Filter过滤器

本文详细解析了web.xml配置文件的结构和使用,包括欢迎页面设置、过滤器配置及其实现,展示了如何通过过滤器控制访问权限,适用于Java Web开发者。

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web.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>Book</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <filter>
  		<filter-name>loginStatusFilter</filter-name>
  		<filter-class>zz.homework.servlet.LoginStatusFilter</filter-class>
  		<init-param>
  			<param-name>unCheckUris</param-name>
  			<param-value>/verifyCode,/login.jsp,/logServlet,/register.jsp,/regServlet,/logout,/regResult.jsp</param-value>
  		</init-param>
  		<init-param>
  			<param-name>keyOfUserInSession</param-name>
  			<param-value>user</param-value>
  		</init-param>
  		<init-param>
  			<param-name>backUrl</param-name>
  			<param-value>/login.jsp</param-value>
  		</init-param>
  	</filter>
  	<filter-mapping>
  		<filter-name>loginStatusFilter</filter-name>
  		<url-pattern>/*</url-pattern>
  	</filter-mapping>
</web-app>

过滤器servlet

package zz.homework.servlet;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

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.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class LoginStatusFilter implements Filter {
	
	//不需要检查的uri集合
	private List<String> unCheckList = new ArrayList<String>();
	//登录成功时在Session中保存的用户信息的键
	private String keyOfUserInSession;
	//检查到未登录时调回登录界面的路径
	private String backUrl;

	@Override
	public void init(FilterConfig cfg) throws ServletException {
		String unCheckUris = cfg.getInitParameter("unCheckUris");
		String[] split = unCheckUris.split(",");//字符串分割
		for (String str : split) {
			unCheckList.add(str.trim());
		}
		keyOfUserInSession = cfg.getInitParameter("keyOfUserInSession");
		backUrl = cfg.getInitParameter("backUrl");
	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		//从Session中获取user
		HttpServletRequest req = (HttpServletRequest)request;
		HttpServletResponse resp = (HttpServletResponse)response;
		
		//获取请求的uri
		String uri = req.getRequestURI();
		uri = uri.replace(req.getContextPath(), "");
		
		//不检查的请求uri直接通过
		if(unCheckList.contains(uri)){
			chain.doFilter(request, response);
		}else{
			Object obj = req.getSession().getAttribute(keyOfUserInSession);
			//判断是否已经登录
			if(null == obj){
				req.setAttribute("errorMsg", "请先登录!");
				req.getRequestDispatcher(backUrl).forward(req, resp);
			}else{
				//已经登录 就直接放行
				chain.doFilter(request, response);
			}
		}
		
	}

	@Override
	public void destroy() {

	}

}

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