过滤器的简介和简单应用（禁止缓存，设置中文乱码等）
1.介绍
??? * servlet技术：Servlet、Filter(过滤器)、Listener(监听器)
??? ??? * servlet：能做什么
??? ??? * filter: 是否能做
??? ??? * listener：在做什么
??? * 过滤器Filter
??? ??? * sun提供对，静态web资源(html/image/avi等)或动态web资源(servlet,jsp),进行拦截（过滤）的技术
??? ??? * 实现接口：javax.servlet.Filter
2.过滤器编写流程
??? * 编写实现类
??? * 配置web.xml
3.过滤器的生命周期
??? * 初始化方法：init(FilterConfig) ,
??? ??? * 初始化时间：服务器启动时
??? ??? * FilterConfig对象，当前过滤器的配置描述对象
??? ??? ??? * java.lang.String getFilterName()? ，获得过滤器的名称，web.xml<filter><filter-name>
??? ??? ??? * java.lang.String getInitParameter(java.lang.String name) ,获得当前web.xml文件中配置的初始化参数
??? ??? ??? * java.util.Enumeration getInitParameterNames() ，获得所有的名称
??? ??? ??? * ServletContext getServletContext()? ，获得当前web项目的上下文对象的引用。
??? * 拦截方法：doFitter(ServletRequest,ServletResponse,FilterChain)
??? ??? * 每一次请求时，进行拦截。
??? ??? ??? * 注意：请求路径必须与拦截的配置路基吻合
??? * 销毁方法：destroy()
??? ??? * 销毁时间：服务器正常关闭时
??? ???
4、doFilter详解
??? * request和response与servlet相同
??? ??? * javax.servlet.ServletRequest接口，子接口 javax.servlet.http.HttpServletRequest
??? ??? * javax.servlet.ServletResponse接口，子接口 javax.servlet.http.HttpServletResponse
??? ??? * 强制转换：
??? ??? ??? HttpServletRequest request = (HttpServletRequest) req;
??? ??? ??? HttpServletResponse response = (HttpServletResponse) resp;
??? * FilterChain,过滤器链
??? ??? * 将与请求资源吻合的所有过滤器组成一个过滤器链，如果所有的过滤器都放行，请求资源才可以被访问
??? ??? * 放行：chain.doFilter(request,response??? );
??? ??? * 切忌：编写过滤器时，必须先写“放行”语句
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5.web.xml配置
??? * 注册过滤器
? ??? ??? * <filter-name>，给已经注册的过滤器，名一个当前web.xml文件的中的唯一名称
? ??? ??? * <filter-class>，需要注册的过滤器类的完整路径名
??? ??? * 配置初始化参数
??? ??? ??? <init-param>
??? ??? ??? ??? <param-name>encoding</param-name>
??? ??? ??? ??? <param-value>UTF-8</param-value>
??? ??? ??? </init-param>
??? * 映射过滤器
? ??? ??? * <filter-name> 在当前映射之前已经注册的过滤器的名称
? ??? ??? * <url-pattern> 过滤器也是通过请求路径进行拦截
? ??? ??? ??? * 完整路径名匹配，/demo/testServlet
? ??? ??? ??? * 不完整路径名匹配：/demo/*
? ??? ??? ??? * 扩展名匹配：*.jsp? | *.action
??? * 多个过滤器的过滤顺序：<filter-mapping>在web.xml文档中的顺序就是拦截顺序
??? * 注册一个filter，可以存在多个映射
??? ??? <filter>
??? ??? ??? <filter-name>demo1</filter-name>
??? ??? ??? <filter-class>xxx</filter-class>
??? ??? </filter>
??? ??? <filter-mapping>
??? ??? ??? <filter-name>demo1</filter-name>
??? ??? ??? <url-pattern>/demo1</url-pattern>
??? ??? </filter-mapping>
??? ??? <filter-mapping>
??? ??? ??? <filter-name>demo1</filter-name>
??? ??? ??? <url-pattern>/demo2</url-pattern>
??? ??? </filter-mapping>
??? * 注册多个filter，使用一个映射
??? ??? <filter>
??? ??? ??? <filter-name>demo2</filter-name>
??? ??? ??? <filter-class>yyy</filter-class>
??? ??? </filter>
??? ??? <filter>
??? ??? ??? <filter-name>demo3</filter-name>
??? ??? ??? <filter-class>zzz</filter-class>
??? ??? </filter>
??? ??? <filter-mapping>
??? ??? ??? <filter-name>demo2</filter-name>
??? ??? ??? <url-pattern>/demo2</url-pattern>
??? ??? </filter-mapping>
??? ??? <filter-mapping>
??? ??? ??? <filter-name>demo3</filter-name>
??? ??? ??? <url-pattern>/demo2</url-pattern>
??? ??? </filter-mapping>
??? * dispatcher标签
??? ??? * 位置：<filter-mapping><dispatcher>
??? ??? * 取值
??? ??? ??? * REQUEST，request，确定当前过滤器拦截请求的资源，默认值（浏览器-->服务器）
??? ??? ??? * FORWARD，forward，确定当前过滤器拦截转发的资源，（服务器 --> 服务器）
??? ??? ??? * INCLUDE，include，确定当前过滤器拦截包含的资源，（服务器 --> 服务器）
??? ??? ??? * ERROR，error，确定当前过滤器拦截错误的资源，在web.xml文件中配置有好页面
??? ??? ??? * ASYNC，async，确定当前过滤器拦截异步的资源 （java ee 6.0 /servlet 3.0）
??? ??? ??? ??? * 现在web项目 java ee 5.0 /servlet2.5 ,不支持异步和注解
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Java代码解析
??? 1、配置整站编码
???? java代码：
