过滤器
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过滤器是处于客户端与服务器资源文件之间的一道过滤网，在访问资源文件之前，通过一系列的过滤器对请求进行修改、判断等，把不符合规则的请求在中途拦截或修改。也可以对响应进行过滤，拦截或修改响应。
Filter也称之为过滤器，它是Servlet技术中最实用的技术，WEB开发人员通过Filter技术，对web服务器管理的所有web资源：例如Jsp, Servlet, 静态图片文件或静态 html 文件等进行拦截，从而实现一些特殊的功能。例如实现URL级别的权限访问控制、过滤敏感词汇、压缩响应信息等一些高级功能。
它主要用于对用户请求进行预处理，也可以对HttpServletResponse 进行后处理。使用Filter 的完整流程：Filter 对用户请求进行预处理，接着将请求交给Servlet 进行处理并生成响应，最后Filter 再对服务器响应进行后处理。
过滤器实现自动登录
package com.test.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.test.model.User;
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("username".equals(cookie.getName())){
cookie_username = cookie.getValue();
//恢复中文用户名
cookie_username = URLDecoder.decode(cookie_username, "UTF-8");
System.out.println("拿到用户名");
}
if("password".equals(cookie.getName())){
cookie_password = cookie.getValue();
System.out.println("拿到密码");
}
}
}
//判断username和password是否是null
if(cookie_username!=null&&cookie_password!=null){
System.out.println(cookie_username);
System.out.println(cookie_password);
//登录的代码
if(cookie_username.equals("zhangsan") && cookie_password.equals("123"))
{
//User user=new User(cookie_username,"127.0.0.1");
//将登录的用户的user对象存到session中
session.setAttribute("login_user", "zhangsan");
System.out.println("放行");
}
}
//放行
chain.doFilter(req, resp);
}
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void destroy() {
}
}
package com.test.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.test.model.User;
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("username".equals(cookie.getName())){
cookie_username = cookie.getValue();
//恢复中文用户名
cookie_username = URLDecoder.decode(cookie_username, "UTF-8");
System.out.println("拿到用户名");
}
if("password".equals(cookie.getName())){
cookie_password = cookie.getValue();
System.out.println("拿到密码");
}
}
}
//判断username和password是否是null
if(cookie_username!=null&&cookie_password!=null){
System.out.println(cookie_username);
System.out.println(cookie_password);
//登录的代码
if(cookie_username.equals("zhangsan") && cookie_password.equals("123"))
{
//User user=new User(cookie_username,"127.0.0.1");
//将登录的用户的user对象存到session中
session.setAttribute("login_user", "zhangsan");
System.out.println("放行");
}
}
//放行
chain.doFilter(req, resp);
}
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void destroy() {
}
}
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