servlet中过滤器的使用

在servlet中过滤器的使用，这个例子实现对用户登录的验证，当前用户的session为空的时候，不允许查看数据：

下面看具体的例子：

1.编写过滤器：

 

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

public class SessionFilter implements Filter{

	@Override
	public void init(FilterConfig config) throws ServletException {
		// TODO Auto-generated method stub
		String username = config.getInitParameter("sessionKey");
		System.out.println(username);
	}
	
	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		// TODO Auto-generated method stub
		HttpServletRequest req = (HttpServletRequest)request;
		HttpSession session = req.getSession();
		
		//由于web.xml中设置Filter过滤全部请求，可以排除不需要过滤的url
        String requestURI = req.getRequestURI();
        if(requestURI.endsWith("login.jsp") 
        		|| requestURI.endsWith("error.jsp")
        		|| requestURI.endsWith("LoginServlet")
        		|| requestURI.endsWith("/")){
            chain.doFilter(request, response);
            return;
        }
        
		//判断用户是否登录，进行页面的处理
        if(null == session.getAttribute("user")){
            //未登录用户，重定向到登录页面
        	session.setAttribute("error", "当前用户未登录");
            ((HttpServletResponse)response).sendRedirect("error.jsp");
            return;
        } else {
            //已登录用户，允许访问
            chain.doFilter(request, response);
        }
	}
	
	@Override
	public void destroy() {
		// TODO Auto-generated method stub
		System.out.println("destory");
	}
}

 

 2.在web.xml中进行相应的配置：

 

  <!-- 过滤器的使用  -->
  <filter>
      <filter-name>SessionFilter</filter-name>
      <filter-class>com.filter.SessionFilter</filter-class>
      <init-param>
          <param-name>sessionKey</param-name>
          <param-value>user</param-value>
      </init-param>
  </filter>
  
  <filter-mapping>
      <filter-name>SessionFilter</filter-name>
      <url-pattern>/*</url-pattern>
  </filter-mapping>
  <!-- 过滤器结束 -->

  3.存放session对象，这里为user:

request.getSession().setAttribute("user", userItem);

  4.这样在页面访问时，如果遇到session为空的情况就会自动跳转到登录页面