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<meta name="description" content="知耻而后勇，知弱而图强">
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<meta name="description" content="1234title: 安卓注解处理器-processordate: 2019-01-04 19:02:34tags: annotation、processor、自动生成java文件category: 注解 最近在学习安卓开源框架发现，很多的开源框架都使用到了注解处理器，例如EventBus3.0。本文通过一个简单的Demo来介绍如何使用注解处理器。Demo链接为https://github.com">
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<meta property="og:description" content="1234title: 安卓注解处理器-processordate: 2019-01-04 19:02:34tags: annotation、processor、自动生成java文件category: 注解 最近在学习安卓开源框架发现，很多的开源框架都使用到了注解处理器，例如EventBus3.0。本文通过一个简单的Demo来介绍如何使用注解处理器。Demo链接为https://github.com">
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<meta name="twitter:description" content="1234title: 安卓注解处理器-processordate: 2019-01-04 19:02:34tags: annotation、processor、自动生成java文件category: 注解 最近在学习安卓开源框架发现，很多的开源框架都使用到了注解处理器，例如EventBus3.0。本文通过一个简单的Demo来介绍如何使用注解处理器。Demo链接为https://github.com">
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<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">title: 安卓注解处理器-processor</span><br><span class="line">date: 2019-01-04 19:02:34</span><br><span class="line">tags: annotation、processor、自动生成java文件</span><br><span class="line">category: 注解</span><br></pre></td></tr></table></figure>
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<p>最近在学习安卓开源框架发现，很多的开源框架都使用到了注解处理器，例如EventBus3.0。本文通过一个简单的Demo来介绍如何使用注解处理器。Demo链接为<a href="https://github.com/cugyong/AnnotationProcessor-sample" target="_blank" rel="noopener">https://github.com/cugyong/AnnotationProcessor-sample</a> ，如果喜欢的话，欢迎大家给star。<a id="more"></a></p>
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<h2 id="Demo需求描述"><a href="#Demo需求描述" class="headerlink" title="Demo需求描述"></a>Demo需求描述</h2><p>用户通过执行一个传入参数为A（类对象）的静态方法，该方法会最终把参数A中加了特定注解的所有方法执行一遍。</p>
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<h2 id="需求实现"><a href="#需求实现" class="headerlink" title="需求实现"></a>需求实现</h2><p><img src="/2019/01/04/安卓注解处理器-processor/框架流程.png" alt="框架流程"></p>
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<p>整个项目分为四个部分：</p>
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<ul>
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<li>注解–要使用的注解类型，这部分通常也可以放在lib中；</li>
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<li>注解处理器–要对注解进行处理的逻辑，包括收集有特定注解类型的方法信息以及生成特定的java文件；</li>
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<li>lib–封装合适的接口，供具体调用方调用；</li>
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<li>sample–具体的调用方逻辑。</li>
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</ul>
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<p>首先新建一个安卓工程，点击运行展示的是hello world。</p>
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<h3 id="注解"><a href="#注解" class="headerlink" title="注解"></a>注解</h3><p>在上述工程中new-&gt;Module-&gt;Java Library，新建一个Java Library Module，命名为annotation。在该Module下创建一个文件AnnotationTest.java，</p>
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<p><img src="/2019/01/04/安卓注解处理器-processor/annotation.png" alt="1546591844724"></p>
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<p>AnnotationTest.java里面代码如下：</p>
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<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">@Retention(RetentionPolicy.CLASS)</span><br><span class="line">@Target(ElementType.METHOD)</span><br><span class="line">public @interface AnnotationTest &#123;</span><br><span class="line"> String name() default &quot;test&quot;;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
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<p>1、注解@Retention按生命周期来划分可分为3类：</p>
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<ul>
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<li>RetentionPolicy.SOURCE：注解只保留在源文件，当Java文件编译成class文件的时候，注解被遗弃；</li>
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<li>RetentionPolicy.CLASS：注解被保留到class文件，当jvm加载class文件时候被遗弃，这是默认的生命周期；</li>
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<li>RetentionPolicy.RUNTIME：注解不仅被保存到class文件中，jvm加载class文件之后，仍然存在。</li>
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</ul>
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<p>这3个生命周期分别对应于：Java源文件(.java文件) —&gt; .class文件 —&gt; 内存中的字节码。</p>
