    001    /*
    002     * Licensed to the Apache Software Foundation (ASF) under one or more
    003     * contributor license agreements.  See the NOTICE file distributed with
    004     * this work for additional information regarding copyright ownership.
    005     * The ASF licenses this file to You under the Apache License, Version 2.0
    006     * (the "License"); you may not use this file except in compliance with
    007     * the License.  You may obtain a copy of the License at
    008     *
    009     *      http://www.apache.org/licenses/LICENSE-2.0
    010     *
    011     * Unless required by applicable law or agreed to in writing, software
    012     * distributed under the License is distributed on an "AS IS" BASIS,
    013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014     * See the License for the specific language governing permissions and
    015     * limitations under the License.
    016     */
    017    package org.apache.commons.lang;
    018
    019    import java.io.Serializable;
    020    import java.lang.reflect.Array;
    021    import java.lang.reflect.InvocationTargetException;
    022
    023    import org.apache.commons.lang.exception.CloneFailedException;
    024    import org.apache.commons.lang.reflect.MethodUtils;
    025
    026    /**
    027     * <p>Operations on <code>Object</code>.</p>
    028     *
    029     * <p>This class tries to handle <code>null</code> input gracefully.
    030     * An exception will generally not be thrown for a <code>null</code> input.
    031     * Each method documents its behaviour in more detail.</p>
    032     *
    033     * <p>#ThreadSafe#</p>
    034     * @author Apache Software Foundation
    035     * @author <a href="mailto:nissim@nksystems.com">Nissim Karpenstein</a>
    036     * @author <a href="mailto:janekdb@yahoo.co.uk">Janek Bogucki</a>
    037     * @author Daniel L. Rall
    038     * @author Gary Gregory
    039     * @author Mario Winterer
    040     * @author <a href="mailto:david@davidkarlsen.com">David J. M. Karlsen</a>
    041     * @since 1.0
    042     * @version $Id: ObjectUtils.java 1057434 2011-01-11 01:27:37Z niallp $
    043     */
    044    //@Immutable
    045    public class ObjectUtils {
    046
    047        /**
    048         * <p>Singleton used as a <code>null</code> placeholder where
    049         * <code>null</code> has another meaning.</p>
    050         *
    051         * <p>For example, in a <code>HashMap</code> the
    052         * {@link java.util.HashMap#get(java.lang.Object)} method returns
    053         * <code>null</code> if the <code>Map</code> contains
    054         * <code>null</code> or if there is no matching key. The
    055         * <code>Null</code> placeholder can be used to distinguish between
    056         * these two cases.</p>
    057         *
    058         * <p>Another example is <code>Hashtable</code>, where <code>null</code>
    059         * cannot be stored.</p>
    060         *
    061         * <p>This instance is Serializable.</p>
    062         */
    063        public static final Null NULL = new Null();
    064
    065        /**
    066         * <p><code>ObjectUtils</code> instances should NOT be constructed in
    067         * standard programming. Instead, the class should be used as
    068         * <code>ObjectUtils.defaultIfNull("a","b");</code>.</p>
    069         *
    070         * <p>This constructor is public to permit tools that require a JavaBean instance
    071         * to operate.</p>
    072         */
    073        public ObjectUtils() {
    074            super();
    075        }
    076
    077        // Defaulting
    078        //-----------------------------------------------------------------------
    079        /**
    080         * <p>Returns a default value if the object passed is
    081         * <code>null</code>.</p>
    082         *
    083         * <pre>
    084         * ObjectUtils.defaultIfNull(null, null)      = null
    085         * ObjectUtils.defaultIfNull(null, "")        = ""
    086         * ObjectUtils.defaultIfNull(null, "zz")      = "zz"
    087         * ObjectUtils.defaultIfNull("abc", *)        = "abc"
    088         * ObjectUtils.defaultIfNull(Boolean.TRUE, *) = Boolean.TRUE
    089         * </pre>
    090         *
    091         * @param object  the <code>Object</code> to test, may be <code>null</code>
    092         * @param defaultValue  the default value to return, may be <code>null</code>
    093         * @return <code>object</code> if it is not <code>null</code>, defaultValue otherwise
    094         */
    095        public static Object defaultIfNull(Object object, Object defaultValue) {
