java web--Filter(1)

  1. Filter:

           1). Filter 是什么 ?

                       ①. JavaWEB 的一个重要组件, 可以对发送到 Servlet 的请求进行拦截, 并对响应也进行拦截.
                       ②. Filter 是实现了 Filter 接口的 Java 类.
                       ③. Filter 需要在 web.xml 文件中进行配置和映射.

           2). 如何创建一个 Filter, 并把他跑起来

                       ①. 创建一个 Filter 类: 实现 Filter 接口: public class HelloFilter implements Filter
                       ②. 在 web.xml 文件中配置并映射该 Filter. 其中 url-pattern 指定该 Filter 可以拦截哪些资源, 即可以通过哪些 url 访问到该 Filter

                           <!-- 注册 Filter -->
                                       <filter>
                                                <filter-name>helloFilter</filter-name>
                                                <filter-class>com.atguigu.javaweb.HelloFilter</filter-class>
                                      </filter>

                              <!-- 映射 Filter -->
                                        <filter-mapping>
                                                   <filter-name>helloFilter</filter-name>
                                                   <url-pattern>/test.jsp</url-pattern>
                                         </filter-mapping>

             3). Filter 相关的 API:

                               ①. Filter 接口:

                                      > public void init(FilterConfig filterConfig): 类似于 Servlet 的 init 方法. 在创建 Filter 对象(Filter 对象在 Servlet 容器加载当前 WEB 应用时即被创建)后,
                                         立即被调用, 且只被调用一次. 该方法用于对当前的 Filter 进行初始化操作. Filter 实例是单例的.
                                                * FilterConfig 类似于 ServletConfig
                                                * 可以在 web.xml 文件中配置当前 Filter 的初始化参数. 配置方式也和 Servlet 类似。
                                                   <filter>
                                                          <filter-name>helloFilter</filter-name>
                                                          <filter-class>com.atguigu.javaweb.HelloFilter</filter-class>
                                                              <init-param>
                                                                   <param-name>name</param-name>
                                                                   <param-value>root</param-value>
                                                               </init-param>
                                                  </filter>

                                     > public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain):

                                                      真正 Filter 的逻辑代码需要编写在该方法中. 每次拦截都会调用该方法.
                                                    * FilterChain: Filter 链. 多个 Filter 可以构成一个 Filter 链.
                                                     - doFilter(ServletRequest request, ServletResponse response): 把请求传给 Filter 链的下一个 Filter,
                                                     若当前 Filter 是 Filter 链的最后一个 Filter, 将把请求给到目标 Serlvet(或 JSP)
                                                       - 多个 Filter 拦截的顺序和 <filter-mapping> 配置的顺序有关, 靠前的先被调用.
                                   > public void destroy(): 释放当前 Filter 所占用的资源的方法. 在 Filter 被销毁之前被调用, 且只被调用一次.
                   4). <dispatcher> 元素: 指定过滤器所拦截的资源被 Servlet 容器调用的方式，
                                 可以是REQUEST,INCLUDE,FORWARD和ERROR之一，默认REQUEST.
                                 可以设置多个<dispatcher> 子元素用来指定 Filter 对资源的多种调用方式进行拦截

                                ①. REQUEST：当用户直接访问页面时，Web容器将会调用过滤器。如果目标资源是通过RequestDispatcher的include()或forward()方法访问时，那么该过滤器就不会被调用。

                                                通过 GET 或 POST 请求直接访问。

                                ②. FORWARD：如果目标资源是通过RequestDispatcher的forward()方法访问时，那么该过滤器将被调用，除此之外，该过滤器不会被调用。

                                        或 <jsp:forward page="/..." /> 或 通过 page 指令的 errorPage 转发页面. <%@ page errorPage="test.jsp" %>

