本文主要对Filter的使用进行讲解。
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。
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：
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...");
}
}
<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>
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：
<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>
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;
}
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>
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>
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。
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);
}
}
<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
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">
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;
@Override
public 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>
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
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");
}
}
<%@ 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;">${requestScope.msg }</p>
<form action="<%=path%>/login" method="post">
username : <input type="text" name="username" ><br/>
<input type="submit" value="Sign in">
</form>
</body>
</html>
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'index.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
欢迎你,<c:out value="${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>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。
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cookie
Cookie 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>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;
@Override
public 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cookie
Cookie[] 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>
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;
}
}
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：
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();
}
}
<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>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();
}
}
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。
原文地址：http://blog.csdn.net/ricciozhang/article/details/43800955
