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如何从Java Servlet返回JSON对象

javajsonservlets
168

如何从Java servlet返回JSON对象。

之前在使用servlet进行AJAX时，我返回了一个字符串。是否需要使用JSON对象类型，或者只需返回类似于JSON对象的字符串，例如：

String objectToReturn = "{ key1: 'value1', key2: 'value2' }";
10
你是不是想要更多像 { key1: value1, key2: value2 } 这样的内容呢？Nitpick 的含义是挑剔，可能在这里是指一些微小的问题或建议。 - user240438
16
吹毛求疵的人想要的是 { "key1": "value1", "key2": "value2" }... :-) - PhiLho
如果您决定使用Spring 3.2.0，请查看以下链接：@Ankur checkout the link。 - AmirHd
5
挑剔一点：我们不应该假定这些值是字符串，所以他真正想要的是{ "key1": value1, "key2": value2 }。 - NoBrainer
这些吹毛求疵的细节（特别是按照这个顺序），真是史诗级的 :) - Ankur
13个回答
1

您可以像下面这样使用。

如果您想使用JSON数组：

  1. download json-simple-1.1.1.jar & add to your project class path

  2. Create A class named Model like bellow

    public class Model {

 private String id = "";
 private String name = "";

 //getter sertter here
}

  3. In sevlet getMethod you can use like bellow

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

  //begin get data from databse or other source
  List<Model> list = new ArrayList<>();
  Model model = new Model();
  model.setId("101");
  model.setName("Enamul Haque");
  list.add(model);

  Model model1 = new Model();
  model1.setId("102");
  model1.setName("Md Mohsin");
  list.add(model1);
  //End get data from databse or other source
try {

    JSONArray ja = new JSONArray();
    for (Model m : list) {
        JSONObject jSONObject = new JSONObject();
        jSONObject.put("id", m.getId());
        jSONObject.put("name", m.getName());
        ja.add(jSONObject);
    }
    System.out.println(" json ja = " + ja);
    response.addHeader("Access-Control-Allow-Origin", "*");
    response.setContentType("application/json");
    response.setCharacterEncoding("UTF-8");
    response.getWriter().print(ja.toString());
    response.getWriter().flush();
   } catch (Exception e) {
     e.printStackTrace();
  }

 }

  4. Output:

        [{"name":"Enamul Haque","id":"101"},{"name":"Md Mohsin","id":"102"}]
如果您想要JSON对象，只需像这样使用：

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

        JSONObject json = new JSONObject();
        json.put("id", "108");
        json.put("name", "Enamul Haque");
        System.out.println(" json JSONObject= " + json);
        response.addHeader("Access-Control-Allow-Origin", "*");
        response.setContentType("application/json");
        response.setCharacterEncoding("UTF-8");
        response.getWriter().print(json.toString());
        response.getWriter().flush();
        // System.out.println("Response Completed... ");
    } catch (Exception e) {
        e.printStackTrace();
    }

}

上述函数Output的内容：
{"name":"Enamul Haque","id":"108"}

完整源代码已经上传至GitHub: https://github.com/enamul95/ServeletJson.git

0

使用Google Gson库，只需4行简单的代码就可以接近BalusC的答案。将这些代码添加到servlet方法中：

User objToSerialize = new User("Bill", "Gates");    
ServletOutputStream outputStream = response.getOutputStream();

response.setContentType("application/json;charset=UTF-8");
outputStream.print(new Gson().toJson(objToSerialize));

祝你好运！

0
通过使用Gson，您可以发送JSON响应，请参见下面的代码。
您可以查看此代码。
@WebServlet(urlPatterns = {"/jsonResponse"})
public class JsonResponse extends HttpServlet {

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("application/json");
    response.setCharacterEncoding("utf-8");
    Student student = new Student(12, "Ram Kumar", "Male", "1234565678");
    Subject subject1 = new Subject(1, "Computer Fundamentals");
    Subject subject2 = new Subject(2, "Computer Graphics");
    Subject subject3 = new Subject(3, "Data Structures");
    Set subjects = new HashSet();
    subjects.add(subject1);
    subjects.add(subject2);
    subjects.add(subject3);
    student.setSubjects(subjects);
    Address address = new Address(1, "Street 23 NN West ", "Bhilai", "Chhattisgarh", "India");
    student.setAddress(address);
    Gson gson = new Gson();
    String jsonData = gson.toJson(student);
    PrintWriter out = response.getWriter();
    try {
        out.println(jsonData);
    } finally {
        out.close();
    }

  }
}

从Java Servlet中的JSON响应非常有帮助。

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