RESTful Java client with java.net.URL

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]