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<h1 class="post-title" itemprop="name headline">玩转Class之Class的各种骚操作(反射封装必看)</h1>
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<p><strong>版权声明：本文为博主原创文章，转载请注明出处(www.huangjie.name)，保护原创，从我做起.</strong></p>
<hr>
<blockquote>
<p>文章首发于我的<a href="https://www.jianshu.com/u/2334b8b9f764" target="_blank" rel="noopener">简书</a>,本处只做整理归档用<br><a id="more"></a></p>
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<h2 id="简介"><a href="#简介" class="headerlink" title="简介"></a>简介</h2><p>Class类表示正在运行的Java应用程序中的类和接口，枚举和基本数据类型，我们可以从中获取到类的一切相关信息，包括字段，方法，名称，父类，接口等</p>
<h2 id="常用方法介绍"><a href="#常用方法介绍" class="headerlink" title="常用方法介绍"></a>常用方法介绍</h2><h4 id="名称获取"><a href="#名称获取" class="headerlink" title="名称获取"></a>名称获取</h4><p>此类方法用于获取类的名称信息<br><strong>getName()方法</strong></p>
<ul>
<li><p>如果是一个实体类，则会返回完整包名路径名称,<br>例如位于<code>com.hj.testclass</code>包下的<code>student</code>类，则会返回<code>com.hj.testclass.student</code></p>
</li>
<li><p>如果是一个数组类型，则返回内部嵌套深度的一个或多个”[“字符，后面拼接上基本数据类型的二进制名称,二进制名称表如下：</p>
</li>
</ul>
<table>
<thead>
<tr>
<th>Element Type</th>
<th>Encoding</th>
</tr>
</thead>
<tbody>
<tr>
<td>boolean</td>
<td>Z</td>
</tr>
<tr>
<td>byte</td>
<td>B</td>
</tr>
<tr>
<td>char</td>
<td>C</td>
</tr>
<tr>
<td>class or interface</td>
<td>Lclassname</td>
</tr>
<tr>
<td>double</td>
<td>D</td>
</tr>
<tr>
<td>float</td>
<td>F</td>
</tr>
<tr>
<td>int</td>
<td>I</td>
</tr>
<tr>
<td>long</td>
<td>J</td>
</tr>
<tr>
<td>short</td>
<td>S</td>
</tr>
</tbody>
</table>
<p>示例：</p>
<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></pre></td><td class="code"><pre><span class="line">(new long[1][2][3]).getClass().getName()</span><br><span class="line">输出:</span><br><span class="line">[[[J</span><br></pre></td></tr></table></figure>
<ul>
<li>如果是基本数据类型，则会返回数据类型的关键字<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></pre></td><td class="code"><pre><span class="line">byte.class.getName()</span><br><span class="line">输出：</span><br><span class="line">byte</span><br></pre></td></tr></table></figure>
</li>
</ul>
<p><strong>getSimpleName()方法</strong><br>返回源代码中给出的基础类的简单名称。 如果基础类是匿名的，则返回一个空字符串。<br><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">Student student = new Student();</span><br><span class="line">Class mClass = student.getClass();</span><br><span class="line">log("getSimpleName:"+mClass.getSimpleName());</span><br><span class="line">输出：</span><br><span class="line">Student</span><br></pre></td></tr></table></figure></p>
<p><strong>getPackage()方法</strong><br>返回包名信息</p>
<h4 id="注解相关"><a href="#注解相关" class="headerlink" title="注解相关"></a>注解相关</h4><p>可获取此类是否是注解，是否包含某注解并获取到其对象，获取全部注解</p>
<table>
<thead>
<tr>
<th>方法</th>
<th>作用</th>
</tr>
</thead>
<tbody>
<tr>
<td><strong>getAnnotation(Class<a> annotationClass)</a></strong></td>
<td>获取传入的注解对象，如果不存在，则返回null</td>
</tr>
<tr>
<td><strong>getAnnotations()</strong></td>
<td>返回此类上的所有注解</td>
</tr>
<tr>
<td><strong>getAnnotationsByType(Class<a> annotationClass)</a></strong></td>
<td>返回传入的注解对象数组，与getAnnotation()的区别是检测传入的注解是否是重复元素</td>
</tr>
<tr>
<td><strong>isAnnotation()</strong></td>
<td>判断这个类是否是一个注解类</td>
</tr>
<tr>
<td><strong>isAnnotationPresent(Class<? extends Annotation> annotationClass)</strong></td>
<td>是否包含传入的注解类,效果与getAnnotation()!=null相同</td>
</tr>
</tbody>
</table>
<p>举个栗子：<br>新建一个注解对象：</p>
