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Example subsystem

Our example subsystem will keep track of all deployments of certain types containing a special marker file, and expose operations to see how long these deployments have been deployed.

Create the skeleton project

To make your life easier we have provided a maven archetype which will create a skeleton project for implementing subsystems.

mvn archetype:generate \
    -DarchetypeArtifactId=wildfly-subsystem \
    -DarchetypeGroupId=org.wildfly.archetypes \
    -DarchetypeVersion=8.0.0.Final \
    -DarchetypeRepository=https://repository.jboss.org/nexus/content/groups/public

Maven will download the archetype and it’s dependencies, and ask you some questions:

$ mvn archetype:generate \
    -DarchetypeArtifactId=wildfly-subsystem \
    -DarchetypeGroupId=org.wildfly.archetypes \
    -DarchetypeVersion=8.0.0.Final \
    -DarchetypeRepository=https://repository.jboss.org/nexus/content/groups/public
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building Maven Stub Project (No POM) 1
[INFO] ------------------------------------------------------------------------
[INFO]
 
.........
 
Define value for property 'groupId': : com.acme.corp
Define value for property 'artifactId': : acme-subsystem
Define value for property 'version':  1.0-SNAPSHOT: :
Define value for property 'package':  com.acme.corp: : com.acme.corp.tracker
Define value for property 'module': : com.acme.corp.tracker
[INFO] Using property: name = WildFly subsystem project
Confirm properties configuration:
groupId: com.acme.corp
artifactId: acme-subsystem
version: 1.0-SNAPSHOT
package: com.acme.corp.tracker
module: com.acme.corp.tracker
name: WildFly subsystem project
 Y: : Y
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1:42.563s
[INFO] Finished at: Fri Jul 08 14:30:09 BST 2011
[INFO] Final Memory: 7M/81M
[INFO] ------------------------------------------------------------------------
$
Instruction

1

Enter the groupId you wish to use

2

Enter the artifactId you wish to use

3

Enter the version you wish to use, or just hit Enter if you wish to accept the default 1.0-SNAPSHOT

4

Enter the java package you wish to use, or just hit Enter if you wish to accept the default (which is copied from groupId ).

5

Enter the module name you wish to use for your extension.

6

Finally, if you are happy with your choices, hit Enter and Maven will generate the project for you.

We now have a skeleton project that you can use to implement a subsystem. Import the  acme-subsystem project into your favourite IDE. A nice side-effect of running this in the IDE is that you can see the javadoc of WildFly classes and interfaces imported by the skeleton code. If you do a mvn install in the project it will work if we plug it into WildFly, but before doing that we will change it to do something more useful.

The rest of this section modifies the skeleton project created by the archetype to do something more useful, and the full code can be found in acme-subsystem.zip.

If you do a mvn install in the created project, you will see some tests being run

$mvn install
[INFO] Scanning for projects...
[...]
[INFO] Surefire report directory: /Users/kabir/sourcecontrol/temp/archetype-test/acme-subsystem/target/surefire-reports
 
-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running com.acme.corp.tracker.extension.SubsystemBaseParsingTestCase
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.424 sec
Running com.acme.corp.tracker.extension.SubsystemParsingTestCase
Tests run: 6, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.074 sec
 
Results :
 
Tests run: 3, Failures: 0, Errors: 0, Skipped: 0
[...]

We will talk about these later in the #Testing the parsers section.

Create the schema

First, let us define the schema for our subsystem. Rename src/main/resources/schema/mysubsystem.xsd to src/main/resources/schema/acme.xsd. Then open acme.xsd and modify it to the following

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
            targetNamespace="urn:com.acme.corp.tracker:1.0"
            xmlns="urn:com.acme.corp.tracker:1.0"
            elementFormDefault="qualified"
            attributeFormDefault="unqualified"
            version="1.0">
 
   <!-- The subsystem root element -->
   <xs:element name="subsystem" type="subsystemType"/>
   <xs:complexType name="subsystemType">
      <xs:all>
         <xs:element name="deployment-types" type="deployment-typesType"/>
      </xs:all>
   </xs:complexType>
   <xs:complexType name="deployment-typesType">
      <xs:choice minOccurs="0" maxOccurs="unbounded">
         <xs:element name="deployment-type" type="deployment-typeType"/>
      </xs:choice>
   </xs:complexType>
   <xs:complexType name="deployment-typeType">
      <xs:attribute name="suffix" use="required"/>
      <xs:attribute name="tick" type="xs:long" use="optional" default="10000"/>
   </xs:complexType>
</xs:schema>

Note that we modified the xmlns and targetNamespace values to  urn.com.acme.corp.tracker:1.0. Our new subsystem element has a child called deployment-types, which in turn can have zero or more children called deployment-type. Each deployment-type has a required suffix attribute, and a tick attribute which defaults to true.

Now modify the  com.acme.corp.tracker.extension.SubsystemExtension class to contain the new namespace.

public class SubsystemExtension implements Extension {
 
    /** The name space used for the {@code substystem} element */
    public static final String NAMESPACE = "urn:com.acme.corp.tracker:1.0";
    ...

Design and define the model structure

The following example xml contains a valid subsystem configuration, we will see how to plug this in to WildFly later in this tutorial.

<subsystem xmlns="urn:com.acme.corp.tracker:1.0">
   <deployment-types>
      <deployment-type suffix="sar" tick="10000"/>
      <deployment-type suffix="war" tick="10000"/>
   </deployment-types>
</subsystem>

Now when designing our model, we can either do a one to one mapping between the schema and the model or come up with something slightly or very different. To keep things simple, let us stay pretty true to the schema so that when executing a :read-resource(recursive=true) against our subsystem we’ll see something like:

{
    "outcome" => "success",
    "result" => {"type" => {
        "sar" => {"tick" => "10000"},
        "war" => {"tick" => "10000"}
    }}
}

Each deployment-type in the xml becomes in the model a child resource of the subsystem’s root resource. The child resource’s child-type is type, and it is indexed by its suffix. Each type resource then contains the tick attribute.

We also need a name for our subsystem, to do that change com.acme.corp.tracker.extension.SubsystemExtension:

public class SubsystemExtension implements Extension {
    ...
    /** The name of our subsystem within the model. */
    public static final String SUBSYSTEM_NAME = "tracker";
    ...

Once we are finished our subsystem will be available under /subsystem=tracker.

The SubsystemExtension.initialize() method defines the model, currently it sets up the basics to add our subsystem to the model:

@Override
    public void initialize(ExtensionContext context) {
        //register subsystem with its model version
        final SubsystemRegistration subsystem = context.registerSubsystem(SUBSYSTEM_NAME, 1, 0);
        //register subsystem model with subsystem definition that defines all attributes and operations
        final ManagementResourceRegistration registration = subsystem.registerSubsystemModel(SubsystemDefinition.INSTANCE);
        //register describe operation, note that this can be also registered in SubsystemDefinition
        registration.registerOperationHandler(DESCRIBE, GenericSubsystemDescribeHandler.INSTANCE, GenericSubsystemDescribeHandler.INSTANCE, false, OperationEntry.EntryType.PRIVATE);
        //we can register additional submodels here
        //
        subsystem.registerXMLElementWriter(parser);
    }

The registerSubsystem() call registers our subsystem with the extension context. At the end of the method we register our parser with the returned SubsystemRegistration to be able to marshal our subsystem’s model back to the main configuration file when it is modified. We will add more functionality to this method later.

