How do you return a JSON object from a Java Servlet

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();

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?