10、Filter常见应用
（1）统一全站字符编码的过滤器
通过配置参数encoding指明使用何种字符编码,以处理Html Form请求参数的中文问题
案例：编写jsp 输入用户名，在Servlet中获取用户名，将用户名输出到浏览器上
处理请求post乱码代码
request.setCharacterEncoding("utf-8");
设置响应编码集代码
response.setContentType("text/html;charset=utf-8");
经常会使用，而过滤器可以在目标资源之前执行，将很多程序中处理乱码公共代码，提取到过滤器中 ，以后程序中不需要处理编码问题了
package com.itheima.filter;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.Map;
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.HttpServletRequestWrapper;
public class EncodingFilter implements Filter {
private FilterConfig config = null;
public void destroy() {
}
/**
* 全站乱码解决
*/
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
chain.doFilter(new MyRequest(req), response);
}
class MyRequest extends HttpServletRequestWrapper {
private HttpServletRequest request = null;
private boolean isEncode = false;
public MyRequest(HttpServletRequest request) {
super(request);
this.request = request;
}
@Override
public Map getParameterMap() {
if (request.getMethod().equalsIgnoreCase("post")) {
try {
request.setCharacterEncoding(config.getInitParameter("encode"));
return request.getParameterMap();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
} else if (request.getMethod().equalsIgnoreCase("get")) {
try {
Map<String, String[]> map = request.getParameterMap();
if(!isEncode){
for (String key : map.keySet()) {
String [] vs = map.get(key);
for(int i=0;i<vs.length;i++){
String v = vs[i];
v = new String(v.getBytes("iso8859-1"), config.getInitParameter("encode"));
vs[i] = v;
}
}
isEncode = true;
}
return map;
} catch (Exception e) {
e.printStackTrace();
}
}
return super.getParameterMap();
}
@Override
public String[] getParameterValues(String name) {
if(getParameterMap().get(name)==null)return null;
return (String[])getParameterMap().get(name);
}
@Override
public String getParameter(String name) {
if(getParameterMap().get(name)==null)return null;
return ((String[])getParameterMap().get(name))[0];
}
}
public void init(FilterConfig filterConfig) throws ServletException {
this.config = filterConfig;
}
}
package com.itheima.web;
import java.io.IOException;
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 EncodeTestServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String vs = request.getParameterValues("username")[0];
System.out.println(vs);
String value = request.getParameter("username");
System.out.println(value);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
<filter>
<filter-name>encode</filter-name>
<filter-class>com.itheima.filter.EncodingFilter</filter-class>
<init-param>
<param-name>encode</param-name>
<param-value>utf-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>encode</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
（2）禁止浏览器缓存所有动态页面的过滤器：
有 3 个 HTTP 响应头字段都可以禁止浏览器缓存当前页面，它们在 Servlet 中的示例代码如下：
response.setDateHeader("Expires",-1);
response.setHeader("Cache-Control","no-cache");
response.setHeader("Pragma","no-cache");
并不是所有的浏览器都能完全支持上面的三个响应头，因此最好是同时使用上面的三个响应头。
Expires数据头：值为GMT时间值，为-1指浏览器不要缓存页面
Cache-Control响应头有两个常用值：
no-cache指浏览器不要缓存当前页面。
max-age:xxx指浏览器缓存页面xxx秒。
package com.itheima.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;
import javax.servlet.http.HttpServletResponse;
public class NoChachFilter implements Filter {
public void destroy() {
// TODO Auto-generated method stub
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletResponse resp = (HttpServletResponse) response;
resp.setDateHeader("Expires",-1);
resp.setHeader("Cache-Control","no-cache");
resp.setHeader("Pragma","no-cache");
chain.doFilter(request, response);
}
public void init(FilterConfig filterConfig) throws ServletException {
// TODO Auto-generated method stub
}
}
<filter>
<filter-name>nocach</filter-name>
<filter-class>com.itheima.filter.NoChachFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>nocach</filter-name>
