Filter+Servlet

 代码仓库地址+文档：https://gitee.com/DerekAndroid/FilterServlet.git

保存用户登录信息效果：

自动登录’复选框，实现下次进入在一定cookie时间内自动登录到主页

案例一：完成自动登录
	需求：当用户第一次登录该网站的时候，如果勾选了‘自动登录’复选框，'保存用户登录信息'
	那么关闭浏览器后，下次在访问该网站任何资源的时候，都会显示用户在线
	技术分析：
		session(保证用户在线)
		cookie(保存第一访问网站的状态)
		filter(到达目标资源之前，完成登录操作)
案例二：全局统一编码
	需求：在向服务器发送请求的时候，使用filter过滤乱码问题
	技术分析：
		filter
	
	对方法增强：
		继承
		动态代理
		装饰者模式(静态代理)
		
	如何使用装饰者模式：
		装饰者和被装饰者继承同一个类或者实现同一个接口
		装饰者中需要有被装饰者的引用
		对需要增强的方法进行增强
		对不需要增强的方法，直接使用父类的方法 

filter处理编码乱码问题

方案1：getParameter

package com.itheima.servlet;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.sql.SQLException;
import java.util.Map;
import java.util.Set;

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.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;

import com.itheima.bean.User;
import com.itheima.service.LoginService;

public class LoginFilter implements Filter {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		// TODO Auto-generated method stub

	}

	@Override
	public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
			throws IOException, ServletException {
//		HttpServletRequest request = (HttpServletRequest)req;
//		chain.doFilter(new myCode(request), res);
		
		//把servletReuqest强转为HttpServletRequest
		HttpServletRequest request = (HttpServletRequest)req;
		HttpServletResponse response = (HttpServletResponse)res;
		//判断session中是否有用户存在
		String username1=(String)request.getSession().getAttribute("username");
		if(username1!=null){
			//放行
//			chain.doFilter(request, response);
			chain.doFilter(new myCodeParameter(request), res);
			return;
		}
		//获取所有的cookie
		Cookie[] cookies = request.getCookies();
		Cookie co = null;
		//判断cookies是否为null
		if(cookies!=null){
			//从cookies中查找与usernameAndPwd相匹配的cookie
			for(Cookie cookie:cookies){
				if("usernameAndPwd".equals(cookie.getName())){
					co=cookie;
				}
			}
		}
		
		//判断是否是第一次登录
		if(co!=null){
			
			//获取cookie中的用户名和密码
			String up = co.getValue();
			System.out.println(co.getValue());
			String[] sp = up.split("-");
			String username = sp[0];
			String password = sp[1];
			//完成自动登录,调用LoginService
			LoginService ls = new LoginService();
			try {
				User user = ls.getUserByUsernameAndPwd(username, password);
				System.out.println("查询一次数据库");
				if(user!=null){
					//保证用户在线
					request.getSession().setAttribute("username", user.getUsername());
				}
				//放行
//				chain.doFilter(request, response);
				chain.doFilter(new myCodeParameter(request), res);
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			
		}else{
//			chain.doFilter(request, response);
			chain.doFilter(new myCodeParameter(request), res);
		}
		
	}

	@Override
	public void destroy() {
		// TODO Auto-generated method stub

	}

}

class myCodeParameter extends HttpServletRequestWrapper {

	public myCodeParameter(HttpServletRequest request) {
		super(request);
		// TODO Auto-generated constructor stub
	}

	@Override
	public String getParameter(String name) {
		String method = super.getMethod();
		if("get".equalsIgnoreCase(method)){
//			String value = super.getParameter("username");
//			try {
//				value = new String(value.getBytes("iso-8859-1"),"utf-8");
//			} catch (UnsupportedEncodingException e) {
//				// TODO Auto-generated catch block
//				e.printStackTrace();
//			}
//			return value;
			//返回值有问题,全部拦截了
//			username=阿根
//			password=阿根
//			yzm=阿根
//			yzm=阿根
			//编码转换
			String value=super.getParameter(name);
			System.out.println("value="+value);
			//判断是参数提交才转换编码
			if (null!=value) {
				try {
					value = new String(value.getBytes("iso-8859-1"),"utf-8");
				} catch (UnsupportedEncodingException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}

			return value;
		}else if("post".equalsIgnoreCase(method)){
			try {
				super.setCharacterEncoding("utf-8");
			} catch (UnsupportedEncodingException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			return super.getParameter(name);
		}
		return super.getParameter(name);
	}

}

方案2：重写getParameterValues

package com.itheima.servlet;

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;
import javax.servlet.http.HttpServletResponse;
/**
 * 统一编码
 * @author Administrator
 *
 */
public class EncodingFilter implements Filter {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		// TODO Auto-generated method stub

	}

	@Override
	public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
		//1.强转
		HttpServletRequest request=(HttpServletRequest) req;
		HttpServletResponse response=(HttpServletResponse) resp;
		
		//2.放行
		chain.doFilter(new MyRequest(request), response);
	}

	@Override
	public void destroy() {
		// TODO Auto-generated method stub

	}

}
class MyRequest extends HttpServletRequestWrapper{
	private HttpServletRequest request;
	private boolean flag=true;
	
	
	public MyRequest(HttpServletRequest request) {
		super(request);
		this.request=request;
	}
	
	@Override
	public String getParameter(String name) {  
		if(name==null || name.trim().length()==0){
			return null;
		}
		String[] values = getParameterValues(name);
		if(values==null || values.length==0){
			return null;
		}
		
		return values[0];
	}
	
	@Override
	/**
	 * hobby=[eat,drink]
	 */
	public String[] getParameterValues(String name) {
		if(name==null || name.trim().length()==0){
			return null;
		}
		Map<String, String[]> map = getParameterMap();
		if(map==null || map.size()==0){
			return null;
		}
		
		return map.get(name);
	}
	
	@Override
	/**
	 * map{ username=[tom],password=[123],hobby=[eat,drink]}
	 */
	public Map<String,String[]> getParameterMap() {  
		
		/**
		 * 首先判断请求方式
		 * 若为post  request.setchar...(utf-8)
		 * 若为get 将map中的值遍历编码就可以了
		 */
		String method = request.getMethod();
		if("post".equalsIgnoreCase(method)){
			try {
				request.setCharacterEncoding("utf-8");
				return request.getParameterMap();
			} catch (UnsupportedEncodingException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}else if("get".equalsIgnoreCase(method)){
			Map<String,String[]> map = request.getParameterMap();
			if(flag){
				for (String key:map.keySet()) {
					String[] arr = map.get(key);
					//继续遍历数组
					for(int i=0;i<arr.length;i++){
						//编码
						try {
							arr[i]=new String(arr[i].getBytes("iso8859-1"),"utf-8");
						} catch (UnsupportedEncodingException e) {
							e.printStackTrace();
						}
					}
				}
				flag=false;
			}
			//需要遍历map 修改value的每一个数据的编码
			
			return map;
		}
		
		return super.getParameterMap();
	}
	
}