SCA Java User Guide

This page is under construction- You are welcome to help and complete it

Welcome to the Apache Tuscany SCA User guide. Here you will find information aimed to help you first develop a simple SCA calculator application and then enhance it with more advanced features and concepts. This guide is based on Java SCA implementation in Tuscany.

It is assumed that you are familiar with basic SCA concepts.

This is a work in progress, so please contribute and comment so we can make this valuable to you

Introduction">Introduction

Service Component Architecture (SCA) defines technologies for creating services and assembling them into higher-order service networks. SCA provides a language-independent way to compose and deploy service networks. SCA also defines language-specific client programming models for service authoring including Java, Spring, C++, and PHP. This user guide is for Java SCA implementation in Tuscany.

This user guide will help you build a simple application called calculator sample in Java. It then modifies it to use multiple languages in the same application.

DownLoading SCA"> DownLoading SCA

Download Tuscany Java SCA release.
This sample is going to be tested with the latest release of Tuscany.

Example Overview"> Example Overview

We will use the calculator sample to walk through steps for building an SCA application. As the name indicates, this sample performs the calculator operation. It is given two numbers and asked to perform an operation on those numbers.

This application consists of the calculator applicatoin and the SCA client that invokes it. We will focus on the Calculator application itself.

Step 1 Define how the calculator application can be broken down into distinct operations/components, let's say Add, Subtract, Multiply and Devide

Step 2 Define interfaces for each component in SCDL file

Step 3 Implement each component

Step 4 Create the composite application*

Running the Calculator Sample">Running the Calculator Sample

[Note: We need to provide instruction for how to run sample without getting into IDE]

3 + 2=5.0
3 - 2=1.0
3 * 2=6.0
3 / 2=1.5

Running the Calculator Sample">Running the Calculator Sample

These are preliminary steps...details such as from where to download are forthcoming

1.  Download the sample file.
2.  Unzip it to a local folder such as C:\Temp
3.  In Eclipse, select File -> Import -> General -> Existing Projects into Workspace
4.  Click Next.
5.  Select the Select root directory option and click the "Browse" button to point to C:\Temp.
6.  Select CalcultorSample directory and click Finish. The project is created.
7.  Expand the CalcultorSample. Expand "src/main/java/calculator", right-click CalculatorClient.java and select Run as ... --> Java Application. You will see   the following output in the console view:

3 + 2=5.0
3 - 2=1.0
3 * 2=6.0
3 / 2=1.5

Building your own Calculator Application">Building your own Calculator Application

Topics to include?

Creating Java SCA Components
Creating the implementation for the Java SCA components
Creating the composite file
Creatomg a client to invoke the service
Packaging a Standalone Tuscany Application?
Building a Tuscany Web Application?

Step1: Diagram"> Step1: Diagram

Think about how your application can be broken down into smaller functions/services. In this case, calculator application can be divided into four blocks: Add block, Substract block, Multiply block and Divide block. Each block is a logical unit of operation that can be used in the overall application.

Step2: Define components"> Step2: Define components

Now that you have identified the blocks of functionality in your application, you are ready to create each block. A block is called a component in SCA programming model. A component is the smallest unit of function in your application that provides a service. A component can reference other components and can also be referennced by other components. A group of components can logically be bundled together to form a composite which is a deployable unit in SCA.

Let's tart with the add component. A component has an implementation associated with it. This implementation can be in any language, in this case it is a Java implementation.

[Note: Add the correct diagram to show add component and its interfaces.]

Components">Components

[Note: We need to replace this with Java relevant information. This is for C\+\+]
Compents are the building blocks for creating SOA Applications. They contain the information that defines the program logic or implementation (component implementation), how the component interacts with other components (component type) and defines how it fits in with the other parts of the soluion (composition/assembly).

• A service header file that defines the operations that can be invoked on the component
• An implementation header file that defines the implementation and extends the service header file
• A C++ implementation of the service that implements the operations defined in the service header file
• Proxy and wrapper header and implementation files generated by the Tuscany C++ SCAGEN tool
• A service definition in a .componentType file
• An SCDL component definition within an SCDL composite file. Usually this composite file will contain multiple components configured and assembled together.

Service Component Descritpion Language (SCDL)">Service Component Descritpion Language (SCDL)

Create a client to invoke the service.">Create a client to invoke the service.

1. Create a file and name it CalculatorClient.java 

Your component, composite and subsystem are now ready to be invoked. Create a client that will call the service. E.g. the Calculator client (in the CalculatorClient.cpp file) contains code similar to the following:

package calculator;

import org.apache.tuscany.api.SCAContainer;
import org.osoa.sca.CompositeContext;
import org.osoa.sca.CurrentCompositeContext;

/**
* This client program shows how to create an SCA runtime, start it,
* locate the Calculator service and invoke it.
**/
public class CalculatorClient {
public static void main(String[] args) throws Exception {
  SCAContainer.start("Calculator.composite");
  CompositeContext context = CurrentCompositeContext.getContext();
  CalculatorService calculatorService =
  context.locateService(CalculatorService.class, "CalculatorServiceComponent");
  // Calculate
  System.out.println("3 + 2=" + calculatorService.add(3, 2));
  System.out.println("3 - 2=" + calculatorService.subtract(3, 2));
  System.out.println("3 * 2=" + calculatorService.multiply(3, 2));
  System.out.println("3 / 2=" + calculatorService.divide(3, 2));
  SCAContainer.stop();
 }
}

A look at the Calculator Sample">A look at the Calculator Sample

These are preliminary steps...details such as from where to download are forthcoming

1.  Download the sample file.
2.  Unzip it to a local folder such as C:\Temp
3.  In Eclipse, select File -> Import -> General -> Existing Projects into Workspace
4.  Click Next.
5.  Select the Select root directory option and click the "Browse" button to point to C:\Temp.
6.  Select CalcultorSample directory and click Finish. The project is created.
7.  Expand the CalcultorSample. Expand "src/main/java/calculator", right-click CalculatorClient.java and select Run as ... --> Java Application. You will see   the following output in the console view:

3 + 2=5.0
3 - 2=1.0
3 * 2=6.0
3 / 2=1.5

Building a Tuscany Web Application">Building a Tuscany Web Application

You can run Tuscany inside of a Web application running in any standard Web container such as Apache Tomcat. Once configured, the application is portable across container implementations.