179 lines
21 KiB
HTML
179 lines
21 KiB
HTML
<!DOCTYPE html>
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<html lang="en-us">
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<head>
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<meta charset="UTF-8">
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<title>Redkale(红菜苔)--基于Java 8全新的微服务开源框架 - Redkale官网</title>
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<meta name="keywords" content="Redkale,redkale,java,微服务,架构"/>
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<meta name="description" content="Redkale(红菜苔)是基于Java 8全新的微服务开源框架"/>
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<meta name="viewport" content="width=device-width, initial-scale=1">
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<link rel="stylesheet" type="text/css" href="stylesheets/stylesheet.css" media="screen">
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</head>
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<body>
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<section class="page-header">
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<a href="index.html" class="project-name">Redkale</a>
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<h2 class="project-tagline"></h2>
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<a href="redkale.html" class="btn">Redkale 入门</a>
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<a href="convert.html" class="btn">Convert 组件</a>
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<a href="service.html" class="btn">Service 组件</a>
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<a href="source.html" class="btn">Source 组件</a>
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<a href="net.html" class="btn">Net 组件</a>
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<a href="watch.html" class="btn">Watch 组件</a>
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<a href="plugins.html" class="btn">Redkale 插件</a>
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<a href="articles.html" class="btn">技术文章</a>
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</section>
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<section class="main-content">
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<h3>Redkale 技术详解 04 -- Java DataSource简易的DB操作</h3>
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<p>
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长期以来，Hibernate和Mybatis一直是大家使用最多的持久层开发框架。针对这两种框架网络上是各种比较，各种讨论优缺点。其实这两个框架(算上前身ibatis)都是2002年左右发布, 迄今已有15载已笨重不堪，一个mybatis.jar包大小6M左右，Hibernate更是巨大，毫无轻巧灵活可言，提供简化SQL操作的同时带来了复杂繁琐的配置和高学习门槛。而Redkale的Source组件非常轻量级，通过十多个<span style="color: #2041B4;">interface</span>、<span style="color: #2041B4;">enum</span>和十多个<span style="color: #2041B4;">class</span>完成常见的DB操作功能。<br/>
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Source组件在接口设计上参考了JPA接口，为了降低学习成本，部分注解仍沿用javax.persistence中的类，以多个注解结合一个主操作类 <a href="http://redkale.org/javadoc/org/redkale/source/DataSource.html" target="_blank">DataSource</a> 的方式提供API。在没有IDE自动生成代码的插件支持的情况下Redkale提供了一个Demo代码<a href="https://github.com/redkale/redkale-demo/blob/master/src/org/redkale/demo/base/AutoClassCreator.java" target="_blank"> AutoClassCreator</a> 能很方便的将数据库表生成Entity类。
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</p>
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<p>
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</p>
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<div class="highlight"><pre><span class="n">Constructor</span><span class="o"><</span><span class="n">T</span><span class="o">></span> <span class="n">constructor0</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span>
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<span class="k">for</span> <span class="o">(</span><span class="n">Constructor</span> <span class="n">c</span> <span class="o">:</span> <span class="n">clazz</span><span class="o">.</span><span class="na">getConstructors</span><span class="o">())</span> <span class="o">{</span> <span class="c1">//优先找public 的构造函数</span>
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<span class="k">if</span> <span class="o">(</span><span class="n">c</span><span class="o">.</span><span class="na">getParameterCount</span><span class="o">()</span> <span class="o">==</span> <span class="mi">0</span><span class="o">)</span> <span class="o">{</span>
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<span class="n">constructor0</span> <span class="o">=</span> <span class="n">c</span><span class="o">;</span>
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<span class="k">break</span><span class="o">;</span>
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<a href="articles.html"></a>
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<span class="o">}</span>
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<span class="o">}</span>
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<span class="k">if</span> <span class="o">(</span><span class="n">constructor0</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span><span class="c1">//其次找非private带ConstructorProperties的构造函数</span>
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<span class="k">for</span> <span class="o">(</span><span class="n">Constructor</span> <span class="n">c</span> <span class="o">:</span> <span class="n">clazz</span><span class="o">.</span><span class="na">getDeclaredConstructors</span><span class="o">())</span> <span class="o">{</span>
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<span class="k">if</span> <span class="o">(</span><span class="n">Modifier</span><span class="o">.</span><span class="na">isPrivate</span><span class="o">(</span><span class="n">c</span><span class="o">.</span><span class="na">getModifiers</span><span class="o">()))</span> <span class="k">continue</span><span class="o">;</span>
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<span class="k">if</span> <span class="o">(</span><span class="n">c</span><span class="o">.</span><span class="na">getAnnotation</span><span class="o">(</span><span class="n">ConstructorProperties</span><span class="o">.</span><span class="na">class</span><span class="o">)</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
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<span class="n">constructor0</span> <span class="o">=</span> <span class="n">c</span><span class="o">;</span>
