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What this is

This file is included in the DevDaily.com "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.  */

package org.apache.log4j.net;

import java.io.*;
import java.net.*;
import java.util.*;
import org.apache.log4j.Layout;
import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.AppenderSkeleton;
import org.apache.log4j.helpers.LogLog;

/**
  

The TelnetAppender is a log4j appender that specializes in writing to a read-only socket. The output is provided in a telnet-friendly way so that a log can be monitored over TCP/IP. Clients using telnet connect to the socket and receive log data. This is handy for remote monitoring, especially when monitoring a servlet.

Here is a list of the available configuration options:
Name Requirement Description Sample Value
Port optional This parameter determines the port to use for announcing log events. The default port is 23 (telnet). 5875
@author Jay Funnell */ public class TelnetAppender extends AppenderSkeleton { private SocketHandler sh; private int port = 23; /** This appender requires a layout to format the text to the attached client(s). */ public boolean requiresLayout() { return true; } /** all of the options have been set, create the socket handler and wait for connections. */ public void activateOptions() { try { sh = new SocketHandler(port); sh.start(); } catch(Exception e) { e.printStackTrace(); } } public int getPort() { return port; } public void setPort(int port) { this.port = port; } /** shuts down the appender. */ public void close() { sh.finalize(); } /** Handles a log event. For this appender, that means writing the message to each connected client. */ protected void append(LoggingEvent event) { sh.send(this.layout.format(event)); if(layout.ignoresThrowable()) { String[] s = event.getThrowableStrRep(); if (s != null) { int len = s.length; for(int i = 0; i < len; i++) { sh.send(s[i]); sh.send(Layout.LINE_SEP); } } } } //---------------------------------------------------------- SocketHandler: /** The SocketHandler class is used to accept connections from clients. It is threaded so that clients can connect/disconnect asynchronously. */ protected class SocketHandler extends Thread { private boolean done = false; private Vector writers = new Vector(); private Vector connections = new Vector(); private ServerSocket serverSocket; private int MAX_CONNECTIONS = 20; /** make sure we close all network connections when this handler is destroyed. */ public void finalize() { for(Enumeration e = connections.elements();e.hasMoreElements();) { try { ((Socket)e.nextElement()).close(); } catch(Exception ex) { } } try { serverSocket.close(); } catch(Exception ex) { } done = true; } /** sends a message to each of the clients in telnet-friendly output. */ public void send(String message) { Enumeration ce = connections.elements(); for(Enumeration e = writers.elements();e.hasMoreElements();) { Socket sock = (Socket)ce.nextElement(); PrintWriter writer = (PrintWriter)e.nextElement(); writer.print(message); if(writer.checkError()) { // The client has closed the connection, remove it from our list: connections.remove(sock); writers.remove(writer); } } } /** Continually accepts client connections. Client connections are refused when MAX_CONNECTIONS is reached. */ public void run() { while(!done) { try { Socket newClient = serverSocket.accept(); PrintWriter pw = new PrintWriter(newClient.getOutputStream()); if(connections.size() < MAX_CONNECTIONS) { connections.addElement(newClient); writers.addElement(pw); pw.print("TelnetAppender v1.0 (" + connections.size() + " active connections)\r\n\r\n"); pw.flush(); } else { pw.print("Too many connections.\r\n"); pw.flush(); newClient.close(); } } catch(Exception e) { LogLog.error("Encountered error while in SocketHandler loop.", e); } } } public SocketHandler(int port) throws IOException { serverSocket = new ServerSocket(port); } } }

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