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Java Utilities
There is a newer version: 2.18.0
package com.cedarsoftware.util;

import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Deque;
import java.util.HashMap;
import java.util.IdentityHashMap;
import java.util.LinkedList;
import java.util.Map;

/**
 * Java Object Graph traverser.  It will visit all Java object
 * reference fields and call the passed in Visitor instance with
 * each object encountered, including the root.  It will properly
 * detect cycles within the graph and not hang.
 *
 * @author John DeRegnaucourt ([email protected])
 *         

 *         Copyright (c) Cedar Software LLC
 *         


 *         Licensed under the Apache License, Version 2.0 (the "License");
 *         you may not use this file except in compliance with the License.
 *         You may obtain a copy of the License at
 *         


 *         License
 *         


 *         Unless required by applicable law or agreed to in writing, software
 *         distributed under the License is distributed on an "AS IS" BASIS,
 *         WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *         See the License for the specific language governing permissions and
 *         limitations under the License.
 */
@SuppressWarnings("unchecked")
public class Traverser
{
    public interface  Visitor
    {
        void process(Object o);
    }

    private final Map _objVisited = new IdentityHashMap<>();
    protected final Map _classCache = new HashMap<>();

    /**
     * @param o Any Java Object
     * @param visitor Visitor is called for every object encountered during
     * the Java object graph traversal.
     */
    public static void traverse(Object o, Visitor visitor)
    {
        traverse(o, null, visitor);
    }

    /**
     * @param o Any Java Object
     * @param skip String[] of class names to not include in the tally
     * @param visitor Visitor is called for every object encountered during
     * the Java object graph traversal.
     */
    public static void traverse(Object o, Class[] skip, Visitor visitor)
    {
        Traverser traverse = new Traverser();
        traverse.walk(o, skip, visitor);
        traverse._objVisited.clear();
        traverse._classCache.clear();
    }

    /**
     * Traverse the object graph referenced by the passed in root.
     * @param root Any Java object.
     * @param skip Set of classes to skip (ignore).  Allowed to be null.
     */
    public void walk(Object root, Class[] skip, Visitor visitor)
    {
        Deque stack = new LinkedList();
        stack.add(root);

        while (!stack.isEmpty())
        {
            Object current = stack.removeFirst();

            if (current == null || _objVisited.containsKey(current))
            {
                continue;
            }

            final Class clazz = current.getClass();
            ClassInfo classInfo = getClassInfo(clazz, skip);
            if (classInfo._skip)
            {  // Do not process any classes that are assignableFrom the skip classes list.
                continue;
            }

            _objVisited.put(current, null);
            visitor.process(current);

            if (clazz.isArray())
            {
                final int len = Array.getLength(current);
                Class compType = clazz.getComponentType();

                if (!compType.isPrimitive())
                {   // Speed up: do not walk primitives
                    ClassInfo info = getClassInfo(compType, skip);
                    if (!info._skip)
                    {   // Do not walk array elements of a class type that is to be skipped.
                        for (int i=0; i < len; i++)
                        {
                            Object element = Array.get(current, i);
                            if (element != null)
                            {   // Skip processing null array elements
                                stack.add(Array.get(current, i));
                            }
                        }
                    }
                }
            }
            else
            {   // Process fields of an object instance
                if (current instanceof Collection)
                {
                    walkCollection(stack, (Collection) current);
                }
                else if (current instanceof Map)
                {
                    walkMap(stack, (Map) current);
                }
                else
                {
                    walkFields(stack, current, skip);
                }
            }
        }
    }

    private void walkFields(Deque stack, Object current, Class[] skip)
    {
        ClassInfo classInfo = getClassInfo(current.getClass(), skip);

        for (Field field : classInfo._refFields)
        {
            try
            {
                Object value = field.get(current);
                if (value == null || value.getClass().isPrimitive())
                {
                    continue;
                }
                stack.add(value);
            }
            catch (IllegalAccessException ignored) { }
        }
    }

    private static void walkCollection(Deque stack, Collection col)
    {
        for (Object o : col)
        {
            if (o != null && !o.getClass().isPrimitive())
            {
                stack.add(o);
            }
        }
    }

    private static void walkMap(Deque stack, Map map)
    {
        for (Map.Entry entry : map.entrySet())
        {
            Object o = entry.getKey();

            if (o != null && !o.getClass().isPrimitive())
            {
                stack.add(entry.getKey());
                stack.add(entry.getValue());
            }
        }
    }

    private ClassInfo getClassInfo(Class current, Class[] skip)
    {
        ClassInfo classCache = _classCache.get(current);
        if (classCache != null)
        {
            return classCache;
        }

        classCache = new ClassInfo(current, skip);
        _classCache.put(current, classCache);
        return classCache;
    }

    /**
     * This class wraps a class in order to cache the fields so they
     * are only reflectively obtained once.
     */
    public static class ClassInfo
    {
        private boolean _skip = false;
        private final Collection _refFields = new ArrayList<>();

        public ClassInfo(Class c, Class[] skip)
        {
            if (skip != null)
            {
                for (Class klass : skip)
                {
                    if (klass.isAssignableFrom(c))
                    {
                        _skip = true;
                        return;
                    }
                }
            }

            Collection fields = ReflectionUtils.getDeepDeclaredFields(c);
            for (Field field : fields)
            {
                Class fc = field.getType();

                if (!fc.isPrimitive())
                {
                    _refFields.add(field);
                }
            }
        }
    }
}