This commit is contained in:
RedKale
@@ -26,11 +26,134 @@
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</section>
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<section class="main-content">
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<h3><a id="watch-intro" class="anchor" href="#welcome-to-github-pages" aria-hidden="true"></a>Watch 组件介绍</h3>
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<h3>Redkale 技术详解 02 -- Creator构建对象</h3>
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<p>敬请期待…… <br/>
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<p>
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org.redkale.util.Creator是采用ASM技术来实现代替反射构造函数的对象构建类。在根据流反序列化成对象、数据表记录转换成对象时都需要构建对象。常见的处理办法是利用反射，如Gson框架中反序列化是通过反射进行对象创建。众所周知反射的性能是比较低的，所以Redkale需要自实现一个对象构建类。
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</p>
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<p>
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Creator是一个接口， 只有一个public T create(Object... params)方法，可变参数既适合空参数的Constructor也适合含参数的Constructor。得利于Java 8的新语法特性可以在接口上加上静态方法，Creator对象可以通过Creator.create(Class clazz)方法创建。构建原理是通过Constructor的参数来动态创建的。
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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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<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="http://redkale.org/javadoc/org/redkale/util/Attribute.html" target="_blank">org.redkale.util.Attribute</a>、<a href="http://redkale.org/javadoc/org/redkale/util/Reproduce.html" target="_blank">org.redkale.util.Reproduce</a>。
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</p>
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<footer class="site-footer">
|
||||
<span class="site-footer-owner"> 欢迎加入Redkale QQ群: 527523235</span>
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</footer>
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@@ -26,20 +26,20 @@
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</section>
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<section class="main-content">
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<p class="art-list">
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<a href="article_parents.html" target="_blank" class="art-title">Redkale 技术详解 01 -- 双亲委托模型</a>
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<label class="art-date">2016-02</label><br/>
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<label class="art-desc">Redkale 里大量使用了双亲委托模型，序列化的ConvertFactory、依赖注入的ResourceFactory、服务管理的WatchFactory均采用双亲委托模型。</label>
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</p>
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<!--
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<p class="art-list">
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<a href="article_creator.html" target="_blank" class="art-title">Redkale 技术详解 02 -- Creator对象构造</a>
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<a href="article_creator.html" target="_blank" class="art-title">Redkale 技术详解 02 -- Creator构建对象</a>
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<label class="art-date">2016-02</label><br/>
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<label class="art-desc">...</label>
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<label class="art-desc">org.redkale.util.Creator是采用ASM技术来实现代替反射构造函数的对象构建类。</label>
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</p>
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-->
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<br/>
|
||||
<footer class="site-footer">
|
||||
<span class="site-footer-owner"> 欢迎加入Redkale QQ群: 527523235</span>
|
||||
|
||||
Reference in New Issue
Block a user