过滤器是什么玩意？
所谓过滤器，其实就是一个服务端组件，用来截取用户端的请求与响应信息。
过滤器的应用场景：
1.对用户请求进行统一认证，保证不会出现用户账户安全性问题
2.编码转换，可在服务端的过滤器中设置统一的编码格式，避免出现乱码
3.对用户发送的数据进行过滤替换
4.转换图像格式
5.对响应的内容进行压缩
其中，第1,2场景经常涉及。
login.jsp
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<%@ page language="java" import="java.util.*" contenttype="text/html; charset=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 'login.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>
<form action="<%=path %>/servlet/loginservlet" method="post" >
用户名:<input type="text" name="username" />
密码:<input type="password" name="password" />
<input type="submit" value="登录" />
</form>
</body>
</html>
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success.jsp
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<%@ page language="java" import="java.util.*" pageencoding="utf-8" contenttype="text/html; charset=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 'index.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>
</body>
</html>
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failure.jsp
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<%@ page language="java" import="java.util.*" contenttype="text/html; charset=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 'login.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>
登录失败，请检查用户名或密码！
</body>
</html>
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loginfilter.java
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package com.cityhuntshou.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;
public void destroy() {
}
public void dofilter(servletrequest arg0, servletresponse arg1,
filterchain arg2) throws ioexception, servletexception {
httpservletrequest request = (httpservletrequest) arg0;
httpservletresponse response = (httpservletresponse) arg1;
httpsession session = request.getsession();
//过滤器实际应用场景之二-----编码转换
string charset = config.getinitparameter("charset");
if(charset == null)
{
charset = "utf-8";
}
request.setcharacterencoding(charset);
string nologinpaths = config.getinitparameter("nologinpaths");
if(nologinpaths != null)
{
string[] strarray = nologinpaths.split(";");
for(int i = 0; i < strarray.length; i++)
{
//空元素，放行
if(strarray[i] == null || "".equals(strarray[i]))
continue;
if(request.getrequesturi().indexof(strarray[i]) != -1)
{
arg2.dofilter(arg0, arg1);
return;
}
}
}
if(request.getrequesturi().indexof("login.jsp") != -1
|| request.getrequesturi().indexof("loginservlet") != -1)
{
arg2.dofilter(arg0, arg1);
return;
}
if(session.getattribute("username") != null)
{
arg2.dofilter(arg0, arg1);
}
else
{
response.sendredirect("login.jsp");
}
}
public void init(filterconfig arg0) throws servletexception {
config = arg0;
}
}
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loginservlet.java
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package com.cityhuntshou.servlet;
import java.io.ioexception;
import java.io.printwriter;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
import javax.servlet.http.httpsession;
public class loginservlet extends httpservlet {
/**
* constructor of the object.
*/
public loginservlet() {
super();
}
/**
* destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // just puts "destroy" string in log
// put your code here
}
/**
* the doget method of the servlet. <br>
*
* this method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws servletexception if an error occurred
* @throws ioexception if an error occurred
*/
public void doget(httpservletrequest request, httpservletresponse response)
throws servletexception, ioexception {
}
/**
* the dopost method of the servlet. <br>
*
* this method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws servletexception if an error occurred
* @throws ioexception if an error occurred
*/
public void dopost(httpservletrequest request, httpservletresponse response)
throws servletexception, ioexception {
string username = request.getparameter("username");
string password = request.getparameter("password");
//new string(username.getbytes("iso-8859-1"),"utf-8")
system.out.println(username);
if("admin".equals(username) && "admin".equals(password))
{
//校验通过
httpsession session = request.getsession();
session.setattribute("username", username);
response.sendredirect(request.getcontextpath()+"/success.jsp");
}
else
{
//校验失败
response.sendredirect(request.getcontextpath()+"/failure.jsp");
}
}
/**
* initialization of the servlet. <br>
*
* @throws servletexception if an error occurs
*/
public void init() throws servletexception {
// put your code here
}
}
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web.xml
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<?xml version="1.0" encoding="utf-8"?>
<web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/xmlschema-instance"
xsi:schemalocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<display-name></display-name>
<servlet>
<description>this is the description of my j2ee component</description>
<display-name>this is the display name of my j2ee component</display-name>
<servlet-name>loginservlet</servlet-name>
<servlet-class>com.cityhuntshou.servlet.loginservlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>loginservlet</servlet-name>
<url-pattern>/servlet/loginservlet</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<filter>
<filter-name>loginfilter</filter-name>
<filter-class>com.cityhuntshou.filter.loginfilter</filter-class>
<init-param>
<param-name>nologinpaths</param-name>
<param-value>login.jsp;failure.jsp;loginservlet</param-value>
</init-param>
<init-param>
<param-name>charset</param-name>
<param-value>utf-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>loginfilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
</web-app>
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运行效果：
访问结果：
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：http://www.cnblogs.com/cityhuntshou/p/7443688.html