Package org.apache.log4j.net

Class 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 Detail

      • ZONE

        public static final java.lang.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

      • 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.

      • 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​(java.lang.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 java.lang.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 java.net.ServerSocket createServerSocket​(int socketPort)
                                            throws java.io.IOException
        Creates a server socket to accept connections.
        Parameters:
        socketPort - port on which the socket should listen, may be zero.
        Returns:
        new socket.
        Throws:
        java.io.IOException - IO error when opening the socket.