简单的例子说明filter的执行顺序

第一个过滤器类

package web;

import java.io.IOException;

import java.io.PrintWriter;

import javax.servlet.Filter;

import javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class CommentFile1 implements Filter {

private FilterConfig config;

/*

* 容器在删除过滤器实例之前，会调用 destroy方法。该方法只会执行一次。

*/

public void destroy() {

System.out.println("destroy...");

}

/*

* 容器会调用doFilter方法来处理请求( 相当于servlet的service方法)。

* 容器会将request对象(arg0)和response对象 (arg1)作为参数传给doFilter方法。

* 如果调用了FilterChain(arg2)的doFilter(request, response)方法，则容器会调用后续的过滤器或者

* servlet，否则请求处理完毕。

*/

public void doFilter(ServletRequest arg0, ServletResponse arg1,

FilterChain arg2) throws IOException, ServletException {

HttpServletRequest request = (HttpServletRequest) arg0;

HttpServletResponse response = (HttpServletResponse) arg1;

System.out.println("Filter1's doFilter begin...");

request.setCharacterEncoding("utf-8");

response.setContentType("text/html;charset=utf-8");

String content = request.getParameter("content");

PrintWriter out = response.getWriter();

String illegalStr = config.getInitParameter("illegalStr");

if (content.indexOf(illegalStr) != -1) {

out.println("包含敏感字符");

} else {

// FilterChain的doFilter只要执行，容器就会调用后续的过滤器或者servlet。

arg2.doFilter(arg0, arg1);

}

System.out.println("Filter1's doFilter end.");

}

public CommentFile1() {

System.out.println("CommentFilter1's constructor...");

}

/*

* 容器启动之后，会创建过滤器实例。 接下来，容器会调用过滤器的init方法(容器 会事先创建好FilterConfig对象)。

* FilterConfig对象可以用来访问过滤器的初始 化参数。 init方法只会执行一次。

*/

public void init(FilterConfig arg0) throws ServletException {

System.out.println("init...");

config = arg0;

}

}

第二个过滤器类

package web;

import java.io.IOException;

import java.io.PrintWriter;

import javax.servlet.Filter;

import javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class CommentFilter2 implements Filter {

public void destroy() {

}

public void doFilter(ServletRequest arg0, ServletResponse arg1,

FilterChain arg2) throws IOException, ServletException {

System.out.println("Filter2's doFilter begin...");

HttpServletRequest request = (HttpServletRequest) arg0;

HttpServletResponse response = (HttpServletResponse) arg1;

request.setCharacterEncoding("utf-8");

response.setContentType("text/html;charset=utf-8");

String str = request.getParameter("content");

PrintWriter out = response.getWriter();

if (str.length() > 20) {

out.print("<h1>评论不能超过20个字</h1>");

} else {

arg2.doFilter(arg0, arg1);

}

System.out.println("Filter2's doFilter end...");

}

public void init(FilterConfig arg0) throws ServletException {

}

}

配置文件



执行顺序