通過spring在filter注入bean(DelegatingFilterProxy與servlet filter)

web應用中，我們經常使用filter機制來确定外部請求的使用者是否登入，角色是否合法等。Spring提供了

一個DelegatingFilterProxy機制來完成filter的部分功能。通過例子做一個簡單對比。   二者看起來

沒有什麼太大的差別，在spring中，filter被納入了bean 管理機制。

1.servlet filter

* LoginFilter .java

package servlet.filter;

import javax.servlet.*;

import javax.servlet.http.*;

import java.io.*;

public class LoginFilter implements Filter {

 protected FilterConfig filterConfig;

 public void init(FilterConfig filterConfig) throws ServletException {

  this.filterConfig = filterConfig;

 }

 public void destroy() {

  this.filterConfig = null;

 }

 public void doFilter(ServletRequest request, ServletResponse response,

   FilterChain chain) throws java.io.IOException, ServletException {

  HttpServletRequest req = (HttpServletRequest) request;

  HttpServletResponse res = (HttpServletResponse) response;

  String username = req.getParameter("j_username");

  System.out.println("this is in servlet filter");

  chain.doFilter(request, response);

 }

}

*web.xml

<filter>

  <filter-name>simplelogin</filter-name>

  <filter-class>servlet.filter.LoginFilter</filter-class>

  <init-param>

   <param-name>hello</param-name>

   <param-value>hello filter</param-value>

  </init-param>

 </filter>

 <filter-mapping>

          <filter-name>simplelogin</filter-name>

           <url-pattern>/*</url-pattern>

    </filter-mapping>

2. Spring filter

*LoginFilter.java

package filter;

import java.io.IOException;

import java.security.Principal;

import javax.servlet.*;

import javax.servlet.http.*;

import org.apache.commons.logging.*;

public class LoginFilter implements Filter {

 private FilterConfig filterConfig = null;

 Log log = LogFactory.getLog(LoginFilter.class);

 public void doFilter(ServletRequest req, ServletResponse res,

   FilterChain chain) throws IOException, ServletException {

  HttpServletRequest request = (HttpServletRequest) req;

  Principal principal=request.getUserPrincipal();

  HttpServletResponse response=(HttpServletResponse)res;

  log.info("filter user name:"+request.getParameter("j_username")+":"+principal.toString

());

  log.info("filter password :"+request.getParameter("j_password"));

  chain.doFilter(req,res);

 }

 public void init(FilterConfig config) throws ServletException {

  this.filterConfig = config;

 }

 public void destroy() {

  filterConfig = null;

 }

}

    *

      web.xml

<filter>

  <description>LoginFilter</description>

  <display-name> LoginFilter</display-name>

  <filter-name>LoginFilter</filter-name>

  <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>

  <init-param>

   <description>

   </description>

   <param-name>targetBeanName</param-name>

   <param-value>loginFilter</param-value>

  </init-param>

 </filter>

<filter-mapping>

  <filter-name>LoginFilter</filter-name>

  <url-pattern>/*</url-pattern>

 </filter-mapping>

*spring context config

<bean id="loginFilter" class="filter.LoginFilter" />