Let's now create a Java client application that calls the previous web service. Create a simple Maven project and call it CourseManagementRESTClient:

Open pom.xml and add a dependency for the Jersey client module:

  <dependencies> 
    <dependency> 
      <groupId>org.glassfish.jersey.core</groupId> 
      <artifactId>jersey-client</artifactId> 
      <version>2.18</version> 
    </dependency> 
  </dependencies>

Create a Java class called CourseManagementRESTClient in the packt.jee.eclipse.rest.ws.client package:

You could invoke a RESTful web service using java.net.HttpURLConnection or other external HTTP client libraries. But JAX-RS client APIs make this task a lot easier, as you can see in the following code:

package packt.jee.eclipse.rest.ws.client; 
 
import javax.ws.rs.client.Client; 
import javax.ws.rs.client.ClientBuilder; 
import javax.ws.rs.client.WebTarget; 
import javax.ws.rs.core.MediaType; 
import javax.ws.rs.core.Response; 
 
/** 
 * This is a simple test class for invoking RESTful web service 
 * using JAX-RS client APIs 
 */ 
public class CourseManagementClient { 
 
  public static void main(String[] args) { 
 
testGetCoursesJSON(); 
 
  } 
 
  //Test getCourse method (XML or JSON) of CourseService 
  public static void testGetCoursesJSON() { 
    //Create JAX-RS client 
    Client client = ClientBuilder.newClient(); 
    //Get WebTarget for a URL 
    WebTarget webTarget = 
 client.target("http://localhost:8080/CourseManagementREST/services/course"); 
    //Add paths to URL 
    webTarget = webTarget.path("get").path("10"); 
 
    //We could also have create webTarget in one call with the full URL - 
    //WebTarget webTarget = 
 client.target("http://localhost:8080/CourseManagementREST/services/course/get/10"); 
 
 
    //Execute HTTP get method 
    Response response = 
     webTarget.request(MediaType.APPLICATION_JSON).get(); 
 
    //Check response code. 200 is OK 
    if (response.getStatus() != 200) { 
      System.out.println("Error invoking REST web service - " + 
       response.getStatusInfo().getReasonPhrase()); 
      return; 
    } 
 
    //REST call was successful. Print the response 
    System.out.println(response.readEntity(String.class)); 
  } 
}