Functions to get the String representation of any Java Object

deepToString.java

/**
* After some benchmarking with JMH, I found that the best way to implement the part that manage maps and collections was
* to use an Iterator and its built-in function that take a lambda (forEachRemaning).
* List of others solutions I tried:
* - Iterator (using for...in loop)
* - Iterator + while loop
* - Spliterator + Stream
* - Spliterator + lambda
*/
public class DeepToString {

	/**
	 *
	 * @param o The object to scan
	 * @return A string representation of {@code o}
	 * @see #deepToString(Object, boolean)
	 */
	public static String deepToString(Object o) {
		return deepToString(o, true);
	}
	
	/**
	 *
	 * @param o The object to scan
	 * @param preventLoop Whether or not to prevent reference loops when scanning the object
	 * @return A string representation of {@code o}
	 * @see #deepToString(Object)
	 */
	public static String deepToString(Object o, boolean preventLoop) {
		if (o == null) {
			return "null";
		}
		
		StringBuilder buf = new StringBuilder(64);
		deepToString(o, buf, (preventLoop ? new HashSet<>() : null));
		return buf.toString();
	}
	
	/**
	 * Internal function, scan an object and get its string representation
	 * @param o An object to scan
	 * @param buf A String buffer to prevent high alloc count
	 * @param dejaVu A Set of object already scanned to prevent reference loop
	 */
	private static void deepToString(Object o, StringBuilder buf, Set<Object> dejaVu) {
		if (o == null) {
			buf.append("null");
			return;
		}
		
		if(dejaVu != null) {
			if (dejaVu.contains(o)) {
				buf.append("[...]");
				return;
			}
			
			dejaVu.add(o);
		}
		
		Class<?> clazz = o.getClass();
		if (clazz.isArray()) {
			if (clazz == byte[].class) {
				buf.append(Arrays.toString((byte[]) o));
			} else if (clazz == short[].class) {
				buf.append(Arrays.toString((short[]) o));
			} else if (clazz == int[].class) {
				buf.append(Arrays.toString((int[]) o));
			} else if (clazz == long[].class) {
				buf.append(Arrays.toString((long[]) o));
			} else if (clazz == char[].class) {
				buf.append(Arrays.toString((char[]) o));
			} else if (clazz == float[].class) {
				buf.append(Arrays.toString((float[]) o));
			} else if (clazz == double[].class) {
				buf.append(Arrays.toString((double[]) o));
			} else if (clazz == boolean[].class) {
				buf.append(Arrays.toString((boolean[]) o));
			} else { // element is an array of object references
				Object[] objs = (Object[]) o;
				if(objs.length == 0) {
					buf.append("[]");
				} else {
					int last = objs.length - 1;
					buf.append('[');
					for (int t = 0; t < last; t++) {
						deepToString(objs[t], buf, dejaVu);
						buf.append(", ");
					}
					deepToString(objs[last], buf, dejaVu);
					buf.append(']');
				}
			}
		} else if (o instanceof Map) {
			Iterator<Map.Entry<?, ?>> iter = ((Set<Map.Entry<?, ?>>) ((Map) o).entrySet()).iterator();
			if(iter.hasNext()) {
				buf.append('{');
				Map.Entry<?, ? > first = iter.next();
				deepToString(first.getKey(), buf, dejaVu);
				buf.append("->");
				deepToString(first.getValue(), buf, dejaVu);
				
				iter.forEachRemaining(entry -> {
					buf.append(", ");
					deepToString(entry.getKey(), buf, dejaVu);
					buf.append("->");
					deepToString(entry.getValue(), buf, dejaVu);
				});
				buf.append('}');
			} else {
				buf.append("{}");
			}
		} else if (o instanceof Collection) {
			Iterator<Object> iter = ((Collection) o).iterator();
			if(iter.hasNext()) {
				buf.append('(');
				deepToString(iter.next(), buf, dejaVu);
				
				iter.forEachRemaining(elem -> {
					buf.append(", ");
					deepToString(elem, buf, dejaVu);
				});
				
				buf.append(')');
			} else {
				buf.append("()");
			}
		} else if (o instanceof String) {
			buf.append('\"').append((String) o).append('\"');
		} else if (clazz == Object.class) {
			buf.append("obj");
		} else {
			buf.append(o.toString());
		}
	}
	
}