在输入员工ID后，以html格式预填充电子邮件

Question

我刚刚开始学习jsp，我遇到了一个特殊的问题。我一直试图通过从数据库中获取电子邮件来预先填充我的html。员工需要输入他们的员工ID，并根据员工ID将电子邮件发送到表单

我试图使用jstl发送员工ID，我失败了我总是得到一个错误，说员工id为null，也许我不明白使用servlets或jstl发送雇员id的逻辑

用户registration.jsp

<div class="regtop">
<h2>User Registration</h2>
</div>  
       <!--  <form action="RegisterControllerServlet">  -->
     <c:url var="templink" value="RegisterControllerServlet">
      <c:param  name="command" value="LOAD"/>

     </c:url>
  <div class="container">

    <p>Please fill in this form to create an account.</p>
    <hr>

     <label for="email"><b>Enter employee id</b></label>
    <input type="text"  name="u_eid"  >


    <a href="${templink}" >Get email</a>
    <br>
    <label for="email"><b>Email</b></label>
    <input type="text"  name="email" value="${THE_USER.email}">

register controller Servlet.Java

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


        try {
            //read the "command" parameter
            String theCommand=request.getParameter("command");

            //if the command is missing,then default to listing pharmacists
            //route to the appropriate method
            switch(theCommand)
            {

            case "LOAD":
                loadUser(request,response);
                break;

            }



    } catch (Exception e) {
        // TODO Auto-generated catch block
        throw new ServletException(e);
    }

}
    private void loadUser(HttpServletRequest request, HttpServletResponse response) throws Exception {


        String eid=request.getParameter("u_eid");

        Employee themp=registerDbutil.getUser(eid);

        //plaqce user in the request attribute
                request.setAttribute("THE_USER", themp);


        //send to jsp page:update -user-reg.jsp 
                RequestDispatcher dispatcher=
                        request.getRequestDispatcher("/user registartion.jsp");
                dispatcher.forward(request,response);

    }

register D but IL.Java

public Employee getUser(String eid) throws Exception{

        Employee theuser=null;

        Connection myConn =null;
        PreparedStatement myStmt=null;
        ResultSet myRs=null;

        try
        {
        //get connection to db
        myConn=dataSource.getConnection();


        //create sql to get selected user email
        String sql="select email from employee where eid=? ";   

        //create prepared statements
        myStmt=myConn.prepareStatement(sql);
        myStmt.setString(1, eid);


        //execute state
        myRs=myStmt.executeQuery();


        if(myRs.next())
        {
            String email=myRs.getString("email");


            theuser=new Employee(email);
        }
        else
        {
            throw new Exception("Could not find employee id:" +eid);
        }


        return theuser;
    }finally
        {
        close(myConn,myStmt,null);
    }

}

我希望输出在输入员工ID时预先填充员工的html表单

Answer 1

它是null，因为当您单击RegisterControllerServlet的链接时，您没有将employee id作为参数传递：

  <c:url var="templink" value="RegisterControllerServlet">
      <c:param  name="command" value="LOAD"/>
  </c:url>

您需要在此JSTL url标记中添加employee id作为参数...但是因为您希望用户在输入字段中编写employee id，所以您需要使用form标记，而不是JSTL url标记（因为您不知道员工的身份是什么）。

     <!--  <c:url var="templink" value="RegisterControllerServlet">
      <c:param  name="command" value="LOAD"/>
     </c:url>  -->

  <div class="container">

    <p>Please fill in this form to create an account.</p>
    <hr>
  <form action="RegisterControllerServlet">
     <label for="email"><b>Enter employee id</b></label>
    <input type="text"  name="u_eid"  >

    <label for="email"><b>Email</b></label>
    <input type="text"  name="email" value="${THE_USER.email}">

    <input type="submit" name="command" value="LOAD"/> 
</form>

</div>