过滤器Filter

Posted 2021-12-05 wuxu

 

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);
	}
}