JAVAWeb开发之Servlet-19.Filter

–Filter 简介
–创建Filter的步骤
–获得Filter的初始化参数
–Filter 实例
?字符编码 Filter
?权限验证 Filter

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? Filter 简介
–Filter位于客户端和请求资源之间，在此起到过滤作用
–请求资源可以是，Servlet、JSP页面、HTML页面等
–他们在请求资源的前后来执行
–请求和响应通过Filter可以被修改
–Filter 常用在如下几个方面：
? Session 管理
? 权限验证
? 日志记录
? 字符编码转换

Filter 简介图示

? 创建Filter的步骤

– Filter 接口
? init 方法
public void init(FilterConfig filterConfig) throws ServletException
? doFilter 方法
public void doFilter(ServletRequest request,
ServletResponse response,
FilterChain chain)
throws java.io.IOException,
ServletException
? Destroy 方法
public void destroy()

– 创建Filter步骤
? 创建一个类实现Filter接口
– 方法: doFilter, init, destroy
?在doFilter方法中处理逻辑
– 参数: ServletRequest, ServletResponse, FilterChain
? FilterChain 调用doFilter方法
– 调用下一个过滤器或实际资源
? 注册filter，来过滤Servlet 和Jsp
–在web.xml中，使用 filter 和 filter-mapping

简单的Filter实例

 

调用WebRoot下面的testFilter.html测试Filter起作用了没？

Filter没有执行哈~

再次测试admin下的testFilter有没起作用？

pass herer~~~~~~在控制台打印出来了,但是页面没有显示Test Filter 1,证明被Filter拦截了。下面我们过滤链调用doFilter方法。

再次执行页面。

页面显示了Test Filter 1了

结构与Servlet相似。

MyFilter.java

package com.michael.servlet;    

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 MyFilter implements Filter {    

         public void destroy() {    
        }    

         public void doFilter(ServletRequest arg0, ServletResponse arg1,    
                        FilterChain chain) throws IOException, ServletException {    
                System.out.println( "pass here~~~~~~~~");    
                chain.doFilter(arg0, arg1);    
        }    

         public void init(FilterConfig arg0) throws ServletException {    
        }    

}

web.xml

"1.0" encoding= "UTF-8"?>    
"2.4"    
        xmlns= "http://java.sun.com/xml/ns/j2ee"    
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    
        xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee    
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">    
            
                MyFilter    
                class>com.michael.servlet.MyFilterclass>    
            
            
                MyFilter    
                /admin/*    
            

testFilter.html

"-//W3C//DTD HTML 4.01 Transitional//EN">    
    
        
            
        "keywords" content="keyword1,keyword2,keyword3">    
        "description" content="this is my page">    
        "content-type" content="text/html; charset=UTF-8">    
            
        
        
    

Test Filter 1

    
        

? 获得Filter的初始化参数
–在web.xml配置文件的Filter声明中配置初始化参数

–在Filter实现类中获得初始化参数

 

 

? Filter 实例
–字符编码 Filter

测试一下提交的中文是否乱码？

用户名显示为乱码

下面我们将整个页面设置统一编码，用Filter来解决哈~

web.xml

"1.0" encoding= "UTF-8"?>    
"2.4"    
        xmlns= "http://java.sun.com/xml/ns/j2ee"    
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    
        xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee    
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">    
            
                MyFilter    
                class>com.michael.servlet.MyFilterclass>    
                    
                        encoding    
                        gbk    
                    
            
            
                MyFilter    
                /admin/*    
            
            
                EncodingFilter    
                class>com.michael.servlet.EncodingFilterclass>    
            
            
                EncodingFilter    
                /*    
            
        
        RegisterServlet    
        class>com.michael.servlet.RegisterServletclass>    
        
        
        RegisterServlet    
        /servlet/RegisterServlet    
        

register.html

"-//W3C//DTD HTML 4.01 Transitional//EN">    
    
        
            
        "keywords" content="keyword1,keyword2,keyword3">    
        "description" content="this is my page">    
        "content-type" content="text/html; charset=UTF-8">    
            
        
        
        

"f1" id="f1" action="/Servlet_Filter/servlet/RegisterServlet" method="post">    
            "0">    
                    
                        
                        
                    
                    
                        
                        
                    
                    
                        
                    
            

Username:	"text" name="username" id="login">
Password:	"password" name="password" id="password">
"2" align="center">"submit" value="Register">

    
        

    
        

RegisterServlet.java

package com.michael.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;    
public class RegisterServlet extends HttpServlet {    
         /**    
         * Constructor of the object.    
         */    
         public RegisterServlet() {    
                 super();    
        }    
         /**    
         * Destruction of the servlet.
    
         */    
         public void destroy() {    
                 super.destroy(); // Just puts "destroy" string in log    
                 // Put your code here    
        }    
         /**    
         * The doGet method of the servlet.
    
         *    
         * 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 {    
                doPost(request,response);    
        }    
         /**    
         * The doPost method of the servlet.
    
         *    
         * 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");    
                response.setContentType( "text/html");    
                PrintWriter out = response.getWriter();    
                out    
                                .println( "//W3C//DTD HTML 4.01 Transitional//EN\">");    
                out.println("");    
                out.println("    ");    
                out.println("    ");    
                out.print(username);    
                out.print(password);    
                out.println("    ");    
                out.println("");    
                out.flush();    
                out.close();    
        }    
        /**    
         * Initialization of the servlet.
    
