SocketAppender

Class Overview

Sends LoggingEvent objects to a remote a log server, usually a SocketNode.

The SocketAppender has the following properties:

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

• SocketAppenders do not use a layout. They ship a serialized 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 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 close() the SocketAppender either explicitly or by calling the shutdown() method before exiting the application.

Summary

[Expand] Inherited Fields

From class org.apache.log4j.AppenderSkeleton protected boolean closed Is this appender closed? protected ErrorHandler errorHandler It is assumed and enforced that errorHandler is never null. protected Filter headFilter The first filter in the filter chain. protected Layout layout The layout variable does not need to be set if the appender implementation has its own layout. protected String name Appenders are named. protected Filter tailFilter The last filter in the filter chain. protected Priority threshold There is no level threshold filtering by default.

[Expand] Inherited Methods
From class org.apache.log4j.AppenderSkeleton void activateOptions() Derived appenders should override this method if option structure requires it. void addFilter(Filter newFilter) Add a filter to end of the filter list. abstract void append(LoggingEvent event) Subclasses of AppenderSkeleton should implement this method to perform actual logging. void clearFilters() Clear the filters chain. synchronized void doAppend(LoggingEvent event) This method performs threshold checks and invokes filters before delegating actual logging to the subclasses specific append(LoggingEvent) method. void finalize() Finalize this appender by calling the derived class' close method. ErrorHandler getErrorHandler() Return the currently set ErrorHandler for this Appender. Filter getFilter() Returns the head Filter. final Filter getFirstFilter() Return the first filter in the filter chain for this Appender. Layout getLayout() Returns the layout of this appender. final String getName() Returns the name of this appender. Priority getThreshold() Returns this appenders threshold level. boolean isAsSevereAsThreshold(Priority priority) Check whether the message level is below the appender's threshold. synchronized void setErrorHandler(ErrorHandler eh) Set the ErrorHandler for this Appender. void setLayout(Layout layout) Set the layout for this appender. void setName(String name) Set the name of this Appender. void setThreshold(Priority threshold) Set the threshold level.
From class java.lang.Object Object clone() boolean equals(Object arg0) void finalize() final Class<?> getClass() int hashCode() final void notify() final void notifyAll() String toString() final void wait() final void wait(long arg0, int arg1) final void wait(long arg0)
From interface org.apache.log4j.Appender abstract void addFilter(Filter newFilter) Add a filter to the end of the filter list. abstract void clearFilters() Clear the list of filters by removing all the filters in it. abstract void close() Release any resources allocated within the appender such as file handles, network connections, etc. abstract void doAppend(LoggingEvent event) Log in Appender specific way. abstract ErrorHandler getErrorHandler() Returns the ErrorHandler for this appender. abstract Filter getFilter() Returns the head Filter. abstract Layout getLayout() Returns this appenders layout. abstract String getName() Get the name of this appender. abstract boolean requiresLayout() Configurators call this method to determine if the appender requires a layout. abstract void setErrorHandler(ErrorHandler errorHandler) Set the ErrorHandler for this appender. abstract void setLayout(Layout layout) Set the Layout for this appender. abstract void setName(String name) Set the name of this appender.
From interface org.apache.log4j.spi.OptionHandler abstract void activateOptions() Activate the options that were previously set with calls to option setters.