拦截JSP页面，校验是否已登录详解及实现代码

<span style="font-size:18px;">package com.common; 
 
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; 
 
public class LoginFilter extends HttpServlet implements Filter {  
    
  private static final long serialVersionUID = 1L;  
  
  @Override  
  public void doFilter(ServletRequest request, ServletResponse response,  
      FilterChain chain) throws IOException, ServletException {  
    HttpServletRequest req = (HttpServletRequest)request;  
    HttpServletResponse res = (HttpServletResponse)response;  
    String path = req.getContextPath(); 
    String indexPath = req.getScheme()+"://"+req.getServerName()+":"+req.getServerPort()+path+ "/pages/login.jsp"; 
    if(req.getRequestURI().endsWith("login.jsp")) 
    { 
      chain.doFilter(request, response);  
      return; 
    } 
     
    Object loginuser = req.getSession().getAttribute("<strong><span style="color:#ff0000;">loginSession</span></strong>");  
    if(loginuser == null){ 
      res.sendRedirect(indexPath);  
      return;  
    } 
    chain.doFilter(request, response);  
  }  
  
  @Override  
  public void init(FilterConfig arg0) throws ServletException {  
    // TODO Auto-generated method stub   
  }  
  
}  
</span> 

<span style="font-size:18px;"> public String login() 
  { 
    Login login = new Login(); 
       
    //.......校验登录信息 
    ActionContext ctx = ActionContext.getContext(); 
    Map<String, Object> session = ctx.getSession(); 
    session.put("<strong><span style="color:#ff0000;">loginSession</span></strong>", login); 
    return "success"; 
  }</span> 

<filter>  
   <filter-name>setlog</filter-name>  
   <filter-class>com.common.LoginFilter</filter-class>  
</filter>  
<filter-mapping>  
   <filter-name>setlog</filter-name>  
   <url-pattern>/pages/home.jsp</url-pattern> 
   <url-pattern>/pages/channel/*</url-pattern> 
   <url-pattern>/pages/content/*</url-pattern> 
   <url-pattern>/pages/product/*</url-pattern> 
   <url-pattern>/pages/vodtask/*</url-pattern> 
</filter-mapping> 

<span style="font-size: 18px;">  <script language="javascript">   
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