<url-pattern>*.jsp</url-pattern>
</filter-mapping>
（3）控制浏览器缓存页面中的静态资源的过滤器：
场景：有些动态页面中引用了一些图片或css文件以修饰页面效果，这些图片和css文件经常是不变化的，所以为减轻服务器的压力，可以使用filter控制浏览器缓存这些文件，以提升服务器的性能。
Tomcat缓存策略
对于服务器端经常不变化文件，设置客户端缓存时间，在客户端资源缓存时间到期之前，就不会去访问服务器获取该资源 -------- 比tomcat内置缓存策略更优手段
* 减少服务器请求次数，提升性能
设置静态资源缓存时间，需要设置 Expires 过期时间 ，在客户端资源没有过期之前，不会产生对该资源的请求的
* 设置Expires 通常使用 response.setDateHeader 进行设置 设置毫秒值
package com.itheima.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;
import javax.servlet.http.HttpServletResponse;
public class CacheFilter implements Filter {
public void destroy() {
// TODO Auto-generated method stub
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletResponse resp = (HttpServletResponse) response;
resp.setDateHeader("Expires", System.currentTimeMillis()+3600l*24*30*1000);
chain.doFilter(request, response);
}
public void init(FilterConfig filterConfig) throws ServletException {
// TODO Auto-generated method stub
}
}
<filter>
<filter-name>cache</filter-name>
<filter-class>com.itheima.filter.CacheFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>cache</filter-name>
<url-pattern>*.jpg</url-pattern>
<url-pattern>*.gif</url-pattern>
<url-pattern>*.png</url-pattern>
<dispatcher>REQUEST</dispatcher>
</filter-mapping>
（4）实现用户自动登陆的过滤器
在用户登陆成功后，以cookis形式发送用户名、密码给客户端
编写一个过滤器，filter方法中检查cookie中是否带有用户名、密码信息，如果存在则调用业务层登陆方法，登陆成功后则向session中存入user对象（即用户登陆标记），以实现程序完成自动登陆。
在访问一个站点，登陆时勾选自动登陆（三个月内不用登陆），操作系统后，关闭浏览器；过几天再次访问该站点时，直接进行登陆后状态
在数据库中创建 user表
create table user (
id int primary key auto_increment,
username varchar(20),
password varchar(40),
role varchar(10)
);
insert into user values(null,'admin','123','admin');
insert into user values(null,'aaa','123','user');
insert into user values(null,'bbb','123','user');
自动登陆 ：未登录、存在自动登陆信息、自动登陆信息正确
在用户完成登陆后，勾选自动登陆复选框，服务器端将用户名和密码 以Cookie形式，保存在客户端 。当用户下次访问该站点，AutoLoginFilter 过滤器从Cookie中获取 自动登陆信息
1、判断用户是否已经登陆，如果已经登陆，没有自动登陆的必要
2、判断Cookie中是否含有自动登陆信息 ，如果没有，无法完成自动登陆
3、使用cookie用户名和密码 完成自动登陆
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
</head>
<body>
<form action="${pageContext.request.contextPath }/servlet/LoginServlet2" method="post">
用户名<input type="text" name="username"/>
密码<input type="text" name="password"/>
<input type="checkbox" name="autoLogin" value="true" />一个月内自动登录
<input type="submit" value="登录"/>
</form>
</body>
</html>
package com.itheima.autologin;
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 org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import com.itheima.domain.User;
import com.itheima.util.DaoUtil;
import com.itheima.util.MD5Util;
public class LoginServlet2 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
try{
//1.校验用户名密码是否正确
QueryRunner runner = new QueryRunner(DaoUtil.getSource());
User user = runner.query("select * from user where username=? and password=?", new BeanHandler<User>(User.class),request.getParameter("username"),MD5Util.md5(request.getParameter("password")));
if(user == null){
request.setAttribute("msg", "用户名密码不正确！！");
request.getRequestDispatcher("/login.jsp").forward(request, response);
return;
}else{
//用户名密码都正确，在session域中保存用户的登录状态
request.getSession().setAttribute("user", user);
//如果勾选过一个月内自动登录，发送cookie信息给浏览器，使浏览器保存用户名密码一个月
if(request.getParameter("autoLogin")!=null){
Cookie cookie = new Cookie("autologin",user.getUsername()+":"+user.getPassword());
cookie.setMaxAge(3600*24*30);
cookie.setPath(request.getContextPath());
response.addCookie(cookie);
}
response.sendRedirect(request.getContextPath()+"/autologin/homepage.jsp");
}
}catch (Exception e) {
e.printStackTrace();
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
</head>
<body>
<c:if test="${sessionScope.user == null}">
欢迎光临游客！<a href="${pageContext.request.contextPath }/autologin/login.jsp">登录</a>
</c:if>
<c:if test="${sessionScope.user != null}">
欢迎回来
</c:if>
</body>
</html>