Registering the core subsystem model

Next we obtain a ManagementResourceRegistration by registering the subsystem model. This is a compulsory step for every new subsystem.

final ManagementResourceRegistration registration = subsystem.registerSubsystemModel(SubsystemDefinition.INSTANCE);

Its parameter is an implementation of the ResourceDefinition interface, which means that when you call /subsystem=tracker:read-resource-description the information you see comes from model that is defined by SubsystemDefinition.INSTANCE.

public class SubsystemDefinition extends SimpleResourceDefinition {
    public static final SubsystemDefinition INSTANCE = new SubsystemDefinition();
 
    private SubsystemDefinition() {
        super(SubsystemExtension.SUBSYSTEM_PATH,
                SubsystemExtension.getResourceDescriptionResolver(null),
                //We always need to add an 'add' operation
                SubsystemAdd.INSTANCE,
                //Every resource that is added, normally needs a remove operation
                SubsystemRemove.INSTANCE);
    }
 
    @Override
    public void registerOperations(ManagementResourceRegistration resourceRegistration) {
        super.registerOperations(resourceRegistration);
        //you can register aditional operations here
    }
 
    @Override
    public void registerAttributes(ManagementResourceRegistration resourceRegistration) {
        //you can register attributes here
    }
}

Since we need child resource type we need to add new ResourceDefinition,

The ManagementResourceRegistration obtained in SubsystemExtension.initialize() is then used to add additional operations or to register submodels to the /subsystem=tracker address. Every subsystem and resource must have an ADD method which can be achieved by the following line inside registerOperations in your ResourceDefinition or by providing it in constructor of your SimpleResourceDefinition just as we did in example above.

//We always need to add an 'add' operation
        resourceRegistration.registerOperationHandler(ADD, SubsystemAdd.INSTANCE, new DefaultResourceAddDescriptionProvider(resourceRegistration,descriptionResolver), false);

The parameters when registering an operation handler are:

  1. The name - i.e. ADD.

  2. The handler instance - we will talk more about this below

  3. The handler description provider - we will talk more about this below.

  4. Whether this operation handler is inherited - false means that this operation is not inherited, and will only apply to /subsystem=tracker. The content for this operation handler will be provided by 3.

Let us first look at the description provider which is quite simple since this operation takes no parameters. The addition of type children will be handled by another operation handler, as we will see later on.

There are two way to define DescriptionProvider, one is by defining it by hand using ModelNode, but as this has show to be very error prone there are lots of helper methods to help you automatically describe the model. Following example is done by manually defining Description provider for ADD operation handler

/**
     * Used to create the description of the subsystem add method
     */
    public static DescriptionProvider SUBSYSTEM_ADD = new DescriptionProvider() {
        public ModelNode getModelDescription(Locale locale) {
            //The locale is passed in so you can internationalize the strings used in the descriptions
 
            final ModelNode subsystem = new ModelNode();
            subsystem.get(OPERATION_NAME).set(ADD);
            subsystem.get(DESCRIPTION).set("Adds the tracker subsystem");
 
            return subsystem;
        }
    };

Or you can use API that helps you do that for you. For Add and Remove methods there are classes DefaultResourceAddDescriptionProvider and DefaultResourceRemoveDescriptionProvider that do work for you. In case you use SimpleResourceDefinition even that part is hidden from you.

resourceRegistration.registerOperationHandler(ADD, SubsystemAdd.INSTANCE, new DefaultResourceAddDescriptionProvider(resourceRegistration,descriptionResolver), false);
resourceRegistration.registerOperationHandler(REMOVE, SubsystemRemove.INSTANCE, new DefaultResourceRemoveDescriptionProvider(resourceRegistration,descriptionResolver), false);

For other operation handlers that are not add/remove you can use DefaultOperationDescriptionProvider that takes additional parameter of what is the name of operation and optional array of parameters/attributes operation takes. This is an example to register operation " `add-mime`" with two parameters:

container.registerOperationHandler("add-mime",
                MimeMappingAdd.INSTANCE,
                new DefaultOperationDescriptionProvider("add-mime", Extension.getResourceDescriptionResolver("container.mime-mapping"), MIME_NAME, MIME_VALUE));
Note
 When descriping an operation its description provider’s OPERATION_NAME must match the name used when calling ManagementResourceRegistration.registerOperationHandler()

Next we have the actual operation handler instance, note that we have changed its populateModel() method to initialize the type child of the model.

class SubsystemAdd extends AbstractBoottimeAddStepHandler {
 
    static final SubsystemAdd INSTANCE = new SubsystemAdd();
 
    private SubsystemAdd() {
    }
 
    /** {@inheritDoc} */
    @Override
    protected void populateModel(ModelNode operation, ModelNode model) throws OperationFailedException {
        log.info("Populating the model");
        //Initialize the 'type' child node
        model.get("type").setEmptyObject();
    }
    ....

SubsystemAdd also has a performBoottime() method which is used for initializing the deployer chain associated with this subsystem. We will talk about the deployers later on. However, the basic idea for all operation handlers is that we do any model updates before changing the actual runtime state.

The rule of thumb is that every thing that can be added, can also be removed so we have a remove handler for the subsystem registered
in SubsystemDefinition.registerOperations or just provide the operation handler in constructor.

//Every resource that is added, normally needs a remove operation
        registration.registerOperationHandler(REMOVE, SubsystemRemove.INSTANCE, DefaultResourceRemoveDescriptionProvider(resourceRegistration,descriptionResolver) , false);

SubsystemRemove extends AbstractRemoveStepHandler which takes care of removing the resource from the model so we don’t need to override its performRemove() operation, also the add handler did not install any services (services will be discussed later) so we can delete the performRuntime() method generated by the archetype.

class SubsystemRemove extends AbstractRemoveStepHandler {
 
    static final SubsystemRemove INSTANCE = new SubsystemRemove();
 
    private final Logger log = Logger.getLogger(SubsystemRemove.class);
 
    private SubsystemRemove() {
    }
}

The description provider for the remove operation is simple and quite similar to that of the add handler where just name of the method changes.

Registering the subsystem child

The type child does not exist in our skeleton project so we need to implement the operations to add and remove them from the model.

First we need an add operation to add the type child, create a class called com.acme.corp.tracker.extension.TypeAddHandler. In this case we extend the org.jboss.as.controller.AbstractAddStepHandler class and implement the org.jboss.as.controller.descriptions.DescriptionProvider interface. org.jboss.as.controller.OperationStepHandler is the main interface for the operation handlers, and AbstractAddStepHandler is an implementation of that which does the plumbing work for adding a resource to the model.

class TypeAddHandler extends AbstractAddStepHandler implements DescriptionProvider {
 
    public static final TypeAddHandler INSTANCE = new TypeAddHandler();
 
    private TypeAddHandler() {
    }

Then we define subsystem model. Lets call it TypeDefinition and for ease of use let it extend SimpleResourceDefinition instead just implement ResourceDefinition.

public class TypeDefinition extends SimpleResourceDefinition {
 
 public static final TypeDefinition INSTANCE = new TypeDefinition();
 
 //we define attribute named tick
protected static final SimpleAttributeDefinition TICK =
new SimpleAttributeDefinitionBuilder(TrackerExtension.TICK, ModelType.LONG)
  .setAllowExpression(true)
  .setXmlName(TrackerExtension.TICK)
  .setFlags(AttributeAccess.Flag.RESTART_ALL_SERVICES)
  .setDefaultValue(new ModelNode(1000))
  .setRequired(true)
  .build();
 
private TypeDefinition(){
   super(TYPE_PATH, TrackerExtension.getResourceDescriptionResolver(TYPE),TypeAdd.INSTANCE,TypeRemove.INSTANCE);
}
 
@Override
public void registerAttributes(ManagementResourceRegistration resourceRegistration){
   resourceRegistration.registerReadWriteAttribute(TICK, null, TrackerTickHandler.INSTANCE);
}
 
}

Which will take care of describing the model for us. As you can see in example above we define SimpleAttributeDefinition named TICK, this is a mechanism to define Attributes in more type safe way and to add more common API to manipulate attributes. As you can see here we define default value of 1000 as also other constraints and capabilities. There could be other properties set such as validators, alternate names, xml name, flags for marking it attribute allows expressions and more.

