java web filter 基础

     本文主要对Filter的使用进行讲解。

1、Filter是什么？

      Filter 技术是servlet 2.3 新增加的功能。Filter翻译过来的意思就是过滤器，能对客户端的消息进行预处理，然后将请求转发给其它的web组件，可以对ServletHttpRequest和ServletHttpResponse进行修改和检查。例如：在Filter中可以检查用户是否登录，对未登录的用户跳转到登陆界面。

2、过滤器快速入门

     要定义一个过滤器，则需要实现javax.servlet.Filter接口，一个过滤器中包含了三个与生命周期相关的方法：

• void init(FilterConfig  config)  过滤器初始化时执行，FilterConfig 可以用来获取过滤器的初始化参数。
  
• void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
  

           过滤器过滤请求时执行，包含了request和response，chain用来是否执行下一步请求。

• destroy()   web容器（tomcat）停止时执行

    第一步：创建DemoFilter.java

package cn.zq.filter;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 DemoServlet implements Filter{public void init(FilterConfig config) throws ServletException {System.out.println("DemoServlet.init...");}public void doFilter(ServletRequest req, ServletResponse resp,FilterChain chain) throws IOException, ServletException {System.out.println("DemoServlet.doFilter...");                System.out.println("this = " + this);        }public void destroy() {System.out.println("DemoServlet.destroy...");}}

第二步：在web.xml文件中添加如下配置：

  <filter>  <filter-name>demo</filter-name>  <filter-class>cn.zq.filter.DemoServlet</filter-class>  </filter>  <filter-mapping>  <filter-name>demo</filter-name>  <url-pattern>/*</url-pattern>  </filter-mapping>

url-pattern配置为/*，表示过滤所有请求。

启动tomcat，可以看到如下输出：

说明Filter的init方法在web容器启动的时候执行，读者可以自行验证destroy()方法会在web容器停止时执行，访问主页：

在访问主页的时候浏览器是一片空白的，控制台输出上面的消息，Filter只会实例化一次，为什么我们访问不到我们要访问的内容呢？只需要在doFilter方法中加入如下的语句就可以了：

chain.doFilter(req, resp);

   FilterChain（过滤器链）是用来干什么的呢？这个对象只包含一个void doFilter(ServletRequest request, ServletResponse response)方法，Filter调用此方法去调用下一个web组件（Filter,Servlet等），如果不调用此方法，那么下一个web组件不会被执行。

再放行之前，我们可以在Filter中设置响应头信息，如下：

        resp.setContentType("text/html;charset=UTF-8");        chain.doFilter(req, resp);

过滤器的过滤过程如下：

过滤器中的各项配置：

• 配置初始化参数：

 <filter>  <filter-name>demo</filter-name>  <filter-class>cn.zq.filter.DemoServlet</filter-class>  <init-param>  <param-name>encoding</param-name>  <param-value>UTF-8</param-value>  </init-param>  <init-param>  <param-name>name</param-name>  <param-value>RiccioZhang</param-value>  </init-param>  </filter>  <filter-mapping>  <filter-name>demo</filter-name>  <url-pattern>/*</url-pattern>  </filter-mapping>

然后在init方法中获取：

public void init(FilterConfig config) throws ServletException {System.out.println("DemoServlet.init...");String encoding = config.getInitParameter("encoding");String name = config.getInitParameter("name");System.out.println("encoding="+encoding);System.out.println("name="+name);}

<filter>  <!-- filter的名字 -->  <filter-name>demo</filter-name>  <!-- 类名 -->  <filter-class>cn.zq.filter.DemoServlet</filter-class>  </filter>  <!-- 可以有多个 -->  <filter-mapping>  <!-- 对哪个filter进行配置 -->  <filter-name>demo</filter-name>  <!--   配置过滤的url，不能是/  其他与servlet配置类似   -->  <url-pattern>/*</url-pattern>  <!--   根据名字配置对哪个servlet进行过滤   -->  <servlet-name>DemoServlet</servlet-name>  <!--   ERROR: <error-page>过来的请求  FORWARD: 对转发过来的请求进行过滤，也就是对request.getRequestDispatcher(path).forward(request, response)  INCLUDE:对request.getRequestDispatcher(path).include(request, response)过来的请求进行过滤  REQUEST(默认): 对客户端的请求进行拦截  可以配置多个   -->  <dispatcher>ERROR</dispatcher>  </filter-mapping>

