Servlet3.0+环境下使用注解注册Servlet、Filter和Listener组件

【1】Servlet3.0前

① Servlet实例

实例代码如下，通常继承HttpServlet

public class HelloWorld extends HttpServlet {
 
  private String message;

  public void init() throws ServletException {
      // 执行必需的初始化
      message = "Hello World";
  }

  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
            throws ServletException, IOException {
      // 设置响应内容类型
      response.setContentType("text/html");

      // 实际的逻辑是在这里
      PrintWriter out = response.getWriter();
      out.println("<h1>" + message + "</h1>");
  }
  
  public void destroy() {
      // 什么也不做
  }
}

---

web.xml配置如下：

<web-app>      
    <servlet>
        <servlet-name>HelloWorld</servlet-name>
        <servlet-class>HelloWorld</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>HelloWorld</servlet-name>
        <url-pattern>/HelloWorld</url-pattern>
    </servlet-mapping>
</web-app>

---

② Filter实例

实例类如下，通常继承Filter

public class UserFilter implements Filter {

  @Override
  public void destroy() {
    // TODO Auto-generated method stub
    
  }

  @Override
  public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
      throws IOException, ServletException {
    // 过滤请求
    System.out.println("UserFilter...doFilter...");
    //放行
    arg2.doFilter(arg0, arg1);
    
  }

  @Override
  public void init(FilterConfig arg0) throws ServletException {
    // TODO Auto-generated method stub
    
  }

}

---

web.xml配置如下：

<filter>  
      <filter-name>FilterTest</filter-name>  
      <filter-class>com.web.UserFilter</filter-class>  
  </filter>  
  <!--映射过滤器-->  
  <filter-mapping>  
      <filter-name>FilterTest</filter-name>  
      <!--“/*”表示拦截所有的请求 -->  
      <url-pattern>/*</url-pattern>  
  </filter-mapping>

---

③ Listener

按监听的对象划分，可以分为

• ServletContext对象监听器
• HttpSession对象监听器
• ServletRequest对象监听器

按监听的事件划分

• 对象自身的创建和销毁的监听器
• 对象中属性的创建和消除的监听器
• session中的某个对象的状态变化的监听器

对应类如下：

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

---

实例代码如下：

public class UserListener implements ServletContextListener {

  //监听ServletContext销毁
  @Override
  public void contextDestroyed(ServletContextEvent arg0) {
    System.out.println("UserListener...contextDestroyed...");
  }

  //监听ServletContext启动初始化
  @Override
  public void contextInitialized(ServletContextEvent arg0) {
    ServletContext servletContext = arg0.getServletContext();
    System.out.println("UserListener...contextInitialized...");
  }

}

---

web.xml配置如下：

<listener>
  <listener-class>com.web.UserListener</listener-class>
</listener>

---

【2】Servlet3.0新特性

Servlet3.0提供了注解支持，可以不用使用web.xml配置。

---

① @WebServlet

其参数如下：

---

注解实例如下：

@WebServlet(name="helloServlet",urlPatterns={"/hello"},
initParams={@WebInitParam(name="age",value="11")})

---

实例类如下：

@WebServlet(name="helloServlet",urlPatterns={"/hello"},initParams={@WebInitParam(name="age",value="11")})
public class HelloServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;

  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    // TODO Auto-generated method stub
    String age = getServletConfig().getInitParameter("age");
    System.out.println("age-->"+age);
    System.out.println(Thread.currentThread()+" start...");
    try {
      sayHello();
    } catch (Exception e) {
      e.printStackTrace();
    }
    resp.getWriter().write("hello...");
    System.out.println(Thread.currentThread()+" end...");
  }
  
  public void sayHello() throws Exception{
    System.out.println(Thread.currentThread()+" processing...");
//    Thread.sleep(3000);
  }

}

---

测试结果如下：

age-->11
Thread[http-apr-8080-exec-12,5,main] start...
Thread[http-apr-8080-exec-12,5,main] processing...
Thread[http-apr-8080-exec-12,5,main] end...

---

② @WebFilter

其参数如下：

---

实例类如下：

@WebFilter(urlPatterns={"/*"})
public class UserFilter implements Filter {

  @Override
  public void destroy() {
    // TODO Auto-generated method stub
    
  }

  @Override
  public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
      throws IOException, ServletException {
    // 过滤请求
    System.out.println("UserFilter...doFilter...");
    //放行
    arg2.doFilter(arg0, arg1);
    
  }

  @Override
  public void init(FilterConfig arg0) throws ServletException {
    // TODO Auto-generated method stub
    
  }
}

---

测试结果如下：

注意哦，这里先执行了过滤器，后执行了servlet。

---

③ @WebListener

其注解源码如下：

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface WebListener {

    /**
     * @return description of the listener, if present
     */
    String value() default "";
}

---

实例代码如下：

@WebListener
public class UserListener implements ServletContextListener {
  //监听ServletContext销毁
  @Override
  public void contextDestroyed(ServletContextEvent arg0) {
    System.out.println("UserListener...contextDestroyed...");
  }

  //监听ServletContext启动初始化
  @Override
  public void contextInitialized(ServletContextEvent arg0) {
    ServletContext servletContext = arg0.getServletContext();
    System.out.println("UserListener...contextInitialized...");
  }

}

---

测试结果如下：