org.ops4j.pax.logging.log4j2.internal.LogReaderServiceImpl Maven / Gradle / Ivy

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Pax Logging backend implementation based on Apache Log4J2. It provides Log4J2 specific implementation of PaxLoggingService interface and Log4J2 specific configuration methods. Users may customize Log4J2 behaviour (appenders, layouts) by creating fragment attached to this bundle.

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/*  Copyright 2007 Niclas Hedhman.
 *
 * Licensed 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.ops4j.pax.logging.log4j2.internal;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

import org.osgi.service.log.LogEntry;
import org.osgi.service.log.LogListener;
import org.osgi.service.log.LogReaderService;

/**
 * @noinspection SynchronizeOnNonFinalField
 */
public class LogReaderServiceImpl
    implements LogReaderService
{

    private List m_listeners;
    private final LinkedList m_entries;
    private int m_maxEntries;

    public LogReaderServiceImpl(int maxEntries)
    {
        m_maxEntries = maxEntries;
        m_entries = new LinkedList();
    }

    public void addLogListener( LogListener logListener )
    {
        synchronized( this )
        {
            // Do not update the list directly to avoid
            // the cost of a synchronized block when iterating
            // listeners in fireEvent()
            ArrayList clone;
            if( m_listeners == null )
            {
                clone = new ArrayList();
            }
            else
            {
                clone = new ArrayList( m_listeners );
            }
            clone.add( logListener );
            m_listeners = clone;
        }
    }

    public void removeLogListener( LogListener logListener )
    {
        synchronized( this )
        {
            // Do not update the list directly to avoid
            // the cost of a synchronized block when iterating
            // listeners in fireEvent()
            if( m_listeners == null )
            {
                return;
            }
            ArrayList clone = new ArrayList( m_listeners );
            clone.remove( logListener );
            if( clone.size() == 0 )
            {
                m_listeners = null;
            }
            else
            {
                m_listeners = clone;
            }
        }
    }

    public Enumeration getLog()
    {
        // Need to do a copy to avoid a ConcurrentModificationException if
        // a new event is logged while the enumeration is iterated.
        synchronized (m_entries)
        {
            return Collections.enumeration( new ArrayList( m_entries ) );
        }
    }

    private void cleanUp()
    {
        // caller must synchronize on m_entries
        while( m_entries.size() > m_maxEntries )
        {
            m_entries.removeLast();
        }
    }

    final void fireEvent( LogEntry entry )
    {
        synchronized( m_entries )
        {
            m_entries.addFirst( entry );
            cleanUp();
        }
        final List listeners = m_listeners;
        if( listeners == null )
        {
            return;
        }
        Iterator iterator = listeners.iterator();
        while( iterator.hasNext() )
        {
            LogListener listener = (LogListener) iterator.next();
            fire( listener, entry );
        }
    }

    private void fire( LogListener listener, LogEntry entry )
    {
        try
        {
            listener.logged( entry );
        }
        catch( Throwable e )
        {
            //TODO: Log that we are removing the LogListener, since it is throwing exception. For now System.err
            System.err.println( "'" + listener + "' is removed as a LogListener, since it threw an exception." );
            removeLogListener( listener );
        }
    }

    /**
     * Sets the max number of entries that should be allowed in the LogReader buffer.
     *
     * @param maxSize the maximum number of entries in the LogReader buffer.
     */
    final void setMaxEntries( int maxSize )
    {
        synchronized (m_entries)
        {
            m_maxEntries = maxSize;
        }
    }
}