You are also very welcome to try out https://github.com/clanie/bitcoind-client - it is in early development, but already supports almost all the methods provided by bitcoind.

I had the same issue and created an implementation here: https://github.com/johannbarbie/BitcoindClient4J

Library under Apache Licence: https://github.com/SulacoSoft/BitcoindConnector4J

Since I could not find working code snippet anywhere, here is a complete working example (in Scala):

First I created a helper object:

import java.net.URL
import java.net.HttpURLConnection
import org.apache.commons.io.IOUtils

object CurlJsonData {
  def curl(url:String, jsonEncodedString:String) = {
    val httpcon = new URL(url).openConnection.asInstanceOf[HttpURLConnection]
    httpcon.setDoOutput(true);
    httpcon.setRequestProperty("Content-Type", "application/json");
    httpcon.setRequestProperty("Accept", "application/json");
    httpcon.setRequestMethod("POST");
    httpcon.connect;

    val outputBytes = jsonEncodedString.getBytes("UTF-8");

    // 'using' method from: https://stackoverflow.com/a/5218279/243233

    using(httpcon.getOutputStream){os =>
      os.write(outputBytes)
    }
    val code = httpcon.getResponseCode
    val isError = code >= 400 && code <= 500
    val resp = using{
      if (isError) httpcon.getErrorStream else httpcon.getInputStream
    }{is =>
      val writer = new StringWriter;
      IOUtils.copy(is, writer, "UTF-8");
      writer.toString;
    }
    httpcon.disconnect
    if (isError) throw new Exception(
      s"Resp code $code. Error: ${resp.take(200)}"
    ) else resp
  }
}

Then, I used it as follows:

import java.net.Authenticator
import java.net.PasswordAuthentication

val rpcuser = "alice";
val rpcpassword = "secret";

Authenticator.setDefault(
  new Authenticator {
    override def getPasswordAuthentication:PasswordAuthentication = {
      new PasswordAuthentication (rpcuser, rpcpassword.toCharArray)
    }
  }
)  

CurlJsonData.curl(
  "http://localhost:8332", 
  """{"method":"getblockchaininfo","params":[],"id":1,"jsonrpc":"1.0"}"""
) 

If Scala is not your thing, here is Jus12's code in Kotlin:

package com.my.blockchainparser

import java.net.Authenticator
import java.net.PasswordAuthentication
import java.net.URL
import java.net.HttpURLConnection

fun main(args: Array<String>) {
    val rpcuser = "user"
    val rpcpassword = "password"
    Authenticator.setDefault(object : Authenticator() {
        override fun getPasswordAuthentication(): PasswordAuthentication {
            return PasswordAuthentication(rpcuser, rpcpassword.toCharArray())
        }
    })

    System.out.println(curl(
            "http://localhost:8332",
            """{"method":"getblockchaininfo","params":[],"id":1,"jsonrpc":"1.0"}"""
    ))
}

fun curl(url:String, jsonEncodedString:String): String {
    val httpcon = URL(url).openConnection() as HttpURLConnection
    httpcon.setDoOutput(true);
    httpcon.setRequestProperty("Content-Type", "application/json");
    httpcon.setRequestProperty("Accept", "application/json");
    httpcon.setRequestMethod("POST");
    httpcon.connect();

    val outputBytes = jsonEncodedString.toByteArray();

    httpcon.getOutputStream().use {
        it.write(outputBytes)
    }
    val code = httpcon.getResponseCode()
    val isError = code >= 400 && code <= 500
    val text = (if (isError) httpcon.getErrorStream() else httpcon.getInputStream())
            ?.bufferedReader()?.use {
        it.readText()
    } ?: "no connection"
    if (isError) throw Exception(
            "Resp code $code. Error: ${text.take(200)}"
    )
    return text
}