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<p>2、注解@Target表示修饰的注解能使用的范围，ElementType.METHOD表示@AnnotationTest注解只能作用在方法上。</p>
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<h3 id="注解处理器"><a href="#注解处理器" class="headerlink" title="注解处理器"></a>注解处理器</h3><p>参照上部分，在工程中new-&gt;Module-&gt;Java Library，新建一个Java Library Module， 在该Module下创建一个文件ProcessorTest.java。在该Module下的build.gradle的dependencies中添加如下配置：</p>
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<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">// 自动为processor注册</span><br><span class="line">implementation &apos;com.google.auto.service:auto-service:1.0-rc2&apos;</span><br><span class="line">// 该Module依赖上部分建立的annotation Module</span><br><span class="line">implementation project(&apos;:annotation&apos;)</span><br></pre></td></tr></table></figure>
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<p>com.google.auto.service:auto-service:1.0-rc2依赖的作用是为注解处理器自动注册，它会生成META-INF文件夹。</p>
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<p>注解处理器ProcessorTest的定义如下，其中@AutoService(Processor.class)就是build.gradle中加的依赖帮助其自动注册。</p>
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<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">@AutoService(Processor.class) // 自动为ProcessorTest注册，生成META-INF文件</span><br><span class="line">public class ProcessorTest extends AbstractProcessor&#123;</span><br></pre></td></tr></table></figure>
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<p>注解处理器ProcessorTest主要包含以下几个部分：</p>
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<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">@Override</span><br><span class="line">public synchronized void init(ProcessingEnvironment processingEnvironment) &#123;</span><br><span class="line"> super.init(processingEnvironment);</span><br><span class="line"></span><br><span class="line"> mMessager = processingEnvironment.getMessager();</span><br><span class="line"> mFiler = processingEnvironment.getFiler();</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
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<p>init方法是注解处理器会自动调用的初始化方法，其中mFiler是用来生成java源文件的工具，mMessager是用来打印日志的，它们的具体使用会在后面介绍。</p>
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<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">@Override</span><br><span class="line">public Set&lt;String&gt; getSupportedAnnotationTypes() &#123;</span><br><span class="line"> Set&lt;String&gt; supportAnnotationTypes = new HashSet&lt;&gt;();</span><br><span class="line"> supportAnnotationTypes.add(AnnotationTest.class.getCanonicalName());</span><br><span class="line"> return supportAnnotationTypes;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
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<p>getSupportedAnnotationTypes()方法返回该注解处理器支持的注解类型，这里返回的就是我们之前声明的新的注解类型@AnnotationTest。</p>
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<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">@Override</span><br><span class="line">public SourceVersion getSupportedSourceVersion() &#123;</span><br><span class="line"> return SourceVersion.latestSupported();</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
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<p>getSupportedSourceVersion()方法一般就按照上述实现就行。</p>
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<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br></pre></td><td class="code"><pre><span class="line">@Override</span><br><span class="line">public boolean process(Set&lt;? extends TypeElement&gt; annotations, RoundEnvironment roundEnvironment) &#123;</span><br><span class="line"> // 打印日志</span><br><span class="line"> mMessager.printMessage(Diagnostic.Kind.NOTE, &quot;process start&quot;);</span><br><span class="line"> Map&lt;String, List&lt;String&gt;&gt; collectInfos = new HashMap&lt;&gt;();</span><br><span class="line"> for (TypeElement annotation: annotations)&#123;</span><br><span class="line"> Set&lt;? extends Element&gt; elements = roundEnvironment.getElementsAnnotatedWith(annotation);</span><br><span class="line"> for (Element element: elements)&#123;</span><br><span class="line"> // 检查element是否符合我们定义的规范</span><br><span class="line"> if (!checkValid(element))&#123;</span><br><span