In this article, we will show you two examples to make HTTP GET/POST request via following APIs

1. Standard HttpURLConnection.
2. Apache HttpClient library.

1. Java HttpURLConnection example

This example uses HttpURLConnection (http) and HttpsURLConnection (https) to

1. Send an HTTP GET request to Google.com to get the search result.
2. Send an HTTP POST request to Apple.com search form to check the product detail.

package com.mkyong;

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

import javax.net.ssl.HttpsURLConnection;

public class HttpURLConnectionExample {

	private final String USER_AGENT = "Mozilla/5.0";

	public static void main(String[] args) throws Exception {

		HttpURLConnectionExample http = new HttpURLConnectionExample();

		System.out.println("Testing 1 - Send Http GET request");
		http.sendGet();

		System.out.println("\nTesting 2 - Send Http POST request");
		http.sendPost();

	}

	// HTTP GET request
	private void sendGet() throws Exception {

		String url = "http://www.google.com/search?q=mkyong";

		URL obj = new URL(url);
		HttpURLConnection con = (HttpURLConnection) obj.openConnection();

		// optional default is GET
		con.setRequestMethod("GET");

		//add request header
		con.setRequestProperty("User-Agent", USER_AGENT);

		int responseCode = con.getResponseCode();
		System.out.println("\nSending 'GET' request to URL : " + url);
		System.out.println("Response Code : " + responseCode);

		BufferedReader in = new BufferedReader(
		        new InputStreamReader(con.getInputStream()));
		String inputLine;
		StringBuffer response = new StringBuffer();

		while ((inputLine = in.readLine()) != null) {
			response.append(inputLine);
		}
		in.close();

		//print result
		System.out.println(response.toString());

	}

	// HTTP POST request
	private void sendPost() throws Exception {

		String url = "https://selfsolve.apple.com/wcResults.do";
		URL obj = new URL(url);
		HttpsURLConnection con = (HttpsURLConnection) obj.openConnection();

		//add reuqest header
		con.setRequestMethod("POST");
		con.setRequestProperty("User-Agent", USER_AGENT);
		con.setRequestProperty("Accept-Language", "en-US,en;q=0.5");

		String urlParameters = "sn=C02G8416DRJM&cn=&locale=&caller=&num=12345";

		// Send post request
		con.setDoOutput(true);
		DataOutputStream wr = new DataOutputStream(con.getOutputStream());
		wr.writeBytes(urlParameters);
		wr.flush();
		wr.close();

		int responseCode = con.getResponseCode();
		System.out.println("\nSending 'POST' request to URL : " + url);
		System.out.println("Post parameters : " + urlParameters);
		System.out.println("Response Code : " + responseCode);

		BufferedReader in = new BufferedReader(
		        new InputStreamReader(con.getInputStream()));
		String inputLine;
		StringBuffer response = new StringBuffer();

		while ((inputLine = in.readLine()) != null) {
			response.append(inputLine);
		}
		in.close();

		//print result
		System.out.println(response.toString());

	}

}

Output

Sending 'GET' request to URL : http://www.google.com/search?q=mkyong
Response Code : 200
Google search result...

Testing 2 - Send Http POST request

Sending 'POST' request to URL : https://selfsolve.apple.com/wcResults.do
Post parameters : sn=C02G8416DRJM&cn=&locale=&caller=&num=12345
Response Code : 200
Apple product detail...

2. Apache HttpClient

This is the equivalent example, but using Apache HttpClient to make HTTP GET/POST request.

package com.mkyong;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;

public class HttpClientExample {

	private final String USER_AGENT = "Mozilla/5.0";

	public static void main(String[] args) throws Exception {

		HttpClientExample http = new HttpClientExample();

		System.out.println("Testing 1 - Send Http GET request");
		http.sendGet();

		System.out.println("\nTesting 2 - Send Http POST request");
		http.sendPost();

	}

	// HTTP GET request
	private void sendGet() throws Exception {

		String url = "http://www.google.com/search?q=developer";

		HttpClient client = new DefaultHttpClient();
		HttpGet request = new HttpGet(url);

		// add request header
		request.addHeader("User-Agent", USER_AGENT);

		HttpResponse response = client.execute(request);

		System.out.println("\nSending 'GET' request to URL : " + url);
		System.out.println("Response Code : " +
                       response.getStatusLine().getStatusCode());

		BufferedReader rd = new BufferedReader(
                       new InputStreamReader(response.getEntity().getContent()));

		StringBuffer result = new StringBuffer();
		String line = "";
		while ((line = rd.readLine()) != null) {
			result.append(line);
		}

		System.out.println(result.toString());

	}

	// HTTP POST request
	private void sendPost() throws Exception {

		String url = "https://selfsolve.apple.com/wcResults.do";

		HttpClient client = new DefaultHttpClient();
		HttpPost post = new HttpPost(url);

		// add header
		post.setHeader("User-Agent", USER_AGENT);

		List<NameValuePair> urlParameters = new ArrayList<NameValuePair>();
		urlParameters.add(new BasicNameValuePair("sn", "C02G8416DRJM"));
		urlParameters.add(new BasicNameValuePair("cn", ""));
		urlParameters.add(new BasicNameValuePair("locale", ""));
		urlParameters.add(new BasicNameValuePair("caller", ""));
		urlParameters.add(new BasicNameValuePair("num", "12345"));

		post.setEntity(new UrlEncodedFormEntity(urlParameters));

		HttpResponse response = client.execute(post);
		System.out.println("\nSending 'POST' request to URL : " + url);
		System.out.println("Post parameters : " + post.getEntity());
		System.out.println("Response Code : " +
                                    response.getStatusLine().getStatusCode());

		BufferedReader rd = new BufferedReader(
                        new InputStreamReader(response.getEntity().getContent()));

		StringBuffer result = new StringBuffer();
		String line = "";
		while ((line = rd.readLine()) != null) {
			result.append(line);
		}

		System.out.println(result.toString());

	}

}