过滤器和拦截器

过滤器：实现Filter接口

1.过滤器的作用

• 常用来做项目中的一些共性的需求
• 如：记录日志、过滤敏感词、权限检查
• 过滤器会以极低的耦合度来处理这样的需求

共性的需求：几乎每个请求都要做的事情

2.使用步骤

• 写一个类，实现Filter接口
• 在web.xml中配置此Filter

package web;

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.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class LoginFilter implements Filter {

	public void destroy() {
		

	}

	public void doFilter(
		ServletRequest req, 
		ServletResponse res, 
		FilterChain chain)
		throws IOException, ServletException {
		//tomcat调用此方法并传入参数，
		//传入的是Http开头的参数。
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) res;
		//有三个请求不需要过滤,将它们排除掉。
		String[] paths = new String[]{
				"/toLogin.do",
				"/login.do",
				"/createImg.do"
		};
		String currPath = request.getServletPath();
		for(String p:paths){
			if(p.equals(currPath)){
				chain.doFilter(request, response);
				return;
			}
		}
		//尝试从session中获取账号
		//登录成功时可以获取到账号，
		//否则获取不到账号。
		HttpSession session = request.getSession();
		String adminCode = (String) session.getAttribute("adminCode");
		//根据账号判断是否已登录
		if(adminCode == null){
			//没登录，重定向到toLogin.do,因为不知道是什么请求，所以用绝对
			response.sendRedirect("/netctoss/toLogin.do");
		} else {
			//已登录，让请求继续执行
			chain.doFilter(request, response);
		}
	}
	//加载时执行，也没必要执行
	public void init(FilterConfig arg0) throws ServletException {
		
	}

}

另一个项目中的登陆过滤器

package cn.tedu.note.util;

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 javax.servlet.http.HttpServletResponse;

public class AccessFilter implements Filter{

	public void destroy() {
		
	}

	public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
			throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) res;
		//获取请求的路径
		String path = request.getRequestURI();
		String reg = ".*edit\\.html$";
		if(path.matches(reg)){
			checkLogin(request,response,chain);
			return;
		}
		reg=".*\\.do";
		String account = ".*account.*\\.do";
		if(path.matches(reg) && !path.matches(account)){
			checkdo(request,response,chain);
		}
		chain.doFilter(request, response);
	}

	private void checkdo(HttpServletRequest request, HttpServletResponse response,FilterChain chain) throws IOException, ServletException {
		//
		String name = "token";
		String value = null;
		value = getCookie(request, name, value);
		if(value==null){
			String json = "{\"state\":1, "
					+ "\"message\":\"必须登录\"}";
			response.setContentType("application/json;charset=utf-8");
			response.getWriter().println(json);
			return;//如果写了if,没写else，就要写return;
		}
		chain.doFilter(request, response);
	}

	private void checkLogin(HttpServletRequest request, HttpServletResponse response,FilterChain chain) throws IOException, ServletException {
		//读取cookie 检查是否登录
		  String name = "token";
		  String value = null;
		  value = getCookie(request, name, value);
		  if(value==null){//没有cookie没有登录,重定向到登录页面
			 String path= "log_in.html";
			 response.sendRedirect(path);
			 return;
		  }
		  //有cookie就通过
		  chain.doFilter(request, response);
	}

	private String getCookie(HttpServletRequest request, String name, String value) {
		Cookie[] cookies = request.getCookies();
		  for(Cookie cookie:cookies){
			  if(cookie.getName().equals(name)){
				  value = cookie.getValue();
			  }
		  }
		return value;
	}

	public void init(FilterConfig arg0) throws ServletException {
		
	}


}

web.xml文件中配置过滤器

 <!-- 登录检查的过滤器 -->
   <filter>
   	<filter-name>login</filter-name>
   	<filter-class>web.LoginFilter</filter-class>
   </filter>
   <filter-mapping>
   	<filter-name>login</filter-name>
   	<url-pattern>*.do</url-pattern>
   </filter-mapping>

拦截器

1.什么是拦截器?

前端控制器在调用处理器之前，如果发现有拦截器存在， 则会先调用拦截器，然后再调用处理器。
注：过滤器属于servlet规范当中定义的组件，而拦截器 属于spring框架定义的组件。

2.如何写一个拦截器?

step1. 写一个java类，实现HandlerInterceptor接口。
step2. 将拦截处理逻辑写在相应的接口方法里面:
preHandle方法：前端控制器先调用拦截器的preHandle方法， 如果该方法返回值为true,则拦截器继续向后调用；如果 该方法返回值为false,则拦截器不再向后调用，请求处理 完成。
postHandle方法：处理器方法已经执行完成，正准备将 ModelAndView对象返回给前端控制器之前执行。可以在 该方法里面，修改ModelAndView对象。
afterCompletion方法：最后执行的方法，要注意，如果 preHandle方法返回值为false,该方法不会执行。
step3. 配置拦截器。

  请看如下示例

package com.tarena.netctoss.interceptors;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

public class SessionInterceptor implements HandlerInterceptor {

	public boolean preHandle(HttpServletRequest request, 
			HttpServletResponse response, Object handler)
			throws Exception {
		System.out.println("preHandle()");
		HttpSession session = request.getSession();
		Object admin = session.getAttribute("admin");
		if(admin == null){
			//没有登录,跳转到登录页面
			response.sendRedirect("toLogin.do");
			return false;
		}
		//已经登录过,则继续向下执行
		return true;
	}

	public void postHandle(HttpServletRequest request, 
			HttpServletResponse response, Object handler,
			ModelAndView modelAndView) throws Exception {

	}

	public void afterCompletion(HttpServletRequest request,
			HttpServletResponse response, Object handler, Exception ex)
			throws Exception {

	}

}