Java java.lang.IllegalArgumentException: wrong number of arguments

Question

I try access info(String var) method in a final class that has a non visible contstructor Class(String var0, Logger var1, LoggerContext var2)

try {
Constructor<? extends Logger> var0 = logger.getClass().getDeclaredConstructor(String.class, Logger.class, LoggerContext.class);

var0.setAccessible(true);

logger.getClass().getDeclaredMethod("info", String.class).invoke(var0.newInstance(), new String(message));

} catch (NoSuchMethodException | SecurityException | IllegalAccessException | IllegalArgumentException | InvocationTargetException | InstantiationException e) {
            e.printStackTrace();
}

and this is the error

java.lang.IllegalArgumentException: wrong number of arguments
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)

The question is: what you are trying to actually do, this looks like you are trying to do something else, that's not how you are supposed to use any kind of logger. — GotoFinal
– GotoFinal, Commented Jan 24, 2020 at 16:33
I am trying to access a method from logback, specificly Logger#info(String) — Conclure
– Conclure, Commented Jan 24, 2020 at 16:34
Then you should get instance of logger from logger manager/factory, like LoggerFactory.getLogger("myLogger").info("message") where name of logger is often name of class but it does not need to be. — GotoFinal
– GotoFinal, Commented Jan 24, 2020 at 16:38

dan1st · Accepted Answer · 2020-01-24 16:32:57Z

1

You can only use var0.newInstance() with the args of it.

Just pass objects of the String, Logger and LoggerContext to the newInstance() method.

edited Jan 24, 2020 at 16:32

answered Jan 24, 2020 at 16:30

dan1st

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3 Comments

Conclure Over a year ago

Then I get java.lang.IllegalArgumentException: object is not an instance of declaring class logger.getClass().getDeclaredMethod("info", String.class).invoke(var0, new String(message));

Conclure Over a year ago

var0.newInstance(String.class, Logger.class, LoggerContext.class) @dan1st java.lang.IllegalArgumentException: argument type mismatch

dan1st Over a year ago

You have to call it with objects of the type of these classes.

Conclure · Accepted Answer · 2020-01-24 16:46:31Z

0

Solved! Then you should get instance of logger from logger manager/factory, like LoggerFactory.getLogger("myLogger").info("message") where name of logger is often name of class but it does not need to be. - @GotoFinal

EDIT: Sorry I don't know how to mark the right answer, quite new here.

answered Jan 24, 2020 at 16:46

Conclure

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2 Comments

GotoFinal Over a year ago

and for future: xyproblem.info, please always include what you are trying to do, not just how.

Conclure Over a year ago

Yeah sorry for that, will always include it in future questions ;)

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