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What this is

This file is included in the "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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The source code

 * Copyright (C) The Apache Software Foundation. All rights reserved.
 * This software is published under the terms of the Apache Software License
 * version 1.1, a copy of which has been included  with this distribution in
 * the LICENSE.txt file.

// Contributors: Dan MacDonald 



import org.apache.log4j.helpers.LogLog;
import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.AppenderSkeleton;

    Sends {@link LoggingEvent} objects to a remote a log server,
    usually a {@link SocketNode}.


The SocketAppender has the following properties:

  • If sent to a {@link SocketNode}, remote logging is non-intrusive as far as the log event is concerned. In other words, the event will be logged with the same time stamp, {@link org.apache.log4j.NDC}, location info as if it were logged locally by the client.

  • SocketAppenders do not use a layout. They ship a serialized {@link LoggingEvent} object to the server side.

  • Remote logging uses the TCP protocol. Consequently, if the server is reachable, then log events will eventually arrive at the server.

  • If the remote server is down, the logging requests are simply dropped. However, if and when the server comes back up, then event transmission is resumed transparently. This transparent reconneciton is performed by a connector thread which periodically attempts to connect to the server.

  • Logging events are automatically buffered by the native TCP implementation. This means that if the link to server is slow but still faster than the rate of (log) event production by the client, the client will not be affected by the slow network connection. However, if the network connection is slower then the rate of event production, then the client can only progress at the network rate. In particular, if the network link to the the server is down, the client will be blocked.

    On the other hand, if the network link is up, but the server is down, the client will not be blocked when making log requests but the log events will be lost due to server unavailability.

  • Even if a SocketAppender is no longer attached to any category, it will not be garbage collected in the presence of a connector thread. A connector thread exists only if the connection to the server is down. To avoid this garbage collection problem, you should {@link #close} the the SocketAppender explicitly. See also next item.

    Long lived applications which create/destroy many SocketAppender instances should be aware of this garbage collection problem. Most other applications can safely ignore it.

  • If the JVM hosting the SocketAppender exits before the SocketAppender is closed either explicitly or subsequent to garbage collection, then there might be untransmitted data in the pipe which might be lost. This is a common problem on Windows based systems.

    To avoid lost data, it is usually sufficient to {@link #close} the SocketAppender either explicitly or by calling the {@link org.apache.log4j.LogManager#shutdown} method before exiting the application.

@author Ceki Gülcü @since 0.8.4 */ public class SocketAppender extends AppenderSkeleton { /** The default port number of remote logging server (4560). */ static final int DEFAULT_PORT = 4560; /** The default reconnection delay (30000 milliseconds or 30 seconds). */ static final int DEFAULT_RECONNECTION_DELAY = 30000; /** We remember host name as String in addition to the resolved InetAddress so that it can be returned via getOption(). */ String remoteHost; InetAddress address; int port = DEFAULT_PORT; ObjectOutputStream oos; int reconnectionDelay = DEFAULT_RECONNECTION_DELAY; boolean locationInfo = false; private Connector connector; int counter = 0; // reset the ObjectOutputStream every 70 calls //private static final int RESET_FREQUENCY = 70; private static final int RESET_FREQUENCY = 1; public SocketAppender() { } /** Connects to remote server at address and port. */ public SocketAppender(InetAddress address, int port) { this.address = address; this.remoteHost = address.getHostName(); this.port = port; connect(address, port); } /** Connects to remote server at host and port. */ public SocketAppender(String host, int port) { this.port = port; this.address = getAddressByName(host); this.remoteHost = host; connect(address, port); } /** Connect to the specified RemoteHost and Port. */ public void activateOptions() { connect(address, port); } /** * Close this appender. * *