    096            return object != null ? object : defaultValue;
    097        }
    098
    099        /**
    100         * <p>Compares two objects for equality, where either one or both
    101         * objects may be <code>null</code>.</p>
    102         *
    103         * <pre>
    104         * ObjectUtils.equals(null, null)                  = true
    105         * ObjectUtils.equals(null, "")                    = false
    106         * ObjectUtils.equals("", null)                    = false
    107         * ObjectUtils.equals("", "")                      = true
    108         * ObjectUtils.equals(Boolean.TRUE, null)          = false
    109         * ObjectUtils.equals(Boolean.TRUE, "true")        = false
    110         * ObjectUtils.equals(Boolean.TRUE, Boolean.TRUE)  = true
    111         * ObjectUtils.equals(Boolean.TRUE, Boolean.FALSE) = false
    112         * </pre>
    113         *
    114         * @param object1  the first object, may be <code>null</code>
    115         * @param object2  the second object, may be <code>null</code>
    116         * @return <code>true</code> if the values of both objects are the same
    117         */
    118        public static boolean equals(Object object1, Object object2) {
    119            if (object1 == object2) {
    120                return true;
    121            }
    122            if ((object1 == null) || (object2 == null)) {
    123                return false;
    124            }
    125            return object1.equals(object2);
    126        }
    127
    128        /**
    129         * <p>Compares two objects for inequality, where either one or both
    130         * objects may be <code>null</code>.</p>
    131         *
    132         * <pre>
    133         * ObjectUtils.notEqual(null, null)                  = false
    134         * ObjectUtils.notEqual(null, "")                    = true
    135         * ObjectUtils.notEqual("", null)                    = true
    136         * ObjectUtils.notEqual("", "")                      = false
    137         * ObjectUtils.notEqual(Boolean.TRUE, null)          = true
    138         * ObjectUtils.notEqual(Boolean.TRUE, "true")        = true
    139         * ObjectUtils.notEqual(Boolean.TRUE, Boolean.TRUE)  = false
    140         * ObjectUtils.notEqual(Boolean.TRUE, Boolean.FALSE) = true
    141         * </pre>
    142         *
    143         * @param object1  the first object, may be <code>null</code>
    144         * @param object2  the second object, may be <code>null</code>
    145         * @return <code>false</code> if the values of both objects are the same
    146         * @since 2.6
    147         */
    148        public static boolean notEqual(Object object1, Object object2) {
    149            return ObjectUtils.equals(object1, object2) == false;
    150        }
    151
    152        /**
    153         * <p>Gets the hash code of an object returning zero when the
    154         * object is <code>null</code>.</p>
    155         *
    156         * <pre>
    157         * ObjectUtils.hashCode(null)   = 0
    158         * ObjectUtils.hashCode(obj)    = obj.hashCode()
    159         * </pre>
    160         *
    161         * @param obj  the object to obtain the hash code of, may be <code>null</code>
    162         * @return the hash code of the object, or zero if null
    163         * @since 2.1
    164         */
    165        public static int hashCode(Object obj) {
    166            return (obj == null) ? 0 : obj.hashCode();
    167        }
    168
    169        // Identity ToString
    170        //-----------------------------------------------------------------------
    171        /**
    172         * <p>Gets the toString that would be produced by <code>Object</code>
    173         * if a class did not override toString itself. <code>null</code>
    174         * will return <code>null</code>.</p>
    175         *
    176         * <pre>
    177         * ObjectUtils.identityToString(null)         = null
    178         * ObjectUtils.identityToString("")           = "java.lang.String@1e23"
    179         * ObjectUtils.identityToString(Boolean.TRUE) = "java.lang.Boolean@7fa"
    180         * </pre>
    181         *
    182         * @param object  the object to create a toString for, may be
    183         *  <code>null</code>
    184         * @return the default toString text, or <code>null</code> if
    185         *  <code>null</code> passed in
    186         */
    187        public static String identityToString(Object object) {
    188            if (object == null) {
    189                return null;
    190            }
