org.apache.log4j.net

Class SocketHubAppender

java.lang.Object

org.apache.log4j.AppenderSkeleton

org.apache.log4j.net.SocketHubAppender

All Implemented Interfaces:

Appender, OptionHandler

public class SocketHubAppender
extends AppenderSkeleton

Sends LoggingEvent objects to a set of remote log servers, usually a SocketNodes.

Acts just like SocketAppender except that instead of connecting to a given remote log server, SocketHubAppender accepts connections from the remote log servers as clients. It can accept more than one connection. When a log event is received, the event is sent to the set of currently connected remote log servers. Implemented this way it does not require any update to the configuration file to send data to another remote log server. The remote log server simply connects to the host and port the SocketHubAppender is running on.

The SocketHubAppender does not store events such that the remote side will events that arrived after the establishment of its connection. Once connected, events arrive in order as guaranteed by the TCP protocol.

This implementation borrows heavily from the SocketAppender.

The SocketHubAppender has the following characteristics:

• If sent to a SocketNode, 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, NDC, location info as if it were logged locally.

• SocketHubAppender does not use a layout. It ships a serialized LoggingEvent object to the remote side.

• SocketHubAppender relies on the TCP protocol. Consequently, if the remote side is reachable, then log events will eventually arrive at remote client.

• If no remote clients are attached, the logging requests are simply dropped.

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

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

  The single remote client case extends to multiple clients connections. The rate of logging will be determined by the slowest link.

• If the JVM hosting the SocketHubAppender exits before the SocketHubAppender 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 close() the SocketHubAppender either explicitly or by calling the LogManager.shutdown() method before exiting the application.

Author:

Mark Womack

Field Summary

Fields

Modifier and Type	Field and Description
static String	ZONE The MulticastDNS zone advertised by a SocketHubAppender

Fields inherited from class org.apache.log4j.AppenderSkeleton

closed, errorHandler, headFilter, layout, name, tailFilter, threshold

Constructor Summary

Constructors

Constructor and Description
SocketHubAppender()
SocketHubAppender(int _port) Connects to remote server at address and port.

Method Summary

Modifier and Type	Method and Description
void	activateOptions() Set up the socket server on the specified port.
void	append(LoggingEvent event) Append an event to all of current connections.
void	cleanUp() Release the underlying ServerMonitor thread, and drop the connections to all connected remote servers.
void	close() Close this appender.
protected ServerSocket	createServerSocket(int socketPort) Creates a server socket to accept connections.
String	getApplication() Returns value of the Application option.
int	getBufferSize() Returns value of the bufferSize option.
boolean	getLocationInfo() Returns value of the LocationInfo option.
int	getPort() Returns value of the Port option.
boolean	isAdvertiseViaMulticastDNS()
boolean	requiresLayout() The SocketHubAppender does not use a layout.
void	setAdvertiseViaMulticastDNS(boolean advertiseViaMulticastDNS)
void	setApplication(String lapp) The App option takes a string value which should be the name of the application getting logged.
void	setBufferSize(int _bufferSize) The BufferSize option takes a positive integer representing the number of events this appender will buffer and send to newly connected clients.
void	setLocationInfo(boolean _locationInfo) The LocationInfo option takes a boolean value.
void	setPort(int _port) The Port option takes a positive integer representing the port where the server is waiting for connections.

Methods inherited from class org.apache.log4j.AppenderSkeleton

addFilter, clearFilters, doAppend, finalize, getErrorHandler, getFilter, getFirstFilter, getLayout, getName, getThreshold, isAsSevereAsThreshold, setErrorHandler, setLayout, setName, setThreshold

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

ZONE

public static final String ZONE

The MulticastDNS zone advertised by a SocketHubAppender

See Also:

Constant Field Values

Constructor Detail

SocketHubAppender

public SocketHubAppender()

SocketHubAppender

public SocketHubAppender(int _port)

Connects to remote server at address and port.

Method Detail

activateOptions

public void activateOptions()

Set up the socket server on the specified port.

Specified by:

activateOptions in interface OptionHandler

Overrides:

activateOptions in class AppenderSkeleton

close

public void close()

Close this appender.

This will mark the appender as closed and call then cleanUp() method.

cleanUp

public void cleanUp()

Release the underlying ServerMonitor thread, and drop the connections to all connected remote servers.

append

public void append(LoggingEvent event)

Append an event to all of current connections.

Specified by:

append in class AppenderSkeleton

requiresLayout

public boolean requiresLayout()

The SocketHubAppender does not use a layout. Hence, this method returns false.

setPort

public void setPort(int _port)

The Port option takes a positive integer representing the port where the server is waiting for connections.

setApplication

public void setApplication(String lapp)

The App option takes a string value which should be the name of the application getting logged. If property was already set (via system property), don't set here.

getApplication

public String getApplication()

Returns value of the Application option.

getPort

public int getPort()

Returns value of the Port option.

setBufferSize

public void setBufferSize(int _bufferSize)

The BufferSize option takes a positive integer representing the number of events this appender will buffer and send to newly connected clients.

getBufferSize

public int getBufferSize()

Returns value of the bufferSize option.

setLocationInfo

public void setLocationInfo(boolean _locationInfo)

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.

getLocationInfo

public boolean getLocationInfo()

Returns value of the LocationInfo option.

setAdvertiseViaMulticastDNS

public void setAdvertiseViaMulticastDNS(boolean advertiseViaMulticastDNS)

isAdvertiseViaMulticastDNS

public boolean isAdvertiseViaMulticastDNS()

createServerSocket

protected ServerSocket createServerSocket(int socketPort)
                                   throws IOException

Creates a server socket to accept connections.

Parameters:

socketPort - port on which the socket should listen, may be zero.

Returns:

new socket.

Throws:

IOException - IO error when opening the socket.