session.invalidate（）拋出空指針異常

Question

當我失效HTTP會話扔像下面一個空指針異常的東西：

2012年12月14日下午九時49分52秒org.apache.catalina.session.StandardSession到期 SEVERE：會話事件偵聽器拋出異常 java.lang.NullPointerException

建議。

Answer 1

在代碼中放入一些斷點並在DEBUG模式下使用您最喜歡的IDE來確認此「會話」引用變量是否指向空對象。

之後，只是檢查，以澄清圍繞getSession（）方法的所有細節的文件（它可能給你一些想法）：http://tomcat.apache.org/tomcat-5.5-doc/servletapi/javax/servlet/http/HttpServletRequest.html#getSession%28boolean%29

Answer 2

我認爲你的問題解決了將使用此請嘗試。通過Gourav Gavate 公共無效的doGet（HttpServletRequest的請求，HttpServletResponse的響應） 拋出了ServletException，IOException異常{

response.setContentType("text/html"); 
    PrintWriter out = response.getWriter(); 

    String op = request.getParameter("operation"); 
    System.out.println("operation valuse is ->"+op); 
    LoginService service = null; 
    ResultSet rs= null; 
    HttpSession session=null; 
    if (op.equals("Login")){ 
    //System.out.println("1"); 
    String un=request.getParameter("username"); 
    String psd=request.getParameter("password"); 
    try { 
     rs = service.searchByUsernameandPassword(un, psd); 
     //System.out.println("2"); 

     while (rs.next()) { 
       //System.out.print(rp.getInt(1)); 
       //System.out.print("\t"+rs.getString(2)); 
      // System.out.println("in while"); 
      if(un.equals(rs.getString(3))&& psd.equals(rs.getString(4))) 
      { 
      // System.out.println("in if"); 
      session=request.getSession(true); 
      String name = rs.getString(1)+""+rs.getString(2); 
      session.setAttribute("name",name); 
      // System.out.println("set into session"); 
       response.sendRedirect("http://localhost:8080/Registration/Registration.jsp"); 
      }else{ 

        response.sendRedirect("http://localhost:8080/Registration/Login.jsp"); 

      } 
     } 

    } catch (Exception e4) { 
     System.out.println(e4); 
    } 

} else if (op.equals("Logout")){ 
    /*System.out.println("Into logout"); 
    if(session!=null){ 

     System.out.println("Into logout if");  
      session.removeAttribute("name"); 
      session.invalidate(); 
      response.sendRedirect("http://localhost:8080/Registration/Login.jsp"); 
    }else{ 
     System.out.println("Into logout else"); 
     // session.removeAttribute("name"); 
       session.invalidate(); 
       response.sendRedirect("http://localhost:8080/Registration/Login.jsp"); 
    } 
    */ 
    HttpSession session1 = request.getSession(); 
    //session.removeAttribute("name"); 
    session1.invalidate(); 
    response.setHeader("Cache-Control","no-cache"); 
    response.setHeader("Cache-Control","no-store"); 
    response.setDateHeader("Expires", 0); 
    response.sendRedirect("http://localhost:8080/Registration/Login.jsp"); 

} 

}