package com.itheima.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;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import com.itheima.domain.User;
import com.itheima.util.DaoUtil;
public class AutoLoginFilter implements Filter {
public void destroy() {
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
//1.检查用户是否已经登录
if(req.getSession(false) == null || req.getSession().getAttribute("user")==null){
//2.如果用户没有登录过，则检查是否带了autologincookie
Cookie [] cs = req.getCookies();
Cookie findc = null;
if(cs!=null){
for(Cookie c : cs){
if(c.getName().equals("autologin")){
findc = c;
break;
}
}
}
if(findc != null){
//3.如果有autologin cookie，获取cookie的值，检查用户名密码是否正确
String username = findc.getValue().split(":")[0];
String password = findc.getValue().split(":")[1];
//4.如果用户名密码都正确，则自动登录一把
try{
QueryRunner runner = new QueryRunner(DaoUtil.getSource());
User user = runner.query("select * from user where username=? and password=?", new BeanHandler<User>(User.class),username,password);
if(user!=null){
req.getSession().setAttribute("user", user);
}
}catch (Exception e) {
e.printStackTrace();
}
}
}
//5.放行资源
chain.doFilter(request, response);
}
public void init(FilterConfig filterConfig) throws ServletException {
// TODO Auto-generated method stub
}
}
<filter>
<filter-name>autologinFilter</filter-name>
<filter-class>com.itheima.filter.AutoLoginFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>autologinFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
（5）使用Filter实现URL级别的权限认证
（1）情景：在实际开发中我们经常把一些执行敏感操作的servlet映射到一些特殊目录中，并用filter把这些特殊目录保护起来，限制只能拥有相应访问权限的用户才能访问这些目录下的资源。从而在我们系统中实现一种URL级别的权限功能。
要求：为使Filter具有通用性，Filter保护的资源和相应的访问权限通过filter参数的形式予以配置。
（2）系统中存在很多资源，将需要进行权限控制的资源，放入特殊路径中，编写过滤器管理访问特殊路径的请求，如果没有相应身份和权限，控制无法访问
认证：who are you ? 用户身份的识别 ------------ 登陆功能
权限：以认证为基础 what can you do ? 您能做什么？ 必须先登陆，才有身份，有了身份，才能确定可以执行哪些操作
package com.itheima.filter;
import java.io.IOException;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
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.HttpSession;
import com.itheima.domain.User;
public class PrivilegeFilter implements Filter {
private FilterConfig config = null;
private Map<String, String> map = new HashMap<String, String>();
public void destroy() {
// TODO Auto-generated method stub
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
//1.当前访问的资源是否需要权限（当前访问资源路径是否是map中具有的需要权限控制的路径的子路径）
HttpServletRequest req = (HttpServletRequest) request;
String uri = req.getRequestURI();
uri = uri.substring(config.getServletContext().getContextPath().length());
String privilege = null;
for(String name : map.keySet()){
if(uri.startsWith(name)){
privilege = map.get(name);
}
}
if(privilege == null){
//2.如果不需要权限，直接放行
chain.doFilter(request, response);
return;
}else{//3.如果需要权限，判断当前用户具有的权限和访问该资源需要的权限是否相匹配，如果匹配就放行，如果不匹配则提示
HttpSession session = req.getSession(false);
if(session == null || session.getAttribute("user")==null){
throw new RuntimeException("请先登录");
}
User user = (User) session.getAttribute("user");
if(user.getRole().equals(privilege)){
chain.doFilter(request, response);
return;
}else{
throw new RuntimeException("没有对应的权限！！！！");
}
}
}
public void init(FilterConfig filterConfig) throws ServletException {
this.config = filterConfig;
Enumeration enumeration = config.getInitParameterNames();
while(enumeration.hasMoreElements()){
String name = (String) enumeration.nextElement();
String value = config.getInitParameter(name);
map.put(name, value);
}
}
}
<filter>
<filter-name>PrivilegeFilter</filter-name>
<filter-class>com.itheima.filter.PrivilegeFilter</filter-class>
<init-param>
<param-name>/admin</param-name>
<param-value>admin</param-value>
</init-param>
<init-param>
<param-name>/user</param-name>
<param-value>user</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>PrivilegeFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>