This will mark the appender as closed and call then {@link * #cleanUp} method. * */ synchronized public void close() { if(closed) return; this.closed = true; cleanUp(); } /** * Drop the connection to the remote host and release the underlying * connector thread if it has been created * */ public void cleanUp() { if(oos != null) { try { oos.close(); } catch(IOException e) { LogLog.error("Could not close oos.", e); } oos = null; } if(connector != null) { //LogLog.debug("Interrupting the connector."); connector.interrupted = true; connector = null; // allow gc } } void connect(InetAddress address, int port) { if(this.address == null) return; try { // First, close the previous connection if any. cleanUp(); oos = new ObjectOutputStream(new Socket(address, port).getOutputStream()); } catch(IOException e) { String msg = "Could not connect to remote log4j server at [" +address.getHostName()+"]."; if(reconnectionDelay > 0) { msg += " We will try again later."; fireConnector(); // fire the connector thread } LogLog.error(msg, e); } } public void append(LoggingEvent event) { if(event == null) return; if(address==null) { errorHandler.error("No remote host is set for SocketAppender named \""+"\"."); return; } if(oos != null) { try { if(locationInfo) { event.getLocationInformation(); } oos.writeObject(event); //LogLog.debug("=========Flushing."); oos.flush(); if(++counter >= RESET_FREQUENCY) { counter = 0; // Failing to reset the object output stream every now and // then creates a serious memory leak. //System.err.println("Doing oos.reset()"); oos.reset(); } } catch(IOException e) { oos = null; LogLog.warn("Detected problem with connection: "+e); if(reconnectionDelay > 0) { fireConnector(); } } } } void fireConnector() { if(connector == null) { LogLog.debug("Starting a new connector thread."); connector = new Connector(); connector.setDaemon(true); connector.setPriority(Thread.MIN_PRIORITY); connector.start(); } } static InetAddress getAddressByName(String host) { try { return InetAddress.getByName(host); } catch(Exception e) { LogLog.error("Could not find address of ["+host+"].", e); return null; } } /** * The SocketAppender does not use a layout. Hence, this method * returns false. * */ public boolean requiresLayout() { return false; } /** * The RemoteHost option takes a string value which should be * the host name of the server where a {@link SocketNode} is * running. * */ public void setRemoteHost(String host) { address = getAddressByName(host); remoteHost = host; } /** Returns value of the RemoteHost option. */ public String getRemoteHost() { return remoteHost; } /** The Port option takes a positive integer representing the port where the server is waiting for connections. */ public void setPort(int port) { this.port = port; } /** Returns value of the Port option. */ public int getPort() { return port; } /** The LocationInfo option takes a boolean value. If true, the information sent to the remote host will include location information. By default no location information is sent to the server. */ public void setLocationInfo(boolean locationInfo) { this.locationInfo = locationInfo; } /** Returns value of the LocationInfo option. */ public boolean getLocationInfo() { return locationInfo; } /** The ReconnectionDelay option takes a positive integer representing the number of milliseconds to wait between each failed connection attempt to the server. The default value of this option is 30000 which corresponds to 30 seconds.

Setting this option to zero turns off reconnection capability. */ public void setReconnectionDelay(int delay) { this.reconnectionDelay = delay; } /** Returns value of the ReconnectionDelay option. */ public int getReconnectionDelay() { return reconnectionDelay; } /** The Connector will reconnect when the server becomes available again. It does this by attempting to open a new connection every reconnectionDelay milliseconds.

It stops trying whenever a connection is established. It will restart to try reconnect to the server when previpously open connection is droppped. @author Ceki Gülcü @since 0.8.4 */ class Connector extends Thread { boolean interrupted = false; public void run() { Socket socket; while(!interrupted) { try { sleep(reconnectionDelay); LogLog.debug("Attempting connection to "+address.getHostName()); socket = new Socket(address, port); synchronized(this) { oos = new ObjectOutputStream(socket.getOutputStream()); connector = null; LogLog.debug("Connection established. Exiting connector thread."); break; } } catch(InterruptedException e) { LogLog.debug("Connector interrupted. Leaving loop."); return; } catch( e) { LogLog.debug("Remote host "+address.getHostName() +" refused connection."); } catch(IOException e) { LogLog.debug("Could not connect to " + address.getHostName()+ ". Exception is " + e); } } //LogLog.debug("Exiting method."); } /** public void finalize() { LogLog.debug("Connector finalize() has been called."); } */ } }

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