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 Demo1EncodingFilter implements Filter {private String encoding ;private String contentType ;@Overridepublic void init(FilterConfig config) throws ServletException {encoding = config.getInitParameter("encoding");contentType = config.getInitParameter("contentType");}@Overridepublic void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {//设置中文编码request.setCharacterEncoding(this.encoding);response.setContentType(this.contentType);//放行chain.doFilter(request, response);}@Overridepublic void destroy() {}}?web.xml配置：
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<!-- 中文过滤器 start --> <filter> <filter-name>Demo1EncodingFilter</filter-name> <filter-class>cn.itcast.filter.demo1.Demo1EncodingFilter</filter-class> <!-- 给当前过滤器配置初始化参数 --> <init-param> <param-name>encoding</param-name> <param-value>UTF-8</param-value> </init-param> <init-param> <param-name>contentType</param-name> <param-value>text/html;charset=UTF-8</param-value> </init-param> </filter> <filter-mapping> <filter-name>Demo1EncodingFilter</filter-name> <url-pattern>/demo1/*</url-pattern> </filter-mapping>
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2、.配置所有的图片不进行缓存
java代码：
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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;public class DispatcherImageNoCacher implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {}@Overridepublic void doFilter(ServletRequest req, ServletResponse resp,FilterChain chain) throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest) req;HttpServletResponse response = (HttpServletResponse) resp;/* * <meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"> */response.setDateHeader("expires", -1);response.setHeader("Cache-Control", "no-cache");response.setHeader("Pragma", "no-cache"); chain.doFilter(request, response);}@Overridepublic void destroy() {}}<%@ 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><%=request.getContextPath() %><form action="${pageContext.request.contextPath}/login/loginServlet" method="post"><table border="1"><tr><td>用户名</td><td><input type="text" name="username" /></td></tr><tr><td>密码</td><td><input type="password" name="password" /></td></tr><tr><td></td><td><input type="checkbox" name="remeberme" />自动登录</td></tr><tr><td></td><td><input type="submit" value="登录"/></td></tr></table></form></body></html>??web.xml配置
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<!-- 图片不缓存 --> <filter> <filter-name>DispatcherImageNoCacher</filter-name> <filter-class>cn.itcast.filter.dispatcher.demo2.DispatcherImageNoCacher</filter-class> </filter> <filter-mapping> <filter-name>DispatcherImageNoCacher</filter-name> <url-pattern>*.jpg</url-pattern> <url-pattern>*.gif</url-pattern> </filter-mapping>
?jsp页面：
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<%@ 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><img src="1.jpg"/><img src="2.jpg"/><img src="3.jpg"/></body></html>
?3、设置图片的有效时间
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java代码
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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;public class ExpiresImageDemo3 implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {}@Overridepublic void doFilter(ServletRequest req, ServletResponse resp,FilterChain chain) throws IOException, ServletException {HttpServletResponse response = (HttpServletResponse) resp;HttpServletRequest request = (HttpServletRequest) req;response.setDateHeader("expires", System.currentTimeMillis() + 1000l * 60 * 60 * 24 * 30);chain.doFilter(request, response);}@Overridepublic void destroy() {}}?web.xml配置
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<!-- 图片有效时间 --> <filter> <filter-name>ExpiresImageDemo3</filter-name> <filter-class>cn.itcast.filter.expires.demo3.ExpiresImageDemo3</filter-class> </filter> <filter-mapping> <filter-name>ExpiresImageDemo3</filter-name> <url-pattern>*.jpg</url-pattern> <url-pattern>*.gif</url-pattern> </filter-mapping>
?4、 自动登录（session，cookie）
??? ??? * 如果用户已经登录，并且需要自动登录，将用户的信息保存到cookie
??? ??? * 如果用户访问其他页面，通过cookie信息判断进行自动登录，将登录的用户写的session
