Generic "quasi toString()" using Java Class reflection

Question

I have been trying to create a robust code that prints out any Java class for debugging. For that, I use reflections. In order to protect against recursive definition such as "Boolean contains static final Boolean TRUE", I ignore fields equal to their parents. I use String += just out of laziness. It doesn't have to be efficient.

Yet, is there a nicer way to do recursive description of objects with reflections?

public String reflectionShowFields(Object parentObject) {
    String stringData = "";

    for (Field field:parentObject.getClass().getFields()) {
        try {
            Class<?> type = field.getType();
            String typeSimpleName = type.getSimpleName();
            Object fieldValue = field.get(parentObject);
            String fieldName = field.getName();
            if (type.isPrimitive() || type.isEnum() || CharSequence.class.isAssignableFrom(type)) {
                stringData += String.format("%s: %s\n", fieldName, fieldValue);
            } else if (Iterable.class.isAssignableFrom(type)) {
                stringData += String.format(">>> %s[%s]: \n", fieldName, typeSimpleName);
                for (Object item:(Iterable)fieldValue) {
                    stringData += reflectionShowFields(item);
                }
                stringData += String.format("<<< %s[%s]: \n", fieldName, typeSimpleName);
            } else if (!fieldValue.equals(parentObject)) {
                stringData += String.format(">>> %s[%s]: %s \n--------\n", fieldName, typeSimpleName, fieldValue.toString());
                stringData+= reflectionShowFields(fieldValue);
                stringData += String.format("<<< %s[%s]: \n", fieldName, typeSimpleName);
            }
        } catch (IllegalAccessException ignored) {}
    }
    return stringData;
}

Can't eclipse generate a toString() for you? This seems like more trouble than it's worth. — Rob, Feb 19 '13 at 15:43
See also [Auto-generating toString Method](http://stackoverflow.com/questions/2653268/auto-generating-tostring-method) — Vadzim, Dec 06 '13 at 18:50

score 4 · Answer 1 · edited Jan 25 '16 at 15:44

4

You could use Apache commons-lang ReflectionToStringBuilder https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/builder/ReflectionToStringBuilder.html

edited Jan 25 '16 at 15:44

CupawnTae

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answered Feb 19 '13 at 15:48

Evgeniy Dorofeev

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Could have worked if I could easily join libs :( I am running Android so I have to be thin on libs and thin on footprint. Since the whole thing is for debugging, I better not waste precious memory when the final product doesn't need it. Thanks. S.M – Meymann Mar 03 '13 at 09:22

Stephen C · Answer 2 · 2013-02-19T16:04:06.420

I don't think this is going to work.

Ignoring fields "that are equal to their parents" won't work. What if you have an A that refers to a B that refers back to the A.
You want to know about the cycles, and also the shared nodes in a DAG.
Iterating an Iterable can have side-effects, or it might never terminate, or it might throw exceptions.
Producing a readable rendering of an arbitrary graph is likely to really hard.
This is going to be an order of magnitude slower than a hand-built toString() method.

But think about it this way. If this was a good idea, there would be high profile 3rd-party libraries that did this kind of thing. And we'd all be using them already. It turns out that there ARE 3rd-party libraries, but you'd hardly call them high profile.

Incidentally, you could use JAXB or a JSON binding to render your POJOs as text. That achieves the same ends ...

Finally, your example of Boolean with a static field of type Boolean is not apropos. You wouldn't want to render static fields when displaying an instance.

Agree, had to fix it so that it works. Had to give up recursive types. If you have a recursive type that doesn't define toString() - tough luck. It's a pity but I didn't want to put too much time on debug tools. As for 3rd parties etc. I prefer not. I am a lib so I better not mess the user with other libs. Also, it's Android. I need to be memory skinny. So for me, it's only POJO. — Meymann, Mar 03 '13 at 09:16

Generic "quasi toString()" using Java Class reflection

2 Answers2