Then we do the work of updating the model by implementing the populateModel() method from the AbstractAddStepHandler, which populates the model’s attribute from the operation parameters. First we get hold of the model relative to the address of this operation (we will see later that we will register it against /subsystem=tracker/type=*), so we just specify an empty relative address, and we then populate our model with the parameters from the operation. There is operation validateAndSet on AttributeDefinition that helps us validate and set the model based on definition of the attribute.

@Override
    protected void populateModel(ModelNode operation, ModelNode model) throws OperationFailedException {
         TICK.validateAndSet(operation,model);
    }

We then override the performRuntime() method to perform our runtime changes, which in this case involves installing a service into the controller at the heart of WildFly. ( AbstractAddStepHandler.performRuntime() is similar to AbstractBoottimeAddStepHandler.performBoottime() in that the model is updated before runtime changes are made.

@Override
    protected void performRuntime(OperationContext context, ModelNode operation, ModelNode model,
            ServiceVerificationHandler verificationHandler, List<ServiceController<?>> newControllers)
            throws OperationFailedException {
        String suffix = PathAddress.pathAddress(operation.get(ModelDescriptionConstants.ADDRESS)).getLastElement().getValue();
        long tick = TICK.resolveModelAttribute(context,model).asLong();
        TrackerService service = new TrackerService(suffix, tick);
        ServiceName name = TrackerService.createServiceName(suffix);
        ServiceController<TrackerService> controller = context.getServiceTarget()
                .addService(name, service)
                .addListener(verificationHandler)
                .setInitialMode(Mode.ACTIVE)
                .install();
        newControllers.add(controller);
    }
}

Since the add methods will be of the format /subsystem=tracker/suffix=war:add(tick=1234), we look for the last element of the operation address, which is war in the example just given and use that as our suffix. We then create an instance of TrackerService and install that into the service target of the context and add the created service controller to the newControllers list.

The tracker service is quite simple. All services installed into WildFly must implement the org.jboss.msc.service.Service interface.

public class TrackerService implements Service<TrackerService>{

We then have some fields to keep the tick count and a thread which when run outputs all the deployments registered with our service.

private AtomicLong tick = new AtomicLong(10000);
 
    private Set<String> deployments = Collections.synchronizedSet(new HashSet<String>());
    private Set<String> coolDeployments = Collections.synchronizedSet(new HashSet<String>());
    private final String suffix;
 
    private Thread OUTPUT = new Thread() {
        @Override
        public void run() {
            while (true) {
                try {
                    Thread.sleep(tick.get());
                    System.out.println("Current deployments deployed while " + suffix + " tracking active:\n" + deployments
                       + "\nCool: " + coolDeployments.size());
                } catch (InterruptedException e) {
                    interrupted();
                    break;
                }
            }
        }
    };
 
    public TrackerService(String suffix, long tick) {
        this.suffix = suffix;
        this.tick.set(tick);
    }

Next we have three methods which come from the Service interface. getValue() returns this service, start() is called when the service is started by the controller, stop is called when the service is stopped by the controller, and they start and stop the thread outputting the deployments.

@Override
    public TrackerService getValue() throws IllegalStateException, IllegalArgumentException {
        return this;
    }
 
    @Override
    public void start(StartContext context) throws StartException {
        OUTPUT.start();
    }
 
    @Override
    public void stop(StopContext context) {
        OUTPUT.interrupt();
    }

Next we have a utility method to create the ServiceName which is used to register the service in the controller.

public static ServiceName createServiceName(String suffix) {
        return ServiceName.JBOSS.append("tracker", suffix);
}

Finally we have some methods to add and remove deployments, and to set and read the tick. The 'cool' deployments will be explained later.

public void addDeployment(String name) {
        deployments.add(name);
    }
 
    public void addCoolDeployment(String name) {
        coolDeployments.add(name);
    }
 
    public void removeDeployment(String name) {
        deployments.remove(name);
        coolDeployments.remove(name);
    }
 
    void setTick(long tick) {
        this.tick.set(tick);
    }
 
    public long getTick() {
        return this.tick.get();
    }
}//TrackerService - end

Since we are able to add type children, we need a way to be able to remove them, so we create a com.acme.corp.tracker.extension.TypeRemoveHandler. In this case we extend AbstractRemoveStepHandler which takes care of removing the resource from the model so we don’t need to override its performRemove() operationa. But we need to implement the DescriptionProvider method to provide the model description, and since the add handler installs the TrackerService, we need to remove that in the performRuntime() method.

public class TypeRemoveHandler extends AbstractRemoveStepHandler {
 
    public static final TypeRemoveHandler INSTANCE = new TypeRemoveHandler();
 
    private TypeRemoveHandler() {
    }
 
 
    @Override
    protected void performRuntime(OperationContext context, ModelNode operation, ModelNode model) throws OperationFailedException {
        String suffix = PathAddress.pathAddress(operation.get(ModelDescriptionConstants.ADDRESS)).getLastElement().getValue();
        ServiceName name = TrackerService.createServiceName(suffix);
        context.removeService(name);
    }
 
}

We then need a description provider for the type part of the model itself, so we modify TypeDefinitnion to registerAttribute

class TypeDefinition{
...
@Override
public void registerAttributes(ManagementResourceRegistration resourceRegistration){
    resourceRegistration.registerReadWriteAttribute(TICK, null, TrackerTickHandler.INSTANCE);
}
 
}

Then finally we need to specify that our new type child and associated handlers go under /subsystem=tracker/type=* in the model by adding registering it with the model in SubsystemExtension.initialize(). So we add the following just before the end of the method.

@Override
public void initialize(ExtensionContext context)
{
 final SubsystemRegistration subsystem = context.registerSubsystem(SUBSYSTEM_NAME, 1, 0);
 final ManagementResourceRegistration registration = subsystem.registerSubsystemModel(TrackerSubsystemDefinition.INSTANCE);
 //Add the type child
 ManagementResourceRegistration typeChild = registration.registerSubModel(TypeDefinition.INSTANCE);
 subsystem.registerXMLElementWriter(parser);
}

The above first creates a child of our main subsystem registration for the relative address type=*, and gets the typeChild registration.
To this we add the TypeAddHandler and TypeRemoveHandler.
The add variety is added under the name add and the remove handler under the name remove, and for each registered operation handler we use the handler singleton instance as both the handler parameter and as the DescriptionProvider.

Finally, we register tick as a read/write attribute, the null parameter means we don’t do anything special with regards to reading it, for the write handler we supply it with an operation handler called TrackerTickHandler.
Registering it as a read/write attribute means we can use the :write-attribute operation to modify the value of the parameter, and it will be handled by TrackerTickHandler.

Not registering a write attribute handler makes the attribute read only.

TrackerTickHandler extends AbstractWriteAttributeHandler
directly, and so must implement its applyUpdateToRuntime and revertUpdateToRuntime method.
This takes care of model manipulation (validation, setting) but leaves us to do just to deal with what we need to do.

class TrackerTickHandler extends AbstractWriteAttributeHandler<Void> {
 
    public static final TrackerTickHandler INSTANCE = new TrackerTickHandler();
 
    private TrackerTickHandler() {
        super(TypeDefinition.TICK);
    }
 
    protected boolean applyUpdateToRuntime(OperationContext context, ModelNode operation, String attributeName,
              ModelNode resolvedValue, ModelNode currentValue, HandbackHolder<Void> handbackHolder) throws OperationFailedException {
 
        modifyTick(context, operation, resolvedValue.asLong());
 
        return false;
    }
 
    protected void revertUpdateToRuntime(OperationContext context, ModelNode operation, String attributeName, ModelNode valueToRestore, ModelNode valueToRevert, Void handback){
        modifyTick(context, operation, valueToRestore.asLong());
    }
 
    private void modifyTick(OperationContext context, ModelNode operation, long value) throws OperationFailedException {
 
        final String suffix = PathAddress.pathAddress(operation.get(ModelDescriptionConstants.ADDRESS)).getLastElement().getValue();
        TrackerService service = (TrackerService) context.getServiceRegistry(true).getRequiredService(TrackerService.createServiceName(suffix)).getValue();
        service.setTick(value);
    }
 
}

The operation used to execute this will be of the form /subsystem=tracker/type=war:write-attribute(name=tick,value=12345) so we first get the suffix from the operation address, and the tick value from the operation parameter’s resolvedValue parameter, and use that to update the model.

