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' }";
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.
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").
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());
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();
Just write a string to the output stream. You might set the MIME-type to text/javascript (edit: application/json is apparently officialer) if you're feeling helpful. (There's a small but nonzero chance that it'll keep something from messing it up someday, and it's a good practice.)
Gson is very usefull for this. easier even. here is my example:
public class Bean {
private String nombre="juan";
private String apellido="machado";
private List<InnerBean> datosCriticos;
class InnerBean
{
private int edad=12;
}
public Bean() {
datosCriticos = new ArrayList<>();
datosCriticos.add(new InnerBean());
}
}
Bean bean = new Bean();
Gson gson = new Gson();
String json =gson.toJson(bean);
out.print(json);
{"nombre":"juan","apellido":"machado","datosCriticos":[{"edad":12}]}
Have to say people if yours vars are empty when using gson it wont build the json for you.Just the
{}
There might be a JSON object for Java coding convenience. But at last the data structure will be serialized to string. Setting a proper MIME type would be nice.
Depending on the Java version (or JDK, SDK, JRE... i dunno, im new to the Java ecosystem), the JsonObject is abstract. So, this is a new implementation:
import javax.json.Json;
import javax.json.JsonObject;
...
try (PrintWriter out = response.getWriter()) {
response.setContentType("application/json");
response.setCharacterEncoding("UTF-8");
JsonObject json = Json.createObjectBuilder().add("foo", "bar").build();
out.print(json.toString());
}
response.setContentType("text/json");
//create the JSON string, I suggest using some framework.
String your_string;
out.write(your_string.getBytes("UTF-8"));
You may use bellow like.
If you want use json array:
Create A class named Model like bellow
public class Model {
private String id = "";
private String name = "";
//getter sertter here
}
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();
}
}
Output:
[{"name":"Enamul Haque","id":"101"},{"name":"Md Mohsin","id":"102"}]
I you want json Object just use like:
@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();
}
}
Above function Output:
{"name":"Enamul Haque","id":"108"}
Full source is given to GitHub: https://github.com/enamul95/ServeletJson.git
Close to BalusC answer in 4 simple lines using Google Gson lib. Add this lines to the servlet method:
User objToSerialize = new User("Bill", "Gates");
ServletOutputStream outputStream = response.getOutputStream();
response.setContentType("application/json;charset=UTF-8");
outputStream.print(new Gson().toJson(objToSerialize));
Good luck!
By Using Gson you can send json response see below code
You can see this code
@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();
}
}
}
helpful from json response from servlet in java
