Make HTTP POST request from Java SE – no frills, no libraries, just plain Java

This article shows a very simple, straightforward example of making an HTTP POST call to a url (http://localhost:8080/movieevents) and sending a JSON payload to that URL.

The REST service invoked in this example is the service published from Java EE as described in this article.

In this second example, the service that is being called here is exposed by a PL/SQL procedure as described in this recent article). This example does not use any additional libraries – just the standard Java SE libraries.

package nl.amis.rest;

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;

import java.io.Reader;

import java.io.UnsupportedEncodingException;

import java.net.HttpURLConnection;
import java.net.URL;

import java.net.URLEncoder;

import java.util.LinkedHashMap;
import java.util.Map;

public class CinemaEventRouter {
/*
* Thanks to: http://stackoverflow.com/questions/4205980/java-sending-http-parameters-via-post-method-easily?rq=1
*/

private static final String USER_AGENT = “Mozilla/5.0”;
private static final String targeturl = “http://localhost:8080/api/movieevents”;

public static void sendPost(String json) {
try {
Map params = new LinkedHashMap<>();
params.put(“p_json_payload”, json);

StringBuilder postData = new StringBuilder();
for (Map.Entry param : params.entrySet()) {
if (postData.length() != 0)
postData.append(‘&’);
postData.append(URLEncoder.encode(param.getKey(), “UTF-8”));
postData.append(‘=’);
postData.append(URLEncoder.encode(String.valueOf(param.getValue()), “UTF-8”));
}
byte[] postDataBytes = postData.toString().getBytes(“UTF-8”);

URL url = new URL(targeturl);

HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod(“POST”);
conn.setRequestProperty(“Content-Type”, “application/x-www-form-urlencoded”);
conn.setRequestProperty(“Content-Length”, String.valueOf(postDataBytes.length));
conn.setDoOutput(true);
conn.getOutputStream().write(postDataBytes);

Reader in = new BufferedReader(new InputStreamReader(conn.getInputStream(), “UTF-8”));
for (int c; (c = in.read()) >= 0; System.out.print((char) c))
;
}
catch (Exception e) {
System.out.println(“Call to “+targeturl+” failed.”);
e.printStackTrace();
}

}
}