HTTP POST using JSON in Java

I would like to make a simple HTTP POST using JSON in Java.

Let's say the URL is www.site.com

and it takes in the value {"name":"myname","age":"20"} labeled as 'details' for example.

How would I go about creating the syntax for the POST?

I also can't seem to find a POST method in the JSON Javadocs.

Here is what you need to do:

1. Get the Apache HttpClient, this would enable you to make the required request
2. Create an HttpPost request with it and add the header application/x-www-form-urlencoded
3. Create a StringEntity that you will pass JSON to it
4. Execute the call

The code roughly looks like (you will still need to debug it and make it work):

// @Deprecated HttpClient httpClient = new DefaultHttpClient();
HttpClient httpClient = HttpClientBuilder.create().build();
try {
	HttpPost request = new HttpPost("http://yoururl");
	StringEntity params = new StringEntity("details={\"name\":\"xyz\",\"age\":\"20\"} ");
	request.addHeader("content-type", "application/x-www-form-urlencoded");
	request.setEntity(params);
	HttpResponse response = httpClient.execute(request);
} catch (Exception ex) {
} finally {
    // @Deprecated httpClient.getConnectionManager().shutdown(); 
}

You can make use of Gson library to convert your java classes to JSON objects.

Create a pojo class for variables you want to send as per above Example

{"name":"myname","age":"20"}

becomes

class pojo1
{
   String name;
   String age;
   //generate setter and getters
}

once you set the variables in pojo1 class you can send that using the following code

String       postUrl       = "www.site.com";// put in your url
Gson         gson          = new Gson();
HttpClient   httpClient    = HttpClientBuilder.create().build();
HttpPost     post          = new HttpPost(postUrl);
StringEntity postingString = new StringEntity(gson.toJson(pojo1));//gson.tojson() converts your pojo to json
post.setEntity(postingString);
post.setHeader("Content-type", "application/json");
HttpResponse  response = httpClient.execute(post);

and these are the imports

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.HttpClientBuilder;

and for GSON

import com.google.gson.Gson;

@momo's answer for Apache HttpClient, version 4.3.1 or later. I'm using JSON-Java to build my JSON object:

JSONObject json = new JSONObject();
json.put("someKey", "someValue");    

CloseableHttpClient httpClient = HttpClientBuilder.create().build();
		
try {
    HttpPost request = new HttpPost("http://yoururl");
    StringEntity params = new StringEntity(json.toString());
    request.addHeader("content-type", "application/json");
    request.setEntity(params);
    httpClient.execute(request);
// handle response here...
} catch (Exception ex) {
    // handle exception here
} finally {
    httpClient.close();
}

It's probably easiest to use HttpURLConnection.

http://www.xyzws.com/Javafaq/how-to-use-httpurlconnection-post-data-to-web-server/139

You'll use JSONObject or whatever to construct your JSON, but not to handle the network; you need to serialize it and then pass it to an HttpURLConnection to POST.

protected void sendJson(final String play, final String prop) {
     Thread t = new Thread() {
     public void run() {
        Looper.prepare(); //For Preparing Message Pool for the childThread
        HttpClient client = new DefaultHttpClient();
        HttpConnectionParams.setConnectionTimeout(client.getParams(), 1000); //Timeout Limit
        HttpResponse response;
        JSONObject json = new JSONObject();

            try {
                HttpPost post = new HttpPost("http://192.168.0.44:80");
                json.put("play", play);
                json.put("Properties", prop);
                StringEntity se = new StringEntity(json.toString());
                se.setContentType(new BasicHeader(HTTP.CONTENT_TYPE, "application/json"));
                post.setEntity(se);
                response = client.execute(post);

                /*Checking response */
                if (response != null) {
                    InputStream in = response.getEntity().getContent(); //Get the data in the entity
                }

            } catch (Exception e) {
                e.printStackTrace();
                showMessage("Error", "Cannot Estabilish Connection");
            }

            Looper.loop(); //Loop in the message queue
        }
    };
    t.start();
}

Try this code:

HttpClient httpClient = new DefaultHttpClient();

try {
    HttpPost request = new HttpPost("http://yoururl");
    StringEntity params =new StringEntity("details={\"name\":\"myname\",\"age\":\"20\"} ");
    request.addHeader("content-type", "application/json");
    request.addHeader("Accept","application/json");
    request.setEntity(params);
    HttpResponse response = httpClient.execute(request);

    // handle response here...
}catch (Exception ex) {
    // handle exception here
} finally {
    httpClient.getConnectionManager().shutdown();
}

I found this question looking for solution about how to send post request from java client to Google Endpoints. Above answers, very likely correct, but not work in case of Google Endpoints.