<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">/**</span><br><span class="line"> * Created by hj on 2019/1/10.</span><br><span class="line"> * 说明：</span><br><span class="line"> */</span><br><span class="line">@Retention(RetentionPolicy.RUNTIME)</span><br><span class="line">public @interface MyAnnotation {</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>新建一个Student并加入<code>@MyAnnotation</code>注解：<br><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></pre></td><td class="code"><pre><span class="line">/**</span><br><span class="line"> * Created by hj on 2019/1/10.</span><br><span class="line"> * 说明：</span><br><span class="line"> */</span><br><span class="line">@MyAnnotation</span><br><span class="line">public class Student{</span><br><span class="line"></span><br><span class="line"> public static void main(String[] args) {</span><br><span class="line"> Student student = new Student();</span><br><span class="line"> Class studentClass = student.getClass();</span><br><span class="line"> boolean isAnnotation = studentClass.isAnnotation();</span><br><span class="line"> log(studentClass.getSimpleName()+"是否是注解类:"+isAnnotation);</span><br><span class="line"> boolean isContainAnnotation = studentClass.isAnnotationPresent(MyAnnotation.class);</span><br><span class="line"> log(studentClass.getSimpleName()+"是否包含MyAnnotation注解类:"+isContainAnnotation);</span><br><span class="line"> Annotation annotation = studentClass.getAnnotation(MyAnnotation.class);</span><br><span class="line"> Annotation[] annotations = studentClass.getAnnotations();</span><br><span class="line"> if (annotation != null) {</span><br><span class="line"> log("获取指定的MyAnnotation类:"+annotation.toString());</span><br><span class="line"> }</span><br><span class="line"> if (annotations.length > 0){</span><br><span class="line"> log("获取注解集合中的第一个元素:"+annotations[0].toString());</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> private static void log(String value) {</span><br><span class="line"> System.out.print(value);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>打印：<br><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">Student是否是注解类:false</span><br><span class="line">Student是否包含MyAnnotation注解类:true</span><br><span class="line">获取指定的MyAnnotation类:@jie.com.imageoptimize.mclass.MyAnnotation()</span><br><span class="line">获取注解集合中的第一个元素:@jie.com.imageoptimize.mclass.MyAnnotation()</span><br></pre></td></tr></table></figure></p>
<h4 id="构造方法相关"><a href="#构造方法相关" class="headerlink" title="构造方法相关"></a>构造方法相关</h4><p>在介绍构造方法之前，先介绍一个类<code>Constructor</code>,它的作用是提供一个类的单个构造方法的信息访问，如果一个类有两个构造方法，那么这个类就会对应有两个<code>Constructor</code>类，它可以使用<code>newInstance</code>方法来进行类的构造方法实现并进行扩展，但如果发生缩小转换则会抛出<code>IllegalArgumentException</code>异常，比如这个类有两个构造参数却只传入一个，就会抛异常。<br>获取<code>Constructor</code>信息的方法有：</p>
<table>
<thead>
<tr>
<th>方法</th>
<th>作用</th>
</tr>
</thead>
<tbody>
<tr>
<td><strong>getConstructors()</strong></td>
<td>返回这个类的公共构造函数的 Constructor对象的数组</td>
</tr>
<tr>
<td><strong>getConstructor(Class<?>..parameterTypes)</strong></td>
<td>传入一个指定的参数类型来获取特定的公共构造方法类</td>
</tr>
<tr>
<td><strong>getDeclaredConstructors()</strong></td>
<td>与getConstructors的区别是返回所有的构造方法数组，不限于public protected private</td>
</tr>
<tr>
<td><strong>getDeclaredConstructor(Class<?>..parameterTypes)</strong></td>
<td>与getConstructor的区别是会返回所有类型的构造方法</td>
</tr>
</tbody>
</table>
<p>接下来介绍一下<code>Constructor</code>类的<code>newInstance</code>方法，这个方法说白了就是执行构造函数的，你传入一个当前构造函数的类型的值进去，那么就会执行这个类的构造方法。<br>下面举一个反射调用构造方法的栗子：<br>新建一个Student类，分别添加两个私有构造方法，一个公有构造方法，并添加两个参数，在构造方法处执行打印逻辑，代码如下：</p>
