a way to use log4j pass set flags in my code

Question

I need to pass some value to enable certain code in may app (in this case is to optionally enable writing some stats to a file in certain conditions, but it might be anything generally).

My java app is installed as a service. So every way I have thought of has some drawbacks:

1. Add another param to main(): cumbersome as customers already have the tool installed, and the command line would need to be changed every time.
2. Adding java -DmyEnvVar=A_VALUE to my command line: same as above.
3. Set an environment variable: service should at least be restarted, and even then you must take care of what user is the service running under etc.
4. Adding the property in the config file: I prefer not to have this visible on the config file so the user does not see it, it is something for debugging etc.

So I thought maybe there is some way (or hack) to use log4j loggers to pass that value to my code. I have thought of one way already, although is very limited:

1. Add a dummy class to my codebase com.dummy.DevOptions

   public class DevOptions { public static final Logger logger = Logger.getLogger(DevOptions.class);

2. In my code, use it like this:

   if (DevOptions.logger.isInfoEnabled()){ //do my optional stuff } //... if (DevOptions.logger.isDebugEnabled()){ //do other stuff }

This allows me to use discriminate among various values, and I could increase the number by adding more loggers to DevOptions. But I wonder whether there is a cleaner way, possibly by configuring the loggers only in log4j.xml??

Answer 1

In log4j you dont need Java classes at all to create loggers (This may come as a surprise). All you need is a package qualified string and not a Java class to create logger category. If I were you I would do the following

PS: Code not guaranteed to compile/run

public class SomeAppCode {
      public static final Logger specialLogger = Logger.getLogger("com.mypackage.mysubpackage.speciallogger");

      public void someMethod() {
        if(specialLogger.isDebugEnabled()) {
           //do low level stuff
        } 

      }
}

In your log4j.xml add a category for this string mentioned and if you want you could set "additivity" to be true/false (depending on whether you want to propogate this log message to multiple loggerS)

PS: Note specialLogger is public static and such can be used by 100s of classes like it were their own loggers.

Answer 2

ok I think I found what I needed, wasn't that difficult actually...

 public class DevOptions{
  public static boolean isEnabled(String myvalue){
    Logger logger = Logger.getLogger(myvalue);
    return logger.isDebugEnabled();
  }

}

public class SomeAppCode {
  public void someMethod() {
    if(DevOptions.isEnabled("value.A")) {
       //do low level stuff
    } 
  }

}

And I can add as many values like value.A in log4j.xml:

  <logger name="value.A" additivity="true"><level value="debug" /></logger>

This way I can add as many values as I want by only modifying log4j.xml, no need to add more loggers to DevOptions, only one is sufficient.