reflectiontostringbuilder.java

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/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2002-2003 The Apache Software Foundation.  All rights
 * reserved.
 *
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 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowledgement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgement may appear in the software itself,
 *    if and wherever such third-party acknowledgements normally appear.
 *
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 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.commons.lang.builder;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.HashSet;
import java.util.Set;

import org.apache.commons.lang.ClassUtils;

/**
 * <p>Assists in implementing {@link Object#toString()} methods using reflection.</p>
 *
 * <p>This class uses reflection to determine the fields to append. 
 * Because these fields are usually private, the class 
 * uses <code>AccessibleObject.setAccessible</code> to
 * change the visibility of the fields. This will fail under a security manager,
 * unless the appropriate permissions are set up correctly.</p>
 *
 * <p>A typical invocation for this method would look like:</p>
 * <pre>
 * public String toString() {
 *   return ReflectionToStringBuilder.toString(this);
 * }</pre>
 *
 * <p>You can also use the builder to debug 3rd party objects:</p>
 * <pre>
 * System.out.println("An object: " + ReflectionToStringBuilder.toString(anObject));</pre>
 * 
 * <p>A subclass can control field output by overriding the methods:
 * <ul> 
 *  <li>{@link #accept(java.lang.reflect.Field)}</li>
 *  <li>{@link #getValue(java.lang.reflect.Field)}</li>
 * </ul>
 * </p>
 * <p>For example, this method does <i>not</i> include the <code>password</code> field in the returned 
 * <code>String</code>:</p>
 * <pre>
 * public String toString() {
 *     return (new ReflectionToStringBuilder(this) {
 *         protected boolean accept(Field f) {
 *             return super.accept(f) && !f.getName().equals("password");
 *         }
 *     }).toString();
 * }</pre>
 * 
 * <p>The exact format of the <code>toString</code> is determined by
 * the {@link ToStringStyle} passed into the constructor.</p>
 *
 * @author Gary Gregory
 * @author Stephen Colebourne
 * @author Pete Gieser
 * @since 2.0
 * @version $Id: ReflectionToStringBuilder.java,v 1.10 2003/08/23 00:21:49 ggregory Exp $
 */
public class ReflectionToStringBuilder extends ToStringBuilder {

    /**
     * <p>A registry of objects used by <code>reflectionToString</code> methods
     * to detect cyclical object references and avoid infinite loops.</p>
     */
    private static ThreadLocal registry = new ThreadLocal() {
        protected synchronized Object initialValue() {
            // The HashSet implementation is not synchronized, 
            // which is just what we need here. 
            return new HashSet();
        }
    };

    /**
     * <p>Returns the registry of objects being traversed by the
     * <code>reflectionToString</code> methods in the current thread.</p>
     *
     * @return Set the registry of objects being traversed 
     */
    static Set getRegistry() {
        return (Set) registry.get();
    }

    /**
     * <p>Returns <code>true</code> if the registry contains the given object.
     * Used by the reflection methods to avoid infinite loops.</p>
     * 
     * @param value The object to lookup in the registry.
     * @return boolean <code>true</code> if the registry contains the given object.
     */
    static boolean isRegistered(Object value) {
        return getRegistry().contains(value);
    }

    /**
     * <p>Registers the given object.
     * Used by the reflection methods to avoid infinite loops.</p>
     * 
     * @param value The object to register.
     */
    static void register(Object value) {
        getRegistry().add(value);
    }
    
    /**
     * <p>This method uses reflection to build a suitable
     * <code>toString</code> using the default <code>ToStringStyle</code>.
     *
     * <p>It uses <code>AccessibleObject.setAccessible</code> to gain access to private
     * fields. This means that it will throw a security exception if run
     * under a security manager, if the permissions are not set up correctly.
     * It is also not as efficient as testing explicitly.</p>
     *
     * <p>Transient members will be not be included, as they are likely derived.
     * Static fields will not be included. Superclass fields will be appended.</p>
     *
     * @param object  the Object to be output
     * @return the String result
     * @throws IllegalArgumentException if the Object is <code>null</code>
     */
    public static String toString(Object object) {
        return toString(object, null, false, null);
    }

    /**
     * <p>This method uses reflection to build a suitable
     * <code>toString</code>.</p>
     *
     * <p>It uses <code>AccessibleObject.setAccessible</code> to gain access to private
     * fields. This means that it will throw a security exception if run
     * under a security manager, if the permissions are not set up correctly.
     * It is also not as efficient as testing explicitly.</p>
     *
     * <p>Transient members will be not be included, as they are likely derived.
     * Static fields will not be included. Superclass fields will be appended.</p>
     *
     * <p>If the style is <code>null</code>, the default
     * <code>ToStringStyle</code> is used.</p>
     * 
     * @param object  the Object to be output
     * @param style  the style of the <code>toString</code> to create,
     *  may be <code>null</code>
     * @return the String result
     * @throws IllegalArgumentException if the Object or
     *  <code>ToStringStyle</code> is <code>null</code>
     */
    public static String toString(Object object, ToStringStyle style) {
        return toString(object, style, false, null);
    }

    /**
     * <p>This method uses reflection to build a suitable
     * <code>toString</code>.</p>
     *
     * <p>It uses <code>AccessibleObject.setAccessible</code> to gain access to private
     * fields. This means that it will throw a security exception if run
     * under a security manager, if the permissions are not set up correctly.
     * It is also not as efficient as testing explicitly. </p>
     *
     * <p>If the <code>outputTransients</code> is <code>true</code>,
     * transient members will be output, otherwise they are ignored,
     * as they are likely derived fields, and not part of the value of the
     * Object.</p>
     *
     * <p>Static fields will not be included. Superclass fields will be appended.</p>
     *
     * <p>If the style is <code>null</code>, the default
     * <code>ToStringStyle</code> is used.</p>
     * 
     * @param object  the Object to be output
     * @param style  the style of the <code>toString</code> to create,
     *  may be <code>null</code>
     * @param outputTransients  whether to include transient fields
     * @return the String result
     * @throws IllegalArgumentException if the Object is <code>null</code>
     */
    public static String toString(Object object, ToStringStyle style, boolean outputTransients) {
        return toString(object, style, outputTransients, null);
    }

    /**
     * <p>This method uses reflection to build a suitable
     * <code>toString</code>.</p>
     *
     * <p>It uses <code>AccessibleObject.setAccessible</code> to gain access to private
     * fields. This means that it will throw a security exception if run
     * under a security manager, if the permissions are not set up correctly.
     * It is also not as efficient as testing explicitly. </p>
     *
     * <p>If the <code>outputTransients</code> is <code>true</code>,
     * transient members will be output, otherwise they are ignored,
     * as they are likely derived fields, and not part of the value of the
     * Object.</p>
     *
     * <p>Static fields will not be included. Superclass fields will be appended
     * up to and including the specified superclass. A null superclass is treated
     * as <code>java.lang.Object</code>.</p>
     *
     * <p>If the style is <code>null</code>, the default
     * <code>ToStringStyle</code> is used.</p>
     * 
     * @param object  the Object to be output
     * @param style  the style of the <code>toString</code> to create,
     *  may be <code>null</code>
     * @param outputTransients  whether to include transient fields
     * @param reflectUpToClass  the superclass to reflect up to (inclusive),
     *  may be <code>null</code>
     * @return the String result
     * @throws IllegalArgumentException if the Object is <code>null</code>
     */
    public static String toString(
        Object object,
        ToStringStyle style,
        boolean outputTransients,
        Class reflectUpToClass) {
        return new ReflectionToStringBuilder(object, style, null, reflectUpToClass, outputTransients).toString();
    }

    /**