class="line"> mMessager.printMessage(Diagnostic.Kind.NOTE, &quot;checkValid not pass&quot;);</span><br><span class="line"> return false;</span><br><span class="line"> &#125;else &#123;</span><br><span class="line"> ExecutableElement executableElement = (ExecutableElement) element;</span><br><span class="line"> // 获取被注解的方法所在的类</span><br><span class="line"> TypeElement typeElement = (TypeElement) executableElement.getEnclosingElement();</span><br><span class="line"> // 获取类的全名，包括包名</span><br><span class="line"> String classFullName = typeElement.getQualifiedName().toString();</span><br><span class="line"> // 被注解的方法的名字</span><br><span class="line"> String methodName = executableElement.getSimpleName().toString();</span><br><span class="line"> List&lt;String&gt; methods = collectInfos.get(classFullName);</span><br><span class="line"> if (methods == null)&#123;</span><br><span class="line"> methods = new ArrayList&lt;&gt;();</span><br><span class="line"> collectInfos.put(classFullName, methods);</span><br><span class="line"> &#125;</span><br><span class="line"> methods.add(methodName);</span><br><span class="line"> &#125;</span><br><span class="line"> &#125;</span><br><span class="line"> &#125;</span><br><span class="line"></span><br><span class="line"> for (Map.Entry&lt;String, List&lt;String&gt;&gt; entry: collectInfos.entrySet())&#123;</span><br><span class="line"> mMessager.printMessage(Diagnostic.Kind.NOTE, entry.getKey());</span><br><span class="line"> // 生成java源文件</span><br><span class="line"> createJavaFile(entry.getKey(), entry.getValue());</span><br><span class="line"> &#125;</span><br><span class="line"></span><br><span class="line"> return true;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
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<p>process方法是我们的主要逻辑处理的地方，主要逻辑就是收集所有有@AnnotationTest注解的方法以及其所在的类信息，然后根据每个类信息，生成一个新的类文件，并在新的类文件的特定方法中调用所有关联的注解方法。生成java源文件将使用Filer对象，具体如何使用请下载demo看源代码。</p>
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<p><strong>注：</strong> </p>
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<p>1、当你点击buid project时，注解处理器将会执行，而Messager对象打印出来的日志信息可以在Gradle Console窗口中看到。</p>
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<p>2、如果你在该Module中使用中文注解，因为该Module为java library，可能会报GBK编码错误，解决办法是在该Module的build.gradle中添加如下代码：</p>
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<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">//指定编译的编码</span><br><span class="line">tasks.withType(JavaCompile)&#123;</span><br><span class="line"> options.encoding = &quot;UTF-8&quot;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
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<h3 id="Lib"><a href="#Lib" class="headerlink" title="Lib"></a>Lib</h3><p>在工程中new-&gt;Module-&gt;Android Library ，新建一个Android Library Module，封装接口给调用方使用，具体逻辑请参考demo。</p>
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<p>最终该demo的功能是点击Hello world文字，会依此执行MainActivity中使用@AnnotationTest注解的方法。</p>
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<div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-2"><a class="nav-link" href="#Demo需求描述"><span class="nav-text">Demo需求描述</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#需求实现"><span class="nav-text">需求实现</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#注解"><span class="nav-text">注解</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#注解处理器"><span class="nav-text">注解处理器</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#Lib"><span class="nav-text">Lib</span></a></li></ol></li></ol></div>
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<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">title: 安卓注解处理器-processor</span><br><span class="line">date: 2019-01-04 19:02:34</span><br><span class="line">tags: annotation、processor、自动生成java文件</span><br><span class="line">category: 注解</span><br></pre></td></tr></table></figure>
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<p>最近在学习安卓开源框架发现，很多的开源框架都使用到了注解处理器，例如EventBus3.0。本文通过一个简单的Demo来介绍如何使用注解处理器。Demo链接为<a href="https://github.com/cugyong/AnnotationProcessor-sample" target="_blank" rel="noopener">https://github.com/cugyong/AnnotationProcessor-sample</a> ，如果喜欢的话，欢迎大家给star。</p>
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