We then add a new step associated with the RUNTIME stage to update the tick of the TrackerService for our suffix. This is essential since the call to context.getServiceRegistry() will fail unless the step accessing it belongs to the RUNTIME stage.

Note
 When implementing execute(), you must call context.completeStep() when you are done.

Parsing and marshalling of the subsystem xml

WildFly uses the Stax API to parse the xml files. This is initialized in SubsystemExtension by mapping our parser onto our namespace:

public class SubsystemExtension implements Extension {
 
    /** The name space used for the {@code subsystem} element */
    public static final String NAMESPACE = "urn:com.acme.corp.tracker:1.0";
    ...
    protected static final PathElement SUBSYSTEM_PATH = PathElement.pathElement(SUBSYSTEM, SUBSYSTEM_NAME);
    protected static final PathElement TYPE_PATH = PathElement.pathElement(TYPE);
 
   /** The parser used for parsing our subsystem */
    private final SubsystemParser parser = new SubsystemParser();
 
   @Override
    public void initializeParsers(ExtensionParsingContext context) {
        context.setSubsystemXmlMapping(NAMESPACE, parser);
    }
    ...

We then need to write the parser. The contract is that we read our subsystem’s xml and create the operations that will populate the model with the state contained in the xml. These operations will then be executed on our behalf as part of the parsing process. The entry point is the readElement() method.

public class SubsystemExtension implements Extension {
 
    /**
     * The subsystem parser, which uses stax to read and write to and from xml
     */
    private static class SubsystemParser implements XMLStreamConstants, XMLElementReader<List<ModelNode>>, XMLElementWriter<SubsystemMarshallingContext> {
 
        /** {@inheritDoc} */
        @Override
        public void readElement(XMLExtendedStreamReader reader, List<ModelNode> list) throws XMLStreamException {
            // Require no attributes
            ParseUtils.requireNoAttributes(reader);
 
            //Add the main subsystem 'add' operation
            final ModelNode subsystem = new ModelNode();
            subsystem.get(OP).set(ADD);
            subsystem.get(OP_ADDR).set(PathAddress.pathAddress(SUBSYSTEM_PATH).toModelNode());
            list.add(subsystem);
 
            //Read the children
            while (reader.hasNext() && reader.nextTag() != END_ELEMENT) {
                if (!reader.getLocalName().equals("deployment-types")) {
                    throw ParseUtils.unexpectedElement(reader);
                }
                while (reader.hasNext() && reader.nextTag() != END_ELEMENT) {
                    if (reader.isStartElement()) {
                        readDeploymentType(reader, list);
                    }
                }
            }
        }
 
        private void readDeploymentType(XMLExtendedStreamReader reader, List<ModelNode> list) throws XMLStreamException {
            if (!reader.getLocalName().equals("deployment-type")) {
                throw ParseUtils.unexpectedElement(reader);
            }
            ModelNode addTypeOperation = new ModelNode();
            addTypeOperation.get(OP).set(ModelDescriptionConstants.ADD);
 
            String suffix = null;
            for (int i = 0; i < reader.getAttributeCount(); i++) {
                String attr = reader.getAttributeLocalName(i);
                String value = reader.getAttributeValue(i);
                if (attr.equals("tick")) {
                    TypeDefinition.TICK.parseAndSetParameter(value, addTypeOperation, reader);
                } else if (attr.equals("suffix")) {
                    suffix = value;
                } else {
                    throw ParseUtils.unexpectedAttribute(reader, i);
                }
            }
            ParseUtils.requireNoContent(reader);
            if (suffix == null) {
                throw ParseUtils.missingRequiredElement(reader, Collections.singleton("suffix"));
            }
 
            //Add the 'add' operation for each 'type' child
            PathAddress addr = PathAddress.pathAddress(SUBSYSTEM_PATH, PathElement.pathElement(TYPE, suffix));
            addTypeOperation.get(OP_ADDR).set(addr.toModelNode());
            list.add(addTypeOperation);
        }
        ...

So in the above we always create the add operation for our subsystem. Due to its address /subsystem=tracker defined by SUBSYSTEM_PATH this will trigger the SubsystemAddHandler we created earlier when we invoke /subsystem=tracker:add. We then parse the child elements and create an add operation for the child address for each type child. Since the address will for example be /subsystem=tracker/type=sar (defined by TYPE_PATH ) and TypeAddHandler is registered for all type subaddresses the TypeAddHandler will get invoked for those operations. Note that when we are parsing attribute tick we are using definition of attribute that we defined in TypeDefintion to parse attribute value and apply all rules that we specified for this attribute, this also enables us to property support expressions on attributes.

The parser is also used to marshal the model to xml whenever something modifies the model, for which the entry point is the writeContent() method:

private static class SubsystemParser implements XMLStreamConstants, XMLElementReader<List<ModelNode>>, XMLElementWriter<SubsystemMarshallingContext> {
        ...
        /** {@inheritDoc} */
        @Override
        public void writeContent(final XMLExtendedStreamWriter writer, final SubsystemMarshallingContext context) throws XMLStreamException {
            //Write out the main subsystem element
            context.startSubsystemElement(TrackerExtension.NAMESPACE, false);
            writer.writeStartElement("deployment-types");
            ModelNode node = context.getModelNode();
            ModelNode type = node.get(TYPE);
            for (Property property : type.asPropertyList()) {
 
                //write each child element to xml
                writer.writeStartElement("deployment-type");
                writer.writeAttribute("suffix", property.getName());
                ModelNode entry = property.getValue();
                TypeDefinition.TICK.marshallAsAttribute(entry, true, writer);
                writer.writeEndElement();
            }
            //End deployment-types
            writer.writeEndElement();
            //End subsystem
            writer.writeEndElement();
        }
    }

Then we have to implement the SubsystemDescribeHandler which translates the current state of the model into operations similar to the ones created by the parser. The SubsystemDescribeHandler is only used when running in a managed domain, and is used when the host controller queries the domain controller for the configuration of the profile used to start up each server. In our case the SubsystemDescribeHandler adds the operation to add the subsystem and then adds the operation to add each type child. Since we are using ResourceDefinitinon for defining subsystem all that is generated for us, but if you want to customize that you can do it by implementing it like this.

private static class SubsystemDescribeHandler implements OperationStepHandler, DescriptionProvider {
        static final SubsystemDescribeHandler INSTANCE = new SubsystemDescribeHandler();
 
        public void execute(OperationContext context, ModelNode operation) throws OperationFailedException {
            //Add the main operation
            context.getResult().add(createAddSubsystemOperation());
 
            //Add the operations to create each child
 
            ModelNode node = context.readModel(PathAddress.EMPTY_ADDRESS);
            for (Property property : node.get("type").asPropertyList()) {
 
                ModelNode addType = new ModelNode();
                addType.get(OP).set(ModelDescriptionConstants.ADD);
                PathAddress addr = PathAddress.pathAddress(SUBSYSTEM_PATH, PathElement.pathElement("type", property.getName()));
                addType.get(OP_ADDR).set(addr.toModelNode());
                if (property.getValue().hasDefined("tick")) {
                   TypeDefinition.TICK.validateAndSet(property,addType);
                }
                context.getResult().add(addType);
            }
            context.completeStep();
        }
 
 
}

Testing the parsers

Changes to tests between 7.0.0 and 7.0.1

Note
 The testing framework was moved from the archetype into the core JBoss AS 7 sources between JBoss AS 7.0.0 and JBoss AS 7.0.1, and has been improved upon and is used internally for testing JBoss AS 7’s subsystems. The differences between the two versions is that in 7.0.0.Final the testing framework is bundled with the code generated by the archetype (in a sub-package of the package specified for your subsystem, e.g. com.acme.corp.tracker.support), and the test extends the AbstractParsingTest class.

