Apache HttpClient tutorial

The general process for using HttpClient consists of a number of steps:

1. Create an instance of HttpClient.
2. Create an instance of one of the methods (GetMethod in this case). The URL to connect to is passed in to the the method constructor.
3. Tell HttpClient to execute the method.
4. Read the response.
5. Release the connection.
6. Deal with the response.

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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.

HttpURLConnectionExample.java

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.

HttpClientExample.java

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());

 }

}