A library for tracing executed bytecode instructions.

Usage: Simply instantiate Tracer with a class name and call run with a method name, parameter classes, and argument values.

For example, to trace the following method:

package test.bt;

public class Demo {
	public static int[] createIntArray(int size) {
		if (size < 0)
			throw new IllegalArgumentException();
		return new int[size];
	}
}

with the argument 4:

Tracer tracer = new Tracer("test.bt.Demo");
String[] is = tracer.run("createIntArray", new Class<?>[] { int.class }, 4);

The returned array of strings is the list of executed bytecode instructions:

LABEL test/bt/DemoTest.createIntArray(I)[I0
ILOAD 0
IFGE test/bt/DemoTest.createIntArray(I)[I2 test/bt/DemoTest.createIntArray(I)[I1
LABEL test/bt/DemoTest.createIntArray(I)[I2
ILOAD 0
NEWARRAY 10
ARETURN

Alternatively, the library also comes with a command-line tool. Compiling with gradle fatJar will create bytecode-tracer-all-0.1.jar which can be used as follows:

java -cp .:bytecode-tracer-all-0.1.jar bt.Main "test.bt.DemoTest" "createIntArray" "(I)[I" "4"

to print out the above list of bytecode instructions.

The library uses ASM to inject and trace executions. As a result, it also returns non-standard bytecode instructions from ASM such as LABEL in the above example.