Java Web过滤器详解_Java

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。

<%@ 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>

success.jsp

<%@ 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>

failure.jsp

<%@ 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>

loginfilter.java

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;

  }

}

loginservlet.java

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
  }

}

web.xml

<?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>

运行效果：