import java.io.*;
import java.net.*;
import java.util.*;
import org.apache.log4j.Layout;
import org.apache.log4j.spi.Filter;
import org.apache.log4j.spi.ErrorHandler;
import org.apache.log4j.spi.OptionHandler;
import org.apache.log4j.spi.LoggingEvent;
import org.apache.log4j.helpers.OnlyOnceErrorHandler;
import org.apache.log4j.helpers.LogLog;
import org.apache.log4j.AppenderSkeleton;
/** 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:
*
* <table border=1>
* <tr>
* <th>Name</th>
* <th>Requirement</th>
* <th>Description</th>
* <th>Sample Value</th>
* </tr>
* <tr>
* <td>Port</td>
* <td>optional</td>
* <td>This parameter determines the port to use for announcing log events. The default port is 23 (telnet).</td>
* <td>5875</td>
* </table>
*
* @author <a HREF=""
*/
public class TelnetAppender extends AppenderSkeleton {
private SocketHandler sh;
private int port = 23;
private static final String PORT_OPTION = "Port";
/** 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();
}
}
/** sets an option on this appender. */
public void setOption(String key, String value) {
if(key.equalsIgnoreCase(PORT_OPTION)) {
port = Integer.parseInt(value);
}
}
/** determines the options that this appender allows. */
public String[] getOptionStrings() {
return new String[] {
PORT_OPTION
};
}
/** 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()) {
if(event.throwable != null) {
ByteArrayOutputStream bout = new ByteArrayOutputStream();
PrintWriter pw = new PrintWriter(bout);
event.throwable.printStackTrace(pw);
pw.close();
sh.send(bout.toString());
}
else {
if(event.throwableInformation != null) {
sh.send(event.throwableInformation);
}
}
}
}
//---------------------------------------------------------- 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 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) {
}
}
/** 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(true) {
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) {
e.printStackTrace();
}
}
}
public SocketHandler(int port) throws IOException {
serverSocket = new ServerSocket(port);
}
}
}