<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><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br></pre></td><td class="code"><pre><span class="line">/**</span><br><span class="line"> * Created by hj on 2019/1/10.</span><br><span class="line"> * 说明：</span><br><span class="line"> */</span><br><span class="line"></span><br><span class="line">public class Student {</span><br><span class="line"></span><br><span class="line"> private String name;</span><br><span class="line"> private int age;</span><br><span class="line"></span><br><span class="line"> private Student() {</span><br><span class="line"></span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> public Student(String name) {</span><br><span class="line"> this.name = name;</span><br><span class="line"> log("公有构造方法执行了，打印传入的名称为:"+name);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> private Student(int age){</span><br><span class="line"> this.age = age;</span><br><span class="line"> log("私有构造方法执行了，打印传入的年龄为:"+age);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> public static void main(String[] args) {</span><br><span class="line"> Student student = new Student();</span><br><span class="line"> Class mClass = student.getClass();</span><br><span class="line"> Constructor[] constructors = mClass.getConstructors();</span><br><span class="line"> log("获取" + mClass.getSimpleName() + "的公共构造方法数量为:" + constructors.length);</span><br><span class="line"> try {</span><br><span class="line"> Constructor constructor = mClass.getConstructor(String.class);</span><br><span class="line"></span><br><span class="line"> constructor.newInstance("张三");</span><br><span class="line"></span><br><span class="line"> } catch (NoSuchMethodException | IllegalAccessException | InstantiationException | InvocationTargetException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> Constructor[] declaredConstructors = mClass.getDeclaredConstructors();</span><br><span class="line"> log("获取" + mClass.getSimpleName() + "的所有构造方法数量为:" + declaredConstructors.length);</span><br><span class="line"> try {</span><br><span class="line"> Constructor constructor = mClass.getDeclaredConstructor(int.class);</span><br><span class="line"></span><br><span class="line"> constructor.newInstance(18);</span><br><span class="line"></span><br><span class="line"> } catch (NoSuchMethodException | IllegalAccessException | InstantiationException | InvocationTargetException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> private static void log(String value) {</span><br><span class="line"> System.out.print(value);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>打印结果如下：<br><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">获取Student的公共构造方法数量为:1</span><br><span class="line">公有构造方法执行了，打印传入的名称为:张三</span><br><span class="line">获取Student的所有构造方法数量为:3</span><br><span class="line">私有构造方法执行了，打印传入的年龄为:18</span><br></pre></td></tr></table></figure></p>
<p>怎么样，反射调用类的构造方法技能get到了吗</p>
<h5 id="字段相关"><a href="#字段相关" class="headerlink" title="字段相关"></a>字段相关</h5><p>此类型方法是用的最多的一种，希望小伙伴们可以熟练掌握<br>在介绍字段方法之前，先介绍一个类<code>Field</code>,它用于保存，修改字段的信息，甚至可以修改字段的访问权限,常用的方法如下:</p>
<table>
<thead>
<tr>
<th>方法</th>
<th>作用</th>
</tr>
</thead>
<tbody>
<tr>
<td><strong>getName()</strong></td>
<td>获取字段名称</td>
</tr>
<tr>
<td><strong>get()</strong></td>
<td>传入需要获取的值的类的对象，获取该字段的值,返回object类型，使用的时候需要做类型判断</td>
</tr>
<tr>
<td><strong>getBoolean(),getInt()…</strong></td>
<td>获取指定类型的字段值</td>
</tr>
<tr>
<td><strong>set()，setBoolean()…</strong></td>
<td>将指定的类的指定值设置为新值</td>
</tr>
<tr>
<td><strong>isAccessible()</strong></td>
<td>判断此字段是否有访问权限</td>
</tr>
<tr>
<td><strong>setAccessible()</strong></td>
<td>设置字段的权限，为true代表可以访问</td>
</tr>
</tbody>
</table>
<p>接下来再来看看如何使用Class来获取字段信息:</p>
<table>
<thead>
<tr>
<th>方法</th>
<th>作用</th>
</tr>
</thead>
<tbody>
<tr>
<td><strong>getFields()</strong></td>
<td>获取所有的公共字段</td>
</tr>
<tr>
<td><strong>getField()</strong></td>
<td>传入字段的名称，返回公共字段对象</td>
</tr>
<tr>
<td><strong>getDeclaredFields()</strong></td>
<td>获取所有字段，返回一个Field数组</td>
</tr>
<tr>
<td><strong>getDeclaredField</strong></td>
<td>传入字段的名称，返回字段对象,无访问限制</td>
</tr>
</tbody>
</table>
<p>下面举个获取字段名称和内容的例子，并分享一个常用的套路写法，一般的都可以按照这个套路来写：</p>
