Java Servlet @WebListener 注解示例

迈不过友情╰ 2023-09-30 09:09 28阅读 0赞

**@WebListener**  \_注释用于将类注册为 Web 应用程序的侦听器。带注释的类必须实现以下一个或多个接口：

*  javax.servlet.ServletContextListener
 *  javax.servlet.ServletContextAttributeListener
 *  javax.servlet.ServletRequestListener
 *  javax.servlet.ServletRequestAttributeListener
 *  javax.servlet.http.HttpSessionListener
 *  javax.servlet.http.HttpSessionAttributeListener

##  ##

### **@WebListener 注解的语法：** ###

@WebListener(\[可选描述\])

##  ##

### **@WebListener 注解的属性：** ###

<table> 
 <tbody> 
  <tr> 
   <td style="vertical-align:top;"> <p><strong>Name</strong></p> </td> 
   <td style="vertical-align:top;"> <p><strong>Type</strong></p> </td> 
   <td style="vertical-align:top;"> <p><strong>Required</strong></p> </td> 
   <td style="vertical-align:top;"> <p><strong>Description</strong></p> </td> 
  </tr> 
  <tr> 
   <td style="vertical-align:top;"> <p><strong>value</strong></p> </td> 
   <td> <p><em>String</em></p> </td> 
   <td> <p>Optional</p> </td> 
   <td style="vertical-align:top;"> <p>Description of the listener.</p> </td> 
  </tr> 
 </tbody> 
</table>

### **@WebListener 注解的一些示例：** ###

*  以下示例代码使用@WebListener将类注册为ServletContextListener事件的侦听器的注释：
    
    <table> 
     <tbody> 
      <tr> 
       <td style="text-align:left;vertical-align:baseline;"> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">1</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">2</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">3</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">4</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">5</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">6</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">7</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">8</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">9</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">10</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">11</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">12</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">13</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">14</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">15</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">16</span></span> 
        </div> 
        <div style="margin-left:0;text-align:right;"> 
         <span style="background-color:#FFFFFF;"><span style="color:#787878;">17</span></span> 
        </div> </td> 
       <td style="text-align:left;vertical-align:baseline;"> 
        <div style="margin-left:0;text-align:left;"> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>import</code> <code>javax.servlet.ServletContextEvent;</code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>import</code> <code>javax.servlet.ServletContextListener;</code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>import</code> <code>javax.servlet.annotation.WebListener;</code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;">&nbsp;</span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>@WebListener</code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>public</code> <code>class</code> <code>ContextListener&nbsp;</code><code>implements</code> <code>ServletContextListener { </code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;">&nbsp;</span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>@Override</code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>public</code> <code>void</code> <code>contextInitialized(ServletContextEvent event) { </code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>System.out.println(</code><code>"The application started"</code><code>);</code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>}</code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>&nbsp;&nbsp;&nbsp;&nbsp;</code>&nbsp;</span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>@Override</code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>public</code> <code>void</code> <code>contextDestroyed(ServletContextEvent event) { </code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>System.out.println(</code><code>"The application stopped"</code><code>);</code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>}</code></span></span> 
         </div> 
         <div style="margin-left:0;text-align:left;"> 
          <span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>}</code></span></span> 
         </div> 
        </div> </td> 
      </tr> 
     </tbody> 
    </table>
 *  以下示例代码注册了一个侦听器，该侦听器实现了两个带有描述的接口：

