Hessian Client Extender With Dynamic Proxy Inside OSGi

III- Extender bundle listener

1- Listen to updated and installed bundle
2- Check the MANIFEST.MF file
3- Get the url and parse an XML resource
4- Register a proxy service

package com.jtunisie.osgi.hessian.client;

import com.jtunisie.osgi.hessian.client.Parser.Pair;
import java.net.URL;
import java.util.Dictionary;
import java.util.List;
import org.osgi.framework.Bundle;
import org.osgi.framework.BundleContext;
import org.osgi.framework.BundleEvent;
import org.osgi.framework.SynchronousBundleListener;
import static org.osgi.framework.BundleEvent.*;

/**
 *
 * @author slim
 */
public class BundleListner implements SynchronousBundleListener {

    private static final String HESSIAN_HEADER = "Hessian-File";
    private final BundleContext context;

    public BundleListner(BundleContext context) {
        this.context = context;
    }

    @Override
    public void bundleChanged(BundleEvent event) {   
        if (event.getType() == UPDATED || event.getType() == STARTED) {

            try {             
                addBundle(event.getBundle());
            } catch (ClassNotFoundException ex) {
               ex.printStackTrace();
            }
        }
        if (BundleEvent.STOPPED == event.getType()) {
            removeBundle(event.getBundle());
        }
    }

    private void addBundle(Bundle bundle) throws ClassNotFoundException {
        @SuppressWarnings("unchecked")
        Dictionary<String, String> headers = bundle.getHeaders();
        String indexPath = headers.get(HESSIAN_HEADER);
        
        if (indexPath == null) {
            return;
        }      
        URL resource = bundle.getResource(indexPath);
        if (resource == null) {
            return;
        }
        
        List<Pair> remotes = Parser.parseRemoteconfig(resource);
        if (remotes != null) {
            for (Pair pair : remotes) {          
                pair.setServiceRegistration(new ClientExtender().registerService(context, pair));
            }
        }
    }

    private void removeBundle(Bundle bundle) {
        // TODO
    }
}

IV-DynamicImport-Package :

As this extender will manipulate unknown class and interfaces we must enable DynamicImport-Package to all packages. To do this, add <DynamicImport-Package>*</DynamicImport-Package> in pom file.

V- Dynamic Proxys

1 -Create generic proxy class GenericClientProxy to forward calls to remote implementation according to requested service and destination:

package com.jtunisie.osgi.hessian.client;

import com.caucho.hessian.client.HessianProxyFactory;
import com.jtunisie.osgi.hessian.client.Parser.Pair;
import java.io.Serializable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

/**
 *
 * @author slim
 */
public class GenericClientProxy implements InvocationHandler, Serializable {

    private Pair pair;

    public GenericClientProxy(Pair pair) throws ClassNotFoundException {
        this.pair = pair;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        HessianProxyFactory factory = new HessianProxyFactory();
        Serializable service = (Serializable) factory.create(pair.getClazz(), pair.getRemoteAdress());
        return method.invoke(service, args);
    }
}

2- The ClientExtender class will register this proxy inside local OSGi as if it is present.

package com.jtunisie.osgi.hessian.client;

import com.jtunisie.osgi.hessian.client.Parser.Pair;
import java.lang.reflect.Proxy;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceRegistration;

/**
 *
 * @author slim
 */
public class ClientExtender {

    ServiceRegistration registerService(BundleContext context, Pair pair) throws ClassNotFoundException {
        String _interface = pair.getRemoteInterface();
        Class[] interfaces = {pair.getClazz()};
        GenericClientProxy clientProxy = new GenericClientProxy(pair);
        Object newProxyInstance = Proxy.newProxyInstance(this.getClass().getClassLoader(), interfaces, clientProxy);
        return context.registerService(_interface, newProxyInstance, null);
    }

    void unregisterService(BundleContext context, Pair pair) {
        //TODO
    }
}

VI- Execution

If we run the extender bundle and a test client, we will see that our extender will register the remote service inside the local registry

osgi> b <extender-id>
........
 Id=41, Status=ACTIVE      Data Root=/home/slim/work/svn/hessianextender-read-only/env.client/configuration/org.eclipse.osgi/bundles/41/data
  Registered Services
    {com.jtunisie.osgi.hessian.IService}={service.id=47}
  No services in use.
  Exported packages
    com.caucho.hessian.security; version="0.0.0"[exported]
    com.caucho.hessian.io; version="0.0.0"[exported]
    com.caucho.hessian.client; version="0.0.0"[exported]
    com.caucho.hessian.server; version="0.0.0"[exported]
    com.caucho.hessian.jmx; version="0.0.0"[exported]
    com.caucho.hessian.mux; version="0.0.0"[exported]
    com.caucho.hessian.util; version="0.0.0"[exported]
    com.caucho.hessian.micro; version="0.0.0"[exported]
    com.caucho.hessian; version="0.0.0"[exported]
    com.caucho.hessian.test; version="0.0.0"[exported]
  Imported packages
    javax.crypto; version="0.0.0"<System Bundle [0]>
    javax.management; version="0.0.0"<System Bundle [0]>
    javax.naming; version="0.0.0"<System Bundle [0]>
    javax.naming.spi; version="0.0.0"<System Bundle [0]>
    javax.servlet; version="2.5.0"<initial@reference:file:plugins/web/pax-web-service-0.4.1.jar/ [37]>
    javax.servlet.http; version="2.5.0"<initial@reference:file:plugins/web/pax-web-service-0.4.1.jar/ [37]>
    javax.xml.namespace; version="0.0.0"<System Bundle [0]>
    javax.xml.stream; version="0.0.0"<System Bundle [0]>
    javax.xml.stream.events; version="0.0.0"<System Bundle [0]>
    org.osgi.framework; version="1.4.0"<System Bundle [0]>
    org.w3c.dom; version="0.0.0"<System Bundle [0]>
  No fragment bundles
  Named class space
    com.jtunisie.osgi.hessian.client; bundle-version="1.0.0"[provided]
  No required bundles

VII - Conclusion

Using extenders in OSGi is a powerful tool. This post outlines :
 Extender pattern.
 Bundle listener.
 Dynamic proxy for remoting.
 Stax XML parsing
 Hessian service client.

It's not for production :) but as didactic use. If you want a powerful api check Eclipse Riena.

The Source code is available under svn link : svn checkout http://hessianclient.googlecode.com/svn/trunk/ hessianclient-read-only