From 7.0.1 the testing framework is now brought in via the org.jboss.as:jboss-as-subsystem-test maven artifact, and the test’s superclass is org.jboss.as.subsystem.test.AbstractSubsystemTest. The concepts are the same but more and more functionality will be available as JBoss AS 7 is developed.

Now that we have modified our parsers we need to update our tests to reflect the new model. There are currently three tests testing the basic functionality, something which is a lot easier to debug from your IDE before you plug it into the application server. We will talk about these tests in turn and they all live in com.acme.corp.tracker.extension.SubsystemParsingTestCase. SubsystemParsingTestCase extends AbstractSubsystemTest which does a lot of the setup for you and contains utility methods for verifying things from your test. See the javadoc of that class for more information about the functionality available to you. And by all means feel free to add more tests for your subsystem, here we are only testing for the best case scenario while you will probably want to throw in a few tests for edge cases.

The first test we need to modify is testParseSubsystem(). It tests that the parsed xml becomes the expected operations that will be parsed into the server, so let us tweak this test to match our subsystem. First we tell the test to parse the xml into operations

@Test
    public void testParseSubsystem() throws Exception {
        //Parse the subsystem xml into operations
        String subsystemXml =
                "<subsystem xmlns=\"" + SubsystemExtension.NAMESPACE + "\">" +
                "   <deployment-types>" +
                "       <deployment-type suffix=\"tst\" tick=\"12345\"/>" +
                "   </deployment-types>" +
                "</subsystem>";
        List<ModelNode> operations = super.parse(subsystemXml);

There should be one operation for adding the subsystem itself and an operation for adding the deployment-type, so check we got two operations

///Check that we have the expected number of operations
        Assert.assertEquals(2, operations.size());

Now check that the first operation is add for the address /subsystem=tracker:

//Check that each operation has the correct content
        //The add subsystem operation will happen first
        ModelNode addSubsystem = operations.get(0);
        Assert.assertEquals(ADD, addSubsystem.get(OP).asString());
        PathAddress addr = PathAddress.pathAddress(addSubsystem.get(OP_ADDR));
        Assert.assertEquals(1, addr.size());
        PathElement element = addr.getElement(0);
        Assert.assertEquals(SUBSYSTEM, element.getKey());
        Assert.assertEquals(SubsystemExtension.SUBSYSTEM_NAME, element.getValue());

Then check that the second operation is add for the address /subsystem=tracker, and that 12345 was picked up for the value of the tick parameter:

//Then we will get the add type operation
        ModelNode addType = operations.get(1);
        Assert.assertEquals(ADD, addType.get(OP).asString());
        Assert.assertEquals(12345, addType.get("tick").asLong());
        addr = PathAddress.pathAddress(addType.get(OP_ADDR));
        Assert.assertEquals(2, addr.size());
        element = addr.getElement(0);
        Assert.assertEquals(SUBSYSTEM, element.getKey());
        Assert.assertEquals(SubsystemExtension.SUBSYSTEM_NAME, element.getValue());
        element = addr.getElement(1);
        Assert.assertEquals("type", element.getKey());
        Assert.assertEquals("tst", element.getValue());
    }

The second test we need to modify is testInstallIntoController() which tests that the xml installs properly into the controller. In other words we are making sure that the add operations we created earlier work properly. First we create the xml and install it into the controller. Behind the scenes this will parse the xml into operations as we saw in the last test, but it will also create a new controller and boot that up using the created operations

@Test
    public void testInstallIntoController() throws Exception {
        //Parse the subsystem xml and install into the controller
        String subsystemXml =
                "<subsystem xmlns=\"" + SubsystemExtension.NAMESPACE + "\">" +
                "   <deployment-types>" +
                "       <deployment-type suffix=\"tst\" tick=\"12345\"/>" +
                "   </deployment-types>" +
                "</subsystem>";
        KernelServices services = super.installInController(subsystemXml);

The returned KernelServices allow us to execute operations on the controller, and to read the whole model.

//Read the whole model and make sure it looks as expected
        ModelNode model = services.readWholeModel();
        //Useful for debugging :-)
        //System.out.println(model);

Now we make sure that the structure of the model within the controller has the expected format and values

Assert.assertTrue(model.get(SUBSYSTEM).hasDefined(SubsystemExtension.SUBSYSTEM_NAME));
        Assert.assertTrue(model.get(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME).hasDefined("type"));
        Assert.assertTrue(model.get(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME, "type").hasDefined("tst"));
        Assert.assertTrue(model.get(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME, "type", "tst").hasDefined("tick"));
        Assert.assertEquals(12345, model.get(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME, "type", "tst", "tick").asLong());
    }

The last test provided is called testParseAndMarshalModel(). It’s main purpose is to make sure that our SubsystemParser.writeContent() works as expected. This is achieved by starting a controller in the same way as before

@Test
    public void testParseAndMarshalModel() throws Exception {
        //Parse the subsystem xml and install into the first controller
        String subsystemXml =
                "<subsystem xmlns=\"" + SubsystemExtension.NAMESPACE + "\">" +
                "   <deployment-types>" +
                "       <deployment-type suffix=\"tst\" tick=\"12345\"/>" +
                "   </deployment-types>" +
                "</subsystem>";
        KernelServices servicesA = super.installInController(subsystemXml);

Now we read the model and the xml that was persisted from the first controller, and use that xml to start a second controller

//Get the model and the persisted xml from the first controller
        ModelNode modelA = servicesA.readWholeModel();
        String marshalled = servicesA.getPersistedSubsystemXml();
 
        //Install the persisted xml from the first controller into a second controller
        KernelServices servicesB = super.installInController(marshalled);

Finally we read the model from the second controller, and make sure that the models are identical by calling compare() on the test superclass.

ModelNode modelB = servicesB.readWholeModel();
 
        //Make sure the models from the two controllers are identical
        super.compare(modelA, modelB);
    }

We then have a test that needs no changing from what the archetype provides us with. As we have seen before we start a controller

@Test
    public void testDescribeHandler() throws Exception {
        //Parse the subsystem xml and install into the first controller
        String subsystemXml =
                "<subsystem xmlns=\"" + SubsystemExtension.NAMESPACE + "\">" +
                "</subsystem>";
        KernelServices servicesA = super.installInController(subsystemXml);

We then call /subsystem=tracker:describe which outputs the subsystem as operations needed to reach the current state (Done by our SubsystemDescribeHandler)

//Get the model and the describe operations from the first controller
        ModelNode modelA = servicesA.readWholeModel();
        ModelNode describeOp = new ModelNode();
        describeOp.get(OP).set(DESCRIBE);
        describeOp.get(OP_ADDR).set(
                PathAddress.pathAddress(
                        PathElement.pathElement(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME)).toModelNode());
        List<ModelNode> operations = super.checkResultAndGetContents(servicesA.executeOperation(describeOp)).asList();

Then we create a new controller using those operations

//Install the describe options from the first controller into a second controller
        KernelServices servicesB = super.installInController(operations);

And then we read the model from the second controller and make sure that the two subsystems are identical
ModelNode modelB = servicesB.readWholeModel();

//Make sure the models from the two controllers are identical
        super.compare(modelA, modelB);
 
    }

To test the removal of the the subsystem and child resources we modify the testSubsystemRemoval() test provided by the archetype:

/**
     * Tests that the subsystem can be removed
     */
    @Test
    public void testSubsystemRemoval() throws Exception {
        //Parse the subsystem xml and install into the first controller

We provide xml for the subsystem installing a child, which in turn installs a TrackerService

String subsystemXml =
                "<subsystem xmlns=\"" + SubsystemExtension.NAMESPACE + "\">" +
                "   <deployment-types>" +
                "       <deployment-type suffix=\"tst\" tick=\"12345\"/>" +
                "   </deployment-types>" +
                "</subsystem>";
        KernelServices services = super.installInController(subsystemXml);

Having installed the xml into the controller we make sure the TrackerService is there

//Sanity check to test the service for 'tst' was there
        services.getContainer().getRequiredService(TrackerService.createServiceName("tst"));

This call from the subsystem test harness will call remove for each level in our subsystem, children first and validate
that the subsystem model is empty at the end.

