Get Json / Resonse body from Curl Post Request in Java

Question

This is the method I have written which sends a POST request to send an Email. I am able to send the email and get the Response Code 200 Ok. But I don't know how to get the JSON Response and convert it into an Object. Can someone please tell me how to do this?

public void sendEmail() {
        try {
            URL url = new URL("https://mandrillapp.com/api/1.0/messages/send");

            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            httpURLConnection.setRequestMethod("POST");
            httpURLConnection.setDoOutput(true);
            httpURLConnection.setRequestProperty("Content-Type", "application/json");

            String data =
                    "{\"key\": \"" + mailchimpApiKey + "\", " +
                            "\"message\": {" +
                            "\"from_email\": \"from@gmail.com\", " +
                            "\"subject\": \"Hello World\", " +
                            "\"text\": \"Welcome to Mailchimp Transactional!\", " +
                            "\"to\": [{ \"email\": \"to@gmail.com\", \"type\": \"to\" }]}}";

            byte[] out = data.getBytes(StandardCharsets.UTF_8);

            OutputStream stream = httpURLConnection.getOutputStream();
            stream.write(out);

            System.out.println(httpURLConnection.getResponseCode() + " " + httpURLConnection.getResponseMessage());

            httpURLConnection.disconnect();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

Answer 1

A basic search reveals: https://www.baeldung.com/httpurlconnection-post#8-read-the-response-from-input-stream

try(BufferedReader br = new BufferedReader(
  new InputStreamReader(con.getInputStream(), "utf-8"))) {
    StringBuilder response = new StringBuilder();
    String responseLine = null;
    while ((responseLine = br.readLine()) != null) {
        response.append(responseLine.trim());
    }
    System.out.println(response.toString());
}

If the response is in JSON format, use any third-party JSON parsers such as Jackson library, Gson, or org.json to parse the response.

Answer 2

In addition to the answer by @mdre

I use the org.json library to convert responses into JSON Objects. The following method does exactly this:

import org.json.JSONException;
import org.json.JSONObject;

    public static JSONObject convertResponseToJSONObject(String responseString) {
        try {
            JSONObject jsonObj = new JSONObject(responseString);
            return jsonObj;
        } catch (JSONException e) {
            System.err.println(
                "It is not possible to create a JSONObject from the input string, returning null. Exception:");
            e.printStackTrace();
        }
        return null;
    }

Note that the response only represents a JSON object if it starts with a { . If it starts with a [ the response represents a JSON array.

Answer 3

You can get errorStream or inputStream based on the response code you receive and get the response from it. Below example creates a BufferedReader from the stream

BufferedReader br = null;
if (100 <= httpURLConnection.getResponseCode() && httpURLConnection.getResponseCode() <= 399) {
    br = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream()));
} else {
    br = new BufferedReader(new InputStreamReader(httpURLConnection.getErrorStream()));
}

You can then read from the br and store data based on your requirement. Below will store data into StringBuilder

StringBuilder data = new StringBuilder();
    String dataLine = null;
    while ((dataLine = br.readLine()) != null) {
        data.append(dataLine.trim());
    }
    System.out.println(data.toString());

Instead of printing as String you can also convert it into JSON by using JSON libraries. You may follow this guide