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Filter代码：
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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.Cookie;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import cn.itcast.login.domain.User;public class LoginFilter implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {}@Overridepublic void doFilter(ServletRequest req, ServletResponse resp,FilterChain chain) throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest) req;HttpServletResponse response = (HttpServletResponse) resp;//1判读用户是否登录 sessionUser user = (User) request.getSession().getAttribute("loginUser");if(user != null){chain.doFilter(request, response);} else {//2获得cookieCookie[] allCookie = request.getCookies();if(allCookie != null){//3自动登录user sessionString loginUserCookieValue = null;for(Cookie cookie : allCookie){if("loginCookie".equals(cookie.getName())){loginUserCookieValue = cookie.getValue();break;}}//勾选了自动登录if(loginUserCookieValue != null){//查询数据库User loginUser = new User();loginUser.setUsername(loginUserCookieValue.split("@")[0]);loginUser.setPassword(loginUserCookieValue.split("@")[1]);//将用户信息放置sessionrequest.getSession().setAttribute("loginUser", loginUser);}}chain.doFilter(request, response);}//chain.doFilter(request, response);}?servlet代码：
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import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import cn.itcast.login.domain.User;public class LoginServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {this.doPost(request, response);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=UTF-8");//1获得数据--并封装String username = request.getParameter("username");String password = request.getParameter("password");String remeberme = request.getParameter("remeberme"); //没有选为null ，选中默认为onUser user = new User(username, password);//2在数据库中查询账号与密码是否匹配，如果匹配，将用户信息放置到session，// * 假设 jack 1234if("jack".equals(user.getUsername()) && "1234".equals(user.getPassword())){//登录成功// * 是否选中自动登录if(remeberme != null){// ## 自动登录 --将用户的信息放置到cookie，下一次浏览器将携带Cookie loginCookie = new Cookie("loginCookie",user.getUsername() + "@" + user.getPassword());loginCookie.setMaxAge(60 * 60 * 24);loginCookie.setPath("/"); //所有人可以访问//将cookie通知浏览器response.addCookie(loginCookie);} //用户信息sessionrequest.getSession().setAttribute("loginUser", user);//转发//request.getRequestDispatcher("/login/show.jsp").forward(request, response);response.sendRedirect(request.getContextPath() + "/login/show.jsp");} else {//不成功response.getWriter().print("您没有登录");}//3选择视图--展示登录之后的页面}}?Jsp代码：
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<%@ 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><%=request.getContextPath() %><form action="${pageContext.request.contextPath}/login/loginServlet" method="post"><table border="1"><tr><td>用户名</td><td><input type="text" name="username" /></td></tr><tr><td>密码</td><td><input type="password" name="password" /></td></tr><tr><td></td><td><input type="checkbox" name="remeberme" />自动登录</td></tr><tr><td></td><td><input type="submit" value="登录"/></td></tr></table></form></body></html>?实体类：
public class User {private String username;private String password;public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}@Overridepublic String toString() {return "User [username=" + username + ", password=" + password + "]";}public User() {super();}public User(String username, String password) {super();this.username = username;this.password = password;}}?web.xml配置文件
<!-- login start --> <filter> <filter-name>LoginFilter</filter-name> <filter-class>cn.itcast.login.filter.LoginFilter</filter-class> </filter> <filter-mapping> <filter-name>LoginFilter</filter-name> <url-pattern>/login/*</url-pattern> </filter-mapping> <!-- login end -->
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