How do you return a JSON object from a Java Servlet

Question

How do you return a JSON object form a Java servlet.

Previously when doing AJAX with a servlet I have returned a string. Is there a JSON object type that needs to be used, or do you just return a String that looks like a JSON object e.g.

String objectToReturn = "{ key1: 'value1', key2: 'value2' }";

Answer 1

Write the JSON object to the response object's output stream.

You should also set the content type as follows, which will specify what you are returning:

response.setContentType("application/json");
// Get the printwriter object from response to write the required json object to the output stream      
PrintWriter out = response.getWriter();
// Assuming your json object is **jsonObject**, perform the following, it will return your json object  
out.print(jsonObject);
out.flush();

Answer 2

First convert the JSON object to String. Then just write it out to the response writer along with content type of application/json and character encoding of UTF-8.

Here's an example assuming you're using Google Gson to convert a Java object to a JSON string:

protected void doXxx(HttpServletRequest request, HttpServletResponse response) {
    // ...

    String json = new Gson().toJson(someObject);
    response.setContentType("application/json");
    response.setCharacterEncoding("UTF-8");
    response.getWriter().write(json);
}

That's all.

See also:

• How to use Servlets and Ajax?
• What is the correct JSON content type?

Answer 3

I do exactly what you suggest (return a String).

You might consider setting the MIME type to indicate you're returning JSON, though (according to this other stackoverflow post it's "application/json").

Answer 4

How do you return a JSON object from a Java Servlet

response.setContentType("application/json");
response.setCharacterEncoding("utf-8");
PrintWriter out = response.getWriter();

  //create Json Object
  JsonObject json = new JsonObject();

    // put some value pairs into the JSON object .
    json.addProperty("Mobile", 9999988888);
    json.addProperty("Name", "ManojSarnaik");

    // finally output the json string       
    out.print(json.toString());

Answer 5

I used Jackson to convert Java Object to JSON string and send as follows.

PrintWriter out = response.getWriter();
ObjectMapper objectMapper= new ObjectMapper();
String jsonString = objectMapper.writeValueAsString(MyObject);
response.setContentType("application/json");
response.setCharacterEncoding("UTF-8");
out.print(jsonString);
out.flush();