//Checks that the subsystem was removed from the model
        super.assertRemoveSubsystemResources(services);

Finally we check that all the services were removed by the remove handlers

//Check that any services that were installed were removed here
        try {
            services.getContainer().getRequiredService(TrackerService.createServiceName("tst"));
            Assert.fail("Should have removed services");
        } catch (Exception expected) {
        }
    }

For good measure let us throw in another test which adds a deployment-type and also changes its attribute at runtime. So first of all boot up the controller with the same xml we have been using so far

@Test
    public void testExecuteOperations() throws Exception {
        String subsystemXml =
                "<subsystem xmlns=\"" + SubsystemExtension.NAMESPACE + "\">" +
                "   <deployment-types>" +
                "       <deployment-type suffix=\"tst\" tick=\"12345\"/>" +
                "   </deployment-types>" +
                "</subsystem>";
        KernelServices services = super.installInController(subsystemXml);

Now create an operation which does the same as the following CLI command /subsystem=tracker/type=foo:add(tick=1000)

//Add another type
        PathAddress fooTypeAddr = PathAddress.pathAddress(
                PathElement.pathElement(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME),
                PathElement.pathElement("type", "foo"));
        ModelNode addOp = new ModelNode();
        addOp.get(OP).set(ADD);
        addOp.get(OP_ADDR).set(fooTypeAddr.toModelNode());
        addOp.get("tick").set(1000);

Execute the operation and make sure it was successful

ModelNode result = services.executeOperation(addOp);
        Assert.assertEquals(SUCCESS, result.get(OUTCOME).asString());

Read the whole model and make sure that the original data is still there (i.e. the same as what was done by testInstallIntoController()

ModelNode model = services.readWholeModel();
        Assert.assertTrue(model.get(SUBSYSTEM).hasDefined(SubsystemExtension.SUBSYSTEM_NAME));
        Assert.assertTrue(model.get(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME).hasDefined("type"));
        Assert.assertTrue(model.get(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME, "type").hasDefined("tst"));
        Assert.assertTrue(model.get(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME, "type", "tst").hasDefined("tick"));
        Assert.assertEquals(12345, model.get(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME, "type", "tst", "tick").asLong());

Then make sure our new type has been added:

Assert.assertTrue(model.get(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME, "type").hasDefined("foo"));
        Assert.assertTrue(model.get(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME, "type", "foo").hasDefined("tick"));
        Assert.assertEquals(1000, model.get(SUBSYSTEM, SubsystemExtension.SUBSYSTEM_NAME, "type", "foo", "tick").asLong());

Then we call write-attribute to change the tick value of /subsystem=tracker/type=foo:

//Call write-attribute
        ModelNode writeOp = new ModelNode();
        writeOp.get(OP).set(WRITE_ATTRIBUTE_OPERATION);
        writeOp.get(OP_ADDR).set(fooTypeAddr.toModelNode());
        writeOp.get(NAME).set("tick");
        writeOp.get(VALUE).set(3456);
        result = services.executeOperation(writeOp);
        Assert.assertEquals(SUCCESS, result.get(OUTCOME).asString());

To give you exposure to other ways of doing things, now instead of reading the whole model to check the attribute, we call read-attribute instead, and make sure it has the value we set it to.

//Check that write attribute took effect, this time by calling read-attribute instead of reading the whole model
        ModelNode readOp = new ModelNode();
        readOp.get(OP).set(READ_ATTRIBUTE_OPERATION);
        readOp.get(OP_ADDR).set(fooTypeAddr.toModelNode());
        readOp.get(NAME).set("tick");
        result = services.executeOperation(readOp);
        Assert.assertEquals(3456, checkResultAndGetContents(result).asLong());

Since each type installs its own copy of TrackerService, we get the TrackerService for type=foo from the service container exposed by the kernel services and make sure it has the right value

TrackerService service = (TrackerService)services.getContainer().getService(TrackerService.createServiceName("foo")).getValue();
        Assert.assertEquals(3456, service.getTick());
    }

TypeDefinition.TICK.

Add the deployers

When discussing SubsystemAddHandler we did not mention the work done to install the deployers, which is done in the following method:

    @Override
    public void performBoottime(OperationContext context, ModelNode operation, ModelNode model,
            ServiceVerificationHandler verificationHandler, List<ServiceController<?>> newControllers)
            throws OperationFailedException {
 
        log.info("Populating the model");
 
        //Add deployment processors here
        //Remove this if you don't need to hook into the deployers, or you can add as many as you like
        //see SubDeploymentProcessor for explanation of the phases
        context.addStep(new AbstractDeploymentChainStep() {
            public void execute(DeploymentProcessorTarget processorTarget) {
                processorTarget.addDeploymentProcessor(SubsystemDeploymentProcessor.PHASE, SubsystemDeploymentProcessor.priority, new SubsystemDeploymentProcessor());
 
            }
        }, OperationContext.Stage.RUNTIME);
 
    }

This adds an extra step which is responsible for installing deployment processors. You can add as many as you like, or avoid adding any all together depending on your needs. Each processor has a Phase and a priority. Phases are sequential, and a deployment passes through each phases deployment processors. The priority specifies where within a phase the processor appears. See org.jboss.as.server.deployment.Phase for more information about phases.

In our case we are keeping it simple and staying with one deployment processor with the phase and priority created for us by the maven archetype. The phases will be explained in the next section. The deployment processor is as follows:

public class SubsystemDeploymentProcessor implements DeploymentUnitProcessor {
    ...
 
    @Override
    public void deploy(DeploymentPhaseContext phaseContext) throws DeploymentUnitProcessingException {
        String name = phaseContext.getDeploymentUnit().getName();
        TrackerService service = getTrackerService(phaseContext.getServiceRegistry(), name);
        if (service != null) {
            ResourceRoot root = phaseContext.getDeploymentUnit().getAttachment(Attachments.DEPLOYMENT_ROOT);
            VirtualFile cool = root.getRoot().getChild("META-INF/cool.txt");
            service.addDeployment(name);
            if (cool.exists()) {
                service.addCoolDeployment(name);
            }
        }
    }
 
    @Override
    public void undeploy(DeploymentUnit context) {
        context.getServiceRegistry();
        String name = context.getName();
        TrackerService service = getTrackerService(context.getServiceRegistry(), name);
        if (service != null) {
            service.removeDeployment(name);
        }
    }
 
    private TrackerService getTrackerService(ServiceRegistry registry, String name) {
        int last = name.lastIndexOf(".");
        String suffix = name.substring(last + 1);
        ServiceController<?> container = registry.getService(TrackerService.createServiceName(suffix));
        if (container != null) {
            TrackerService service = (TrackerService)container.getValue();
            return service;
        }
        return null;
    }
}

The deploy() method is called when a deployment is being deployed. In this case we look for the TrackerService instance for the service name created from the deployment’s suffix. If there is one it means that we are meant to be tracking deployments with this suffix (i.e. TypeAddHandler was called for this suffix), and if we find one we add the deployment’s name to it. Similarly undeploy() is called when a deployment is being undeployed, and if there is a TrackerService instance for the deployment’s suffix, we remove the deployment’s name from it.

Deployment phases and attachments

The code in the SubsystemDeploymentProcessor uses an attachment, which is the means of communication between the individual deployment processors. A deployment processor belonging to a phase may create an attachment which is then read further along the chain of deployment unit processors. In the above example we look for the Attachments.DEPLOYMENT_ROOT attachment, which is a view of the file structure of the deployment unit put in place before the chain of deployment unit processors is invoked.

