Java: Finding out *why* a class is loaded

Question

I am currently having the problem that I have a (partial) program that is trying to load a class but fails because it cannot find this class. Looking at the stack trace, I cannot see any particular reason for why the VM tries to load this particular class at the first place. Are there any tools that would let me figure out why a particular class is being loaded? Hint: I am already getting a stack trace at the exact point where the JVM tries to load the class (through an agent). However, the stack trace contains no line numbers. Therefore I only know which method triggers the class being loaded, not which statement. Then, even knowing the statement may not be enough. A single statement can cause a class to be loaded in many ways, because sometimes the VM needs to load part of the transitive closure of classes.

Accepted Answer

Run your program with the `-XX:+TraceClassLoading` and `-XX:+TraceClassResolution` flags. This will create a LOT of output that looks like the following:

```
[Loaded com.kdgregory.example.memory.PermgenExhaustion$MyClassLoader from file:/home/kgregory/Workspace/Website/programming/examples/bin/]
RESOLVE com.kdgregory.example.memory.PermgenExhaustion$MyClassLoader java.net.URLClassLoader
RESOLVE java.net.URLClassLoader java.lang.Class URLClassLoader.java:188
```

You'll need to trace the chain of RESOLVE messages for a particular class. Or more likely, you'll see an error when your program attempts to load the class, preceeded by resolve messages for the class that loads it).

Java: Finding out why a class is loaded

Solution

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