quot;, href=url_for(theme.preloader.pace_css_url || theme.asset.pace_default_css))</span><br><span class="line">script(src=url_for(theme.asset.pace_js))</span><br></pre></td></tr></table></figure>

<p>如果你更偏好轻量、克制一点的视觉效果，我觉得把 <code>preloader.source</code> 切到 <code>2</code> 会更舒服一点。</p>
<h2 id="配置入口"><a href="#配置入口" class="headerlink" title="配置入口"></a>配置入口</h2><p>这部分配置在主题配置文件里：</p>
<figure class="highlight yml"><table><tr><td class="code"><pre><span class="line"><span class="attr">preloader:</span></span><br><span class="line">  <span class="attr">enable:</span> <span class="literal">false</span></span><br><span class="line">  <span class="comment"># 1. fullpage-loading</span></span><br><span class="line">  <span class="comment"># 2. pace (progress bar)</span></span><br><span class="line">  <span class="attr">source:</span> <span class="number">1</span></span><br><span class="line">  <span class="attr">pace_css_url:</span></span><br></pre></td></tr></table></figure>

<p>如果要自己改配置，我觉得最需要关注的还是这两个点：</p>
<ul>
<li><code>enable</code> 控制是否启用加载动画</li>
<li><code>source</code> 控制是全屏遮罩还是进度条</li>
</ul>
]]></content>
      <categories>
        <category>博客搭建</category>
      </categories>
      <tags>
        <tag>Hexo</tag>
        <tag>Butterfly</tag>
        <tag>页面加载</tag>
        <tag>前端</tag>
      </tags>
  </entry>
</search>