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This is a guide for developers who would like to extend Tuscany SCA Java.

• What is an extension?
• How to add a new component implementation?
• How to add a new binding?
• How to add a new interface binding?

• How to add a databinding
• How to add a new monitor extension?
• General guide for developing extensions
• Details on extension architecture can move to architecture doc
• Extension Modules

private void analyseProblems() throws Exception {        
    for (Problem problem : monitor.getProblems()){
        // look for any reported errors. Schema errors are filtered
        // out as there are several that are generally reported at the
        // moment and we don't want to stop 
        if ((problem.getSeverity() == Severity.ERROR) && (!problem.getMessageId().equals("SchemaError"))) {
            if (problem.getCause() != null){
                throw new Exception(problem.getCause());
            } else {
                throw new Exception(problem.toString());
            }    
        }
    }
}

public class MyMonitorImpl implements Monitor {
    private static final Logger logger = Logger.getLogger(DefaultMonitorImpl.class.getName());    
    // Cache all the problem reported to monitor for further analysis
    private List<Problem> problemCache = new ArrayList<Problem>();
    public void problem(Problem problem) {
        // Your custom code to handle the problem
    }
    // Returns a list of reported problems.
    public List<Problem> getProblems(){
        return problemCache;
    }
}

public class MyMonitorFactoryImpl implements MonitorFactory {    
    private Monitor monitor = null;
    public Monitor createMonitor() {
        if (monitor == null) {
            monitor = new MyMonitorImpl();
        }
        return monitor ;
    }
}

UtilityExtensionPoint utilities = extensionPoints.getExtensionPoint(UtilityExtensionPoint.class);
MonitorFactory monitorFactory = utilities.getUtility(MonitorFactory.class);
monitor = monitorFactory.createMonitor();

{panel:title=Apache Tuscany SCA Java Extension Guide |borderStyle=solid|borderColor=#C3CDA1|titleBGColor=#C3CDA1|bgColor=#ECF4D1}

This is a guide for developers who would like to extend Tuscany SCA Java.
* [What is an extension?|#extension]
* [How to add a new component implementation? | #component]
* [How to add a new binding? |#binding]
* [How to add a new interface binding? |#interface]

* [How to add a databinding | #databinding ]
* [General guide for developing extensions| #general guide]
* [Details on extension architecture|#details] *can move to architecture doc*
* [Extension Modules| Java SCA Extension Modules]
* [Extension Modules| Java SCA Extension Modules]
{panel}

{note:title:Notification}{center}This page is under construction\- You are welcome to help and complete it{center}{note}

h3. {anchor:extension}{bgcolor:#C3CDA1}A presentation on how to extend Tuscany in Microsoft PowerPoint format{bgcolor}
*Extending Tuscany* [PPT|^ExtendingTuscany.ppt] [PDF|^ExtendingTuscany-V01.pdf]


h3. {anchor:extension}{bgcolor:#C3CDA1}What is an extension?{bgcolor}

Extension is a module (or a set of modules),when built with Tuscany SCA, can extend it to work with additional bindings, language implementations, programming models or databindings.

SCA assembly model is defined such that extensions can be added for new interface types or for new implementation types such as ruby and python, or new binding types such as CXF. However, the definition of extension SPIs is left to the implementor. Tuscany SCA Java provides a simple set of SPIs for implementing extensions. It also defines additional extension points such as data binding, for example support for SDO and JAXB.

