ToStringHelper.java

package org.slf4j.instrumentation;

import java.util.Map;
import java.util.WeakHashMap;

public class ToStringHelper {

	/**
	 * Prefix to use at the start of the representation. Always used.
	 */
	private static final String ARRAY_PREFIX = "[";

	/**
	 * Suffix to use at the end of the representation. Always used.
	 */
	private static final String ARRAY_SUFFIX = "]";

	/**
	 * String separating each element when rendering an array. To be compatible
	 * with lists comma-space is used.
	 */

	private static final String ELEMENT_SEPARATOR = ", ";

	/**
	 * unrenderableClasses is essentially a Set of Class objects which has for
	 * some reason failed to render properly when invoked through a toString
	 * method call. To avoid memory leaks a data structure using weak references
	 * is needed, but unfortunately the runtime library does not contain a
	 * WeakHashSet class, so the behavior is emulated with a WeakHashmap with
	 * the class as the key, and a Long containing the value of
	 * System.currentTimeMilis when an instance of the class failed to render.
	 */

	final static Map<Class<?>, Object> unrenderableClasses = new WeakHashMap<Class<?>, Object>();

	/**
	 * Returns o.toString() unless it throws an exception (which causes it to be
	 * stored in unrenderableClasses) or already was present in
	 * unrenderableClasses. If so, the same string is returned as would have
	 * been returned by Object.toString(). Arrays get special treatment as they
	 * don't have usable toString methods.
	 * 
	 * @param o
	 *            incoming object to render.
	 * @return
	 */

	public static String render(Object o) {
		if (o == null) {
			return String.valueOf(o);
		}
		Class<?> objectClass = o.getClass();

		if (unrenderableClasses.containsKey(objectClass) == false) {
			try {
				if (objectClass.isArray()) {
					return renderArray(o, objectClass).toString();
				} else {
					return o.toString();
				}
			} catch (Exception e) {
				Long now = new Long(System.currentTimeMillis());

				System.err.println("Disabling exception throwing class "
						+ objectClass.getName() + ", " + e.getMessage());

				unrenderableClasses.put(objectClass, now);
			}
		}
		String name = o.getClass().getName();
		return name + "@" + Integer.toHexString(o.hashCode());
	}

	/**
	 * renderArray returns an array similar to a List. If the array type is an
	 * object they are rendered with "render(object)" for each. If the array
	 * type is a primitive each element is added directly to the string buffer
	 * collecting the result.
	 * 
	 * @param o
	 * @param objectClass
	 * @return
	 */
	private static StringBuffer renderArray(Object o, Class<?> objectClass) {
		Class<?> componentType = objectClass.getComponentType();
		StringBuffer sb = new StringBuffer(ARRAY_PREFIX);

		if (componentType.isPrimitive() == false) {
			Object[] oa = (Object[]) o;
			for (int i = 0; i < oa.length; i++) {
				if (i > 0) {
					sb.append(ELEMENT_SEPARATOR);
				}
				sb.append(render(oa[i]));
			}
		} else {
			if (Boolean.TYPE.equals(componentType)) {
				boolean[] ba = (boolean[]) o;
				for (int i = 0; i < ba.length; i++) {
					if (i > 0) {
						sb.append(ELEMENT_SEPARATOR);
					}
					sb.append(ba[i]);
				}
			} else if (Integer.TYPE.equals(componentType)) {
				int[] ia = (int[]) o;
				for (int i = 0; i < ia.length; i++) {
					if (i > 0) {
						sb.append(ELEMENT_SEPARATOR);
					}
					sb.append(ia[i]);
				}

			} else if (Long.TYPE.equals(componentType)) {
				long[] ia = (long[]) o;
				for (int i = 0; i < ia.length; i++) {
					if (i > 0) {
						sb.append(ELEMENT_SEPARATOR);
					}
					sb.append(ia[i]);
				}
			} else if (Double.TYPE.equals(componentType)) {
				double[] ia = (double[]) o;
				for (int i = 0; i < ia.length; i++) {
					if (i > 0) {
						sb.append(ELEMENT_SEPARATOR);
					}
					sb.append(ia[i]);
				}
			} else if (Float.TYPE.equals(componentType)) {
				float[] ia = (float[]) o;
				for (int i = 0; i < ia.length; i++) {
					if (i > 0) {
						sb.append(ELEMENT_SEPARATOR);
					}
					sb.append(ia[i]);
				}
			} else if (Character.TYPE.equals(componentType)) {
				char[] ia = (char[]) o;
				for (int i = 0; i < ia.length; i++) {
					if (i > 0) {
						sb.append(ELEMENT_SEPARATOR);
					}
					sb.append(ia[i]);
				}
			} else if (Short.TYPE.equals(componentType)) {
				short[] ia = (short[]) o;
				for (int i = 0; i < ia.length; i++) {
					if (i > 0) {
						sb.append(ELEMENT_SEPARATOR);
					}
					sb.append(ia[i]);
				}
			} else if (Byte.TYPE.equals(componentType)) {
				byte[] ia = (byte[]) o;
				for (int i = 0; i < ia.length; i++) {
					if (i > 0) {
						sb.append(ELEMENT_SEPARATOR);
					}
					sb.append(ia[i]);
				}
			}
		}
		sb.append(ARRAY_SUFFIX);
		return sb;
	}
}