Apache HttpClient is a robust and complete solution Java library to perform HTTP operations, including RESTful service. In this tutorial, we show you how to create a RESTful Java client with Apache HttpClient, to perform a “GET” and “POST” request.

Note
The RESTful services from last “Jackson + JAX-RS” article will be reused.

1. Get Apache HttpClient

Apache HttpClient is available in Maven central repository, just declares it in your Maven pom.xml file.

File : pom.xml


	<dependency>
		<groupId>org.apache.httpcomponents</groupId>
		<artifactId>httpclient</artifactId>
		<version>4.1.1</version>
	</dependency>

2. GET Request

Review last REST service again.


@Path("/json/product")
public class JSONService {

	@GET
	@Path("/get")
	@Produces("application/json")
	public Product getProductInJSON() {

		Product product = new Product();
		product.setName("iPad 3");
		product.setQty(999);
		
		return product; 

	}
	//...

Apache HttpClient to send a “GET” request.


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

public class ApacheHttpClientGet {

	public static void main(String[] args) {
	  try {

		DefaultHttpClient httpClient = new DefaultHttpClient();
		HttpGet getRequest = new HttpGet(
			"http://localhost:8080/RESTfulExample/json/product/get");
		getRequest.addHeader("accept", "application/json");

		HttpResponse response = httpClient.execute(getRequest);

		if (response.getStatusLine().getStatusCode() != 200) {
			throw new RuntimeException("Failed : HTTP error code : "
			   + response.getStatusLine().getStatusCode());
		}

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

		String output;
		System.out.println("Output from Server .... \n");
		while ((output = br.readLine()) != null) {
			System.out.println(output);
		}

		httpClient.getConnectionManager().shutdown();

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

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

	}

}

Output…


Output from Server .... 

{"qty":999,"name":"iPad 3"}

3. POST Request

Review last REST service also.


@Path("/json/product")
public class JSONService {

        @POST
	@Path("/post")
	@Consumes("application/json")
	public Response createProductInJSON(Product product) {

		String result = "Product created : " + product;
		return Response.status(201).entity(result).build();
		
	}
	//...

Apache HttpClient to send a “POST” request.


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.DefaultHttpClient;

public class ApacheHttpClientPost {

	public static void main(String[] args) {

	  try {

		DefaultHttpClient httpClient = new DefaultHttpClient();
		HttpPost postRequest = new HttpPost(
			"http://localhost:8080/RESTfulExample/json/product/post");

		StringEntity input = new StringEntity("{\"qty\":100,\"name\":\"iPad 4\"}");
		input.setContentType("application/json");
		postRequest.setEntity(input);

		HttpResponse response = httpClient.execute(postRequest);

		if (response.getStatusLine().getStatusCode() != 201) {
			throw new RuntimeException("Failed : HTTP error code : "
				+ response.getStatusLine().getStatusCode());
		}

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

		String output;
		System.out.println("Output from Server .... \n");
		while ((output = br.readLine()) != null) {
			System.out.println(output);
		}

		httpClient.getConnectionManager().shutdown();

	  } catch (MalformedURLException e) {

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

		e.printStackTrace();

	  }

	}

}

Output…


Output from Server .... 

Product created : Product [name=iPad 4, qty=100]

Download Source Code

References

  1. Jackson Official Website
  2. Apache HttpClient
  3. RESTful Java client with java.net.URL