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<span class="k">break</span><span class="o">;</span>
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<span class="o">}</span>
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<span class="o">}</span>
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<span class="o">}</span>
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<span class="k">if</span> <span class="o">(</span><span class="n">constructor0</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span><span class="c1">//再次找非private且带-parameters编译项的构造函数 java 8以上才支持</span>
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<span class="k">for</span> <span class="o">(</span><span class="n">Constructor</span> <span class="n">c</span> <span class="o">:</span> <span class="n">clazz</span><span class="o">.</span><span class="na">getDeclaredConstructors</span><span class="o">())</span> <span class="o">{</span>
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<span class="k">if</span> <span class="o">(</span><span class="n">Modifier</span><span class="o">.</span><span class="na">isPrivate</span><span class="o">(</span><span class="n">c</span><span class="o">.</span><span class="na">getModifiers</span><span class="o">()))</span> <span class="k">continue</span><span class="o">;</span>
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<span class="n">Parameter</span><span class="o">[]</span> <span class="n">params</span> <span class="o">=</span> <span class="n">c</span><span class="o">.</span><span class="na">getParameters</span><span class="o">();</span>
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<span class="k">if</span> <span class="o">(</span><span class="n">params</span><span class="o">.</span><span class="na">length</span> <span class="o">==</span> <span class="mi">0</span><span class="o">)</span> <span class="k">continue</span><span class="o">;</span>
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<span class="kt">boolean</span> <span class="n">flag</span> <span class="o">=</span> <span class="kc">true</span><span class="o">;</span>
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<span class="k">for</span> <span class="o">(</span><span class="n">Parameter</span> <span class="n">param</span> <span class="o">:</span> <span class="n">params</span><span class="o">)</span> <span class="o">{</span>
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<span class="k">try</span> <span class="o">{</span>
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<span class="n">clazz</span><span class="o">.</span><span class="na">getDeclaredField</span><span class="o">(</span><span class="n">param</span><span class="o">.</span><span class="na">getName</span><span class="o">());</span>
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<span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">Exception</span> <span class="n">e</span><span class="o">)</span> <span class="o">{</span>
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<span class="n">flag</span> <span class="o">=</span> <span class="kc">false</span><span class="o">;</span>
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<span class="k">break</span><span class="o">;</span>
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<span class="o">}</span>
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<span class="o">}</span>
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<span class="k">if</span> <span class="o">(</span><span class="n">flag</span><span class="o">)</span> <span class="o">{</span>
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<span class="n">constructor0</span> <span class="o">=</span> <span class="n">c</span><span class="o">;</span>
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<span class="k">break</span><span class="o">;</span>
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<span class="o">}</span>
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<span class="o">}</span>
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<span class="o">}</span>
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<span class="k">if</span> <span class="o">(</span><span class="n">constructor0</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span><span class="c1">//最后找非private的空构造函数</span>
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<span class="k">for</span> <span class="o">(</span><span class="n">Constructor</span> <span class="n">c</span> <span class="o">:</span> <span class="n">clazz</span><span class="o">.</span><span class="na">getDeclaredConstructors</span><span class="o">())</span> <span class="o">{</span>
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<span class="k">if</span> <span class="o">(</span><span class="n">Modifier</span><span class="o">.</span><span class="na">isPrivate</span><span class="o">(</span><span class="n">c</span><span class="o">.</span><span class="na">getModifiers</span><span class="o">()))</span> <span class="k">continue</span><span class="o">;</span>
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<span class="k">if</span> <span class="o">(</span><span class="n">c</span><span class="o">.</span><span class="na">getParameterCount</span><span class="o">()</span> <span class="o">==</span> <span class="mi">0</span><span class="o">)</span> <span class="o">{</span>
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<span class="n">constructor0</span> <span class="o">=</span> <span class="n">c</span><span class="o">;</span>
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<span class="k">break</span><span class="o">;</span>
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<span class="o">}</span>
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<span class="o">}</span>
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<span class="o">}</span></pre></div>
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<p>
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从以上代码可以看出，根据优先级选择Constructor，为了减少学习成本，Creator直接重用了java.beans.ConstructorProperties注解，又因ConstructorProperties只能标记在Constructor上，因此定义一个Creator.ConstructorParameters注解，用于标记在Creator的create方法上。
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</p>