3、Filter的应用

为了便于编写Filter，本节的所有应用中提供了一个通过的Filter的实现：

package cn.zq.filter;import java.io.IOException;import java.io.Serializable;import java.util.Enumeration;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;/** * 通用的Filter的实现 * @author zq * */public abstract class GenericFilter implements Filter,FilterConfig, Serializable{private static final long serialVersionUID = 5497978960987185665L;private FilterConfig filterConfig;/** * 需要初始化，应该覆盖整个方法 */public void init(){}public void init(FilterConfig filterConfig) throws ServletException {this.filterConfig = filterConfig;init();}abstract public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException;public void destroy() {}public String getFilterName() {return getFilterConfig().getFilterName();}public String getInitParameter(String name) {return getFilterConfig().getInitParameter(name);}public Enumeration<String> getInitParameterNames() {return getFilterConfig().getInitParameterNames();}public ServletContext getServletContext() {return getFilterConfig().getServletContext();}public FilterConfig getFilterConfig() {return filterConfig;}}

package cn.zq.filter;import java.io.IOException;import javax.servlet.FilterChain;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public abstract class HttpFilter extends GenericFilter{private static final long serialVersionUID = 1029993995265394412L;public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {HttpServletRequest req = (HttpServletRequest) request;HttpServletResponse resp = (HttpServletResponse) response;doFilter(req, resp, chain);}protected abstract void doFilter(HttpServletRequest request, HttpServletResponse response,FilterChain chain) throws IOException, ServletException;}

3.1、解决GET和POST获取参数的乱码问题

第一步：创建Filter

package cn.zq.filter;import java.io.IOException;import java.io.UnsupportedEncodingException;import java.util.Iterator;import java.util.Map;import javax.servlet.FilterChain;import javax.servlet.ServletException;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletRequestWrapper;import javax.servlet.http.HttpServletResponse;/** * 处理字符编码的Filter * @author zq * */public class CharacterEncodingFilter extends HttpFilter{private static final long serialVersionUID = -4329981031091311164L;private String characterEncoding = "UTF-8";public void init() {String ce = getInitParameter("characterEncoding");if(ce != null && !ce.equals("")){characterEncoding = ce.toUpperCase();}}public void doFilter(HttpServletRequest request,HttpServletResponse response, FilterChain chain)throws IOException, ServletException {request.setCharacterEncoding(characterEncoding);response.setContentType("text/html;charset="+characterEncoding);//优化：只对GET请求的request进行包装if(request.getMethod().equals("GET")){request = new ParameterHandlerRequest(request);}chain.doFilter(request, response);}private class ParameterHandlerRequest extends HttpServletRequestWrapper{public ParameterHandlerRequest(HttpServletRequest request) {super(request);}public String getParameter(String name) {String value = super.getParameter(name);return getString(value);}private String getString(String value){if(value != null){try {value =  new String( value.getBytes("ISO-8859-1"), getRequest().getCharacterEncoding() );} catch (UnsupportedEncodingException e) {e.printStackTrace();}}return value;}public String[] getParameterValues(String name) {String[] values = super.getParameterValues(name);if(null != values){for(int i = 0; i < values.length; i++){values[i] = getString(values[i]);}}return values;}public Map<String, String[]> getParameterMap() {Map<String, String[]> paramMap = super.getParameterMap();Iterator<String[]> it = paramMap.values().iterator();while(it.hasNext()){String[] values = it.next();if(null != values){for(int i = 0; i < values.length; i++){values[i] = getString(values[i]);}}}return paramMap;}}}

第二步：编写配置文件

  <filter>  <filter-name>CharacterEncodingFilter</filter-name>  <filter-class>cn.zq.filter.CharacterEncodingFilter</filter-class>  </filter>  <filter-mapping>  <filter-name>CharacterEncodingFilter</filter-name>  <url-pattern>/*</url-pattern>  </filter-mapping>

这个过滤器应该配置在所有过滤器的前面

第三步：测试

package cn.zq.servlet;import java.io.IOException;import java.util.Iterator;import java.util.Map;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class DemoServlet extends HttpServlet {    private static final long serialVersionUID = -4363281555738840730L;    public void doGet(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        doPost(request, response);    }    public void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        System.out.println("--------"+request.getMethod()+"--------");        System.out.println("request = " + request);        System.out.println("name = " + request.getParameter("name"));                String[] names = request.getParameterValues("name");        if(names != null && names.length > 0){            System.out.println("names[0] = " + names[0]);        }        Map<String, String[]> parameterMap = request.getParameterMap();        for(Iterator<String> it = parameterMap.keySet().iterator();                it.hasNext();){            String key = it.next();            String[] values = parameterMap.get(key);            System.out.println(key+"="+values[0] );        }    }}