<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><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br></pre></td><td class="code"><pre><span class="line">/**</span><br><span class="line"> * Created by hj on 2019/1/10.</span><br><span class="line"> * 说明：</span><br><span class="line"> */</span><br><span class="line"></span><br><span class="line">public class Student {</span><br><span class="line"></span><br><span class="line"> public String name;</span><br><span class="line"> private int age;</span><br><span class="line"></span><br><span class="line"> public Student(String name, int age) {</span><br><span class="line"> this.name = name;</span><br><span class="line"> this.age = age;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> public static void main(String[] args) {</span><br><span class="line"> Student student = new Student("张三", 18);</span><br><span class="line"> setAllComponentsName(student);</span><br><span class="line"> }</span><br><span class="line"> </span><br><span class="line"> private static void setAllComponentsName(Object f) {</span><br><span class="line"> Field[] fields = f.getClass().getDeclaredFields();</span><br><span class="line"> for (Field field : fields) {</span><br><span class="line"> // 对于每个属性，获取属性名</span><br><span class="line"> String varName = field.getName();</span><br><span class="line"> try {</span><br><span class="line"> // 获取原来的访问控制权限</span><br><span class="line"> boolean accessFlag = field.isAccessible();</span><br><span class="line"> // 修改访问控制权限</span><br><span class="line"> field.setAccessible(true);</span><br><span class="line"> // 获取在对象f中属性fields[i]对应的对象中的变量</span><br><span class="line"> Object o = field.get(f);</span><br><span class="line"> if (!"".equals(varName)) {</span><br><span class="line"> //这里可以处理相关逻辑</span><br><span class="line"> if (o != null) {</span><br><span class="line"> if (o instanceof String) {</span><br><span class="line"> String value = (String) o;</span><br><span class="line"> log("String类型字段:" + value);</span><br><span class="line"> } else if (o instanceof Integer) {</span><br><span class="line"> int value = (int) o;</span><br><span class="line"> log("int类型字段:" + value);</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> // 恢复访问控制权限</span><br><span class="line"> field.setAccessible(accessFlag);</span><br><span class="line"> } catch (IllegalArgumentException | IllegalAccessException ex) {</span><br><span class="line"> ex.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> private static void log(String value) {</span><br><span class="line"> System.out.print(value);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>打印结果：<br><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">String类型字段:张三</span><br><span class="line">int类型字段:18</span><br></pre></td></tr></table></figure></p>
<p>一般都是先将权限修改为true,再去读取字段内容，随后进行逻辑处理，最后记得将权限改回来.</p>
<h5 id="方法相关"><a href="#方法相关" class="headerlink" title="方法相关"></a>方法相关</h5><p>此类型方法也是用的比较多的一种，是反射调用方法的关键<br>class中关于方法的封装都是给<code>Method</code>类来操作的，它可以获取，修改，执行类的方法，核心方法就是<code>invoke()</code>，作用是执行方法，第一个参数是需要执行的方法的类对象，随后是需要执行的方法参数值。<br>获取<code>Method</code>对象有四个方法:</p>
<table>
<thead>
<tr>
<th>方法</th>
<th>作用</th>
</tr>
</thead>
<tbody>
<tr>
<td><strong>getMethods()</strong></td>
<td>获取类的所有公共方法</td>
</tr>
<tr>
<td><strong>getMethod()</strong></td>
<td>获取指定公共方法，传入一个方法的名称与参数的类型</td>
</tr>
<tr>
<td><strong>getDeclaredMethods()</strong></td>
<td>获取类的所有方法</td>
</tr>
<tr>
<td><strong>getDeclaredMethod()</strong></td>
<td>获取类的指定方法，传入参数同getMethod()</td>
</tr>
</tbody>
</table>
<p>举个例子，将本来为张三的名称修改为李四：</p>
