How to get logs from a .jar file?

Question

I have an abc.jar file and it has some Java classes in it. I don't have the source code of it. I want to get logs of the classes/methods that's been hit while debugging.How can I do that?

P.S - I could have used log4j for it but I don't have the source code.

No, that abc.jar does not use/implement any logging framework. — Ravish Rawat, Aug 20 '15 at 09:34
`java -jar abc.jar >out.txt 2>err.txt` will capture standard output and error to two separate files. — Joop Eggen, Aug 20 '15 at 10:04
I think you should be able to use AOP/aspectJ to dynamically add logging to the classes in the jar. Have a look at this: http://stackoverflow.com/questions/8839077/how-to-use-aop-with-aspectj-for-logging — Dakshinamurthy Karra, Aug 20 '15 at 10:04
If it doesn't use any logging framework how can you possibly get logs out of it? Your question doesn't make sense. — user207421, Aug 20 '15 at 23:31

score 5 · Answer 1 · answered Oct 15 '15 at 09:39

5

Let's say if you have abc.jar and it doesn't use any framework for logging, and you don't have any source code as you have mentioned. No, you can't get logs this way.

answered Oct 15 '15 at 09:39

Nadim parvej

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2

score 5 · Answer 2 · answered Oct 16 '15 at 09:19

You need to use a profiling tools such as Java's hprof. It is a good introduction to profiling. While not powerful, it is a good start. There are plenty of other useful profiling tools. Just google them.

For hprof, the modes of CPU Usage Sampling Profiles (cpu=samples)

e.g. javac -J-agentlib:hprof=cpu=samples Hello.java

and CPU Usage Times Profile (cpu=times)

e.g. javac -J-agentlib:hprof=cpu=times Hello.java

sound like what you needs. They can tell you what is called and how often. What they won't tell you is the state of variables. This is what debugging is used for given that logging is not an option.

score 4 · Answer 3 · answered Aug 20 '15 at 09:45

You state in your comment that you know that abc.jar doesn't use any logging framework.

In that case, it is impossible to get logs from it.

However, what you can do is use a debugger. All IDEs have debuggers. This can help you know the state of the classes being called when you use them.

How to get logs from a .jar file?

3 Answers3