This guide explains the steps to add each of these extension types. Please help us refine the guide as you go through the steps of adding extensions.

h4. Name spaces used by extensions


h3. {anchor:component}{bgcolor:#C3CDA1}How to add a new component implementation?{bgcolor}

[Musings on Adding a New Component Type by Mike E|Mike Edwards Ramble through Adding a New Component Type] 

h3. {anchor:binding}{bgcolor:#C3CDA1}How to add a new binding?{bgcolor}


h3. {anchor:interface}{bgcolor:#C3CDA1}How to add a new interface binding?{bgcolor}


h3. {anchor:databinding}{bgcolor:#C3CDA1}How to add a new databinding?{bgcolor}


h3. {anchor:general guide}{bgcolor:#C3CDA1}General guide for developing extensions{bgcolor}

* Familiarize yourself with SCA 1.0 Assembly and the SCA Java 1.0 programming model. Specifications can be found at www.osoa.org.
* Never reference any classes in core. These classes are implementation-specific and subject to change; they are not part of the public SPI contract.
* Use autowire when assembling extension components.
* Do not play with classloaders such as setting the current context classloader unless it is absolutely necessary, i.e. a library used by an extension makes assumptions about context classloaders. Ideally the library can be refactored to not make these assumptions. If not, make sure the extension properly resets the current context classloader.

h3. {anchor:details}{bgcolor:#C3CDA1}Detail on extension architecture{bgcolor}


h4. The ExtensionPointRegistry

{code}
package org.apache.tuscany.sca.core;


/**
 * The registry for the Tuscany core extension points. As the point of contact
 * for all extension artifacts this registry allows loaded extensions to find
 * all other parts of the system and register themselves appropriately.
 *
 * @version $Rev: 539355 $ $Date: 2007-05-18 03:05:14 -0700 (Fri, 18 May 2007) $
 */
public interface ExtensionPointRegistry {

    /**
     * Add an extension point to the registry
     * @param extensionPoint The instance of the extension point
     */
    void addExtensionPoint(Object extensionPoint);

    /**
     * Get the extension point by the interface
     * @param extensionPointType The lookup key (extension point interface)
     * @return The instance of the extension point
     */
    <T> T getExtensionPoint(Class<T> extensionPointType);

    /**
     * Remove an extension point
     * @param extensionPoint The extension point to remove
     */
    void removeExtensionPoint(Object extensionPoint);
}
{code}

h4. The ModuleActivator

{code}

package org.apache.tuscany.sca.core;

import java.util.Map;

/**
 * ModuleActivator represents a module that plugs into the Tuscany system. Each
* module should
 * provide an implementation of this interface and registryregister the
* ModuleActivator implementation class by defining
 * a file named
*
* as "META-INF/services/org.apache.tuscany.spi.bootstrpcore.ModuleActivator".
*
* The
 * content of the file is the class name of the ModuleActivator implementation.
* The implementation class must
 * have a no-arg constructor. The same instance
* will be used to invoke all the methods during
 * different phases of the module
* activation.
 *
Note *that @versionthe $Rev:start 529327and $stop $Date: 2007-04-16 10:10:43 -0700 (Mon, 16 Apr 2007) $
 */
public interface ModuleActivator {
    /**
     * Get a map of themethods defined by this interface
* take a reference to the Tuscany SCA runtime ExtensionPointRegistry. This
* gives the ModuleActivator the oppotunity to add extension points defined by this module. The key is to the
* registry as it is *requested java interface to representstart theup extensionand pointremove andthem thewhen the valueit is therequested
     * instanceto of the implementation of the interface.
     *
     * @return All the extension points defined by this module
     */
    Map<Class, Object> getExtensionPoints();

    /**
     shut down.
*
* @version $Rev: 564429 $ $Date: 2007-08-09 16:49:11 -0700 (Thu, 09 Aug 2007) $
*/
public interface ModuleActivator {

/**
* This method is invoked when the module is started by the Tuscany system.
     * It can be used by this module to registr extensions against extension
     * points.
     *
     * @param registry The extension point registry
     */
    void start(ExtensionPointRegistry registry);

    /**
     * This method is invoked when the module is stopped by the Tuscany system.
     * It can be used by this module to unregister extensions against the
     * extension points.
     *
     * @param registry The extension point registry
     */
    void stop(ExtensionPointRegistry registry);
}
{code}

org.apache.tuscany.sca.implementation.java.xml.JavaImplementationProcessor;qname=http://www.osoa.org/xmlns/sca/1.0#implementation.java,model=org.apache.tuscany.sca.implementation.java.JavaImplementation