Friday, August 9, 2013

Weblogic log files and log4j tricks

I have relied on weblogic log files for trouble shooting for many years, but never given a serious thought where they are configured and how to customize them. Well, I still don't know the whole story, but I managed to learn a couple of interesting things lately.

1. By default, WebLogic uses Java logging API which is based on log4j, but it is not exactly log4j. Therefore, if you install an out of box domain, there is no direct reference to log4j.

2. Your application can choose to use log4j for logging, then you can control how things are logged and where to log to etc.

3. If you want to system to dynamically pick up log4j.xml changes during run time, you can use I'll show a full example below.

4. We also need to send certain log messages to sensage, which monitors the syslog. What we need was using log4j "syslogger" to direct log msgs to syslog, then we configured the /etc/syslog.conf to forward the messages to senage like:
# Sensage Configuration

However, in order to send message to syslog file, we had to modify "syslogd" start up script and add "-r" parameter.

Now, for the sample log4j and DOMConfigurator example. I grabbed some sample file online and modified it with the configurator:

import org.apache.log4j.Logger;
import java.sql.SQLException;
import java.util.*;
import org.apache.log4j.xml.DOMConfigurator;
public class logExample{
  static Logger log = Logger.getLogger(logExample.class.getName());
  public static void main(String[] args)
                throws IOException,SQLException{
BufferedReader reader = new BufferedReader(new InputStreamReader(;
String file = System.getProperty("Log4jConfigFile");
DOMConfigurator.configureAndWatch(file, 3000);

     while (true) {
     log.debug("Hello this is an debug message");"Hello this is an info message");
     System.out.println("modify your log4j.xml, then hit enter to continue, monitor the changes take effect.");

String x = null;
try {
x = reader.readLine();
} catch (IOException e) {

Here is my local compile and run script:

javac -cp .;C:\Oracle\Middleware\Oracle_OSB1\lib\external\log4j_1.2.8.jar -d .

java -cp .;C:\Oracle\Middleware\Oracle_OSB1\lib\external\log4j_1.2.8.jar -DLog4jConfigFile="c:\proj\poc\log4j\config\log4j.xml" logExample

You can use your own log4j.xml or grab a sample from here

Finally, to integrate this sample into your web application, you need to find your initialization function, such as servlet context initializer, and insert the DCOMConfigurator over there. Of course, remember to put in -DLog4jConfigFile in your server startup script if your server is started with the script, or put it in the weblogic console server startup argument field if you use nodeManager to start your server(s).

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