使用Filter实现登录权限验证

<filter>
<filter-name>myFilter</filter-name>
<filter-class>com.zyk.ctrl.MyFilter</filter-class>
 <!-- 配置初始化参数，指明再没有登录的情况下放行的资源 -->
 <init-param>
 //初始化参数名
  <param-name>letgo</param-name>
  //初始化参数值
  <param-value>/login.jsp;/loginServlet;/css;/images;/js</param-value>
 </init-param>
 </filter>
 <filter-mapping>
 //必须和上面的一样
 <filter-name>myFilter</filter-name>
 //过滤所有
 <url-pattern>/*</url-pattern>
 
</filter-mapping>

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

/**
 * Servlet Filter implementation class MyFilter
 */

public class MyFilter implements Filter {
//定义一个存放放行资源路径的数组
 private static String[] paths;

 /**
 * Default constructor.
 */
 public MyFilter() {
 // TODO Auto-generated constructor stub
 }

 /**
 * @see Filter#destroy()
 */
 public void destroy() {
 // TODO Auto-generated method stub
 }

 /**
 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
 */
 public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
  throws IOException, ServletException {
 HttpServletRequest request = (HttpServletRequest) req;
 HttpServletResponse response = (HttpServletResponse) res;
  //获取资源URI路径
  String path = request.getServletPath();
  
  for (int i = 0; i < paths.length; i++) {
  //如果当前请求的URI路径是要放行的资源中的一个，放行
  if (path.startsWith(paths[i])) {
   chain.doFilter(request, response);
   return;//放行之后返回，避免程序继续执行，往下面执行是拦截的代码
  }
  
  }
  //判断用户是否已经登录，如果登录则放行资源，否则重定向到登录界面
  String name = (String) request.getSession().getAttribute("name");
  //如果name为空，则证明用户没有登录过，跳转到登录界面
  if (name==null) {
  request.getSession().setAttribute("error", "尚未登录，请登录");
  response.sendRedirect("/BookManagerSystem/login.jsp");
  return;
  
  }
  //剩下的情况为已登录，放行
  chain.doFilter(request, response); 
 

 }

 /**
 * @see Filter#init(FilterConfig)
 */
 public void init(FilterConfig fConfig) throws ServletException {
 //读取初始化参数，得到放行的资源
 String initParameter = fConfig.getInitParameter("letgo");
 paths =initParameter.split(";");
 }

}

if ("login".equals(action)) {
  String name = request.getParameter("name");
  String pwd = request.getParameter("pwd");
  User user = new User(name, pwd);

  if (dao.ValidateLogin(user)) {
  //ValidateLogin为登录验证方法，如果验证成功，则设置一个属性名为“name”值为用户名的session，用于Myfilter验证是否登录过
  request.getSession().setAttribute("name", name);
  response.sendRedirect("admin/admin.jsp");

  } else {
  request.getSession().setAttribute("error", "账号或者密码错误");
  response.sendRedirect("login.jsp");
  }

 }