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h2. {anchor:build}{bgcolor:#C3CDA1}Build The Calculator Sample In Java{bgcolor}

This example illustrates how to define your application while staying focused on the business logic. It walks you through the steps of building the calculator sample. All connections between the components within the composite are local and described using Java interfaces.

*Step 1 - Define what building blocks are needed:* Think about how your application can be broken down into smaller functions/services. Each block is a logical unit of operation that can be used in the overall application. In this case, calculator application can be divided into five blocks: AddService block, SubstractService block, MultiplyService block and DivideService block and a main block that takes a request and routes it to the right operation. We have called this main block the CalculatorService  

!calculatorblocks.png|align=centre!

*Step 2 - Implement each block:* Now that you have identified the blocks of functionality in your application, you are ready to create each block. In SCA the blocks of functionality are referred to as components so let's look at how we implement a component. We'll take the AddService component as our first example. 

The AddService component will provide a service that adds two numbers together. The CalculatorService component uses the AddService component whenever it is asked to perform additions. If we were writing the AddService component in plain old Java we would start by describing a (Java) interface.

{code}
public interface AddService {

    double add(double n1, double n2);
}
{code}

{code}
public interface CalculatorService {

    double add(double n1, double n2);
    double subtract(double n1, double n2);
    double multiply(double n1, double n2);
    double divide(double n1, double n2);
}
{code}

 

{code}
public class CalculatorServiceImpl implements CalculatorService {

    private AddService addService;
    private SubtractService subtractService;
    private MultiplyService multiplyService;
    private DivideService divideService;
   
    @Reference
    public void setAddService(AddService addService) {
        this.addService = addService;
    }

    ...set methods for the other attributes would go here

    public double add(double n1, double n2) {
        return addService.add(n1, n2);
    }

    ...implementations of the other methods would go here
}
{code}

 case.

!calculator3.png|align=centre!


h2. {anchor:assemble}{bgcolor:#C3CDA1}Assemble the Calculator Application{bgcolor}
So far we have created the components. How do we actually run the calculator application? Well of course the java programmer in us wants to get down to it, write a mainline to connect our two components together and run then. We could still do that easily in this case.

{code}
public class CalculatorClient {
    public static void main(String[] args) throws Exception {

        CalculatorServiceImpl calculatorService = new CalculatorServiceImpl();
        AddService            addService        = new AddServiceImpl();
        calculatorService.setAddService(addService);
      
        System.out.println("3 + 2=" + calculatorService.add(3, 2));
        // calls to other methods go here if we have implemented SubtractService, MultiplyService, DivideService
    }
}
{code}

 

{code}
public class CalculatorClient {
    public static void main(String[] args) throws Exception {

        SCADomain scaDomain = SCADomain.newInstance("Calculator.composite");
        CalculatorService calculatorService = scaDomain.getService(CalculatorService.class, "CalculatorServiceComponent");

        System.out.println("3 + 2=" + calculatorService.add(3, 2));
        // calls to other methods go here if we have implemented SubtractService, MultiplyService, DivideService

        scaDomain.close();
    }
}
{code}

 

{code}
<composite xmlns="http://www.osoa.org/xmlns/sca/1.0"
           name="Calculator">

    <component name="CalculatorServiceComponent">
	<implementation.java class="calculator.CalculatorServiceImpl"/>
        <reference name="addService" target="AddServiceComponent" />
        <!-- You can add references to SubtractComponent, MultiplyComponent and DivideComponent  -->
    </component>

    <component name="AddServiceComponent">
        <implementation.java class="calculator.AddServiceImpl"/>
    </component>

    <!-- definitions of SubtractComponent, MultiplyComponent and DivideComponent -->

</composite>

{code}
You can see that we define two components here and specify the Java implementation classes that Tuscany SCA needs to load to make them work. These are the classes we have just implemented.

Also note that the CalculatorServiceComponent has a reference named "addService". In the XML, this reference targets the AddServiceComponent. It is no coincidence that the reference name, "addService", matches the name of the addService field we created when we implemented CalculatorServiceImpl. The Tuscany SCA runtime parses the information from the XML composite file and uses it to build the objects and relationships that represent our calculator application. It first creates instances of AddServiceImpl and CalcualtorSreviceImpl. It then injects a reference to the AddServiceImpl object into the addService field in the CalculatorServiceImpl object. If you look back at how we implemented the CalculatorService you will see an @Reference annotation that tells SCA which fields are expecting to be set automatically by SCA. This is equivalent to this piece of code from our normal Java client.

{code}
        CalculatorServiceImpl calculatorService = new CalculatorServiceImpl();
        AddService            addService        = new AddServiceImpl();
        calculatorService.setAddService(addService);
{code}

 

{code}
        CalculatorService calculatorService = scaDomain.getService(CalculatorService.class, "CalculatorServiceComponent");
{code}

calculator/AddService.class
calculator/AddServiceImpl.class
calculator/CalculatorClient.class
calculator/CalculatorService.class
calculator/CalculatorServiceImpl.class
calculator/DivideService.class
calculator/DivideServiceImpl.class
calculator/MultiplyService.class
calculator/MultiplyServiceImpl.class
calculator/SubtractService.class
calculator/SubtractServiceImpl.class
Calculator.composite

ant compile

ant run

!calculator4.png|align=centre!

