1．filter的简介
filter是对客户端访问资源的过滤，符合条件放行，不符合条件不放行，并且可以对目 标资源访问前后进行逻辑处理
2．快速入门
步骤：
1）编写一个过滤器的类实现Filter接口
2）实现接口中尚未实现的方法(着重实现doFilter方法)
3）在web.xml中进行配置(主要是配置要对哪些资源进行过滤)
3．Filter的API详解
(1)filter生命周期及其与生命周期相关的方法
Filter接口有三个方法，并且这个三个都是与Filter的生命相关的方法
init(Filterconfig)：代表filter对象初始化方法 filter对象创建时执行
doFilter(ServletRequest,ServletResponse,FilterCha)：代表filter执行过滤的核心方法，如果某资源在已经被配置到这个filter进行过滤的话，那么每次访问这个资源都会执行doFilter方法
destory()：代表是filter销毁方法 当filter对象销毁时执行该方法
Filter对象的生命周期：
Filter何时创建：服务器启动时就创建该filter对象
Filter何时销毁：服务器关闭时filter销毁
(2)Filter的AP详解
1）init(FilterConfig)
其中参数config代表 该Filter对象的配置信息的对象，内部封装是该filter的配置信息。
2）destory()方法
filter对象销毁时执行
3）doFilter方法
doFilter(ServletRequest,ServletResponse,FilterChain)
其中的参数：
ServletRequest/ServletResponse：每次在执行doFilter方法时 web容器负责创建一个request和一个response对象作为doFilter的参数传递进来。该request个该response就是在访问目标资源的service方法时的request和response。
FilterChain：过滤器链对象，通过该对象的doFilter方法可以放行该请求
4．Filter的配置
url-pattern配置时
1）完全匹配 /sertvle1
2）目录匹配 /aaa/bbb/* ----最多的
/user/*：访问前台的资源进入此过滤器
/admin/*：访问后台的资源时执行此过滤器
3）扩展名匹配 *.abc *.jsp
注意：url-pattern可以使用servlet-name替代，也可以混用
dispatcher：访问的方式(了解)
REQUEST：默认值，代表直接访问某个资源时执行filter
FORWARD：转发时才执行filter
INCLUDE: 包含资源时执行filter
ERROR：发生错误时 进行跳转是执行filter
Filter的作用？
1）公共代码的提取
2）可以对request和response中的方法进行增强(装饰者模式/动态代理) 如下：实现批量处理乱码
package com.web.filter;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
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{
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
//request.setCharacterEncoding("UTF-8");
//在传递request之前对request的getParameter方法进行增强
/*
* 装饰者模式(包装)
*
* 1、增强类与被增强的类要实现统一接口
* 2、在增强类中传入被增强的类
* 3、需要增强的方法重写 不需要增强的方法调用被增强对象的
*
*/
//被增强的对象
HttpServletRequest req = (HttpServletRequest) request;
//增强对象
EnhanceRequest enhanceRequest = new EnhanceRequest(req);
chain.doFilter(enhanceRequest, response);
}
@Override
public void destroy() {
}
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
}
class EnhanceRequest extends HttpServletRequestWrapper{
private HttpServletRequest request;
public EnhanceRequest(HttpServletRequest request) {
super(request);
this.request = request;
}
//对getParaameter增强
@Override
public String getParameter(String name) {
String parameter = request.getParameter(name);//乱码
try {
parameter = new String(parameter.getBytes("iso8859-1"),"UTF-8");
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
return parameter;
}
}
package com.web.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 EncodingServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String parameter = request.getParameter("username");//中文
System.out.println(parameter);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
3）进行权限控制 如下：记住密码自动登陆
package com.web.filter;
import java.io.IOException;
import java.net.URLDecoder;
import java.sql.SQLException;
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 javax.servlet.http.HttpSession;
import com.ithiema.domain.User;
import com.ithiema.service.UserService;
public class AutoLoginFilter implements Filter{
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse resp = (HttpServletResponse) response;
HttpSession session = req.getSession();
//获得cookie中用户名和密码 进行登录的操作
//定义cookie_username
String cookie_username = null;
//定义cookie_password
String cookie_password = null;
//获得cookie
Cookie[] cookies = req.getCookies();
if(cookies!=null){
for(Cookie cookie : cookies){
//获得名字是cookie_username和cookie_password
if("cookie_username".equals(cookie.getName())){
cookie_username = cookie.getValue();
//恢复中文用户名
cookie_username = URLDecoder.decode(cookie_username, "UTF-8");
}
if("cookie_password".equals(cookie.getName())){
cookie_password = cookie.getValue();
}
}
}
//判断username和password是否是null
if(cookie_username!=null&&cookie_password!=null){
//登录的代码
UserService service = new UserService();
User user = null;
try {
user = service.login(cookie_username,cookie_password);
} catch (SQLException e) {
e.printStackTrace();
}
//将登录的用户的user对象存到session中
session.setAttribute("user", user);
}
//放行
chain.doFilter(req, resp);
}
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void destroy() {
}
}
package com.web.servlet;
import java.io.IOException;
import java.net.URLEncoder;
import java.sql.SQLException;
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 javax.servlet.http.HttpSession;
import com.ithiema.domain.User;
import com.ithiema.service.UserService;
public class LoginServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("UTF-8");
HttpSession session = request.getSession();
//获取数据
String username = request.getParameter("username");//中文 张三
String password = request.getParameter("password");
UserService service = new UserService();
User user = null;
try {
user = service.login(username,password);
} catch (SQLException e) {
e.printStackTrace();
}
if(user!=null){
//登录成功
//判断用户是否勾选自动登录
String autoLogin = request.getParameter("autoLogin");
if(autoLogin!=null){
//对中文张三进行编码
String username_code = URLEncoder.encode(username, "UTF-8");// %AE4%kfj
Cookie cookie_username = new Cookie("cookie_username",username_code);
Cookie cookie_password = new Cookie("cookie_password",password);
//设置cookie的持久化时间
cookie_username.setMaxAge(60*60);
cookie_password.setMaxAge(60*60);
//设置cookie的携带路径
cookie_username.setPath(request.getContextPath());
cookie_password.setPath(request.getContextPath());
//发送cookie
response.addCookie(cookie_username);
response.addCookie(cookie_password);
}
//将登录的用户的user对象存到session中
session.setAttribute("user", user);
//重定向到首页
response.sendRedirect(request.getContextPath());
}else{
//失败 转发到登录页面 提出提示信息
request.setAttribute("loginInfo", "用户名或密码错误");
request.getRequestDispatcher("/login.jsp").forward(request, response);
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}