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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title | Apache Tuscany SCA User Guide |
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This page is under construction- You are welcome to help and complete it |
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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. Anchor |
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| Quick Guide to SCA |
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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. Anchor |
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| Example Walkthrough |
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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 |
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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. Anchor |
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| Getting Set Up |
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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
If you want to build the sample with Ant rather than Maven you will need to download Ant instead Anchor |
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| Running The Calculator Sample |
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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
Alternatively if you want to run the sample directly from the command line try the following. - if you are using Windows issue the command:
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java -cp ..\..\lib\tuscany-sca-manifest.jar;target\sample-calculator.jar calculator.CalculatorClient
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- if you are using *nix issue the command:
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java -cp ../../lib/tuscany-sca-manifest.jar:target/sample-calculator.jar calculator.CalculatorClient
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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. Anchor |
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| Building The Calculator Sample In Java |
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| Building The Calculator Sample In Java |
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| Building The Calculator Sample In Java |
What you will learnThis 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-throughStep 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 Image Added (?)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. Code Block |
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public interface AddService {
double add(double n1, double n2);
}
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Now, we provide an implementation of this interface. Code Block |
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public class AddServiceImpl implements AddService {
public double add(double n1, double n2) {
return n1 + n2;
}
}
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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. Code Block |
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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);
}
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Now we implement this interface. Code Block |
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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
}
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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. Code Block |
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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
}
}
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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. Code Block |
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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();
}
}
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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. Code Block |
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<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>
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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. Code Block |
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CalculatorServiceImpl calculatorService = new CalculatorServiceImpl();
AddService addService = new AddServiceImpl();
calculatorService.setAddService(addService);
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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". Code Block |
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CalculatorService calculatorService = scaDomain.getService(CalculatorService.class, "CalculatorServiceComponent");
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We can now use this reference as though we had created it ouselves, for example, from the CalculatorServiceImpl.add() method implementation. Code Block |
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return addService.add(n1, n2);
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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. Image Added
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. 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. Background Color |
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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. Code Block |
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<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"> |
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