/*
* Copyright 1999-2005 The Apache Software Foundation.
*
* 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.apache.log4j.net;
import java.util.Vector;
import java.net.Socket;
import java.net.ServerSocket;
import java.net.SocketException;
import java.io.ObjectOutputStream;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.net.InetAddress;
import org.apache.log4j.helpers.LogLog;
import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.AppenderSkeleton;
/**
Sends {@link LoggingEvent} objects to a set of remote log servers,
usually a {@link SocketNode SocketNodes}.
<p>Acts just like {@link SocketAppender} except that instead of
connecting to a given remote log server,
<code>SocketHubAppender</code> 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 <code>SocketHubAppender</code> is running on.
<p>The <code>SocketHubAppender</code> 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.
<p>This implementation borrows heavily from the {@link
SocketAppender}.
<p>The SocketHubAppender has the following characteristics:
<ul>
<p><li>If sent to a {@link 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, {@link org.apache.log4j.NDC},
location info as if it were logged locally.
<p><li><code>SocketHubAppender</code> does not use a layout. It
ships a serialized {@link LoggingEvent} object to the remote side.
<p><li><code>SocketHubAppender</code> relies on the TCP
protocol. Consequently, if the remote side is reachable, then log
events will eventually arrive at remote client.
<p><li>If no remote clients are attached, the logging requests are
simply dropped.
<p><li>Logging events are automatically <em>buffered</em> 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.
<p>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.
<p>The single remote client case extends to multiple clients
connections. The rate of logging will be determined by the slowest
link.
<p><li>If the JVM hosting the <code>SocketHubAppender</code> exits
before the <code>SocketHubAppender</code> 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.
<p>To avoid lost data, it is usually sufficient to {@link #close}
the <code>SocketHubAppender</code> either explicitly or by calling
the {@link org.apache.log4j.LogManager#shutdown} method before
exiting the application.
</ul>
@author Mark Womack */
public class SocketHubAppender extends AppenderSkeleton {
/**
The default port number of the ServerSocket will be created on. */
static final int DEFAULT_PORT = 4560;
private int port = DEFAULT_PORT;
private Vector oosList = new Vector();
private ServerMonitor serverMonitor = null;
private boolean locationInfo = false;
public SocketHubAppender() { }
/**
Connects to remote server at <code>address</code> and <code>port</code>. */
public
SocketHubAppender(int _port) {
port = _port;
startServer();
}
/**
Set up the socket server on the specified port. */
public
void activateOptions() {
startServer();
}
/**
Close this appender.
<p>This will mark the appender as closed and
call then {@link #cleanUp} method. */
synchronized
public
void close() {
if(closed)
return;
LogLog.debug("closing SocketHubAppender " + getName());
this.closed = true;
cleanUp();
LogLog.debug("SocketHubAppender " + getName() + " closed");
}
/**
Release the underlying ServerMonitor thread, and drop the connections
to all connected remote servers. */
public
void cleanUp() {
// stop the monitor thread
LogLog.debug("stopping ServerSocket");
serverMonitor.stopMonitor();
serverMonitor = null;
// close all of the connections
LogLog.debug("closing client connections");
while (oosList.size() != 0) {
ObjectOutputStream oos = (ObjectOutputStream)oosList.elementAt(0);
if(oos != null) {
try {
oos.close();
}
catch(IOException e) {
LogLog.error("could not close oos.", e);
}
oosList.removeElementAt(0);
}
}
}
/**
Append an event to all of current connections. */
public
void append(LoggingEvent event) {
// if no event or no open connections, exit now
if(event == null || oosList.size() == 0)
return;
// set up location info if requested
if (locationInfo) {
event.getLocationInformation();
}
// loop through the current set of open connections, appending the event to each
for (int streamCount = 0; streamCount < oosList.size(); streamCount++) {
ObjectOutputStream oos = null;
try {
oos = (ObjectOutputStream)oosList.elementAt(streamCount);
}
catch (ArrayIndexOutOfBoundsException e) {
// catch this, but just don't assign a value
// this should not really occur as this method is
// the only one that can remove oos's (besides cleanUp).