<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></pre></td><td class="code"><pre><span class="line">/**</span><br><span class="line"> * Created by hj on 2019/1/10.</span><br><span class="line"> * 说明：</span><br><span class="line"> */</span><br><span class="line"></span><br><span class="line">public class Student {</span><br><span class="line"></span><br><span class="line"> public String name;</span><br><span class="line"> private int age;</span><br><span class="line"></span><br><span class="line"> public Student(String name, int age) {</span><br><span class="line"> this.name = name;</span><br><span class="line"> this.age = age;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> private void setName(String name){</span><br><span class="line"> this.name = name;</span><br><span class="line"> log("设置的名称为："+name);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> public static void main(String[] args) {</span><br><span class="line"> Student student = new Student("张三", 18);</span><br><span class="line"> Class mClass = student.getClass();</span><br><span class="line"> try {</span><br><span class="line"> Method method = mClass.getDeclaredMethod("setName",String.class);</span><br><span class="line"> method.invoke(student,"李四");</span><br><span class="line"> } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> private static void log(String value) {</span><br><span class="line"> System.out.print(value);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>打印结果:<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">设置的名称为：李四</span><br></pre></td></tr></table></figure></p>
<p>在项目中使用，可以参考上面的<code>Field</code>类，其实都是差不多的，一通百通。</p>
<h5 id="抽象-继承-接口-泛型相关"><a href="#抽象-继承-接口-泛型相关" class="headerlink" title="抽象,继承,接口,泛型相关"></a>抽象,继承,接口,泛型相关</h5><p>此类方法虽然不常用到，但在某些情况下能发挥意想不到的作用，在许多框架的源码中也能看见它们的身影，如<code>Gson</code>的<code>$Gson$Types</code>类,<code>Retrofit</code>的<code>Util</code>类等，来跟我学习一下把。</p>
<p><strong>泛型</strong><br>首先说说获取类的泛型获取，先介绍一个接口<code>Type</code>,它是java中所有类型的通用接口，类型包括原始类型(class)，参数化类型(ParameterizedType)，数组类型(GenericArrayType)，类型变量(TypeVariable)和基本数据类型。内部实现了一个方法<code>getTypeName()</code>,用于返回类型参数信息，基于它向外扩展的接口有：</p>
<ul>
<li>ParameterizedType<br>表示一个参数化类型，说简单点就是带有参数类型的类型，如Collection ,如果带有了类型，如Collection<string>，那么就是说String将Collection参数化</string></li>
<li>GenericArrayType<br>表示一个参数化类型或类型变量的数组类型，简单说就是泛型A<t>[]或泛型数组T[]</t></li>
<li>TypeVariable<br>所有类型变量的父接口,也就是我们定义抽象类中的那种K,E等泛型变量，可以泛指任何类</li>
<li>WildcardType<br>表示一个通配符表达，例如?,? extends Integer<br><code>Type</code>可以通过<code>class</code>的<code>getGenericInterfaces</code>或<code>getGenericSuperclass()</code>方法来获取<br>这么说或许还有点抽象，<code>ParameterizedType</code>与<code>TypeVariable</code>的概念或许还拎不太清。下面通过示例来加深理解<br>先来说说ParameterizedType<br>举个例子，先声明一个带泛型的超类<code>Person</code></li>
</ul>
<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></pre></td><td class="code"><pre><span class="line">/**</span><br><span class="line"> * Created by hj on 2019/1/10.</span><br><span class="line"> * 说明：</span><br><span class="line"> */</span><br><span class="line"></span><br><span class="line">public class Person<T> {</span><br><span class="line"></span><br><span class="line"> public T feature;</span><br><span class="line"></span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>随后定义一个实体类<code>Feature</code><br><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">/**</span><br><span class="line"> * Created by hj on 2019/1/10.</span><br><span class="line"> * 说明：</span><br><span class="line"> */</span><br><span class="line">public class Feature {</span><br><span class="line"></span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>最后申明一个<code>Student</code>并继承<code>Person</code>,将<code>Feature</code>作为<code>T</code>传入:<br><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></pre></td><td class="code"><pre><span class="line">/**</span><br><span class="line"> * Created by hj on 2019/1/10.