src/main/java/org/apache/felix/shell/remote/ServiceMediator.java

/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.felix.shell.remote;


import org.apache.felix.shell.ShellService;
import org.osgi.framework.Bundle;
import org.osgi.framework.BundleContext;
import org.osgi.framework.Constants;
import org.osgi.framework.InvalidSyntaxException;
import org.osgi.framework.ServiceEvent;
import org.osgi.framework.ServiceListener;
import org.osgi.framework.ServiceReference;
import org.osgi.service.log.LogService;


/**
 * Implements a mediator pattern class for services from the OSGi container.
 */
class ServiceMediator
{

    private BundleContext m_BundleContext;

    private ShellService m_FelixShellService;
    private Latch m_FelixShellServiceLatch;

    private LogService m_LogService;
    private Latch m_LogServiceLatch;


    /**
     * Returns a reference to the <tt>ShellService</tt> (Felix).
     *
     * @param wait time in milliseconds to wait for the reference if it isn't available.
     * @return the reference to the <tt>ShellService</tt> as obtained from the OSGi service layer.
     */
    public ShellService getFelixShellService( long wait )
    {
        try
        {
            if ( wait < 0 )
            {
                m_FelixShellServiceLatch.acquire();
            }
            else if ( wait > 0 )
            {
                m_FelixShellServiceLatch.attempt( wait );
            }
        }
        catch ( InterruptedException e )
        {
            e.printStackTrace( System.err );
        }

        return m_FelixShellService;
    }//getFelixShellService


    public LogService getLogServiceLatch( long wait )
    {
        try
        {
            if ( wait < 0 )
            {
                m_LogServiceLatch.acquire();
            }
            else if ( wait > 0 )
            {
                m_LogServiceLatch.attempt( wait );
            }
        }
        catch ( InterruptedException e )
        {
            e.printStackTrace( System.err );
        }
        return m_LogService;
    }//getLogService


    public void info( String msg )
    {
        if ( m_LogService != null )
        {
            m_LogService.log( LogService.LOG_INFO, msg );
        }
        else
        {
            sysout( msg );
        }
    }//info


    public void error( String msg, Throwable t )
    {
        if ( m_LogService != null )
        {
            m_LogService.log( LogService.LOG_ERROR, msg, t );
        }
        else
        {
            syserr( msg, t );
        }
    }//error


    public void error( String msg )
    {
        if ( m_LogService != null )
        {
            m_LogService.log( LogService.LOG_ERROR, msg );
        }
        else
        {
            syserr( msg, null );
        }
    }//error


    public void debug( String msg )
    {
        if ( m_LogService != null )
        {
            m_LogService.log( LogService.LOG_DEBUG, msg );
        }
        else
        {
            sysout( msg );
        }
    }//debug


    public void warn( String msg )
    {
        if ( m_LogService != null )
        {
            m_LogService.log( LogService.LOG_WARNING, msg );
        }
        else
        {
            syserr( msg, null );
        }
    }//warn


    private void sysout( String msg )
    {
        //Assemble String
        StringBuffer sbuf = new StringBuffer();
        Bundle b = m_BundleContext.getBundle();
        sbuf.append( b.getHeaders().get( Constants.BUNDLE_NAME ) );
        sbuf.append( " [" );
        sbuf.append( b.getBundleId() );
        sbuf.append( "] " );
        sbuf.append( msg );
        System.out.println( sbuf.toString() );
    }//sysout


    private void syserr( String msg, Throwable t )
    {
        //Assemble String
        StringBuffer sbuf = new StringBuffer();
        Bundle b = m_BundleContext.getBundle();
        sbuf.append( b.getHeaders().get( Constants.BUNDLE_NAME ) );
        sbuf.append( " [" );
        sbuf.append( b.getBundleId() );
        sbuf.append( "] " );
        sbuf.append( msg );
        System.err.println( sbuf.toString() );
        if ( t != null )
        {
            t.printStackTrace( System.err );
        }
    }//logToSystem


    /**
     * Activates this mediator to start tracking the required services using the
     * OSGi service layer.
     *
     * @param bc the bundle's context.
     * @return true if activated successfully, false otherwise.
     */
    public boolean activate( BundleContext bc )
    {
        //get the context
        m_BundleContext = bc;

        m_FelixShellServiceLatch = createWaitLatch();
        m_LogServiceLatch = createWaitLatch();

        //prepareDefinitions listener
        ServiceListener serviceListener = new ServiceListenerImpl();

        //prepareDefinitions the filter, ShellService is required,
        //LogService may be missing, in which case we only use the
        // ShellService part of the filter
        String filter = "(objectclass=" + ShellService.class.getName() + ")";
        try
        {
            filter = "(|" + filter + "(objectclass=" + LogService.class.getName() + "))";
        }
        catch ( Throwable t )
        {
            // ignore
        }

        try
        {
            //add the listener to the bundle context.
            bc.addServiceListener( serviceListener, filter );

            //ensure that already registered Service instances are registered with
            //the manager
            ServiceReference[] srl = bc.getServiceReferences( null, filter );
            for ( int i = 0; srl != null && i < srl.length; i++ )
            {
                serviceListener.serviceChanged( new ServiceEvent( ServiceEvent.REGISTERED, srl[i] ) );
            }
        }
        catch ( InvalidSyntaxException ex )
        {
            ex.printStackTrace( System.err );
            return false;
        }
        return true;
    }//activate


    /**
     * Deactivates this mediator, nulling out all references.
     * If called when the bundle is stopped, the framework should actually take
     * care of unregistering the <tt>ServiceListener</tt>.
     */
    public void deactivate()
    {
        m_FelixShellService = null;
        m_FelixShellServiceLatch = null;
        m_BundleContext = null;
    }//deactivate


    /**
     * Creates a simple wait latch to be used for the mechanism that allows entities
     * in the bundles to wait for references.
     *
     * @return a new Latch instance.
     */
    private Latch createWaitLatch()
    {
        return new Latch();
    }//createWaitLatch

    /**
     * The <tt>ServiceListener</tt> implementation.
     */
    private class ServiceListenerImpl implements ServiceListener
    {

        public void serviceChanged( ServiceEvent ev )
        {
            ServiceReference sr = ev.getServiceReference();
            Object o = null;
            switch ( ev.getType() )
            {
                case ServiceEvent.REGISTERED:
                    o = m_BundleContext.getService( sr );
                    if ( o == null )
                    {
                        return;
                    }
                    else if ( o instanceof ShellService )
                    {
                        m_FelixShellService = ( ShellService ) o;
                        m_FelixShellServiceLatch.release();
                    }
                    else if ( o instanceof LogService )
                    {
                        m_LogService = ( LogService ) o;
                        m_LogServiceLatch.release();
                    }
                    else
                    {
                        m_BundleContext.ungetService( sr );
                    }
                    break;
                case ServiceEvent.UNREGISTERING:
                    o = m_BundleContext.getService( sr );
                    if ( o == null )
                    {
                        return;
                    }
                    else if ( o instanceof ShellService )
                    {
                        m_FelixShellService = null;
                        m_FelixShellServiceLatch = createWaitLatch();
                    }
                    else if ( o instanceof LogService )
                    {
                        m_LogService = null;
                        m_LogServiceLatch = createWaitLatch();
                    }
                    else
                    {
                        m_BundleContext.ungetService( sr );
                    }
                    break;
            }
        }
    }//inner class ServiceListenerImpl

    public static long WAIT_UNLIMITED = -1;
    public static long NO_WAIT = 0;

}//class ServiceMediator