java Filter的简单使用

java web中的过滤器的简单使用、直接上代码。
1、web.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
     version="3.0">
     <display-name>testFilter</display-name>

     <filter>
         <filter-name>filter1</filter-name>
         <filter-class>test_servlet_package.SimpleFilter1</filter-class>
     </filter>
     <filter-mapping>
         <filter-name>filter1</filter-name>
         <url-pattern>/*</url-pattern>
     </filter-mapping>

     <filter>
         <filter-name>filter2</filter-name>
         <filter-class>test_servlet_package.SimpleFilter2</filter-class>
     </filter>
     <filter-mapping>
         <filter-name>filter2</filter-name>
         <url-pattern>/*</url-pattern>
     </filter-mapping>

     <servlet>
         <servlet-name>testServlet</servlet-name>
         <servlet-class>test_servlet_package.test_servlet</servlet-class>
         <init-param>
             <param-name>test</param-name>
             <param-value>test1</param-value>
         </init-param>
         <load-on-startup>1</load-on-startup>
     </servlet>
     <servlet-mapping>
         <servlet-name>testServlet</servlet-name>
         <url-pattern>/testServlet</url-pattern>
     </servlet-mapping>
 </web-app>

2、test_servlet.java、SimpleFilter2.java、SimpleFilter1.java

 package test_servlet_package;
 import java.io.IOException;
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
 import javax.servlet.FilterConfig;
 import javax.servlet.ServletException;
 import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;
 public class SimpleFilter1 implements Filter {
     // 随着容器 一起 起来 。。。初始化。。。
     @SuppressWarnings("unused")
     private FilterConfig filterConfig;
     public void init(FilterConfig config) throws ServletException {
         this.filterConfig = config;
     }
     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
         try {
             System.out.println("Within SimpleFilter1:Filtering the Request...");
             chain.doFilter(request, response);// 把处理发送到下一个过滤器
             System.out.println("Within SimpleFilter1:Filtering the Response...");
         } catch (IOException ioe) {
             ioe.printStackTrace();
         } catch (ServletException se) {
             se.printStackTrace();
         }
     }
     public void destroy() {
         this.filterConfig = null;
     }
 }

 package test_servlet_package;

 import java.io.IOException;
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
 import javax.servlet.FilterConfig;
 import javax.servlet.ServletException;
 import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;

 public class SimpleFilter2 implements Filter {
     @SuppressWarnings("unused")
     private FilterConfig filterConfig;

     public void init(FilterConfig config) throws ServletException {
         this.filterConfig = config;
     }

     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
         try {
             System.out.println("Within SimpleFilter2:Filtering the Request...");
             chain.doFilter(request, response); // 把处理发送到下一个过滤器
             System.out.println("Within SimpleFilter2:Filtering the Response...");
         } catch (IOException ioe) {
             ioe.printStackTrace();
         } catch (ServletException se) {
             se.printStackTrace();
         }
     }

     public void destroy() {
         this.filterConfig = null;
     }
     /*
      * Within SimpleFilter1:Filtering the Request... Within
      * SimpleFilter2:Filtering the Request... Within SimpleFilter2:Filtering the
      * Response... Within SimpleFilter1:Filtering the Response...
      */
 }

 package test_servlet_package;
 import java.io.IOException;
 import javax.servlet.ServletConfig;
 import javax.servlet.ServletContext;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 public class test_servlet extends HttpServlet {
     private static final long serialVersionUID = 1L;
     // servlet 第一次 请求 被初始化 ,对象 在 容器 里 只有 一个
     // 但是 在 web.xml 配置 了 <load-on-startup>1</load-on-startup> 则 会 立刻 启动初始化
     // 初始化
     public void init(ServletConfig config) throws ServletException {
         super.init(config);
         // 从配置文件中获得初始化参数
         String test = config.getInitParameter("test");
         ServletContext context = this.getServletContext();
         String filePath = context.getRealPath(test);
         System.out.println("filePath：" + filePath);
     }
     protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
         ServletConfig config = this.getServletConfig();
         ServletContext servletContext =  this.getServletContext();
         res.getWriter().println("test");
         res.getWriter().close();

     }
     protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
         doGet(req, res);
     }
 }