How to separate Console and / or File appenders in Log4J?

[Unnsse Khan]

Hello there,

I am using an init servlet to load my log4j properties file during app start up...

public class Log4jInitServlet extends HttpServlet {
     public void init() throws ServletException {
                Properties props = new Properties();
try {
    props.load(this.getClass().getClassLoader().getResourceAsStream(
"/log4j.properties"));
} catch (IOException e) {
   e.printStackTrace();
}
}
}

The log4j.properties file:

log4j.rootLogger=WARN, stdout
log4j.logger.acme.myapp=DEBUG
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] - %m%n

Question(s):

(1) Let's say I want to use a file appender for logging different parts of the app's behavior, do I need to create a different properties file?

(2) If not, how would I integrate that with the properties file above?

(3) Is there a way I set the DEBUG warning to just log to the Console and the LOG warning to just log to specific files (which I specify)?

(4) What if I wanted two separate log files generated for the file appender?

(e.g. one being for cars.log and another one being planes.log)

(5) Do I have to create a different init servlet and different properties file?

Happy programming,
[ June 01, 2007: Message edited by: Unnsse Khan ]

[Jaikiran Pai]

(1) Let's say I want to use a file appender for logging different parts of the app's behavior, do I need to create a different properties file?

No. You can add the configurations to your existing log4j.properties file.

(2) If not, how would I integrate that with the properties file above?

Have a look at the javadoc of doConfigure method of PropertyConfigurator at doConfigure javadoc which has some examples.

(4) What if I wanted two separate log files generated for the file appender?

A file appender corresponds to one file. So if you want more different log files, you will have to create that many file appenders

(5) Do I have to create a different init servlet and different properties file?

No. A single init servlet and properties file is enough.

A good place to get more details about log4j configurations is the Log4j Manual

[Unnsse Khan]

Hi Jaikiran,

Thank you so much for the response!

This is what I did (I didn't change the Log4JInitServlet):

log4j.rootLogger=WARN, stdout
 
log4j.logger.com.myapp=DEBUG
 
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{MMM dd yyyy, HH:mm:ss} %p [%c:%L] - %m%n
 
log4j.logger.com.myapp=LOG, car
log4j.logger.com.myapp=LOG, plane
 
log4j.appender.add=org.apache.log4j.FileAppender
log4j.appender.add.File=car.log
log4j.appender.add.layout=org.apache.log4j.PatternLayout
log4j.appender.add.layout.ConversionPattern=%d{MM-dd@HH:mm:ss} %-5p (%13F:%L) %3x - %m%n
 
log4j.appender.edit=org.apache.log4j.FileAppender
log4j.appender.edit.File=plane.log
log4j.appender.edit.layout=org.apache.log4j.PatternLayout
log4j.appender.edit.layout.ConversionPattern=%d{MM-dd@HH:mm:ss} %-5p (%13F:%L) %3x - %m%n

Question(s):

(1) Where do the files plane.log and car.log become created?

(2) How do I differentiate the log output for each file?

(e.g. How do I tell the Logger to send "this" message to car.log and "that" message to plane.log)?

(3) I tried doing this:

Logger.getLogger(this.getClass()).log("Plane:" + plane);

But Eclipse displayed this error:

The method log(String, Priority, Object, Throwable) in the type Category is not applicable for the arguments (String)

Many, many thanks!
[ June 01, 2007: Message edited by: Unnsse Khan ]

[Jaikiran Pai]

log4j.appender.add.File=car.log
log4j.appender.edit.File=plane.log
Where do the files plane.log and car.log become created?

The file path that you given in your log4j.properties are relative paths. I prefer giving absolute path like:

log4j.appender.add.File=D:/log/car.log
log4j.appender.edit.File=D:/log/plane.log

Also,

log4j.logger.com.myapp=LOG, car
log4j.logger.com.myapp=LOG, plane

This should be

log4j.logger.com.myapp=DEBUG, add
log4j.logger.com.myapp=DEBUG, edit

You will be mentioning the appender names which correspond to the log files.

How do I differentiate the log output for each file?

Assuming you want the logs from the classes under com.myapp.core to go into car.log then you will have to change your log4j.properties file to include:

log4j.logger.com.myapp.core=DEBUG, add

and in your code, use:

package com.myapp.core;
 
class MyCoreClass {
 
private static Logger logger = Logger.getLogger(MyCoreClass.class);
 
public void doSomeOp() {
 
logger.debug("Hi, do you see this message in car.log?");
}
 
}
 

And then if you want the classes under com.myapp.ui to log into the plane.log then you will have to add this to your log4j.properties:

log4j.logger.com.myapp.ui=DEBUG, edit

and in your code:

package com.myapp.ui;
 
class MyUIClass {
 
private static Logger logger = Logger.getLogger(MyUIClass.class);
 
public void doSomeOp() {
 
logger.debug("Hi, do you see this message in plane.log?");
}
 
}