 <servlet>  <servlet-name>DemoServlet</servlet-name>  <servlet-class>cn.zq.servlet.DemoServlet</servlet-class>  </servlet>  <servlet-mapping>  <servlet-name>DemoServlet</servlet-name>  <url-pattern>/servlet/DemoServlet</url-pattern>  </servlet-mapping>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%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 'index.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"><!--<link rel="stylesheet" type="text/css" href="styles.css">-->  </head>    <body>   <a href="<%=basePath%>servlet/DemoServlet?name=中国">Click</a>   <form action="<%=basePath%>servlet/DemoServlet" method="post">   <input type="text" name="name"><br/>   <input type="submit"/>   </form>  </body></html>

访问并测试：

这个过滤器应该被配置在所有过滤器的前面，就能解决全站的乱码了，这样就不用重复的编写解决乱码问题的代码了。

3.2、设置所有的jsp页面不缓存

因为jsp页面的有些内容是动态生成的，所有混成jsp页面的意义不大，我们通常会设置这些jsp页面不缓存。

第一步：开发Filter

package cn.zq.filter;import java.io.IOException;import javax.servlet.FilterChain;import javax.servlet.ServletException;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class DynamicPageCacheFilter extends HttpFilter {/** *  */private static final long serialVersionUID = -5449451659530735173L;public void doFilter(HttpServletRequest request,HttpServletResponse response, FilterChain chain)throws IOException, ServletException {//设置3个响应头response.setHeader("pragma", "no-cache");response.setHeader("cache-control", "no-cache");response.setDateHeader("expires", 0);chain.doFilter(request, response);}}

第二步：配置web.xml

  <filter>  <filter-name>DynamicPageCacheFilter</filter-name>  <filter-class> cn.zq.filter.DynamicPageCacheFilter</filter-class>  </filter>  <filter-mapping>  <filter-name>DynamicPageCacheFilter</filter-name>  <url-pattern>*.jsp</url-pattern>  <dispatcher>REQUEST</dispatcher>  <dispatcher>FORWARD</dispatcher>  <dispatcher>INCLUDE</dispatcher>  </filter-mapping

第三步：打开ie，清空所有的缓存，cookie，访问本项目的jsp文件看是否有缓存文件，将Filter拿到，再访问看是否有缓存文件。

控制是否缓存，也可以在jsp页面中加入这几个头

<meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">  

3.3、控制静态页面缓存（如html，图片）

第一步：编写Filter

package cn.zq.filter;import java.io.IOException;import java.util.Calendar;import javax.servlet.FilterChain;import javax.servlet.ServletException;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class StaticContentCacheFilter extends HttpFilter{/** *  */private static final long serialVersionUID = 7660878144738222823L;@Overridepublic void doFilter(HttpServletRequest request,HttpServletResponse response, FilterChain chain)throws IOException, ServletException {/* *让图片缓存一个月，html文件缓存一个星期 , *具体的相关信息可以通过配置文件来配置。 */String requestURI = request.getRequestURI();long time = 0;int day = 0;if(requestURI.endsWith(".jpg")){day = 30;}else if(requestURI.endsWith(".html")){day = 7;}Calendar calendar = Calendar.getInstance();calendar.add(Calendar.DATE, day);time = calendar.getTimeInMillis();response.setDateHeader("expires", time);chain.doFilter(request, response);}}

第二步：配置

  <filter>  <filter-name>StaticContentCacheFilter</filter-name>  <filter-class>cn.zq.filter.StaticContentCacheFilter</filter-class>  </filter>  <filter-mapping>  <filter-name>StaticContentCacheFilter</filter-name><url-pattern>*.html</url-pattern><url-pattern>*.jpg</url-pattern>    </filter-mapping>

第三步：测试

请求资源，再次请求。查看状态码为304，及缓存文件的日期为N天以后。这是返回的状态码：HTTP/1.1 304 Not Modified

3.4 验证用户是否登录

第一步：开发filter

package cn.zq.filter;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.FilterChain;import javax.servlet.ServletException;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;/** * 验证用户是否登录的过滤器 * @author Riccio Zhang * */public class LoginFilter extends HttpFilter{/** *  */private static final long serialVersionUID = -6363929637537263967L;protected void doFilter(HttpServletRequest request,HttpServletResponse response, FilterChain chain)throws IOException, ServletException {HttpSession session = request.getSession();Object user = session.getAttribute("user");//没有找到user，则说明用户没有登录，转到登录页面让用户登录if(user == null){PrintWriter out = response.getWriter();out.print("<script>" +  "alert('您还未登录!');" +  "window.location.href='"+request.getContextPath()+"/login.jsp'" +  "</script>");return;}chain.doFilter(request, response);}}