</span><br><span class="line"> * 说明：</span><br><span class="line"> */</span><br><span class="line"></span><br><span class="line">public class Student extends Person<Feature> {</span><br><span class="line"></span><br><span class="line"> public static void main(String[] args) {</span><br><span class="line"> Student student = new Student();</span><br><span class="line"> Class mClass = student.getClass();</span><br><span class="line"> Type type = mClass.getGenericSuperclass();</span><br><span class="line"> //这里获取的type为Person<Feature>，所以属于ParameterizedType</span><br><span class="line"> if (type instanceof ParameterizedType) {</span><br><span class="line"> //父类的泛型可能有多个，这里只写了一个，所以取第一个就行了，这里是取Person<Feature>中的Feature</span><br><span class="line"> Class tClass = (Class) ((ParameterizedType) type).getActualTypeArguments()[0];</span><br><span class="line"> log(tClass.getSimpleName());</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> private static void log(String value) {</span><br><span class="line"> System.out.print(value);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>因为<code>Class</code>类也实现了<code>Type</code>接口，所以是可以强制转化的<br>打印结果如下:<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">Feature</span><br></pre></td></tr></table></figure></p>
<p>可以看到在此示例中，只要是<code>Person<></code>中传入的参数是一个参数类型，不管是<code>实体类</code>，<code>String</code>都行，只要是参数而没有泛指意义，那么它就属于<code>ParameterizedType</code>类型<br>接下来将代码修改一下，将<code>Feature</code>改为<code>T</code>,修改获取逻辑：<br><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></pre></td><td class="code"><pre><span class="line">/**</span><br><span class="line"> * Created by hj on 2019/1/10.</span><br><span class="line"> * 说明：</span><br><span class="line"> */</span><br><span class="line"></span><br><span class="line">public class Student<T> extends Person<T> {</span><br><span class="line"></span><br><span class="line"> public static void main(String[] args) {</span><br><span class="line"> Student student = new Student();</span><br><span class="line"> Class mClass = student.getClass();</span><br><span class="line"> Type type = mClass.getGenericSuperclass();</span><br><span class="line"> //此时这里的type为Person<T>，而不是T，所以依旧属于ParameterizedType</span><br><span class="line"> if (type instanceof ParameterizedType) {</span><br><span class="line"> //这里是从Person<T>中获取T</span><br><span class="line"> Type childType = ((ParameterizedType)type).getActualTypeArguments()[0];</span><br><span class="line"> if (childType instanceof TypeVariable){</span><br><span class="line"> log(((TypeVariable) childType).getName());</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> private static void log(String value) {</span><br><span class="line"> System.out.print(value);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>输出名称为<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">T</span><br></pre></td></tr></table></figure></p>
<p>不知道小伙伴们有没有理解了，当获取的类型是泛指的，如T等，那么就是<code>TypeVariable</code>类型，当类型是参数类型的，例如由子类传入的，具体化的，那么就是<code>ParameterizedType</code>类型。<br>接下来的<code>GenericArrayType</code>和<code>WildcardType</code>就比较好理解了，将以上示例中的<code>Person<T></code>改为<code>Person<T[]></code>，将结果输出，代码如下：<br><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></pre></td><td class="code"><pre><span class="line">/**</span><br><span class="line"> * Created by hj on 2019/1/10.