The SCA specification defines a set of SCA Java annotations that enable service components and service clients to be built in the Java programming language.(more information here).

This section describes how to use the SCA Java annotations on the previous helloworld POJO example.

First, the PrintService Java interface implemented by the server is described with the <service/> tag from lines 22 to 24 of the helloworld-pojo.composite file, in the section called “Hello World SCA composite”. These lines can be omitted when using the @Service annotation on the PrintService Java interface:

package org.ow2.frascati.examples.helloworld.annotated;

/** A basic service used to print messages. */
@Service
public interface PrintService {
    void print(String msg);
}

Concerning the server component, its Java implementation can also be annotated for the description of its property (header), described line 26 in the SCA composite of the section called “Hello World SCA composite”. This annotation exempts also the developper to write getters and setters for SCA properties defined with this annotation. Thus, the Server Java class now looks like:

package org.ow2.frascati.examples.helloworld.annotated;
/** The print service implementation. */
public class Server implements PrintService {
    @Property
    protected String header = "->";
    private int count = 1;
    
    /** Default constructor. */
    public Server() {
        System.out.println("SERVER created.");
    }
    
    /** PrintService implementation. */
    public void print(final String msg) {
        System.out.println("SERVER: begin printing...");
        for (int i = 0; i < count; ++i) {
            System.out.println(header + msg);
        }
        System.out.println("SERVER: print done.");
    }
}

The last annotation we will add to this example is @Reference. This annotation represents the <reference /> tag (lines 14 to 16 of helloworld-pojo.composite in the previous section.

The client component also provides a runnable service named r. Then, the annotated Java class for the client component is:

package org.ow2.frascati.examples.helloworld.annotated;

/** A print service client. */
public class Client implements Runnable {
    
    @Reference
    protected PrintService s;
    
    /** Default constructor. */
    public Client() {
        System.out.println("CLIENT created.");
    }
    
    /** Run the client. */
    public void run() {
        s.print("Hello World!");
    }

}

With these annotations, the helloworld composite file is now much more shorter:

  1 <?xml version="1.0" encoding="ISO-8859-15"?>
  2 <composite xmlns="http://www.osoa.org/xmlns/sca/1.0"
  3            name="helloworld-annotated">
  4 
  5   <service name="r" promote="client/r"/>
  6   
  7   <component name="client">
  8     <implementation.java class="org.ow2.frascati.examples.helloworld.annotated.Client"/>
  9   </component>
 10   
 11   <component name="server">
 12     <implementation.java class="org.ow2.frascati.examples.helloworld.annotated.Server"/>
 13   </component>
 14   
 15 </composite>
 16