As mentioned above, the deployment unit processors are organized in phases, and have a relative order within each phase. A deployment unit passes through all the deployment unit processors in that order. A deployment unit processor may choose to take action or not depending on what attachments are available. Let’s take a quick look at what the deployment unit processors for in the phases described in org.jboss.as.server.deployment.Phase.

STRUCTURE

The deployment unit processors in this phase determine the structure of a deployment, and looks for sub deployments and metadata files.

PARSE

In this phase the deployment unit processors parse the deployment descriptors and build up the annotation index. Class-Path entries from the META-INF/MANIFEST.MF are added.

DEPENDENCIES

Extra class path dependencies are added. For example if deploying a war file, the commonly needed dependencies for a web application are added.

CONFIGURE_MODULE

In this phase the modular class loader for the deployment is created. No attempt should be made loading classes from the deployment until after this phase.

POST_MODULE

Now that our class loader has been constructed we have access to the classes. In this stage deployment processors may use the Attachments.REFLECTION_INDEX attachment which is a deployment index used to obtain members of classes in the deployment, and to invoke upon them, bypassing the inefficiencies of using java.lang.reflect directly.

INSTALL

Install new services coming from the deployment.

CLEANUP

Attachments put in place earlier in the deployment unit processor chain may be removed here.

Integrate with WildFly

Now that we have all the code needed for our subsystem, we can build our project by running mvn install

[kabir ~/sourcecontrol/temp/archetype-test/acme-subsystem]
$mvn install
[INFO] Scanning for projects...
[...]
main:
   [delete] Deleting: /Users/kabir/sourcecontrol/temp/archetype-test/acme-subsystem/null1004283288
   [delete] Deleting directory /Users/kabir/sourcecontrol/temp/archetype-test/acme-subsystem/target/module
     [copy] Copying 1 file to /Users/kabir/sourcecontrol/temp/archetype-test/acme-subsystem/target/module/com/acme/corp/tracker/main
     [copy] Copying 1 file to /Users/kabir/sourcecontrol/temp/archetype-test/acme-subsystem/target/module/com/acme/corp/tracker/main
     [echo] Module com.acme.corp.tracker has been created in the target/module directory. Copy to your JBoss AS 7 installation.
[INFO] Executed tasks
[INFO]
[INFO] --- maven-install-plugin:2.3.1:install (default-install) @ acme-subsystem ---
[INFO] Installing /Users/kabir/sourcecontrol/temp/archetype-test/acme-subsystem/target/acme-subsystem.jar to /Users/kabir/.m2/repository/com/acme/corp/acme-subsystem/1.0-SNAPSHOT/acme-subsystem-1.0-SNAPSHOT.jar
[INFO] Installing /Users/kabir/sourcecontrol/temp/archetype-test/acme-subsystem/pom.xml to /Users/kabir/.m2/repository/com/acme/corp/acme-subsystem/1.0-SNAPSHOT/acme-subsystem-1.0-SNAPSHOT.pom
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 5.851s
[INFO] Finished at: Mon Jul 11 23:24:58 BST 2011
[INFO] Final Memory: 7M/81M
[INFO] ------------------------------------------------------------------------

This will have built our project and assembled a module for us that can be used for installing it into WildFly. If you go to the target/module folder where you built the project you will see the module

$ls target/module/com/acme/corp/tracker/main/
acme-subsystem.jar  module.xml

The module.xml comes from src/main/resources/module/main/module.xml and is used to define your module. It says that it contains the acme-subsystem.jar:

<module xmlns="urn:jboss:module:1.9" name="com.acme.corp.tracker">
    <resources>
        <resource-root path="acme-subsystem.jar"/>
    </resources>

And has a default set of dependencies needed by every subsystem created. If your subsystem requires additional module dependencies you can add them here before building and installing.

    <dependencies>
        <module name="javax.api"/>
        <module name="org.jboss.staxmapper"/>
        <module name="org.jboss.as.controller"/>
        <module name="org.jboss.as.server"/>
        <module name="org.jboss.modules"/>
        <module name="org.jboss.msc"/>
        <module name="org.jboss.logging"/>
        <module name="org.jboss.vfs"/>
    </dependencies>
</module>

Note that the name of the module corresponds to the directory structure containing it. Now copy the target/module/com/acme/corp/tracker/main/ directory and its contents to $WFLY/modules/com/acme/corp/tracker/main/ (where $WFLY is the root of your WildFly install).

Next we need to modify $WFLY/standalone/configuration/standalone.xml. First we need to add our new module to the <extensions> section:

    <extensions>
        ...
        <extension module="org.jboss.as.weld"/>
        <extension module="com.acme.corp.tracker"/>
    </extensions>

And then we have to add our subsystem to the <profile> section:

    <profile>
    ...
 
        <subsystem xmlns="urn:com.acme.corp.tracker:1.0">
            <deployment-types>
                <deployment-type suffix="sar" tick="10000"/>
                <deployment-type suffix="war" tick="10000"/>
            </deployment-types>
        </subsystem>
    ...
    </profile>

Adding this to a managed domain works exactly the same apart from in this case you need to modify $WFLY/domain/configuration/domain.xml.

Now start up WildFly by running $WFLY/bin/standalone.sh and you should see messages like these after the server has started, which means our subsystem has been added and our TrackerService is working:

15:27:33,838 INFO  [org.jboss.as] (Controller Boot Thread) JBoss AS 7.0.0.Final "Lightning" started in 2861ms - Started 94 of 149 services (55 services are passive or on-demand)
15:27:42,966 INFO  [stdout] (Thread-8) Current deployments deployed while sar tracking active:
15:27:42,966 INFO  [stdout] (Thread-8) []
15:27:42,967 INFO  [stdout] (Thread-8) Cool: 0
15:27:42,967 INFO  [stdout] (Thread-9) Current deployments deployed while war tracking active:
15:27:42,967 INFO  [stdout] (Thread-9) []
15:27:42,967 INFO  [stdout] (Thread-9) Cool: 0
15:27:52,967 INFO  [stdout] (Thread-8) Current deployments deployed while sar tracking active:
15:27:52,967 INFO  [stdout] (Thread-8) []
15:27:52,967 INFO  [stdout] (Thread-8) Cool: 0

If you run the command line interface you can execute some commands to see more about the subsystem. For example

[standalone@localhost:9999 /] /subsystem=tracker/:read-resource-description(recursive=true, operations=true)

will return a lot of information, including what we provided in the `DescriptionProvider`s we created to document our subsystem.

To see the current subsystem state you can execute

[standalone@localhost:9999 /] /subsystem=tracker/:read-resource(recursive=true)
{
    "outcome" => "success",
    "result" => {"type" => {
        "war" => {"tick" => 10000L},
        "sar" => {"tick" => 10000L}
    }}
}

We can remove both the deployment types which removes them from the model:

[standalone@localhost:9999 /] /subsystem=tracker/type=sar:remove
{"outcome" => "success"}
[standalone@localhost:9999 /] /subsystem=tracker/type=war:remove
{"outcome" => "success"}
[standalone@localhost:9999 /] /subsystem=tracker/:read-resource(recursive=true)
{
    "outcome" => "success",
    "result" => {"type" => undefined}
}

You should now see the output from the TrackerService instances having stopped.

Now, let’s add the war tracker again:

[standalone@localhost:9999 /] /subsystem=tracker/type=war:add
{"outcome" => "success"}
[standalone@localhost:9999 /] /subsystem=tracker/:read-resource(recursive=true)
{
    "outcome" => "success",
    "result" => {"type" => {"war" => {"tick" => 10000L}}}
}

and the WildFly console should show the messages coming from the war TrackerService again.