                                ③. INCLUDE：如果目标资源是通过RequestDispatcher的include()方法访问时，那么该过滤器将被调用。除此之外，该过滤器不会被调用。

                                          或 <jsp:include file="/..." />

                                ④. ERROR：如果目标资源是通过声明式异常处理机制调用时，那么该过滤器将被调用。除此之外，过滤器不会被调用。

                                        在 web.xml 文件中通过 error-page 节点进行声明:

                                             <error-page>
                                                       <exception-type>java.lang.ArithmeticException</exception-type>
                                                       <location>/test.jsp</location>
                                           </error-page>

                                          <filter-mapping>
                                                      <filter-name>secondFilter</filter-name>
                                                     <url-pattern>/test.jsp</url-pattern>
                                                    <dispatcher>REQUEST</dispatcher>
                                                    <dispatcher>FORWARD</dispatcher>
                                                    <dispatcher>INCLUDE</dispatcher>
                                                    <dispatcher>ERROR</dispatcher>
                                        </filter-mapping>

 2.代码区

package com.atguigu.javaweb;

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 HelloFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("init..");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        System.out.println("1. Before HelloFilter's chain.doFilter ..."); //1
        
        //放行
        chain.doFilter(request, response);
        
        System.out.println("2. After HelloFilter's chain.doFilter ..."); //2
    }

    @Override
    public void destroy() {
        System.out.println("destroy...");
    }

}

package com.atguigu.javaweb;

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 SecondFilter implements Filter{

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("second init...");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        System.out.println("3. Before SecondFilter's chain.doFilter ..."); //3
        
        //放行
        chain.doFilter(request, response);
        
        System.out.println("4. After SecondFilter's chain.doFilter ..."); //4
    }

    //13254          SA 13542                  //13245         八赛                    //12345 谢鹏飞  13245
    //13245                        探索者     15234               //13245    天天向上  13524
    
    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        System.out.println("second destroy");
    }

}

package com.atguigu.javaweb;

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;

/**
 * 自定义的 HttpFilter, 实现自 Filter 接口
 *
 */
public abstract class HttpFilter implements Filter {

    /**
     * 用于保存 FilterConfig 对象. 
     */
    private FilterConfig filterConfig;
    
    /**
     * 不建议子类直接覆盖. 若直接覆盖, 将可能会导致 filterConfig 成员变量初始化失败
     */
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        this.filterConfig = filterConfig;
        init();
    }

    /**
     * 供子类继承的初始化方法. 可以通过 getFilterConfig() 获取 FilterConfig 对象. 
     */
    protected void init() {}

    /**
     * 直接返回 init(ServletConfig) 的 FilterConfig 对象
     */
    public FilterConfig getFilterConfig() {
        return filterConfig;
    }
    
    /**
     * 原生的 doFilter 方法, 在方法内部把 ServletRequest 和 ServletResponse 
     * 转为了 HttpServletRequest 和 HttpServletResponse, 并调用了 
     * doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
     * 
     * 若编写 Filter 的过滤方法不建议直接继承该方法. 而建议继承
     * doFilter(HttpServletRequest request, HttpServletResponse response, 
     *        FilterChain filterChain) 方法
     */
    @Override
    public void doFilter(ServletRequest req, ServletResponse resp,
            FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) resp;
        
        doFilter(request, response, chain);
    }
    
    /**
     * 抽象方法, 为 Http 请求定制. 必须实现的方法. 
     * @param request
     * @param response
     * @param filterChain
     * @throws IOException
     * @throws ServletException
     */
    public abstract void doFilter(HttpServletRequest request, HttpServletResponse response, 
            FilterChain filterChain) throws IOException, ServletException;

    /**
     * 空的 destroy 方法。 
     */
    @Override
    public void destroy() {}

}

package com.atguigu.javaweb;

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;

/**
 * Servlet Filter implementation class UserNameFilter
 */
public class UserNameFilter implements Filter {

    /**
     * Default constructor. 
     */
    public UserNameFilter() {
        // TODO Auto-generated constructor stub
    }