</span><br><span class="line"> * 说明：</span><br><span class="line"> */</span><br><span class="line"></span><br><span class="line">public class Student<T> extends Person<T[]> {</span><br><span class="line"></span><br><span class="line"> public static void main(String[] args) {</span><br><span class="line"> Student student = new Student();</span><br><span class="line"> Class mClass = student.getClass();</span><br><span class="line"> Type type = mClass.getGenericSuperclass();</span><br><span class="line"> if (type instanceof ParameterizedType) {</span><br><span class="line"> //这里获取到的类型为：T[],是一个数组类型，所以是GenericArrayType</span><br><span class="line"> Type childType = ((ParameterizedType)type).getActualTypeArguments()[0];</span><br><span class="line"> if (childType instanceof GenericArrayType){</span><br><span class="line"> log(childType.toString());</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"> private static void log(String value) {</span><br><span class="line"> System.out.print(value);</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>输出名称为：<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">T[]</span><br></pre></td></tr></table></figure></p>
<p><code>WildcardType</code>就不演示了，将<code>T</code>改为带<code>？</code>的类型就可以了，如果封装类型实在太复杂，教大家一个技巧，打个断点，啥类型都帮你显示出来了。<br><img src="https://upload-images.jianshu.io/upload_images/3468978-115865cd6cbf0d07.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240" alt="断点识别参数类型.png"><br>一看就知道是ParameterizedType类型了，哈哈哈，溜不溜。</p>
<p>这里给小伙伴一个作业：<br><code>List<? extends T>[]</code>中的<code>List<? extends T></code>,<code>? extends T</code>，<code>T</code> ,<code>List<? extends T>[]</code>分别代表什么类型呢？</p>
<p><strong>继承</strong><br>获取父级类使用<code>Class.getSuperclass()</code>方法即可获取父类的<code>class</code></p>
<p><strong>接口</strong><br>获取接口也比较简单，一个接口实际上也是一个Class类，通过<code>getInterfaces()</code>获取到一个<code>Class</code>数组，而接口里声明的方法可以通过获取<code>Method</code>的方式来获取,<br>举个栗子，先创建一个<code>MyInterface</code>接口<br><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">/**</span><br><span class="line"> * Created by hj on 2019/1/11.</span><br><span class="line"> * 说明：</span><br><span class="line"> */</span><br><span class="line">public interface MyInterface {</span><br><span class="line"> void getName();</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>在<code>Student</code>类里实现并获取：<br><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></pre></td><td class="code"><pre><span class="line">/**</span><br><span class="line"> * Created by hj on 2019/1/10.</span><br><span class="line"> * 说明：</span><br><span class="line"> */</span><br><span class="line"></span><br><span class="line">public class Student implements MyInterface{</span><br><span class="line"></span><br><span class="line"> public static void main(String[] args) {</span><br><span class="line"> Student student = new Student();</span><br><span class="line"> Class mClass = student.getClass();</span><br><span class="line"> Class interfaces = mClass.getInterfaces()[0];</span><br><span class="line"> try {</span><br><span class="line"> Method methods = interfaces.getMethod("getName",null);</span><br><span class="line"> log(methods.getName());</span><br><span class="line"> } catch (NoSuchMethodException e) {</span><br><span class="line"> e.printStackTrace();</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> private static void log(String value) {</span><br><span class="line"> System.out.print(value);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> @Override</span><br><span class="line"> public void getName() {</span><br><span class="line"></span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure></p>
<p>打印出方法名为：<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">getName</span><br></pre></td></tr></table></figure></p>
<h2 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h2><p>只要拿到Class类，我们就可以获取到它的父类，接口，方法，字段，以及泛型，从而做一些解耦封装，提高类的解耦性。或者在不修改源码的情况下执行或修改源码中的方法，字段，从而达到理想中的效果。小伙伴们快去练习一下把。</p>
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