SCA Java User Guide

Welcome to the Apache Tuscany SCA User guide. Here you will find information aimed to help you understand SCA concepts and an example walk through for building your own SCA application.

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Introduction

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Introduction

This user guide will help you become familiar with SCA concepts and walks you through an example that demonstrates how to build an SCA application. It also describes the different environments that Tuscany supports (such as command line clients or web applications) and how to package up applications to run in these environments.

There's nothing to it really! Building SCA applications is easy. One of the main goals of Tuscany and SCA is to avoid imposing rules and requirements on how people write applications. We want to let people write application code the way they want without being concerned about the environment in which it will be used. After all, writing code to handle plumbing just gets in the way of writing the interesting stuff. So basically, you write the code for interesting bits, and Tuscany provides the environment that lets it run. Therefore, this guide is just an example of how an SCA application can be developed and is not a rule.

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Quick Guide to SCA

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Quick Guide to SCA

The quick guide to SCA gives you an overview of SCA concepts and prepares you to work on the example below. You can skip this step if you are already familiar with SCA.

For more details on SCA please refer to the specifications at Open SOA web site.

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Example Walkthrough

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Example Walkthrough

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Overview of Example

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Overview of Example

We will use the calculator sample to walk through the steps for building an SCA application. As the name indicates, this example performs typical calculator operations. It is given two numbers and asked to perform an operation on them. Our calculator will handle add, subtract, multiply and divide.

We start with a simple variation of the calculator example and extend it to include more advanced SCA features.

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Getting Set Up

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Getting Set Up

• Download Tuscany Java SCA release.
  Please download the latest binary release. You can use the source code release but you will have to use Maven at all stages.
• Download prerequisites
  • Java 5
  • Maven 2.0.4+

If you want to build the sample with Ant rather than Maven you will need to download Ant instead

• • Ant 1.7.0

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Running The Calculator Sample

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Running The Calculator Sample

Calculator is provided as a sample under SCA Java binary distribution. Let's first run the sample before we go about
building it. It is easy!

• Go to the directory ..\samples\calculator

  ant run
  

Alternatively if you want to run the sample directly from the command line try the following.

• if you are using Windows issue the command:

  java -cp ..\..\lib\tuscany-sca-manifest.jar;target\sample-calculator.jar calculator.CalculatorClient
  

• if you are using *nix issue the command:

  java -cp ../../lib/tuscany-sca-manifest.jar:target/sample-calculator.jar calculator.CalculatorClient
  

You should see the following result:

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

If you are using the source disitribution then we suggest you use Maven to build and run the calculator sample because the tuscany-sca-manifest.jar is not provided with the source distribution. This jar is part of the binary distribution and collects together all of the tuscany jars in one place so that the java command line is nice and short when running samples.

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Building The Calculator Sample In Java

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Building The Calculator Sample In Java

What you will learn

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

Example walk-through

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
Unable to render embedded object: File (CalculatorBlocks2.jpg) not found.

(?)TODO - need to update the diagram to change Add -> AddService etc. Who has the editable version?

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 CalcualtorService 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.

public interface AddService {

    double add(double n1, double n2);
}

Now, we provide an implementation of this interface.

public class AddServiceImpl implements AddService {

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

But wait! Aren't we writing an SCA component? It must be more complicated that that - the mere, plain old Java interface and implementation, right? Well, actually an SCA component can just be plain old Java so we have just done all the coding we needed to implement the SCA AddService component. We can use SCA to expose the service that the AddService component provides over any of the supported bindings, for example, WebServices, JMS or RMI, without changing out the AddService implementation.

Let's take a look at the CalculatorService component. This is interesting because it's going to call the AddService component. In the full application it will call the SubtractService, MultiplyService and DivideService components as well, but we will ignore these for the time being as they follow the same pattern as we will implement for the AddService component.

Again we will start by defining an interface because CalcultorService is itself providing an interface that others will call.

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);
}

Now we implement this interface.

public class CalculatorServiceImpl implements CalculatorService {

    private AddService addService;
    private SubtractService subtractService;
    private MultiplyService multiplyService;
    private DivideService divideService;
   
    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
}

Step 3 - Assembling the application:
So all well and good but how do we actually run these two components. Well of course the java programmer in us want's 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.

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
    }
}

But this doesn't run using the Tuscany SCA runtime and extending this code to provide web services interfaces, for example, would be a little more complicated. What do we have to do to make it run in Tuscany where we get all things like web service support for free? Well, not much actually. First let's change the client to fire up the Tuscany SCA runtime before calling our components.

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();
    }
}

You can see that we start by using a static method on SCADomain to create a new instance of itself. The SCADomain is a concept in SCA that represents the boundary of an SCA system. This could be distributed across many processors but that's not implemented in Tuscany yet so lets concentrate on getting this working inside a single Java VM.

The parameter "Calculator.composite" refers to an XML file that tells SCA how the components in our calculator application are assembled into a working applcation. Here is the XML that's inside Calculator.composite.

<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" />
        <!-- references to SubtractComponent, MultiplyComponent and DivideComponent  -->
    </component>

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

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

</composite>

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. This is equivalent to this piece of code from our normal Java client.

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

Once the composite file is loaded into the SCADomain our client code asks the SCADomain to give us a reference to the component called "CalculatorServiceComponent".

