How can I inspect and prettyprint JDI Value objects using Jackson?

Question

I am trying to prettyprint in JSON format objects I retrieve from the Java Debug Interface. These objects are the arguments of the method where my breakpoint hit.

My code inside the BreakpointEvent handler is as follows :

// event is the current BreakpointEvent
StackFrame sf = event.thread().frame(0);
for (Value v : sf.getArgumentValues()) {
    try {
        ObjectMapper mapper = new ObjectMapper();
        System.out.println(mapper.writeValueAsString(v));
    } catch (Exception e) {
        e.printStackTrace();
    }
}
        

However, the only output that I'm getting out of that is a bunch of {"collected":false}, which is not helpful at all...

I can do the inspection manually, by first checking the precise interface implemented by each v (interfaces like ArrayReference, StringReference, ...), then using the coresponding methods (v.getValues() for an object implementing ArrayReference for instance), and doing the same recursively for all values I get.

But manual inspection is more prone to error, and much more heavy in term of code and maintenance. I am confident that Jackson could do the trick here but I'm not getting it to work...

Answer 1

The way I ended up doing is as follows :

I created a wrapper class MyValue, with one public attribute value, and a getter getValue(), which I customize to return either:

• a java base type if possible;
• an ArrayList or HashMap of MyValue objects, for ArrayReference and ObjectReference Value objects.

I also had to take care of infinite reference (cyclic graphs, for example an object A having a ref to object B, and object B having a ref to object A), so the MyValue class also contains an ancestors list, to avoid loops. Hope this will be helpful to someone in the future.