In this tutorial, we show you how to create a RESTful Java client with Java build-in HTTP client library. It’s simple to use and good enough to perform basic operations for REST service.

The RESTful services from last “Jackson + JAX-RS” article will be reused, and we will use “java.net.URL” and “java.net.HttpURLConnection” to create a simple Java client to send “GET” and “POST” request.

1. GET Request

Review last REST service, return “json” data back to client.


@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; 

	}
	//...

Java client to send a “GET” request.


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class NetClientGet {

	// http://localhost:8080/RESTfulExample/json/product/get
	public static void main(String[] args) {

	  try {

		URL url = new URL("http://localhost:8080/RESTfulExample/json/product/get");
		HttpURLConnection conn = (HttpURLConnection) url.openConnection();
		conn.setRequestMethod("GET");
		conn.setRequestProperty("Accept", "application/json");

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

		BufferedReader br = new BufferedReader(new InputStreamReader(
			(conn.getInputStream())));

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

		conn.disconnect();

	  } catch (MalformedURLException e) {

		e.printStackTrace();

	  } catch (IOException e) {

		e.printStackTrace();

	  }

	}

}

Output…


Output from Server .... 

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

2. POST Request

Review last REST service, accept “json” data and convert it into Product object, via Jackson provider automatically.


@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();
		
	}
	//...

Java client to send a “POST” request, with json string.


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class NetClientPost {

	// http://localhost:8080/RESTfulExample/json/product/post
	public static void main(String[] args) {

	  try {

		URL url = new URL("http://localhost:8080/RESTfulExample/json/product/post");
		HttpURLConnection conn = (HttpURLConnection) url.openConnection();
		conn.setDoOutput(true);
		conn.setRequestMethod("POST");
		conn.setRequestProperty("Content-Type", "application/json");

		String input = "{\"qty\":100,\"name\":\"iPad 4\"}";

		OutputStream os = conn.getOutputStream();
		os.write(input.getBytes());
		os.flush();

		if (conn.getResponseCode() != HttpURLConnection.HTTP_CREATED) {
			throw new RuntimeException("Failed : HTTP error code : "
				+ conn.getResponseCode());
		}

		BufferedReader br = new BufferedReader(new InputStreamReader(
				(conn.getInputStream())));

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

		conn.disconnect();

	  } 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

Download it – JAX-RS-Client-JavaURL-Example.zip (8 KB)

References

  1. Jackson Official Website
  2. java.net.URL JavaDoc
  3. java.net.HttpURLConnection JavaDoc