JAVAWeb开发之Servlet-19.Filter-优快云博客

本文详细介绍了Filter的基本概念及其在Web应用中的使用方法。包括Filter的创建步骤、如何获取初始化参数及其实例演示，如字符编码Filter和权限验证Filter的实现。

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–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

web.xml

testFilter.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
    <head>
        <title>testFilter.html</title>
        <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
        <meta http-equiv="description" content="this is my page">
        <meta http-equiv="content-type" content="text/html; charset=UTF-8">
        
    </head>
    <body>
     <h1>Test Filter 1</h1>
    </body>
</html>

? 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

register.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
    <head>
        <title>register.html</title>
        <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
        <meta http-equiv="description" content="this is my page">
        <meta http-equiv="content-type" content="text/html; charset=UTF-8">
        
    </head>
    <body>
        <form name="f1" id="f1" action="/Servlet_Filter/servlet/RegisterServlet" method="post">
            <table border="0">
                <tr>
                    <td>Username:</td>
                    <td><input type="text" name="username" id="login"></td>
                </tr>
                <tr>
                    <td>Password:</td>
                    <td><input type="password" name="password" id="password"></td>
                </tr>
                <tr>
                    <td colspan="2" align="center"><input type="submit" value="Register"></td>
                </tr>
            </table>
        </form>
    </body>
</html>

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. <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 {
                doPost(request,response);
        }
         /**
         * 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");
                response.setContentType( "text/html");
                PrintWriter out = response.getWriter();
                out
                                .println( "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
                out.println("<HTML>");
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
                out.println("    <BODY>");
                out.print(username);
                out.print(password);
                out.println("    </BODY>");
                out.println("</HTML>");
                out.flush();
                out.close();
        }
        /**
         * Initialization of the servlet. <br>
         *
         * @throws ServletException if an error occurs
         */
        public void init() throws ServletException {
                // Put your code here
        }
}

EncodingFilter.java

可以正常显示中文了哈~

–权限验证 Filter

web.xml

<?xml version= "1.0" encoding= "UTF-8"?>
<web-app version= "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">
        <filter>
                <filter-name>MyFilter</filter-name>
                <filter-class>com.michael.servlet.MyFilter</filter-class>
                <init-param>
                        <param-name>encoding</param-name>
                        <param-value>gbk</param-value>
                </init-param>
        </filter>
        <filter-mapping>
                <filter-name>MyFilter</filter-name>
                <url-pattern>/admin/*</url-pattern>
        </filter-mapping>
        <filter>
                <filter-name>EncodingFilter</filter-name>
                <filter-class>com.michael.servlet.EncodingFilter</filter-class>
        </filter>
        <filter-mapping>
                <filter-name>EncodingFilter</filter-name>
                <url-pattern>/*</url-pattern>
        </filter-mapping>
        <filter>
                <filter-name>SessionFilter</filter-name>
                <filter-class>com.michael.servlet.SessionFilter</filter-class>
        </filter>
        <filter-mapping>
                <filter-name>SessionFilter</filter-name>
                <url-pattern>/admin/*</url-pattern>
        </filter-mapping>
    <servlet>
        <servlet-name>RegisterServlet</servlet-name>
        <servlet-class>com.michael.servlet.RegisterServlet</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>com.michael.servlet.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>RegisterServlet</servlet-name>
        <url-pattern>/servlet/RegisterServlet</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/servlet/LoginServlet</url-pattern>
    </servlet-mapping>
</web-app>

login.jsp

<%@ page language= "java" import= "java.util.*" pageEncoding= "gbk"%>
<%
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">
        
    </head>
    <body>
        ${Login_Error }
        <form name="f1" id="f1" action="/Servlet_Filter/servlet/LoginServlet" method="post">
            <table border="0">
                <tr>
                    <td>Username:</td>
                    <td><input type="text" name="username" id="login"></td>
                </tr>
                <tr>
                    <td>Password:</td>
                    <td><input type="password" name="password" id="password"></td>
                </tr>
                <tr>
                    <td colspan="2" align="center"><input type="submit" value="Login"></td>
                </tr>
            </table>
        </form>
    </body>
</html>

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. <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 {
                doPost(request,response);
        }
         /**
         * 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 {
                HttpSession session = request.getSession();
                session.setAttribute( "UserSession", "user");
                response.setContentType( "text/html");
                PrintWriter out = response.getWriter();
                out
                                .println( "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
                out.println("<HTML>");
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");
                out.println("    <BODY>");
                out.print("        Welcome you! ");
                out.println("    </BODY>");
                out.println("</HTML>");
                out.flush();
                out.close();
        }
        /**
         * Initialization of the servlet. <br>
         *
         * @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”。