         *    
         * @throws ServletException if an error occurs    
         */    
        public void init() throws ServletException {    
                // Put your code here    
        }    
}

EncodingFilter.java

package com.michael.servlet;    
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 EncodingFilter implements Filter{    
         public void destroy() {    
                 // TODO Auto-generated method stub    
        }    
         public void doFilter(ServletRequest request, ServletResponse response,    
                        FilterChain chain) throws IOException, ServletException {    
                request.setCharacterEncoding( "gbk");    
                response.setCharacterEncoding( "gbk");    
                chain.doFilter(request, response);    
        }    
         public void init(FilterConfig arg0) throws ServletException {    
                 // TODO Auto-generated method stub    
        }    
}

可以正常显示中文了哈~

–权限验证 Filter

web.xml

"1.0" encoding= "UTF-8"?>    
"2.4"    
        xmlns= "http://java.sun.com/xml/ns/j2ee"    
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    
        xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee    
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">    
            
                MyFilter    
                class>com.michael.servlet.MyFilterclass>    
                    
                        encoding    
                        gbk    
                    
            
            
                MyFilter    
                /admin/*    
            
            
                EncodingFilter    
                class>com.michael.servlet.EncodingFilterclass>    
            
            
                EncodingFilter    
                /*    
            
            
                SessionFilter    
                class>com.michael.servlet.SessionFilterclass>    
            
            
                SessionFilter    
                /admin/*    
            
        
        RegisterServlet    
        class>com.michael.servlet.RegisterServletclass>    
        
        
        LoginServlet    
        class>com.michael.servlet.LoginServletclass>    
        
        
        RegisterServlet    
        /servlet/RegisterServlet    
        
        
        LoginServlet    
        /servlet/LoginServlet    
        

login.jsp

<%@ page language= "java" import= "java.util.*" pageEncoding= "gbk"%>    
<%    
String path = request.getContextPath();    
String basePath = request.getScheme()+ "://"+request.getServerName()+":"+request.getServerPort()+path+"/";    
%>    
"-//W3C//DTD HTML 4.01 Transitional//EN">    
    
        
        "<%=basePath%>">    
            
        "pragma" content="no-cache">    
        "cache-control" content="no-cache">    
        "expires" content="0">        
        "keywords" content="keyword1,keyword2,keyword3">    
        "description" content="This is my page">    
            
        
        
        ${Login_Error }    
        

"f1" id="f1" action="/Servlet_Filter/servlet/LoginServlet" method="post">    
            "0">    
                    
                        
                        
                    
                    
                        
                        
                    
                    
                        
                    
            

Username:	"text" name="username" id="login">
Password:	"password" name="password" id="password">
"2" align="center">"submit" value="Login">

    
        

    
        

LoginServlet.java

package com.michael.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.
    
         */    
         public void destroy() {    
                 super.destroy(); // Just puts "destroy" string in log    
                 // Put your code here    
        }    
         /**    
         * The doGet method of the servlet.
    
         *    
         * 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 {    
                doPost(request,response);    
        }    
         /**    
         * The doPost method of the servlet.
    
         *    
         * 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 {    
                HttpSession session = request.getSession();    
                session.setAttribute( "UserSession", "user");    
                response.setContentType( "text/html");    
                PrintWriter out = response.getWriter();    
                out    
                                .println( "//W3C//DTD HTML 4.01 Transitional//EN\">");    
                out.println("");    
                out.println("    ");    
                out.println("    ");    
                out.print("        Welcome you! ");    
                out.println("    ");    
                out.println("");    
                out.flush();    
                out.close();    
        }    
        /**    
         * Initialization of the servlet.
    
         *    
         * @throws ServletException if an error occurs    
         */    
        public void init() throws ServletException {    
                // Put your code here    
        }    
}

SessionFilter.java

package com.michael.servlet;    
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 SessionFilter implements Filter {    
         public void destroy() {    
                 // TODO Auto-generated method stub    
        }    
         public void doFilter(ServletRequest request, ServletResponse response,    
                        FilterChain chain) throws IOException, ServletException {    
                HttpServletRequest hrequest = (HttpServletRequest)request;    
                HttpServletResponse hresponse = (HttpServletResponse)response;    
                HttpSession session = hrequest.getSession();    
                String session_Value = (String)session.getAttribute( "UserSession");    
                 if(session_Value!= null&&session_Value.length()>=0){    
                        chain.doFilter(request, response);    
                } else{    
                        hrequest.setAttribute( "Login_Error", "请登录");    
                        hrequest.getRequestDispatcher( "/login.jsp").forward(hrequest, hresponse);    
                }    
        }    
         public void init(FilterConfig arg0) throws ServletException {    
                 // TODO Auto-generated method stub    
        }    
}

没有登录的状态下直接访问admin目录下的testFilter.thml页面，页面显示“请登录”。

下面我们输入用户名和密码进行模拟登录验证。

页面显示登录成功！

登录成功后我们再访问admin目录下的页面就可以正常访问了哈~

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