    /**
     * @see Filter#destroy()
     */
    public void destroy() {
        // TODO Auto-generated method stub
    }

    /**
     * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
     */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        
        String initUser = filterConfig.getInitParameter("username");
        String username = request.getParameter("username");
        System.out.println(username);
        if(!initUser.equals(username)){
            request.setAttribute("message", "用户名不正确");
            request.getRequestDispatcher("/login.jsp").forward(request, response);
            return;
        }
        
        chain.doFilter(request, response);
    }

    private FilterConfig filterConfig;
    
    public void init(FilterConfig fConfig) throws ServletException {
        this.filterConfig = fConfig;
    }

}

package com.atguigu.javaweb;

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;

/**
 * Servlet Filter implementation class PasswordFilter
 */
public class PasswordFilter implements Filter {

    /**
     * Default constructor. 
     */
    public PasswordFilter() {
        // TODO Auto-generated constructor stub
    }

    /**
     * @see Filter#destroy()
     */
    public void destroy() {
        // TODO Auto-generated method stub
    }

    /**
     * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
     */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        String initPassword = filterConfig.getServletContext().getInitParameter("password");
        String password = request.getParameter("password");
        System.out.println(password);
        if(!initPassword.equals(password)){
            request.setAttribute("message", "密码不正确");
            request.getRequestDispatcher("/login.jsp").forward(request, response);
            return;
        }
        
        chain.doFilter(request, response);
    }

    /**
     * @see Filter#init(FilterConfig)
     */
    
    private FilterConfig filterConfig;
    
    public void init(FilterConfig fConfig) throws ServletException {
        this.filterConfig = fConfig;
    }

}

package com.atguigu.javaweb.cache;

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.atguigu.javaweb.HttpFilter;

public class NoCacheFilter extends HttpFilter {

    @Override
    public void doFilter(HttpServletRequest request,
            HttpServletResponse response, FilterChain filterChain)
            throws IOException, ServletException {
        
        System.out.println("cacheFilter's doFilter..");
        
        response.setDateHeader("Expires",-1);
        response.setHeader("Cache-Control","no-cache");
        response.setHeader("Pragma","no-cache");
        
        filterChain.doFilter(request, response);
    }

    

}

package com.atguigu.javaweb.encoding;

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.atguigu.javaweb.HttpFilter;

public class EncodingFilter extends HttpFilter{

    private String encoding;
    
    @Override
    protected void init() {
        encoding = getFilterConfig().getServletContext().getInitParameter("encoding");
    }
    
    @Override
    public void doFilter(HttpServletRequest request,
            HttpServletResponse response, FilterChain filterChain)
            throws IOException, ServletException {
        System.out.println(encoding); 
        request.setCharacterEncoding(encoding);
        filterChain.doFilter(request, response);
    }

}

package com.atguigu.javaweb.login;

import java.io.IOException;
import java.util.Arrays;
import java.util.List;

import javax.servlet.FilterChain;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.atguigu.javaweb.HttpFilter;

public class LoginFilter extends HttpFilter{

    //1. 从 web.xml 文件中获取 sessionKey, redirectUrl, uncheckedUrls
    private String sessionKey;
    private String redirectUrl;
    private String unchekcedUrls;
    
    @Override
    protected void init() {
        ServletContext servletContext = getFilterConfig().getServletContext();
        
        sessionKey = servletContext.getInitParameter("userSessionKey");
        redirectUrl = servletContext.getInitParameter("rediretPage");
        ///login/a.jsp,/login/list.jsp,/login/login.jsp,/login/doLogin.jsp
        unchekcedUrls = servletContext.getInitParameter("uncheckedUrls");
    }
    
    @Override
    public void doFilter(HttpServletRequest request,
            HttpServletResponse response, FilterChain filterChain)
            throws IOException, ServletException {
        
        //1. 获取请求的 servletPath
        // /login/b.jsp
        String servletPath = request.getServletPath();
        