第二步：开发登录功能，配置web.xml

package cn.zq.servlet;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class LoginServlet extends HttpServlet {/** *  */private static final long serialVersionUID = 3059445154848670189L;public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//让用户退出登录request.getSession().invalidate();response.sendRedirect(request.getContextPath() + "/login.jsp");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {/* * 让用户登录成功 */String username = request.getParameter("username");if(username == null || username.length() == 0){request.setAttribute("msg", "用户名不能为空！");request.getRequestDispatcher("/login.jsp").forward(request, response);return;}request.getSession().setAttribute("user", username);//重定向到主页response.sendRedirect(request.getContextPath() + "/page/index.jsp");}}

登录页面：/login.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%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>    <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>  <p style="color:red;font: 12px;">${requestScope.msg }</p>    <form action="<%=path%>/login" method="post">    username : <input type="text" name="username" ><br/>    <input type="submit" value="Sign in">    </form>  </body></html>

登录成功跳转页面：/page/index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@ taglib uri="http://java.sun.com/jsp/jstl/core"  prefix="c"%><%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 'index.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"><!--<link rel="stylesheet" type="text/css" href="styles.css">-->  </head>    <body>        欢迎你,<c:out value="${user }"></c:out><br/>  <a href="<%=path%>/login">退出</a>  </body></html>

 <!-- 对/page/*进行过滤 -->  <filter>  <filter-name>LoginFilter</filter-name>  <filter-class>cn.zq.filter.LoginFilter</filter-class>  </filter>  <filter-mapping>  <filter-name>LoginFilter</filter-name><url-pattern>/page/*</url-pattern>    </filter-mapping>  <servlet-mapping>  <servlet-name>DemoServlet</servlet-name>  <url-pattern>/servlet/DemoServlet</url-pattern>  </servlet-mapping>  <servlet-mapping>    <servlet-name>LoginServlet</servlet-name>    <url-pattern>/login</url-pattern>  </servlet-mapping>

第三步：测试，

在访问/page/index.jsp页面时，未登录是否会跳转到登录页面。登录时显示用户的名字。

3.5、自动登录

自动登录是为了让用户下次访问时，不用输入用户名和密码。将用户的信息保存到cookie中，下次直接从cookie中取。

第一步：开发登录页面

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%><%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>    <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><c:choose><c:when test="${empty user }"><p style="color:red;font: 12px;">${requestScope.msg }</p>    <form action="<%=path%>/login" method="post">    username : <input type="text" name="username" ><br/>    <fieldset>    <legend>自动登录</legend>    <input type="radio" name="day" value="0">不自动登录<br/>    <input type="radio" name="day" value="1">1天<br/>    <input type="radio" name="day" value="7">一个星期<br/>    <input type="radio" name="day" value="30">一个月<br/>    </fieldset>    <input type="submit" value="Sign in">    </form></c:when><c:otherwise>欢迎您,<c:out value="${user }"></c:out><br/><a href="<c:url value='/login' />">退出</a></c:otherwise></c:choose>  </body></html>

第二步：开发登录servlet

package cn.zq.servlet;import java.io.IOException;import java.net.URLEncoder;import javax.servlet.ServletException;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class LoginServlet extends HttpServlet {/** *  */private static final long serialVersionUID = 3059445154848670189L;public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//让用户退出登录request.getSession().invalidate();//删除cookieCookie cookie = new Cookie("autoLogin", "");/** * 0表示删除文件和缓存 * -1表示删除文件，但是还有缓存 */cookie.setMaxAge(0);cookie.setPath("/");response.addCookie(cookie);response.sendRedirect(request.getContextPath() + "/login.jsp");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {/* * 让用户登录成功 */String username = request.getParameter("username");if(username == null || username.length() == 0){request.setAttribute("msg", "用户名不能为空！");request.getRequestDispatcher("/login.jsp").forward(request, response);return;}int day = 0;String auto = request.getParameter("day");try {day = Integer.parseInt(auto);} catch (Exception e) {}//对中文要进行编码Cookie cookie = new Cookie("autoLogin", URLEncoder.encode(username, request.getCharacterEncoding()));cookie.setMaxAge(day*24*3600);cookie.setPath("/");response.addCookie(cookie);request.getSession().setAttribute("user", username);response.sendRedirect(request.getContextPath() + "/page/index.jsp");}}

