我正在尝试使用 ajax 调用检索数据，该调用使用 servlet 并传回 JSON 对象。 AJAX 已成功完成，但从 servlet 返回的 JSON 对象为 null。但是当我在 servlet 中打印 JSON 对象时，它正在打印数据，并且形成的 JSON 对象似乎是有效的。
{"orderObj":[{"FIRST_NAME":"John","LAST_NAME":"Mkay"}]}
HTML
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>jQuery UI Dialog - Modal form</title>
<link rel="stylesheet"
href="//code.jquery.com/ui/1.11.2/themes/smoothness/jquery-ui.css">
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"
type="text/javascript"></script>
<link rel="stylesheet" href="/resources/demos/style.css">
<style>
body {
font-size: 62.5%;
}
h1 {
font-size: 1.2em;
margin: .6em 0;
}
div#orders-contain {
width: 450px;
margin: 30px 0;
}
div#orders-contain table {
margin: 1em 0;
border-collapse: collapse;
width: 150%;
}
div#orders-contain table td, div#orders-contain table th {
border: 1px solid #eee;
padding: .6em 10px;
text-align: left;
}
}
</style>
<script>
$(document).ready(function() {
$("#query-order").click(function(e) {
dataString = "countryCode=";
alert("on Load");
$.ajax({
type: "POST",
url: "QueryOrder",
data: dataString,
dataType: "json",
success: function(
data) {
alert("I am in Success");
alert(data);
},
error: function(jqXHR,
textStatus,
errorThrown) {
alert("Error Return from Ajax");
alert(jqXHR
.getResponseHeader('Content-Type'));
alert(jqXHR.responseText);
alert(jqXHR);
alert(errorThrown);
alert(textStatus);
}
}); //end of Ajax call
}); // end of click function
});
</script>
</head>
<body>
<div id="orders-contain" class="ui-widget">
<h1>Orders:</h1>
<table id="Orders" class="ui-widget ui-widget-content">
<thead>
<tr class="ui-widget-header ">
<th>Order Number</th>
<th>Customer Number</th>
<th>First Name</th>
<th>Last Name</th>
<th>Date of Order</th>
<th>Address</th>
<th>Order Total</th>
</tr>
</thead>
<tbody>
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
</tbody>
</table>
</div>
<button id="query-order">Query Orders</button>
</body>
</html>
Servlet
package com.order.pkg;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.google.gson.*;
public class QueryOrder extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public QueryOrder() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
doPost(request,response);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
response.setContentType("application/json");
response.setHeader("Cache-control", "no-cache, no-store");
response.setHeader("Pragma", "no-cache");
response.setHeader("Expires", "-1");
response.setHeader("Access-Control-Allow-Origin", "*");
response.setHeader("Access-Control-Allow-Methods", "POST");
response.setHeader("Access-Control-Allow-Headers", "Content-Type");
response.setHeader("Access-Control-Max-Age", "86400");
try {
Class.forName("oracle.jdbc.OracleDriver");
System.out.println("Driver loaded");
String url = "jdbc:oracle:thin:@localhost:1521:xe";
String user = "dbtest";
String pwd = "dbtest";
Connection DB_mobile_conn = DriverManager.getConnection(url, user,
pwd);
System.out.println("Database Connect ok");
String query = "select * from ORDER_HEADERS";
ArrayList<Order> orderList = new ArrayList<Order>();
if (query != null) {
Statement query_stmt = DB_mobile_conn.createStatement();
ResultSet query_rs = query_stmt.executeQuery(query);
while (query_rs.next()) {
Order orderobj = new Order();
orderobj.setFIRST_NAME(query_rs.getString("FIRST_NAME").trim());
orderobj.setLAST_NAME(query_rs.getString("LAST_NAME").trim());
orderList.add(orderobj);
}
query_rs.close();
query_stmt.close();
}
Gson gson = new Gson();
JsonObject myObj = new JsonObject();
JsonElement orderObj = gson.toJsonTree(orderList);
myObj.add("orderObj", orderObj);
System.out.println(myObj);
System.out.println(response.getContentType());
} catch (Exception exp) {
System.out.println("Exception = " + exp);
}
}
}
请帮助我理解为什么返回 null JSON。感谢您的帮助
最佳答案
您从未将 myObj 对象写入 response。 您必须使用:
response.getWriter().write(myObj.toString());
关于java - Ajax 调用中返回 null json，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/27009878/