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<div class="highlight"><pre><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Record</span> <span class="o">{</span>
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<span class="kd">private</span> <span class="kd">final</span> <span class="kt">int</span> <span class="n">id</span><span class="o">;</span>
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<span class="kd">private</span> <span class="n">String</span> <span class="n">name</span><span class="o">;</span>
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<span class="nd">@ConstructorProperties</span><span class="o">({</span><span class="s">"id"</span><span class="o">,</span> <span class="s">"name"</span><span class="o">})</span>
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<span class="n">Record</span><span class="o">(</span><span class="kt">int</span> <span class="n">id</span><span class="o">,</span> <span class="n">String</span> <span class="n">name</span><span class="o">)</span> <span class="o">{</span>
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<span class="k">this</span><span class="o">.</span><span class="na">id</span> <span class="o">=</span> <span class="n">id</span><span class="o">;</span>
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<span class="k">this</span><span class="o">.</span><span class="na">name</span> <span class="o">=</span> <span class="n">name</span><span class="o">;</span>
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<span class="o">}</span>
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<span class="kd">public</span> <span class="kt">int</span> <span class="nf">getId</span><span class="o">()</span> <span class="o">{</span>
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<span class="k">return</span> <span class="n">id</span><span class="o">;</span>
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<span class="o">}</span>
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<span class="kd">public</span> <span class="n">String</span> <span class="nf">getName</span><span class="o">()</span> <span class="o">{</span>
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<span class="k">return</span> <span class="n">name</span><span class="o">;</span>
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<span class="o">}</span>
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<span class="kd">public</span> <span class="kt">void</span> <span class="nf">setName</span><span class="o">(</span><span class="n">String</span> <span class="n">name</span><span class="o">)</span> <span class="o">{</span>
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<span class="k">this</span><span class="o">.</span><span class="na">name</span> <span class="o">=</span> <span class="n">name</span><span class="o">;</span>
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<span class="o">}</span>
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<span class="o">}</span>
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<span class="na"><b>Record.class通过ASM自动构建与Record同package的Creator类如下:</b></span>
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<span class="kd">public</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">Record_DynCreator</span> <span class="kd">implements</span> <span class="n">Creator</span><span class="o"><</span><span class="n">Record</span><span class="o">></span> <span class="o">{</span>
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<span class="nd">@Override</span>
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<span class="nd">@Creator.ConstructorParameters</span><span class="o">({</span><span class="s">"id"</span><span class="o">,</span> <span class="s">"name"</span><span class="o">})</span>
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<span class="kd">public</span> <span class="n">Record</span> <span class="nf">create</span><span class="o">(</span><span class="n">Object</span><span class="o">...</span> <span class="n">params</span><span class="o">)</span> <span class="o">{</span>
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<span class="k">if</span> <span class="o">(</span><span class="n">params</span><span class="o">[</span><span class="mi">0</span><span class="o">]</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="n">params</span><span class="o">[</span><span class="mi">0</span><span class="o">]</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span>
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<span class="k">return</span> <span class="k">new</span> <span class="nf">Record</span><span class="o">((</span><span class="n">Integer</span><span class="o">)</span> <span class="n">params</span><span class="o">[</span><span class="mi">0</span><span class="o">],</span> <span class="o">(</span><span class="n">String</span><span class="o">)</span> <span class="n">params</span><span class="o">[</span><span class="mi">1</span><span class="o">]);</span>
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<span class="o">}</span>
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<span class="o">}</span></pre></div>
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<p>
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如上代码，若构造参数是primitive类，而Creator.create传入的参数可能是null，因此需要给null的primitive对象赋予默认值0。细心的人可能发现了Record的构造函数并不是public的，虽然Record_DynCreator与Record在同一package，但由于两者不是同一个ClassLoader，故不能直接new Record。Redkale曲线救国，通过URLClassLoader的私有方法在Record.class的ClassLoader加载Record_DynCreator。
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</p>
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<div class="highlight"><pre><span class="k">if</span> <span class="o">(</span><span class="n">loader</span> <span class="k">instanceof</span> <span class="n">URLClassLoader</span> <span class="o">&&</span> <span class="o">!</span><span class="n">Modifier</span><span class="o">.</span><span class="na">isPublic</span><span class="o">(</span><span class="n">constructor</span><span class="o">.</span><span class="na">getModifiers</span><span class="o">()))</span> <span class="o">{</span>
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<span class="k">try</span> <span class="o">{</span>
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<span class="kd">final</span> <span class="n">URLClassLoader</span> <span class="n">urlLoader</span> <span class="o">=</span> <span class="o">(</span><span class="n">URLClassLoader</span><span class="o">)</span> <span class="n">loader</span><span class="o">;</span>
