JSP Servlet的显示inexisting数据

-1

我创建了一个简单的servlet，这是打印一些消息是这样的：JSP Servlet的显示inexisting数据

@WebServlet("/servletExample") 
public class ServletExample extends HttpServlet { 
    private static final long serialVersionUID = 1L; 

    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 

     PrintWriter out = response.getWriter(); 
     out.println("Hello there"); 

    }

一切运作良好。然后，我创建2个JSP页面这样的：

<body> 
    <form method="post" action="servletExample"> 
     <table border="0"> 
      <tr> 
       <td> 
        First name: 
       </td> 
       <td> 
        <input type="text" name="firstname"/> 
       </td>    
      </tr> 
      <tr> 
       <td> 
        Last name: 
       </td> 
       <td> 
        <input type="text" name="lastname"/> 
       </td>    
      </tr> 
      <tr> 
       <td colspan="2"> 
        <input type="submit" value="Submit"/> 
       </td>    
      </tr> 
     </table> 
    </form> 
</body>

和

<body> 
    <% 
     String firstName = (String)request.getAttribute("firstname"); 
     String lastName = (String)request.getAttribute("lastname"); 

     out.println(firstName+ " "+lastName); 
    %> 
</body>

该servlet现在看起来是这样的：

@WebServlet("/servletExample") 
public class ServletExample extends HttpServlet { 
    private static final long serialVersionUID = 1L; 

    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 

     String firstName=request.getParameter("firstname"); 
     String lastName=request.getParameter("lastname"); 

     if(firstName == null || lastName==null){ 
      getServletContext().getRequestDispatcher("/index.jsp").forward(request, response); 
      return; 
     } 

     request.setAttribute("firstname", firstName); 
     request.setAttribute("lastname", lastName); 
     getServletContext().getRequestDispatcher("/output.jsp").forward(request, response); 
    } 
}

当我运行它，我看到这种形式，但是当我提交我从2天前的例子中看到“Hello there”。无论我做什么，我都会看到。我需要清洁什么？我错过了什么？

编辑：我使用的Eclipse和Tomcat 7

来源

2013-02-20 Jack Willson