  <servlet-mapping>  <servlet-name>DemoServlet</servlet-name>  <url-pattern>/servlet/DemoServlet</url-pattern>  </servlet-mapping>  <servlet-mapping>    <servlet-name>LoginServlet</servlet-name>    <url-pattern>/login</url-pattern>  </servlet-mapping>

第三步：开发自动登录过滤器

package cn.zq.filter;import java.io.IOException;import java.net.URLDecoder;import javax.servlet.FilterChain;import javax.servlet.ServletException;import javax.servlet.http.Cookie;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class AutoLoginFilter extends HttpFilter{/** *  */private static final long serialVersionUID = 5891858915933022714L;@Overridepublic void doFilter(HttpServletRequest request,HttpServletResponse response, FilterChain chain)throws IOException, ServletException {/* * 优化：当用户手动登录或退出时，就不需要自动登录， * 并且用户已经登录，也不需要自动登录，自动登录的代码是 * 多此一举 */HttpSession session = request.getSession();String requestURI = request.getRequestURI();Object user = session.getAttribute("user");if(!requestURI.contains("/login") && user == null){//获取cookieCookie[] cookies = request.getCookies();if(cookies != null){for(Cookie c : cookies){if("autoLogin".equals(c.getName())){String username = c.getValue();username = URLDecoder.decode(username, request.getCharacterEncoding());session.setAttribute("user", username);break;}}}}chain.doFilter(request, response);}}

  <filter>  <filter-name>AutoLoginFilter</filter-name>  <filter-class>cn.zq.filter.AutoLoginFilter</filter-class>  </filter>  <filter-mapping>  <filter-name>AutoLoginFilter</filter-name><url-pattern>/*</url-pattern>    </filter-mapping>

3.6、过滤非法语句(脏话)

在过滤器中，包装HttpServletRequest,修改getParameter方法

package cn.zq.filter;import java.io.IOException;import java.util.Arrays;import java.util.List;import javax.servlet.FilterChain;import javax.servlet.ServletException;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletRequestWrapper;import javax.servlet.http.HttpServletResponse;public class DirtyWordsFilter extends HttpFilter{private static final long serialVersionUID = -5025789414017693051L;public void doFilter(HttpServletRequest request,HttpServletResponse response, FilterChain chain)throws IOException, ServletException {request = new MyHttpServletRequest(request);chain.doFilter(request, response);}}class MyHttpServletRequest extends HttpServletRequestWrapper{List<String> dirtyWords = Arrays.asList(new String[]{"SB", "sb", "傻B", "2B"});public MyHttpServletRequest(HttpServletRequest request) {super(request);}public String getParameter(String name) {String value = super.getParameter(name);if(value != null && value.length() > 0){for(String dw : dirtyWords){value = value.replaceAll(dw, "***");}}return value;}}

3.7、全站压缩

实现对输出流的压缩：

在tomcat将数据输出到浏览器前，进行压缩，可以减少传送过去的数据，节约成本。如果在流量很少的情况下查看相同的内容和乐而不为呢？

思路：

• 在调用request.getOutputStream()或request.getWriter()时获取自己的输出流，将数据写到事先准备的缓冲中。
• 在输出完成后获取我们自己的缓冲数据
• 然后在对缓冲的数据进行压缩，在过滤器中将数据传输给浏览器