        //2. 检查 1 获取的 servletPath 是否为不需要检查的 URL 中的一个, 若是, 则直接放行. 方法结束
        List<String> urls = Arrays.asList(unchekcedUrls.split(","));
        if(urls.contains(servletPath)){
            filterChain.doFilter(request, response);
            return;
        }
        
        //3. 从 session 中获取 sessionKey 对应的值, 若值不存在, 则重定向到 redirectUrl
        Object user = request.getSession().getAttribute(sessionKey);
        if(user == null){
            response.sendRedirect(request.getContextPath() + redirectUrl);
            return;
        }
        
        //4. 若存在, 则放行, 允许访问. 
        filterChain.doFilter(request, response);
    }

}

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>    

    <a href="b.html">TO BBB PAGE</a>

    <br><br>
    
    <img alt="" src="Desert.jpg">

</body>
</html>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>    

    <a href="a.html">TO AAA PAGE</a>

    <br><br>

</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <form action="b.jsp" method="post">
        name: <input type="text" name="name"/>
        <input type="submit" value="Submit"/>
    </form>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

    <%--
        //编写一个 EncodingFilter
        //1. 读取 web.xml 文件中配置的当前 WEB 应用的初始化参数 encoding
        //2. 指定请求的字符编码为 1 读取到的编码
        //3. 调用 chain.doFilter() 方法 "放行" 请求
        request.setCharacterEncoding("UTF-8");
    --%>
    
    Hello: ${param.name }
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <h4>AAA PAGE</h4>
    
    <a href="list.jsp">Return...</a>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

    <%-- 
        //检验用户是否登录. 若没有登录, 则直接重定向到 login.jsp
        Object user = session.getAttribute("user");
    
        if(user == null){
            response.sendRedirect("login.jsp");
        }
    --%>
    
    <h4>BBB PAGE</h4>
    
    <a href="list.jsp">Return...</a>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <%-- 
        //检验用户是否登录. 若没有登录, 则直接重定向到 login.jsp
        Object user = session.getAttribute("user");
    
        if(user == null){
            response.sendRedirect("login.jsp");
        }
    --%>
    
    <h4>CCC PAGE</h4>
    
    <a href="list.jsp">Return...</a>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <% 
        //1. 获取用户的登录信息
        String username = request.getParameter("username");
        
        //2. 若登录信息完整, 则把登录信息放到 HttpSession
        if(username != null && !username.trim().equals("")){ 
            session.setAttribute(application.getInitParameter("userSessionKey"), username);
            //3. 重定向到 list.jsp
            response.sendRedirect("list.jsp");
        }else{
            response.sendRedirect("login.jsp");
        }
        
    %>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <a href="a.jsp">AAA</a>
    <br><br>
    
    <a href="b.jsp">BBB</a>
    <br><br>
    
    <a href="c.jsp">CCC</a>
    <br><br>
    
    <a href="d.jsp">DDD</a>
    <br><br>
    
    <a href="e.jsp">EEE</a>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <form action="doLogin.jsp" method="post">
        username: <input type="text" name="username"/>
        <input type="submit" value="Submit"/>
    </form>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

    <font color="red">${message }</font>
    <br><br>
    
    <form action="hello.jsp" method="post">
    
        username: <input type="text" name="username" value="${param.username }"/>
        password: <input type="password" name="password"/>
    
        <input type="submit" value="Submit"/>
        
    </form>
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    Hello: ${param.username }
    
</body>
</html>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <a href="dispatcher.jsp">To Test Page</a>
    
    
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>

    
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <%-- 
    <jsp:forward page="/test.jsp"></jsp:forward>
    <jsp:include page="/test.jsp"></jsp:include>
    --%>
    
    <% 
        int i = 10 / 0;
    %>    
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <h4>Test Page</h4>
    
    <% 
        System.out.println("5. Test JSP"); //5
    %>
    
</body>
</html>