How do you set a breakpoint before executing - jdi

Question

I would like to set a breakpoint in an application before it starts to run, so that I can make sure the application does not pass the breakpoint on startup.
In order to set a breakpoint you need to do something like:
EventRequestManager reqMan = vm.eventRequestManager();
BreakpointRequest bpReq = reqMan.createBreakpointRequest(locationForBreakpoint);
bpReq.enable();
In order to get the Location for the breakpoint, you can do something like:
Method method = location.method();
List<Location> locations = method.locationsOfLine(55);
Location locationForBreakpoint = locations.get(0);
In order to get a Method you can do something like:
classType.concreteMethodByName(methodNname, String signature)
However in order to get that classType you seem to require an ObjectReference which seems to require a running JVM.
Is there any way to set the breakpoint before the application JVM runs, to be sure the breakpoint is not passed during application startup?

Answer 1

First of all start you target program using a LaunchingConnector to get back the target virtual machine.
VirtualMachineManager vmm = Bootstrap.virtualMachineManager();
LaunchingConnector lc = vmm.launchingConnectors().get(0);
// Equivalently, can call:
// LaunchingConnector lc = vmm.defaultConnector();
Map<String, Connector.Argument> env = lc.defaultArguments();
env.get("main").setValue("p.DebugDummy");
env.get("suspend").setValue("true");
env.get("home").setValue("C:/Program Files/Java/jdk1.7.0_51");
VirtualMachine vm = lc.launch(env);
(change environment values according to your needs,but remember to start target VM with suspended=true).
With this VM in you hand intercept a ClassPrepareEvent using a ClassPrepareRequest.
ClassPrepareRequest r = reqMan.createClassPrepareRequest();
r.addClassFilter("myclasses.SampleClass");
r.enable();
Create a ClassPrepareEvent handler
executor.execute(()-> {
try {
while(true)
{
EventQueue eventQueue = vm.eventQueue();
EventSet eventSet = eventQueue.remove();
EventIterator eventIterator = eventSet.eventIterator();
if (eventIterator.hasNext()) {
Event event = eventIterator.next();
if(event instanceof ClassPrepareEvent) {
ClassPrepareEvent evt = (ClassPrepareEvent) event;
ClassType classType = (ClassType) evt.referenceType();
List<Location> locations = referenceType.locationsOfLine(55);
Location locationForBreakpoint = locations.get(0);
vm.resume();
}
}
}
} catch (InterruptedException | AbsentInformationException | IncompatibleThreadStateException e) {
e.printStackTrace();
}
}
then resume target VM with a call to vm.resume() to run program.
I hope this solve your problem.