}
// list size changed unexpectedly? Just exit the append.
if (oos == null)
break;
try {
oos.writeObject(event);
oos.flush();
// Failing to reset the object output stream every now and
// then creates a serious memory leak.
// right now we always reset. TODO - set up frequency counter per oos?
oos.reset();
}
catch(IOException e) {
// there was an io exception so just drop the connection
oosList.removeElementAt(streamCount);
LogLog.debug("dropped connection");
// decrement to keep the counter in place (for loop always increments)
streamCount--;
}
}
}
/**
The SocketHubAppender does not use a layout. Hence, this method returns
<code>false</code>. */
public
boolean requiresLayout() {
return false;
}
/**
The <b>Port</b> option takes a positive integer representing
the port where the server is waiting for connections. */
public
void setPort(int _port) {
port = _port;
}
/**
Returns value of the <b>Port</b> option. */
public
int getPort() {
return port;
}
/**
The <b>LocationInfo</b> 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) {
locationInfo = _locationInfo;
}
/**
Returns value of the <b>LocationInfo</b> option. */
public
boolean getLocationInfo() {
return locationInfo;
}
/**
Start the ServerMonitor thread. */
private
void startServer() {
serverMonitor = new ServerMonitor(port, oosList);
}
/**
This class is used internally to monitor a ServerSocket
and register new connections in a vector passed in the
constructor. */
private
class ServerMonitor implements Runnable {
private int port;
private Vector oosList;
private boolean keepRunning;
private Thread monitorThread;
/**
Create a thread and start the monitor. */
public
ServerMonitor(int _port, Vector _oosList) {
port = _port;
oosList = _oosList;
keepRunning = true;
monitorThread = new Thread(this);
monitorThread.setDaemon(true);
monitorThread.start();
}
/**
Stops the monitor. This method will not return until
the thread has finished executing. */
public
synchronized
void stopMonitor() {
if (keepRunning) {
LogLog.debug("server monitor thread shutting down");
keepRunning = false;
try {
monitorThread.join();
}
catch (InterruptedException e) {
// do nothing?
}
// release the thread
monitorThread = null;
LogLog.debug("server monitor thread shut down");
}
}
/**
Method that runs, monitoring the ServerSocket and adding connections as
they connect to the socket. */
public
void run() {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(port);
serverSocket.setSoTimeout(1000);
}
catch (Exception e) {
LogLog.error("exception setting timeout, shutting down server socket.", e);
keepRunning = false;
return;
}
try {
try {
serverSocket.setSoTimeout(1000);
}
catch (SocketException e) {
LogLog.error("exception setting timeout, shutting down server socket.", e);
return;
}
while (keepRunning) {
Socket socket = null;
try {
socket = serverSocket.accept();
}
catch (InterruptedIOException e) {
// timeout occurred, so just loop
}
catch (SocketException e) {
LogLog.error("exception accepting socket, shutting down server socket.", e);
keepRunning = false;
}
catch (IOException e) {
LogLog.error("exception accepting socket.", e);
}
// if there was a socket accepted
if (socket != null) {
try {
InetAddress remoteAddress = socket.getInetAddress();
LogLog.debug("accepting connection from " + remoteAddress.getHostName()
+ " (" + remoteAddress.getHostAddress() + ")");
// create an ObjectOutputStream
ObjectOutputStream oos = new ObjectOutputStream(socket.getOutputStream());
// add it to the oosList. OK since Vector is synchronized.
oosList.addElement(oos);
}
catch (IOException e) {
LogLog.error("exception creating output stream on socket.", e);
}
}
}
}
finally {
// close the socket
try {
serverSocket.close();
}
catch (IOException e) {
// do nothing with it?
}
}
}
}
}