無法在JSP中顯示servlet值

Question

長話短說，我無法讓我的servlet變量顯示在我的JSP頁面中。我試圖像

<p><$= request.getAttribute("foo") %></p> 

方法以及

<p>"${foo}"</p> 

和導入頁面的頂部，有和沒有。

我的servlet（評論當測試var爲，朝下方）：

@Override 
protected void doGet(HttpServletRequest request, HttpServletResponse response) 
     throws ServletException, IOException 
{ 
    //String that gets returned as HTML 
    StringBuilder returnAsHTML = new StringBuilder(); 

    //Cycles through the parameter(s) sent from the serialized form 
    Enumeration<String> parameterNames; 

    //Holds all of the parameter(s) values 
    LinkedList<String> valuesIn = new LinkedList<String>(); 

    //Gets all of the parameter names from the serialized form 
    parameterNames = request.getParameterNames(); 

    //Iterate through the enumeration of the parameters 
    while(parameterNames.hasMoreElements()) 
    { 
     String currentParameter = parameterNames.nextElement(); 
     String currentValue = request.getParameter(currentParameter); 

     //Prevent a blank value from being added from the text fields (which is what they default to 
     //if the user didn't enter anything for "Section:" or "Teacher:"). 
     if(!currentValue.contentEquals("")) 
     { 
      valuesIn.add(currentValue); 
     }//Else doNothing(); 
    } 

    //Set the section to query, if the user wanted one to search for 
    if(request.getParameter("section").isEmpty()) 
    { 
     sectionToQuery = ""; 
    } 
    else 
    { 
     sectionToQuery = request.getParameter("section").toUpperCase(); 
    } 

    //Set the teacher to query, if the user wanted one to search for 
    if(request.getParameter("teacher").isEmpty()) 
    { 
     teacherToQuery = ""; 
    } 
    else 
    { 
     teacherToQuery = request.getParameter("teacher").toUpperCase(); 
    } 

    //THIS BEGINS THE QUERY - BE SURE TO BREAK THIS DOWN TO OTHER METHODS 

    //STAGE 1 See what semesters they are needing, eliminate the ones they don't need. 
    resultSet = determineSemesters(valuesIn); 

    //STAGE 2 See what locations they are needing, eliminate the ones they don't need. 
    determineLocations(resultSet, valuesIn); 

    //STAGE 3 See what sections they are needing, eliminate the ones they don't need. 
    determineSections(resultSet, valuesIn); 

    //STAGE 4 See what instructors they are needing, eliminate the ones they don't need. 
    determineInstructors(resultSet, valuesIn); 

    //STAGE 5 See if they want to include closed classes or not, eliminate what they don't need. 
    determineClosedOrNotClosedCourses(resultSet, valuesIn); 

    //SEARCH IS DONE, the remaining elements in "resultSet" are the product of their search. Find 
    //The enrollment and the credits that is in resultSet. 

    //THIS IS WHERE I AM TESTING IT//////////////// 
    int foo = 20; 
    request.setAttribute("foo", foo); 

    //Check to see if the result set is empty 
    if(resultSet.isEmpty()) 
    { 
     returnAsHTML.setLength(0); 
     returnAsHTML.append("<tr><td colspan='15'><h1>No Results...</h1></tr>"); 
    } 
    else//It's not empty, so style the classes. 
    { 
     //Make sure results are sorted 
     Collections.sort(resultSet); 

     //Style all the classes 
     for(ClassInfo classes : resultSet) 
     { 
      returnAsHTML.append(styleClass(classes)); 
     }//End styling of classes 
    } 

    //Send back the result 
    response.getWriter().write(returnAsHTML.toString()); 

} 

作爲新的JSP中，我有一些想法。在我看到的例子中，似乎人們使用response.sendRedirect（）或其他方式重定向或轉發頁面。另一個可能是因爲我沒有鑄造int作爲字符串。有什麼想法嗎？

Answer 1

首先，重定向你的servlet適當的，你應該使用RequestDispatcher JSP頁面，如下所示：

RequestDispatcher rd = request.getRequestDispatcher("/someJsp.jsp"); 
rd.forward(request, response); 

要得到你應該使用值：

<p><%= request.getAttribute("foo") %></p> 

但是，這是這是做這件事的不正確的方法。您應該避免在JSP頁面中使用腳本。爲此，我們有Expression Language。對於例如爲：

<p> 
    <c:out value="${requestScope['foo']}"/> 
</p> 

參見：

• SO Servlets Wiki page
• JavaServer Pages Standard Tag Library

Answer 2

試試這個在您的doGet（）實現：

protected void doGet(HttpServletRequest request, HttpServletResponse response) 
{ 
    Object data = "Some data, can be a String or a Javabean"; 
    request.setAttribute("data", data); 
    request.getRequestDispatcher("/WEB-INF/page.jsp").forward(request, response); 
} 

然後在你的JSP：

<p>The data from servlet: ${data}</p> 

希望幫助！