跟踪 java 程序执行

Question

I am having a hard time finding some program to trace the execution of a java program.

For a starter just something that would give me like all method calls and time spent doing each call would be nice.

Do you have any suggestion? Thank you in advance

EDIT: i would like to get the whole call tree, or hierarchy, whatever it is exactly called, from startup, with time spent, and i couldn't get it with VisualVM. I found a screenshot of some tools that supposedly could do it but i haven't gone through with it and i would like something more simple to begin with:

That would be pretty close to what i have in mind: it gives a trace of some method call tree, the time spent in each method, even a representation of it.

What were the original problems i was trying to solve? Here is almost the whole story: First, i am working on some tool that has to populate some knowledge base. I recently realized that it was pretty slow (some specific request, that is adding ~30 entities to the base would take more than 20 seconds), so i would like to know if the time is spent on my code, on the network (REST call to update that knowledge base), in the knowledge base itself, or in my code. And if my code is slow, i want to know what exactly it is doing that is taking so much time.

Another reason is that i was reading "Effective Java 3rd edition", great book btw. In the item 6 "Avoid creating unnecessary objects"

There is this code snippet:

// Hideously slow! Can you spot the object creation?
private static long sum() {
  Long sum = 0L;
  for (long i = 0; i <= Integer.MAX_VALUE; i++)
    sum += i;
  return sum;
}

compared to that one:

private static long sum() {
  long sum = 0L;
  for (long i = 0; i <= Integer.MAX_VALUE; i++)
    sum += i;
  return sum;
}

I can see that he second version will take less time, i understand why, there are no Long object instanciated, etc. but i would like to see, with actual measures, how long exactly it is taking doing instanciations, see with measures the number of instances of Long, and other objects are being created, what percentage of memory Long objects are taking in that case etc.

And some other experiences at work, where we would blindly do some great deal of refactoring, some heated debates about whether some implementation X were "more efficient" than implementation Y, but actually we never have any data to back it up.

All in all, i realize i needed tool to get actual and solid data about what the code is doing, what is happening in the JVM, how much memory is being allocated, by what object, how much time is being spent doing what, etc.

That contains A LOT of specific questions, and my first one was this one: "how can i trace the execution of even a simple program".

Thank you and sorry for not being super specific to begin with.

And the other post that was suggested didn't help THAT much, using VisualVM with the plugin Profile Startup, on the toy example from Effective Java, i can get something when i count up to Integer.MAX_VALUE,

but if i only count up to 1.000.000 for example it looks like VisualVM doesn't have time to get started (although i thought launching my program with the option -agentpath:/home/joseph/dev/visualvm_142/profiler/lib/deployed/jdk16/linux-amd64/libprofilerinterface.so=/home/joseph/dev/visualvm_142/profiler/lib,5140 would let VisualVM start but all i get is a blank screen with "Status: profiling inactive" but it's all the same as the execution where i was counting to Integer.MAX_VALUE, i just dont' get it):

Answer 1

This little "Trace" tool developed by Oracle might help you: https://docs.oracle.com/javase/7/docs/technotes/guides/jpda/trace.html

It is based on Java Debug Interface (JDI).

I was really keen on using it, but I have spent 10 minutes looking for the Oracle examples to download, without being able to find them.

In the past I have used a lot BTrace https://github.com/btraceio/btrace , I see that it's still being actively maintained.

Answer 2

The correct term is profiling . Because of the long list of long (Long?) comments I make it an answer.

Your commercial IntelliJ IDEA, and the NetBeans IDE have a profiler, where you can start a profile, take snapshots to compare, find critical paths, memory usage, bottlenecks, time durations. You might want to compare them, though IntelliJ is likely to be better.

Then there are code style checkers like SonarLint, that just may find things like calculating with wrapped types.