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<span class="kd">final</span> <span class="n">URL</span> <span class="n">url</span> <span class="o">=</span> <span class="k">new</span> <span class="nf">URL</span><span class="o">(</span><span class="s">"memclass"</span><span class="o">,</span> <span class="s">"localhost"</span><span class="o">,</span> <span class="o">-</span><span class="mi">1</span><span class="o">,</span> <span class="s">"/"</span> <span class="o">+</span> <span class="n">newDynName</span><span class="o">.</span><span class="na">replace</span><span class="o">(</span><span class="sc">'/'</span><span class="o">,</span> <span class="sc">'.'</span><span class="o">)</span> <span class="o">+</span> <span class="s">"/"</span><span class="o">,</span> <span class="k">new</span> <span class="nf">URLStreamHandler</span><span class="o">()</span> <span class="o">{</span>
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<span class="nd">@Override</span>
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<span class="kd">protected</span> <span class="n">URLConnection</span> <span class="nf">openConnection</span><span class="o">(</span><span class="n">URL</span> <span class="n">u</span><span class="o">)</span> <span class="kd">throws</span> <span class="n">IOException</span> <span class="o">{</span>
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<span class="k">return</span> <span class="k">new</span> <span class="nf">URLConnection</span><span class="o">(</span><span class="n">u</span><span class="o">)</span> <span class="o">{</span>
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<span class="nd">@Override</span>
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<span class="kd">public</span> <span class="kt">void</span> <span class="nf">connect</span><span class="o">()</span> <span class="kd">throws</span> <span class="n">IOException</span> <span class="o">{</span>
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<span class="o">}</span>
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<span class="nd">@Override</span>
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<span class="kd">public</span> <span class="n">InputStream</span> <span class="nf">getInputStream</span><span class="o">()</span> <span class="kd">throws</span> <span class="n">IOException</span> <span class="o">{</span>
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<span class="k">return</span> <span class="k">new</span> <span class="nf">ByteArrayInputStream</span><span class="o">(</span><span class="n">bytes</span><span class="o">);</span>
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<span class="o">}</span>
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<span class="o">};</span>
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<span class="o">}</span>
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<span class="o">});</span>
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<span class="n">Method</span> <span class="n">addURLMethod</span> <span class="o">=</span> <span class="n">URLClassLoader</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">getDeclaredMethod</span><span class="o">(</span><span class="s">"addURL"</span><span class="o">,</span> <span class="n">URL</span><span class="o">.</span><span class="na">class</span><span class="o">);</span>
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<span class="n">addURLMethod</span><span class="o">.</span><span class="na">setAccessible</span><span class="o">(</span><span class="kc">true</span><span class="o">);</span>
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<span class="n">addURLMethod</span><span class="o">.</span><span class="na">invoke</span><span class="o">(</span><span class="n">urlLoader</span><span class="o">,</span> <span class="n">url</span><span class="o">);</span>
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<span class="n">resultClazz</span> <span class="o">=</span> <span class="n">urlLoader</span><span class="o">.</span><span class="na">loadClass</span><span class="o">(</span><span class="n">newDynName</span><span class="o">.</span><span class="na">replace</span><span class="o">(</span><span class="sc">'/'</span><span class="o">,</span> <span class="sc">'.'</span><span class="o">));</span>
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<span class="o">}</span> <span class="k">catch</span> <span class="o">(</span><span class="n">Throwable</span> <span class="n">t</span><span class="o">)</span> <span class="o">{</span> <span class="c1">//异常无需理会， 使用下一种loader方式</span>
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<span class="n">t</span><span class="o">.</span><span class="na">printStackTrace</span><span class="o">();</span>
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<span class="o">}</span>
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<span class="o">}</span></pre></div>
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<p>
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如上代码，构建一个虚拟协议的URL来实现加载，若Record.class的ClassLoader不是URLClassLoader导致resultClazz为null则会抛出异常。
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</p>
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<p>
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Creator是一个典型通过ASM构建一个简单功能地动态类，同类型还有 <a href="https://redkale.org/javadoc/org/redkale/util/Attribute.html" target="_blank">org.redkale.util.Attribute</a>、<a href="https://redkale.org/javadoc/org/redkale/util/Reproduce.html" target="_blank">org.redkale.util.Reproduce</a>。
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</p>
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<br/>
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<p>
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转载请注明出处：<a href="https://redkale.org/article_creator.html" target="_blank">https://redkale.org/article_creator.html</a>
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</p>
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<footer class="site-footer">
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<span class="site-footer-owner"> 欢迎加入Redkale QQ群: 527523235</span>
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