JDI: How to get the ObjectReference value?

Question

I am using the JDI to recode the variable status in the method. According to the tutorial, I am not found how to get objectReference value, like List, Map or my custom class. It just can get PrimtiveValue.

StackFrame stackFrame = ((BreakpointEvent) event).thread().frame(0);
 Map<LocalVariable, Value> visibleVariables = (Map<LocalVariable, Value>) stackFrame
                            .getValues(stackFrame.visibleVariables());
                        for (Map.Entry<LocalVariable, Value> entry : visibleVariables.entrySet()) {
                            System.out.println("console->>" + entry.getKey().name() + " = " + entry.getValue());
                        }
}

if LocalVariable is PrimtiveValue type, like int a = 10;, then it will print

console->> a = 10

if LocalVariable is ObjectReference type, like Map data = new HashMap();data.pull("a",10), then it will print

console->> data = instance of java.util.HashMap(id=101)

But I want to get result like below

console->> data = {a:10} // as long as get the data of reference value

Thanks!

Oligarch

FYI: the visibleVariables() business will give you nothing unless the code was compiled with javac -g, which most production code won't be. – Eldaelden

Answer 1

There is no 'value' of an ObjectReference. It is itself an instance of Value.

What you probably want is to get a string representation of an object referenced by this ObjectReference. In this case you need to call toString() method on that object.

Call ObjectReference.invokeMethod passing a Method for toString(). As a result, you'll get a StringReference instance, on which you then call value() to obtain the desired string representation.

for (Map.Entry<LocalVariable, Value> entry : visibleVariables.entrySet()) {
    String name = entry.getKey().name();
    Value value = entry.getValue();

    if (value instanceof ObjectReference) {
        ObjectReference ref = (ObjectReference) value;
        Method toString = ref.referenceType()
                .methodsByName("toString", "()Ljava/lang/String;").get(0);
        try {
            value = ref.invokeMethod(thread, toString, Collections.emptyList(), 0);
        } catch (Exception e) {
            // Handle error
        }
    }

    System.out.println(name + " : " + value);
}

Sanatorium

"on which you then call value()". Well, it (somehow) works to call toString() directly as you're doing on the last line. However, that will add some quotes, e.g. when decapsulating a Boolean I get "true", including the quotes printed. – Eldaelden