session过期后，这段代码报空指针异常 如何修改

Question

[code="java"] public String logoff() throws Exception {

    HttpSession session = request.getSession(false);

    session.removeAttribute("SE_SEIMEI");
    session.removeAttribute("SE_MAIL");
    session.removeAttribute(update_date);

    session.invalidate();

    id = null;
    mail = null;

    return "logoff";
}[/code]

Answer 1

[code="java"]

1. public String logoff() throws Exception {
   
2. 
   
3. HttpSession session = request.getSession(false);
   

4.   if (null == session)
     {
         return "logoff";
     }  
   

5. session.removeAttribute("SE_SEIMEI");  
   

6. session.removeAttribute("SE_MAIL");  
   

7. session.removeAttribute(update_date);  
   

9. session.invalidate();  
   

   1. 
      
   2. id = null;
      
   3. mail = null;
      
   4. 
      
   5. return "logoff";
      
   6. }
      

[/code]