<table> 
 <tbody> 
  <tr> 
   <td style="text-align:left;vertical-align:baseline;"> 
    <div style="margin-left:0;text-align:right;"> 
     <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="color:#787878;">1</span></span></span></span> 
    </div> 
    <div style="margin-left:0;text-align:right;"> 
     <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="color:#787878;">2</span></span></span></span> 
    </div> 
    <div style="margin-left:0;text-align:right;"> 
     <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="color:#787878;">3</span></span></span></span> 
    </div> 
    <div style="margin-left:0;text-align:right;"> 
     <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="color:#787878;">4</span></span></span></span> 
    </div> 
    <div style="margin-left:0;text-align:right;"> 
     <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="color:#787878;">5</span></span></span></span> 
    </div> 
    <div style="margin-left:0;text-align:right;"> 
     <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="color:#787878;">6</span></span></span></span> 
    </div> 
    <div style="margin-left:0;text-align:right;"> 
     <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="color:#787878;">7</span></span></span></span> 
    </div> 
    <div style="margin-left:0;text-align:right;"> 
     <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="color:#787878;">8</span></span></span></span> 
    </div> 
    <div style="margin-left:0;text-align:right;"> 
     <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="color:#787878;">9</span></span></span></span> 
    </div> </td> 
   <td style="text-align:left;vertical-align:baseline;"> 
    <div style="margin-left:0;text-align:left;"> 
     <div style="margin-left:0;text-align:left;"> 
      <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>import</code> <code>javax.servlet.http.HttpSessionAttributeListener;</code></span></span></span></span> 
     </div> 
     <div style="margin-left:0;text-align:left;"> 
      <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>import</code> <code>javax.servlet.http.HttpSessionListener;</code></span></span></span></span> 
     </div> 
     <div style="margin-left:0;text-align:left;"> 
      <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;">&nbsp;</span></span></span></span> 
     </div> 
     <div style="margin-left:0;text-align:left;"> 
      <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>@WebListener</code><code>(</code><code>"Session listener for the application"</code><code>)</code></span></span></span></span> 
     </div> 
     <div style="margin-left:0;text-align:left;"> 
      <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>public</code> <code>class</code> <code>MySessionListener&nbsp;</code><code>implements</code> <code>HttpSessionListener,</code></span></span></span></span> 
     </div> 
     <div style="margin-left:0;text-align:left;"> 
      <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>HttpSessionAttributeListener { </code></span></span></span></span> 
     </div> 
     <div style="margin-left:0;text-align:left;"> 
      <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;">&nbsp;</span></span></span></span> 
     </div> 
     <div style="margin-left:0;text-align:left;"> 
      <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>// overrides required methods here...</code></span></span></span></span> 
     </div> 
     <div style="margin-left:0;text-align:left;"> 
      <span style="color:#333333;"><span style="background-color:#ffffff;"><span style="background-color:#FFFFFF;"><span style="background-color:#ffffff;"><code>}</code></span></span></span></span> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

使用@WebListener的一个很好的应用是为Java Web 应用程序实现命中计数器。阅读[本教程][Link 1]以了解更多信息。

####  ####

#### **相关 Java Servlet 注解：** ####

*  [@WebServlet 注解][WebServlet]
 *  [@WebFilter 注解][WebFilter]
 *  [@WebInitParam 注释][WebInitParam]
 *  [@HandlesTypes 注解][HandlesTypes]
 *  [@MultipartConfig 注释][MultipartConfig]
 *  [@ServletSecurity、@HttpMethodContraint 和 @HttpConstraint 注释][ServletSecurity_HttpMethodContraint _ _HttpConstraint]

[Link 1]: https://mail.codejava.net/coding/how-to-code-hit-counter-for-java-web-application
[WebServlet]: https://mail.codejava.net/java-ee/servlet/webservlet-annotation-examples
[WebFilter]: https://mail.codejava.net/java-ee/servlet/webfilter-annotation-examples
[WebInitParam]: https://mail.codejava.net/java-ee/servlet/webinitparam-annotation-examples
[HandlesTypes]: https://mail.codejava.net/java-ee/servlet/handlestypes-annotation-examples
[MultipartConfig]: https://mail.codejava.net/java-ee/servlet/multipartconfig-annotation-examples
[ServletSecurity_HttpMethodContraint _ _HttpConstraint]: https://mail.codejava.net/java-ee/servlet/servletsecurity-httpmethodcontraint-and-httpconstraint-annotations-examples