过滤器的简介跟简单应用（禁止缓存，设置中文乱码等）

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

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

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 ;

	@Override
	public void init(FilterConfig config) throws ServletException {

		encoding = config.getInitParameter("encoding");
		contentType = config.getInitParameter("contentType");
		
	}

	@Override
	public 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);
	}

	@Override
	public void destroy() {

	}

}

web.xml配置：

<!--  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>

2、.配置所有的图片不进行缓存

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

public class DispatcherImageNoCacher implements Filter {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {

	}

	@Override
	public 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);
	}

	@Override
	public 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

 <!-- 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：

<%@ 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

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

public class ExpiresImageDemo3 implements Filter {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {

	}

	@Override
	public 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);
	}

	@Override
	public void destroy() {

	}

}

web.xml配置

<!-- 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

Filter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;
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 {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		
	}

	@Override
	public 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 session
		User user = (User) request.getSession().getAttribute("loginUser");
		if(user != null){
			chain.doFilter(request, response);
		} else {
		
			//2获得cookie
			Cookie[] allCookie = request.getCookies();
			if(allCookie != null){
				//3自动登录user session
				String 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session
					request.getSession().setAttribute("loginUser", loginUser);
				}
				
				
		
		
			}
			chain.doFilter(request, response);
		}
		//chain.doFilter(request, response);
	}

servlet代码：

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on
		User 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 1234
		if("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session
			request.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：

<%@ 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;
	}
	@Override
	public 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 -->

过滤器的简介跟简单应用（禁止缓存，设置中文乱码等）

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