从servlet到jsp，我无法得到json对象。我怎么能做什么?

I am trying to pass a JsonObject to jsp. However, I think I cannot get the JsonObject using getAttribute method. How should I do to make this available.

我试图将JsonObject传递给jsp。但是，我认为我不能使用getAttribute方法获得JsonObject。我该怎么做才能使它可用。

There's a Servlet code, below.

下面是一个Servlet代码。

 import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.Iterator;

 import javax.servlet.ServletException;
 import javax.servlet.annotation.WebServlet;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;

 import com.google.gson.JsonObject;
 import com.google.gson.JsonParser;

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

//Send Json to jsp
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html;charset=euc-kr"); 
    session = request.getSession(true);
    //System.out.println(request.getParameter("tmp").toString());
    JsonObject jsonObject = new JsonObject();
    jsonObject.addProperty("name", "jinny");
    jsonObject.addProperty("title", "web");

    session.setAttribute("jsonObject", jsonObject);
    response.sendRedirect("index.jsp");
    }
 }

There's a jsp code below.

下面有一个jsp代码。

    <%@page import="com.google.gson.JsonObject"%>

    <%@page import="com.google.gson.JsonElement"%>

    <%@page import="com.google.gson.JsonArray"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=EUC-KR">
<title>start page</title>
</head>
<%
    request.setCharacterEncoding("euc-kr");
    response.setContentType("text/html;charset=euc-kr");
    String tmp = "";
    JsonObject json = (JsonObject)session.getAttribute("jsonObject");
    tmp = json.get("name").toString(); //error at this line
%>
<body>
<script>
    $(function(){
        document.getElementByName("formtag").action="ShapeRendererFileManager";
        document.getElementById("formtag").submit();
    })
</script>

<h1><%= tmp %></h1>
<form name="formtag" action="" method="post">
</form>

</body>
</html>

Thanks in advance.

提前谢谢。

5 个解决方案

#1

Here just a sample by use google Gson library. you can download that lib here or here

这里只是使用谷歌Gson库的一个示例。你可以在这里或这里下载这个库

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

   HashMap<Object, Object> obj=new HashMap<>();
    obj.put("name", "Janny");
    obj.put("title", "Coder");

    String jsonObject=new Gson().toJson(obj);
    System.out.println(jsonObject);
    response.setContentType("application/json");
    response.setCharacterEncoding("UTF-8");
    session.setAttribute("jsonObject",jsonObject);
    request.getRequestDispatcher("index.jsp").forward(request, response);
}

Anyway, you can use Ajax to loop data or use JSTL!

无论如何，您可以使用Ajax循环数据或使用JSTL!

#2

@The Neo Noir Develper

@The Neo黑色患病

Even I changed redirection to forward It doesn't work and make same error.

即使我改变了重定向前进它也不能工作，并犯同样的错误。

Here's servlet code below.

这是下面的servlet代码。

            protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html;charset=euc-kr"); 
    session = request.getSession(true);
    //System.out.println(request.getParameter("tmp").toString());
    JsonObject jsonObject = new JsonObject();
    jsonObject.addProperty("name", "jinny");
    jsonObject.addProperty("title", "web");


    session.setAttribute("jsonObject", jsonObject);

    RequestDispatcher rd = request.getRequestDispatcher("index.jsp");
    rd.forward(request, response);
}

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

    response.setContentType("text/html;charset=euc-kr"); 
    session = request.getSession(true);
    //System.out.println(request.getParameter("tmp").toString());
    JsonObject jsonObject = new JsonObject();
    jsonObject.addProperty("name", "jinny");
    jsonObject.addProperty("title", "web");


    session.setAttribute("jsonObject", jsonObject);

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

    //response.sendRedirect("index.jsp");

}

There's jsp code below.

有下面的jsp代码。

    <%@ page language="java" contentType="text/html; charset=EUC-KR"
    pageEncoding="EUC-KR" %>
    <%@page import="com.google.gson.JsonObject"%>
    <%@page import="com.google.gson.JsonElement"%>
    <%@page import="com.google.gson.JsonArray"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=EUC-KR">
<title>start page</title>
</head>
<%
    request.setCharacterEncoding("euc-kr");
    response.setContentType("text/html;charset=euc-kr");
    JsonObject json = (JsonObject)session.getAttribute("jsonObject");
    String tmp = json.get("name").toString(); //error at this line
%>
<body>
<!-- <div id="main_page">
</div> 
<script data-main="main" src="libs/require-2.1.11.js"></script>  -->

<script>
    $(function(){
        document.getElementByName("formtag").method="POST";
        document.getElementByName("formtag").action="ShapeRendererFileManager";
        document.getElementById("formtag").submit();
    });
</script>

<h1><%= tmp %></h1>
<form name="formtag" action="" method="post">
</form>

</body>
</html>

#3

Could you please try to use the below code in your servlet instead of sendRedirect

您可以尝试在您的servlet中使用以下代码而不是sendRedirect吗

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

and also check the jsonObject in your jsp for null either you are getting null or not from session attribute,

还可以检查jsp中的jsonObject是否为null也可以检查session属性是否为null，

JsonObject json = (JsonObject)session.getAttribute("jsonObject");

after doing above changes if you will again get the error then please post the error stack.

在做了以上修改后，如果你将再次得到错误，然后请张贴错误堆栈。

#4

Can you give a try to change the contect type of your response

你能不能试着改变一下你的反应类型

response.setContentType("application/json");

#5

There are multiple things wrong in your code. Apart from using scriptlets.

在您的代码中有许多错误。除了使用scriptlet。

Anyhoo, first, are you sure your session is being carried over? I say this because you are using a redirect instead of a simple RequestDispatcher Forward. A redirect creates a new request.

无论如何，首先，你确定你的会话正在进行中吗?之所以这样说，是因为您使用的是重定向，而不是简单的RequestDispatcher Forward。重定向创建一个新的请求。

I think you should set this object in request and use a RequestDispatcher. Similarly, on the JSP side, you should use the request object to get the attribute back.

我认为您应该将这个对象设置为request并使用一个RequestDispatcher。类似地，在JSP端，您应该使用request对象来获取属性。

Without much info of how the session is created, it would be hard to pinpoint whether the session is being maintained at all or not.

如果没有关于如何创建会话的大量信息，就很难确定会话是否被维护。

#1