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

We can now use this reference as though we had created it ouselves, for example, from the CalculatorServiceImpl.add() method implementation.

return addService.add(n1, n2);

The SCA specifications often descibe SCA applications is diagramatic form. This often helps give a quick overview of what components ar part of an application and how they are wired together. If we draw a diagram of what we have build in the calculator sample we come up with something like.

Unable to render embedded object: File (calculator.png) not found.

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.

Step 4 - Deploying the applcation:

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.

ant compile

Once recompiled you can run it as before in the 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.

ant run

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What Next?

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What Next?

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.

<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>

All we have done is added the <service> element which tells Tuscany SCA how to expose our CalculatorServiceComponent as a JSONRPC service. Note that we didn't have to change the Java code of our components. This is just a configuration change. The helloworld-jsonrpc sample shows a working example of the jsonrpc 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. The helloworld-ws-service and helloworld-ws-reference samples show you how to work with web services.
TODO - we don't have a web services version of the calcualtor 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.

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

<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>

Of course we need the Ruby code that implements the component.

def subtract(n1, n2)
    return n1 - n2
end

The Tuscany SCA runtime handles wiring Java components to Ruby components and performs any required data transformations. The calculator-script sample shows different script languages in use.

So, now that our application is desribed as an SCA assembly there are lots of possibilities as we futher develop it and integration it with other applications. The following sections provide more detail on the features provided by Tuscany SCA.

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Tuscany SCA Extensions

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Tuscany SCA Extensions

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The Extensible Runtime

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The Extensible Runtime

The Tuscany SCA runtime comprises a small set of core software which deals with:

• Managing extesions to the Tuscany SCA Runtime(core)
• Building and in memory assembly model of SCA applications (assembly)
• Processing SCA applcations that are contributed (contribution)
• Supporting databindings (databinding)
• Supporting Tuscany SCA when its embedded in other environments (embedded)
• Supporting Tuscany SCA when its running in a servlet container (http)

The collections of interfaces that describe these features are referred to as the System Programming Interface (SPI). The [developer guide] discusses them in more detail but from a user perspective the important thing to realize is that the majority of interesting functionality in Tuscany SCA is provided by extensions which build upon this core SPI. These extensions provide Tuscany SCA with its ability to support a wide variety features.

• Implementation types
• Binding types
• Databinding types
• Interface description styles
• Hosting environments

So to undestand how to use the Tuscany SCA runtime is to understand how to use its extensions.

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Available Extensions

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Available Extensions

More often than not using an extension involves adding information to you SCDL files or your implementation files but this is not always the case. The links below describe each of the extensions and how they can be used and configured.

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Using Extensions

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Using Extensions

Extensions are loaded into the Tuscany SCA runtime using the Java service loading mechanism. Each extension is packaged as a jar and provides a file;

META-INF/services/org.apache.tuscany.sca.core.ModuleActivator

Using this information the Tuscany SCA runtime will load each extensions present on the the Java CLASSPATH. So if you want to use a particular feature make sure that it's available on your classpath. Conversely if you don't want a particular feature to be active remove it from the classpath.

Writing a new extension is a subject in its own right and is described in the extension guide

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Tuscany SCA And IDEs

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Tuscany SCA And IDEs

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Using The Samples In An IDE Without Maven

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Using The Samples In An IDE Without Maven

We don't provide any IDE project files with our disitributions so you will have to import the sample files into your IDE manually. Here's an example of how it can be done using Eclipse. Here the directory tuscany_sca_install_dir is the directory whch holds the Tuscany SCA Java binary installation after it's been extracted from its archive file, for example, for the 0.90 release this will be tuscany-sca-0.90-incubating.

In a new or existing workspace

• Create a new java project to represent the sample you want to work on, e.g.

  my working dir/calculator
  

• Import all of the sample code and resources into this project, e.g.

  Use the File,Import menu and then select  tuscany_sca_install_dir/samples/calculator from the filesystem
  

• Configure the source path to include

  tuscany_sca_install_dir/samples/calculator/src/main/java
  tuscany_sca_install_dir/samples/calculator/src/main/resources
  

• Configure the output folder to be

  tuscany_sca_install_dir/samples/calculator/target
  

• Configure the build path to include all of the jars provided in

  tuscany_sca_install_dir/lib
  

• If you select calculator.CalculatorClient.java and run as "Java Application" you should see

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

The details of how to do this for other development environments will vary but the process will be similar.

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Using The Samples In An IDE If You Have Maven

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Using The Samples In An IDE If You Have Maven

If you are a Maven user you can use it to generate all of the IDE project files for you automatically. This works best if you generate IDE projects for all of the Apache Tuscany modules. You can then include the ones you are interested in working with in you IDE.

To build IDE project files for all of the modules in Apache Tuscany SCA;

cd sca 

If you are an Eclipse user do the following

mvn -Peclipse eclipse:eclipse  

If you are an IDEA user do the following

mvn idea:idea

These commands generate project files for each module in Apache Tuscany SCA. The modules you are interested in can now be included in your IDE, for example, in Eclipse, if you create a new Java project and use the option to "create a new project from existing source" you can specify an SCA module directory, which includes the generated project files, and Eclipse will treat it like any other Java project.