Run cURL with digest authentication in java

You could use AsyncHttpClient . I have not used it but seeing examples could do something like this:

// el json a enviar
JSONObject params = new JSONObject();
params.put("from", "xxxxx");
params.put("message", "xxxxx");
params.put("frag", "");

// configuración del Realm para la autenticación
Realm realm = new Realm.RealmBuilder()
               .setPrincipal(user)
               .setPassword(admin)
               .setUsePreemptiveAuth(true)
               .setScheme(AuthScheme.DIGEST)
               .build();

// establecemos el header
StringEntity entity = new StringEntity(jsonParams.toString());
entity.setContentType(new BasicHeader(HTTP.CONTENT_TYPE, "application/json"));

// enviamos la petición pasándole la url, la entidad, el mime type y el handler para ella.
client.post('http://xxxxx', entity, 'application/json', new AsyncHttpResponseHandler() {

        @Override
        public void onSuccess(String response) {
            // hacer algo
        }
    })).setRealm(realm).execute();

The advantage is that you can make a request without depending on cURL, you only add the library to your project and that's it.

You are correctly enabling digest authentication, it seems to me that your question is more focused on how to execute the call:

You can do it using Runtime.getRuntime().exec(command)

String command = "curl -X POST 'https://xxxxxxxxxxxxx' --digest -u user:pass -H 'Content-Type: application/json' -H 'Accept: application/json' --data-binary $'{\"from\" : \"xxxx\", \"msg\" : \"xxxxxx\", \"frag\": null}'";

Process p = Runtime.getRuntime().exec(command);             
p.waitFor();
BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
String line = "";
while ((line = reader.readLine())!= null) {
    output.append(line + "\n"); 
}