You will notice that diagrams are provided with all of our samples. If you like to take a visual approach to things this may help you become quickly familiar with the components in the samples. Take a look at the ".png" files in the top level directory of each sample.


h2. {anchor:deploy}{bgcolor:#C3CDA1}Deploy the Calculator Application{bgcolor}

So as long as the "Calculator.composite" file is present on our class path, along with the rest of the tuscany jars, we can run our sample as we did  previously. The samples come with an Ant build.xml file that allows the sample files to be rebuilt so if you want to experiment with the sample code you can do so and then recompile it. 

{code}
ant compile
{code}

Once recompiled you can run it as before in the [Running The Calculator Sample|SCA Java User Guide#Running The Calculator Sample] section, for example, we provide a run target in the Ant build.xml file so the calculator sample can also be run using. 

{noformat}
ant run
{noformat}

h2. {anchor:bindings}{bgcolor:#C3CDA1}Reconfigure The Calculator Application - Change Bindings{bgcolor}

Looking back, the client code we have written to start the calculator application using the Tuscany SCA runtime is no longer than a normal Java client for the application. However we do now have the XML composite file that describes how our application is assembled. 

This concept of assembly is a great advantage as our applications become more complex and we want to change them, reuse them, integrate them with other applications or just further develop them using a programming model consistent with all our other SCA applications. Regardless of what language is used to implement each of them. 

For example, lets say our calculator sample is so poweful and popular that we want to put it on the company intranet and let other people access it as a service directly from their browser based Web2.0 applications. It's at this point we would normally start reaching for the text books to work out how to make this happen. As we have an XML file that describes our application it's easy in Tuscany SCA. The following should do the trick. 


{code}
<composite xmlns="http://www.osoa.org/xmlns/sca/1.0"
           name="Calculator">

     <service name="CalculatorService" promote="CalculatorServiceComponent/CalculatorService">
         <interface.java interface="calculator.CalculatorService"/>
         <binding.jsonrpc/>
     </service>    

    <component name="CalculatorServiceComponent">
		<implementation.java class="calculator.CalculatorServiceImpl"/>
        <reference name="addService" target="AddServiceComponent" />
        <!-- references to SubtractComponent, MultiplyComponent and DivideComponent  -->
    </component>

    <component name="AddServiceComponent">
        <implementation.java class="calculator.AddServiceImpl"/>
    </component>

    <!-- definitions of SubtractComponent, MultiplyComponent and DivideComponent -->

</composite>
{code}

 binding. 
(?) TODO - we don't have a JSONRPC version of the calculator sample

If we really wanted a SOAP/HTTP web service we can do that easily too. 

{code}
<composite xmlns="http://www.osoa.org/xmlns/sca/1.0"
           name="Calculator">

     <service name="CalculatorService" promote="CalculatorServiceComponent/CalculatorService">
         <interface.java interface="calculator.CalculatorService"/>
         <interface.java interface="calculator.CalculatorService"/ <!-- ** Below we added info for json binding ** -->
         <binding.jsonrpc/>
         <binding.ws/>
     </service>    

    <component name="CalculatorServiceComponent">
		<implementation.java class="calculator.CalculatorServiceImpl"/>
        <reference name="addService" target="AddServiceComponent" />
        <!-- references to SubtractComponent, MultiplyComponent and DivideComponent  -->
    </component>

    <component name="AddServiceComponent">
        <implementation.java class="calculator.AddServiceImpl"/>
    </component>

    <!-- definitions of SubtractComponent, MultiplyComponent and DivideComponent -->

</composite>
{code}

reference samples show you how to work with web services. 
(?) TODO - we don't have a web services version of the calculator sample

SCA allows other kinds of flexibility. We can rewire our components, for example, using a one of the remote bindings, like RMI, we could have the CalculatorServiceComponent running on one machine wired to a remote version of the application running on another machine. The calculator-rmi-service and calculator-rmi-reference samples show the RMI binding at work.  


h2. {anchor:implementations}{bgcolor:#C3CDA1}Use Alternative Implementation Types {bgcolor}

We could also introduce components implemented in different languages, for example, let's add the SubtractServiceComponent implemented in Ruby.  

{code}
<composite xmlns="http://www.osoa.org/xmlns/sca/1.0"
           name="Calculator">

    <component name="CalculatorServiceComponent">
        <implementation.java class="calculator.CalculatorServiceImpl"/>
        <reference name="addService" target="AddServiceComponent" />
        <reference name="subtractService" target="SubtractServiceComponent" />
        <!-- references to MultiplyComponent and DivideComponent  -->
    </component>

    <component name="AddServiceComponent">
        <implementation.java class="calculator.AddServiceImpl"/>
    </component>

    <component name="SubtractServiceComponent">
        <implementation.script script="calculator/SubtractServiceImpl.rb"/>
    </component>

    <!-- definitions of MultiplyComponent and DivideComponent -->

</composite>
{code}

 

{code}
def subtract(n1, n2)
    return n1 - n2
end
{code}