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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.

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 with new 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 of HttpUriRequest 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();
                }
        }
}

3. About this website

4. Resources

Not listed yet.

4.1. vogella GmbH training and consulting support

TRAINING SERVICE & SUPPORT

The vogella company provides comprehensive training and education services from experts in the areas of Eclipse RCP, Android, Git, Java, Gradle and Spring. We offer both public and inhouse training. Whichever course you decide to take, you are guaranteed to experience what many before you refer to as “The best IT class I have ever attended”.

The vogella company offers expert consulting services, development support and coaching. Our customers range from Fortune 100 corporations to individual developers.

Copyright © 2012-2016 vogella GmbH. Free use of the software examples is granted under the terms of the EPL License. This tutorial is published under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Germany license.

See Licence.