第一步：编写压缩数据的过滤器

package cn.zq.filter;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.OutputStreamWriter;import java.io.PrintWriter;import java.util.zip.GZIPOutputStream;import javax.servlet.FilterChain;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpServletResponseWrapper;public class GzipFilter extends HttpFilter{/** *  */private static final long serialVersionUID = 3410826595861585118L;public void doFilter(HttpServletRequest request,HttpServletResponse response, FilterChain chain)throws IOException, ServletException {String ac = request.getHeader("Accept-Encoding");//支持gzip压缩if(ac != null && ac.toLowerCase().indexOf("gzip") != -1){BufferedHttpServletResponse bRes = new BufferedHttpServletResponse(response);chain.doFilter(request, bRes);byte[] data = bRes.getData();System.out.println("->压缩前数据大小：" + data.length);ByteArrayOutputStream bos = new ByteArrayOutputStream();GZIPOutputStream gout = new GZIPOutputStream(bos);gout.write(data);gout.close();byte[] compressedData = bos.toByteArray();System.out.println("->压缩后的数据大小："+compressedData.length);//设置头信息response.setContentLength(compressedData.length);response.setHeader("Content-Encoding", "gzip");ServletOutputStream out = response.getOutputStream();out.write(compressedData);}else{chain.doFilter(request, response);}}}class BufferedHttpServletResponse extends HttpServletResponseWrapper{private ByteArrayOutputStream buf = new ByteArrayOutputStream();private PrintWriter pw;public BufferedHttpServletResponse(HttpServletResponse response) {super(response);}public PrintWriter getWriter() throws IOException {pw = new PrintWriter(new OutputStreamWriter(buf, getResponse().getCharacterEncoding()));return pw;}public ServletOutputStream getOutputStream() throws IOException {ServletOutputStream sos = new ServletOutputStream() {public void write(int b) throws IOException {buf.write(b);}};return sos;}public byte[] getData(){if(pw != null){pw.close();}return buf.toByteArray();}}

第二步：配置对所有的jsp进行压缩

   <filter>       <filter-name>GzipFilter</filter-name>       <filter-class>cn.zq.filter.GzipFilter</filter-class>   </filter>   <filter-mapping>       <filter-name>GzipFilter</filter-name>       <servlet-name>DemoServlet</servlet-name>       <url-pattern>*.jsp</url-pattern>   </filter-mapping>

第三步：测试压缩过滤器

使用压缩过滤器应该注意：应该只用这个压缩过滤器对文本进行压缩，例如jsp,html,css,js等进行压缩，对视频和图片的压缩率很低，不要用来压缩视频和图片，如果是下载，那也不应该用来压缩，这样不但压缩率很低，而且还有可能让服务器奔溃。

关于压缩过滤器的优化：

        在doFilter方法中先将数据拿出来，然后放到GzipOutputStream中进行压缩，然后得到压缩后的字节再输出给客户端，这样2次都得到了字节，假如数据量较大，这2次都会占用较多的内存，能不能从包装的response拿出来时直接就是压缩过后的数据呢？改造后的代码如下：

package cn.zq.filter;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.OutputStreamWriter;import java.io.PrintWriter;import java.util.zip.GZIPOutputStream;import javax.servlet.FilterChain;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpServletResponseWrapper;public class GzipFilter extends HttpFilter{/** *  */private static final long serialVersionUID = 3410826595861585118L;public void doFilter(HttpServletRequest request,HttpServletResponse response, FilterChain chain)throws IOException, ServletException {String ac = request.getHeader("Accept-Encoding");//支持gzip压缩if(ac != null && ac.toLowerCase().indexOf("gzip") != -1){BufferedHttpServletResponse bRes = new BufferedHttpServletResponse(response);chain.doFilter(request, bRes);byte[] compressedData = bRes.getData();//设置头信息response.setContentLength(compressedData.length);response.setHeader("Content-Encoding", "gzip");ServletOutputStream out = response.getOutputStream();out.write(compressedData);}else{chain.doFilter(request, response);}}}class BufferedHttpServletResponse extends HttpServletResponseWrapper{private ByteArrayOutputStream buf = new ByteArrayOutputStream();private GZIPOutputStream gout;private PrintWriter pw;public BufferedHttpServletResponse(HttpServletResponse response) throws IOException {super(response);gout = new GZIPOutputStream(buf);}public PrintWriter getWriter() throws IOException {pw = new PrintWriter(new OutputStreamWriter(gout, getResponse().getCharacterEncoding()));return pw;}public ServletOutputStream getOutputStream() throws IOException {ServletOutputStream sos = new ServletOutputStream() {public void write(int b) throws IOException {gout.write(b);}};return sos;}public byte[] getData() throws IOException{if(pw != null){pw.close();}gout.close();return buf.toByteArray();}}

4.总结

          本文的例子可以在这里下载”：http://download.csdn.net/detail/qq791967024/8446629

          利用Filter能对请求和响应进行预处理，在到达目标组件之前，对强求进行处理，诸如：对请求头和响应头进行处理。充分的利用了包装器设计模式，对request或response进行包装，对其方法进行增强。假如我们拒绝某个请求，就可以写一个过滤器对不希望的请求不放行，即不执行chain.doFilter(request, response)方法，过滤器能帮助我们干很多的事情。