Now let us deploy something. You can find two maven projects for test wars already built at test1.zip and test2.zip. If you download them and extract them to /Downloads/test1 and /Downloads/test2, you can see that /Downloads/test1/target/test1.war contains a META-INF/cool.txt while /Downloads/test2/target/test2.war does not contain that file. From CLI deploy test1.war first:

[standalone@localhost:9999 /] deploy ~/Downloads/test1/target/test1.war
'test1.war' deployed successfully.

And you should now see the output from the war TrackerService list the deployments:

15:35:03,712 INFO  [org.jboss.as.server.deployment] (MSC service thread 1-2) Starting deployment of "test1.war"
15:35:03,988 INFO  [org.jboss.web] (MSC service thread 1-1) registering web context: /test1
15:35:03,996 INFO  [org.jboss.as.server.controller] (pool-2-thread-9) Deployed "test1.war"
15:35:13,056 INFO  [stdout] (Thread-9) Current deployments deployed while war tracking active:
15:35:13,056 INFO  [stdout] (Thread-9) [test1.war]
15:35:13,057 INFO  [stdout] (Thread-9) Cool: 1

So our test1.war got picked up as a 'cool' deployment. Now if we deploy test2.war

[standalone@localhost:9999 /] deploy ~/sourcecontrol/temp/archetype-test/test2/target/test2.war
'test2.war' deployed successfully.

You will see that deployment get picked up as well but since there is no META-INF/cool.txt it is not marked as a 'cool' deployment:

15:37:05,634 INFO  [org.jboss.as.server.deployment] (MSC service thread 1-4) Starting deployment of "test2.war"
15:37:05,699 INFO  [org.jboss.web] (MSC service thread 1-1) registering web context: /test2
15:37:05,982 INFO  [org.jboss.as.server.controller] (pool-2-thread-15) Deployed "test2.war"
15:37:13,075 INFO  [stdout] (Thread-9) Current deployments deployed while war tracking active:
15:37:13,075 INFO  [stdout] (Thread-9) [test1.war, test2.war]
15:37:13,076 INFO  [stdout] (Thread-9) Cool: 1

An undeploy

[standalone@localhost:9999 /] undeploy test1.war
Successfully undeployed test1.war.

is also reflected in the TrackerService output:

15:38:47,901 INFO  [org.jboss.as.server.controller] (pool-2-thread-21) Undeployed "test1.war"
15:38:47,934 INFO  [org.jboss.as.server.deployment] (MSC service thread 1-3) Stopped deployment test1.war in 40ms
15:38:53,091 INFO  [stdout] (Thread-9) Current deployments deployed while war tracking active:
15:38:53,092 INFO  [stdout] (Thread-9) [test2.war]
15:38:53,092 INFO  [stdout] (Thread-9) Cool: 0

Finally, we registered a write attribute handler for the tick property of the type so we can change the frequency

[standalone@localhost:9999 /] /subsystem=tracker/type=war:write-attribute(name=tick,value=1000)
{"outcome" => "success"}

You should now see the output from the TrackerService happen every second

15:39:43,100 INFO  [stdout] (Thread-9) Current deployments deployed while war tracking active:
15:39:43,100 INFO  [stdout] (Thread-9) [test2.war]
15:39:43,101 INFO  [stdout] (Thread-9) Cool: 0
15:39:44,101 INFO  [stdout] (Thread-9) Current deployments deployed while war tracking active:
15:39:44,102 INFO  [stdout] (Thread-9) [test2.war]
15:39:44,105 INFO  [stdout] (Thread-9) Cool: 0
15:39:45,106 INFO  [stdout] (Thread-9) Current deployments deployed while war tracking active:
15:39:45,106 INFO  [stdout] (Thread-9) [test2.war]

If you open $WFLY/standalone/configuration/standalone.xml you can see that our subsystem entry reflects the current state of the subsystem:

        <subsystem xmlns="urn:com.acme.corp.tracker:1.0">
            <deployment-types>
                <deployment-type suffix="war" tick="1000"/>
            </deployment-types>
        </subsystem>

Expressions

Expressions are mechanism that enables you to support variables in your attributes, for instance when you want the value of attribute to be resolved using system / environment properties.

An example expression is

${jboss.bind.address.management:127.0.0.1}

which means that the value should be taken from a system property named jboss.bind.address.management and if it is not defined use 127.0.0.1.

What expression types are supported

  • System properties, which are resolved using java.lang.System.getProperty(String key)

  • Environment properties, which are resolved using java.lang.System.getEnv(String name).

  • Encrypted expressions, resolved against the expression resolver in the elytron subsystem.

In all cases, the syntax for the expression is

${expression_to_resolve}

For an expression meant to be resolved against environment properties, the expression_to_resolve must be prefixed with env.. The portion after env. will be the name passed to java.lang.System.getEnv(String name).

Encrypted expressions do not support default values (i.e. the 127.0.0.1 in the jboss.bind.address.management:127.0.0.1 example above.)

How to support expressions in subsystems

The easiest way is by using AttributeDefinition, which provides support for expressions just by using it correctly.

When we create an AttributeDefinition all we need to do is mark that is allows expressions. Here is an example how to define an attribute that allows expressions to be used.

SimpleAttributeDefinition MY_ATTRIBUTE =
            new SimpleAttributeDefinitionBuilder("my-attribute", ModelType.INT, true)
                    .setAllowExpression(true)
                    .setFlags(AttributeAccess.Flag.RESTART_ALL_SERVICES)
                    .setDefaultValue(new ModelNode(1))
                    .build();

Then later when you are parsing the xml configuration you should use the MY_ATTRIBUTE attribute definition to set the value to the management operation ModelNode you are creating.

....
      String attr = reader.getAttributeLocalName(i);
      String value = reader.getAttributeValue(i);
      if (attr.equals("my-attribute")) {
          MY_ATTRIBUTE.parseAndSetParameter(value, operation, reader);
      } else if (attr.equals("suffix")) {
.....

Note that this just helps you to properly set the value to the model node you are working on, so no need to additionally set anything to the model for this attribute. Method parseAndSetParameter parses the value that was read from xml for possible expressions in it and if it finds any it creates special model node that defines that node is of type ModelType.EXPRESSION.

Later in your operation handlers where you implement populateModel and have to store the value from the operation to the configuration model you also use this MY_ATTRIBUTE attribute definition.

 @Override
 protected void populateModel(ModelNode operation, ModelNode model) throws OperationFailedException {
        MY_ATTRIBUTE.validateAndSet(operation,model);
 }

This will make sure that the attribute that is stored from the operation to the model is valid and nothing is lost. It also checks the value stored in the operation ModelNode, and if it isn’t already ModelType.EXPRESSION, it checks if the value is a string that contains the expression syntax. If so, the value stored in the model will be of type ModelType.EXPRESSION. Doing this ensures that expressions are properly handled when they appear in operations that weren’t created by the subsystem parser, but are instead passed in from CLI or admin console users.

As last step we need to use the value of the attribute. This is usually needed inside of the performRuntime method

 protected void performRuntime(OperationContext context, ModelNode operation, ModelNode model, ServiceVerificationHandler verificationHandler, List<ServiceController<?>> newControllers) throws OperationFailedException {
       ....
        final int attributeValue = MY_ATTRIBUTE.resolveModelAttribute(context, model).asInt();     
        ...
 
    }

As you can see resolving of attribute’s value is not done until it is needed for use in the subsystem’s runtime services. The resolved value is not stored in the configuration model, the unresolved expression is. That way we do not lose any information in the model and can assure that also marshalling is done properly, where we must marshall back the unresolved value.

Attribute definitinon also helps you with that:

 public void writeContent(XMLExtendedStreamWriter writer, SubsystemMarshallingContext context) throws XMLStreamException {
    ....
      MY_ATTRIBUTE.marshallAsAttribute(sessionData, writer);
      MY_OTHER_ATTRIBUTE.marshallAsElement(sessionData, false, writer);
    ...
}