Apache HttpClient - Tutorial

Apache HttpClient

This tutorial describes how to use the Apache HttpClient library for accessing HTTP resources. This tutorial is based on Apache HttpClient 4.1.

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Table of Contents

1. Using the Apache HttpClient

2. Examples

2.1. Project and Expectations

2.2. Http Get

2.3. Http Post

3. Thank you

4. Questions and Discussion

5. Resources

1. Using the Apache HttpClient

The Apache HttpClient library simplifies handling HTTP requests. To use this library download the binaries with dependencies from http://hc.apache.org/ and add then to your project classpath.

You retrieve and send data via the HttpClient class. An instance of this class can be created withnew DefaultHttpClient();

DefaultHttpClient is the standard HttpClient and uses the SingleClientConnManager class to handle HTTP connections. SingleClientConnManager is not thread-safe, this means that access to it via several threads will create problems.

The HttpClient uses a HttpUriRequest to send and receive data. Important subclass ofHttpUriRequest are HttpGet and HttpPost. You can get the response of the HttpClient as an InputStream.

2. Examples

2.1. Project and Expectations

The following examples do not necessary work out of the box as we do not provide the required backend for receiving the data. Think of the following as examples how to setup HttpClients. Download the HttpClient libraries from the Apache Website, you can download the "bin" package it includes all dependencies.

Create a new Java project de.vogella.web.httpclient, and add them to the path of your Java project. We use the project for creating our tests.

2.2. Http Get

The following is an example an HTTP Get request via HttpClient.

HttpClient client = new DefaultHttpClient();
HttpGet request = new HttpGet("http://www.vogella.com");
HttpResponse response = client.execute(request);

// Get the response
BufferedReader rd = new BufferedReader
  (new InputStreamReader(response.getEntity().getContent()));
    
String line = "";
while ((line = rd.readLine()) != null) {
  textView.append(line);
} 

2.3. Http Post

The following will send a post request to the URL "http://vogellac2dm.appspot.com/register" and include a parameter "registrationid" which an random value.

package de.vogella.web.httpclient;

import java.io.BufferedReader;
import java.io.IOException;
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.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;

public class SimpleHttpPut { 
  public static void main(String[] args) {
    HttpClient client = new DefaultHttpClient();
    HttpPost post = new HttpPost("http://vogellac2dm.appspot.com/register");
    try {
      List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(1);
      nameValuePairs.add(new BasicNameValuePair("registrationid",
          "123456789"));
      post.setEntity(new UrlEncodedFormEntity(nameValuePairs));
 
      HttpResponse response = client.execute(post);
      BufferedReader rd = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
      String line = "";
      while ((line = rd.readLine()) != null) {
        System.out.println(line);
      }

    } catch (IOException e) {
      e.printStackTrace();
    }
  }
} 

The following request adds several parameters to the post request.

package de.vogella.web.httpclient;

import java.io.BufferedReader;
import java.io.IOException;
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.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;

public class TestHttpClient {
  public static void main(String[] args) {
    HttpClient client = new DefaultHttpClient();
    HttpPost post = new HttpPost("https://www.google.com/accounts/ClientLogin");

    try {

      List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(1);
      nameValuePairs.add(new BasicNameValuePair("Email", "youremail"));
      nameValuePairs
          .add(new BasicNameValuePair("Passwd", "yourpassword"));
      nameValuePairs.add(new BasicNameValuePair("accountType", "GOOGLE"));
      nameValuePairs.add(new BasicNameValuePair("source",
          "Google-cURL-Example"));
      nameValuePairs.add(new BasicNameValuePair("service", "ac2dm"));

      post.setEntity(new UrlEncodedFormEntity(nameValuePairs));
      HttpResponse response = client.execute(post);
      BufferedReader rd = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));

      String line = "";
      while ((line = rd.readLine()) != null) {
        System.out.println(line);
        if (line.startsWith("Auth=")) {
          String key = line.substring(5);
          // do something with the key
        }

      }
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}