Solution for Google Endpoints.

1. Request body must contains only JSON string, not name=value pair.

2. Content type header must be set to "application/json".

    post("http://localhost:8888/_ah/api/langapi/v1/createLanguage",
                       "{\"language\":\"russian\", \"description\":\"dsfsdfsdfsdfsd\"}");
   
   
   
    public static void post(String url, String json ) throws Exception{
      String charset = "UTF-8"; 
      URLConnection connection = new URL(url).openConnection();
      connection.setDoOutput(true); // Triggers POST.
      connection.setRequestProperty("Accept-Charset", charset);
      connection.setRequestProperty("Content-Type", "application/json;charset=" + charset);
   
      try (OutputStream output = connection.getOutputStream()) {
        output.write(json.getBytes(charset));
      }
   
      InputStream response = connection.getInputStream();
    }
   

It sure can be done using HttpClient as well.

You can use the following code with Apache HTTP:

String payload = "{\"name\": \"myname\", \"age\": \"20\"}";
post.setEntity(new StringEntity(payload, ContentType.APPLICATION_JSON));

response = client.execute(request);

Additionally you can create a json object and put in fields into the object like this

HttpPost post = new HttpPost(URL);
JSONObject payload = new JSONObject();
payload.put("name", "myName");
payload.put("age", "20");
post.setEntity(new StringEntity(payload.toString(), ContentType.APPLICATION_JSON));

For Java 11 you can use the new HTTP client:

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
    .uri(URI.create("http://localhost/api"))
    .header("Content-Type", "application/json")
    .POST(ofInputStream(() -> getClass().getResourceAsStream(
        "/some-data.json")))
    .build();

client.sendAsync(request, BodyHandlers.ofString())
    .thenApply(HttpResponse::body)
    .thenAccept(System.out::println)
    .join();

You can use publishers from InputStream, String, File. Converting JSON to a String or IS can be done with Jackson.

Java 8 with apache httpClient 4

CloseableHttpClient client = HttpClientBuilder.create().build();
HttpPost httpPost = new HttpPost("www.site.com");
		

String json = "details={\"name\":\"myname\",\"age\":\"20\"} ";
		
		try {
			StringEntity entity = new StringEntity(json);
			httpPost.setEntity(entity);

            // set your POST request headers to accept json contents
			httpPost.setHeader("Accept", "application/json");
			httpPost.setHeader("Content-type", "application/json");
			
			try {
                // your closeablehttp response
				CloseableHttpResponse response = client.execute(httpPost);

                // print your status code from the response
				System.out.println(response.getStatusLine().getStatusCode());

                // take the response body as a json formatted string 
				String responseJSON = EntityUtils.toString(response.getEntity());

                // convert/parse the json formatted string to a json object
				JSONObject jobj = new JSONObject(responseJSON);

                //print your response body that formatted into json
				System.out.println(jobj);

			} catch (IOException e) {
				e.printStackTrace();
			} catch (JSONException e) {
				
				e.printStackTrace();
			}
			
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
		}

Java 11 standardization of HTTP client API that implements HTTP/2 and Web Socket, and can be found at java.net.HTTP.*:

String payload = "{\"name\": \"myname\", \"age\": \"20\"}";
HttpClient client = HttpClient.newHttpClient();

HttpRequest request = HttpRequest.newBuilder(URI.create("www.site.com"))
			.header("content-type", "application/json")
			.POST(HttpRequest.BodyPublishers.ofString(payload))
		    .build();
	
HttpResponse<String> response = client.send(request, BodyHandlers.ofString());

I recomend http-request built on apache http api.

HttpRequest<String> httpRequest = HttpRequestBuilder.createPost(yourUri, String.class)
    .responseDeserializer(ResponseDeserializer.ignorableDeserializer()).build();

public void send(){
   ResponseHandler<String> responseHandler = httpRequest.execute("details", yourJsonData);

   int statusCode = responseHandler.getStatusCode();
   String responseContent = responseHandler.orElse(null); // returns Content from response. If content isn't present returns null. 
}

If you want send JSON as request body you can:

  ResponseHandler<String> responseHandler = httpRequest.executeWithBody(yourJsonData);

I higly recomend read documentation before use.