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]