简单的Filter实现

1.在xml文件配置过滤器

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">  <display-name>Filter</display-name>  <welcome-file-list>    <welcome-file>index.html</welcome-file>    <welcome-file>index.htm</welcome-file>    <welcome-file>index.jsp</welcome-file>    <welcome-file>default.html</welcome-file>    <welcome-file>default.htm</welcome-file>    <welcome-file>default.jsp</welcome-file>  </welcome-file-list>    <error-page>        <error-code>404</error-code>        <location>/error.jsp</location>    </error-page>    <error-page>        <error-code>500</error-code>        <location>/error.jsp</location>    </error-page>    <filter>        <filter-name>CharsetFilter</filter-name>        <filter-class>com.test.filter.CharsetFilter</filter-class>        <init-param>            <param-name>charset</param-name>            <param-value>UTF-8</param-value>        </init-param>    </filter>    <filter>        <filter-name>LoginFilter</filter-name>        <filter-class>com.test.filter.LoginFilter</filter-class>        <init-param>            <param-name>noLoginPath</param-name>            <param-value>login.jsp;error.jsp;index.jsp</param-value>        </init-param>    </filter>    <filter-mapping>        <filter-name>LoginFilter</filter-name>        <url-pattern>/*</url-pattern>        <dispatcher>REQUEST</dispatcher>    </filter-mapping>    <filter>        <filter-name>ErrorFilter</filter-name>        <filter-class>com.test.filter.ErrorFilter</filter-class>    </filter>    <filter-mapping>        <filter-name>ErrorFilter</filter-name>        <url-pattern>/error.jsp</url-pattern>        <dispatcher>ERROR</dispatcher>    </filter-mapping>    <filter-mapping>        <filter-name>CharsetFilter</filter-name>        <url-pattern>/*</url-pattern>    </filter-mapping></web-app>

2.建立java类实现Filter接口

1.编码转换案例

package com.test.filter;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 CharsetFilter implements Filter{    private FilterConfig config;    @Override    public void destroy() {        // TODO Auto-generated method stub    }    @Override    public void doFilter(ServletRequest request, ServletResponse response,            FilterChain chain) throws IOException, ServletException {        String charset = config.getInitParameter("charset");        if(charset == null || charset.equals("")){            charset = "UTF-8";        }        request.setCharacterEncoding(charset);        response.setCharacterEncoding(charset);        chain.doFilter(request, response);    }    @Override    public void init(FilterConfig arg0) throws ServletException {        config = arg0;    }}

2.错误显示案例

package com.test.filter;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 ErrorFilter implements Filter{    @Override    public void destroy() {        // TODO Auto-generated method stub    }    @Override    public void doFilter(ServletRequest arg0, ServletResponse arg1,            FilterChain chain) throws IOException, ServletException {            System.out.println("error!!!!");            chain.doFilter(arg0, arg1);    }    @Override    public void init(FilterConfig arg0) throws ServletException {        // TODO Auto-generated method stub    }}

3.登录过滤案例

package com.test.filter;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;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class LoginFilter implements Filter{    private FilterConfig config;    @Override    public void destroy() {    }    @Override    public void doFilter(ServletRequest arg0, ServletResponse arg1,            FilterChain chain) throws IOException, ServletException {        HttpServletRequest request = (HttpServletRequest)arg0;        HttpServletResponse response = (HttpServletResponse)arg1;        HttpSession session = request.getSession();        //获取不用过滤的路径        String noLoginPath = config.getInitParameter("noLoginPath");        //对于不用过滤的路径直接放行        if(noLoginPath != null){            String[] strArray = noLoginPath.split(";");            for(String str:strArray){                if(str == null || str.equals(""))   continue;                if(request.getRequestURI().indexOf(str) != -1){                    chain.doFilter(arg0, arg1);                    return;                }            }        }        //如果session中没有用户信息就跳转到登陆界面，否则放行        if(session.getAttribute("user") == null){            response.sendRedirect("login.jsp");        }else{            chain.doFilter(arg0, arg1);        }    }    @Override    public void init(FilterConfig arg0) throws ServletException {        // TODO Auto-generated method stub        config = arg0;    }}

3.建立过滤后显示的页面

1.编码转换案例

package com.test.filter;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 CharsetFilter implements Filter{    private FilterConfig config;    @Override    public void destroy() {        // TODO Auto-generated method stub    }    @Override    public void doFilter(ServletRequest request, ServletResponse response,            FilterChain chain) throws IOException, ServletException {        String charset = config.getInitParameter("charset");        if(charset == null || charset.equals("")){            charset = "UTF-8";        }        request.setCharacterEncoding(charset);        response.setCharacterEncoding(charset);        chain.doFilter(request, response);    }    @Override    public void init(FilterConfig arg0) throws ServletException {        config = arg0;    }}

2.错误显示页面

<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <base href="<%=basePath%>">    <title>My JSP 'error.jsp' starting page</title>    <meta http-equiv="pragma" content="no-cache">    <meta http-equiv="cache-control" content="no-cache">    <meta http-equiv="expires" content="0">        <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">    <meta http-equiv="description" content="This is my page">    <!--    <link rel="stylesheet" type="text/css" href="styles.css">    -->  </head>  <body>    This is my error page. <br>  </body></html>

3.登录过滤页面

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <base href="<%=basePath%>">    <title>My JSP 'success.jsp' starting page</title>    <meta http-equiv="pragma" content="no-cache">    <meta http-equiv="cache-control" content="no-cache">    <meta http-equiv="expires" content="0">        <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">    <meta http-equiv="description" content="This is my page">    <!--    <link rel="stylesheet" type="text/css" href="styles.css">    -->  </head>  <body>    <span><%=request.getParameter("userName") %></span>    <%System.out.println("userName is "+request.getParameter("userName")); %>    <span><%=request.getParameter("password") %></span>    <%System.out.println("pssword is "+request.getParameter("password")); %>  </body></html>