How to extend class and override method of log4j.Logger

[Tom Fischer]

1. I want to test JS code automatically that runs in Rhino (fixed)
2. The JS code uses log4j (v1) for logging
3. I need to run the JS code and catch up the logged messages (add them to an array that I process after executing code)

My idea is to extend the Logger class of org.apache.log4j.Logger and override existing methods (prefer log() but debug/info/warn/error would also fit)

Problems where I stuck:

• overriding debug method not working (ignored?)
  
• some superclass methods are not accessible

Any idea?

Here's how it's done in Java:

https://github.com/apache/log4j/blob/trunk/examples/subclass/MyLogger.java

Here's how I tried (sorry for the super stupid code, I hope it gives some details and highlights the problem):

org.apache.log4j.BasicConfigurator.configure();

var logger = org.apache.log4j.LogManager.getRootLogger();

var overrides = {

debug: function(message) {

java.lang.System.out.println("bingo!");

this.super$debug(message);

},

getLogger: function(name) {

logger.debug("super$debug: " + this.super$debug); // DEBUG root  - super$debug: function super$debug() { void super$debug(java.lang.Object,java.lang.Throwable) void super$debug(java.lang.Object) }

logger.debug("super$info: " + this.super$info); // DEBUG root  - super$info: undefined

logger.debug("super$warn: " + this.super$warn); // DEBUG root  - super$warn: undefined

logger.debug("super$error: " + this.super$error); // DEBUG root  - super$error: undefined

logger.debug("super$log: " + this.super$log); // DEBUG root  - super$log: undefined

logger.debug("super$getLogger: " + this.super$getLogger); // DEBUG root  - super$getLogger: undefined

return org.apache.log4j.Logger.getLogger(name); // works

// return this.super$getLogger(name); // does NOT work (undefined)

}

};

var loggerName = "transformer";

// example 1: using JavaAdapter to extend Logger class

var ja = new JavaAdapter(org.apache.log4j.Logger, overrides, loggerName);

logger.debug("ja.getClass(): " + ja.getClass()); // DEBUG root  - ja.getClass(): class adapter1

logger.debug("ja.getName(): " + ja.getName()); // DEBUG root  - ja.getName(): transformer

var logger_1 = ja.getLogger(loggerName);

logger.debug("logger_1: " + logger_1); // DEBUG root  - logger_1: org.apache.log4j.Logger@6895a785

logger.debug("logger_1.getClass(): " + logger_1.getClass()); // logger_1.getClass(): class org.apache.log4j.Logger

logger.debug("logger_1.getName(): " + logger_1.getName()); // logger_1.getName(): transformer

logger_1.debug("hello 1"); //* DEBUG transformer  - hello 1

// example 2: getLogger(Class clazz) where clazz = JavaAdapter object

var logger_2 = org.apache.log4j.LogManager.getLogger(ja);

logger.debug("logger_2: " + logger_2); // DEBUG root  - logger_2: org.apache.log4j.Logger@56aac163

logger_2.debug("hello 2"); //* DEBUG adapter1@184f6be2  - hello 2

// example 3: getLogger(Class clazz) clazz = Logger object from logger_1 via JavaAdapter

var logger_3 = org.apache.log4j.LogManager.getLogger(logger_1); // 

logger.debug("logger_3: " + logger_3); // DEBUG root  - logger_3: org.apache.log4j.Logger@1f7030a6

logger_3.debug("hello 3"); //* DEBUG org.apache.log4j.Logger@6895a785  - hello 3

//* should print "bingo!" first -> override NOT working

/* output:

0 [main] DEBUG root  - ja.getClass(): class adapter1

2 [main] DEBUG root  - ja.getName(): transformer

2 [main] DEBUG root  - super$debug: function super$debug() {

void super$debug(java.lang.Object,java.lang.Throwable)

void super$debug(java.lang.Object)

}

2 [main] DEBUG root  - super$info: undefined

3 [main] DEBUG root  - super$warn: undefined

3 [main] DEBUG root  - super$error: undefined

3 [main] DEBUG root  - super$log: undefined

3 [main] DEBUG root  - super$getLogger: undefined

3 [main] DEBUG root  - logger_1: org.apache.log4j.Logger@6895a785

3 [main] DEBUG root  - logger_1.getClass(): class org.apache.log4j.Logger

3 [main] DEBUG root  - logger_1.getName(): transformer

3 [main] DEBUG transformer  - hello 1

3 [main] DEBUG root  - logger_2: org.apache.log4j.Logger@56aac163

3 [main] DEBUG adapter1@184f6be2  - hello 2

4 [main] DEBUG root  - logger_3: org.apache.log4j.Logger@1f7030a6

5 [main] DEBUG org.apache.log4j.Logger@6895a785  - hello 3

*/

[Tom Fischer]

If I minimize the code to this:

org.apache.log4j.BasicConfigurator.configure();

var logger = org.apache.log4j.LogManager.getRootLogger();

var overrides = {

getLogger: function(name) {

for(var i in this) {

try {

print(i + ": " + String(this[i]));

} catch(err) {

print(i + ": " + err.message);

}

}

return org.apache.log4j.Logger.getLogger(name);

}

};

var loggerName = "transformer";

var ja = new JavaAdapter(org.apache.log4j.Logger, overrides, loggerName);

var logger_1 = ja.getLogger(loggerName);

for(var i in logger_1) {

try {

print(i + ": " + String(logger_1[i]));

} catch(err) {

print(i + ": " + err.message);

}

}

And compare the output of the 2 for-loops: https://www.diffchecker.com/BhspSvf0

You see some important differences (e.g. logger, parent, NullPointerExceptions)... looks pretty strange like the JavaAdapter didn't properly extend the Logger class.

Any idea what I'm doing wrong?

Many thanks.