    191            StringBuffer buffer = new StringBuffer();
    192            identityToString(buffer, object);
    193            return buffer.toString();
    194        }
    195
    196        /**
    197         * <p>Appends the toString that would be produced by <code>Object</code>
    198         * if a class did not override toString itself. <code>null</code>
    199         * will throw a NullPointerException for either of the two parameters. </p>
    200         *
    201         * <pre>
    202         * ObjectUtils.identityToString(buf, "")            = buf.append("java.lang.String@1e23"
    203         * ObjectUtils.identityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa"
    204         * ObjectUtils.identityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa")
    205         * </pre>
    206         *
    207         * @param buffer  the buffer to append to
    208         * @param object  the object to create a toString for
    209         * @since 2.4
    210         */
    211        public static void identityToString(StringBuffer buffer, Object object) {
    212            if (object == null) {
    213                throw new NullPointerException("Cannot get the toString of a null identity");
    214            }
    215            buffer.append(object.getClass().getName())
    216                  .append('@')
    217                  .append(Integer.toHexString(System.identityHashCode(object)));
    218        }
    219
    220        /**
    221         * <p>Appends the toString that would be produced by <code>Object</code>
    222         * if a class did not override toString itself. <code>null</code>
    223         * will return <code>null</code>.</p>
    224         *
    225         * <pre>
    226         * ObjectUtils.appendIdentityToString(*, null)            = null
    227         * ObjectUtils.appendIdentityToString(null, "")           = "java.lang.String@1e23"
    228         * ObjectUtils.appendIdentityToString(null, Boolean.TRUE) = "java.lang.Boolean@7fa"
    229         * ObjectUtils.appendIdentityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa")
    230         * </pre>
    231         *
    232         * @param buffer  the buffer to append to, may be <code>null</code>
    233         * @param object  the object to create a toString for, may be <code>null</code>
    234         * @return the default toString text, or <code>null</code> if
    235         *  <code>null</code> passed in
    236         * @since 2.0
    237         * @deprecated The design of this method is bad - see LANG-360. Instead, use identityToString(StringBuffer, Object).
    238         */
    239        public static StringBuffer appendIdentityToString(StringBuffer buffer, Object object) {
    240            if (object == null) {
    241                return null;
    242            }
    243            if (buffer == null) {
    244                buffer = new StringBuffer();
    245            }
    246            return buffer
    247                .append(object.getClass().getName())
    248                .append('@')
    249                .append(Integer.toHexString(System.identityHashCode(object)));
    250        }
    251
    252        // ToString
    253        //-----------------------------------------------------------------------
    254        /**
    255         * <p>Gets the <code>toString</code> of an <code>Object</code> returning
    256         * an empty string ("") if <code>null</code> input.</p>
    257         *
    258         * <pre>
    259         * ObjectUtils.toString(null)         = ""
    260         * ObjectUtils.toString("")           = ""
    261         * ObjectUtils.toString("bat")        = "bat"
    262         * ObjectUtils.toString(Boolean.TRUE) = "true"
    263         * </pre>
    264         *
    265         * @see StringUtils#defaultString(String)
    266         * @see String#valueOf(Object)
    267         * @param obj  the Object to <code>toString</code>, may be null
    268         * @return the passed in Object's toString, or nullStr if <code>null</code> input
    269         * @since 2.0
    270         */
    271        public static String toString(Object obj) {
    272            return obj == null ? "" : obj.toString();
    273        }
    274
    275        /**
    276         * <p>Gets the <code>toString</code> of an <code>Object</code> returning
    277         * a specified text if <code>null</code> input.</p>
    278         *
    279         * <pre>
    280         * ObjectUtils.toString(null, null)           = null
    281         * ObjectUtils.toString(null, "null")         = "null"
    282         * ObjectUtils.toString("", "null")           = ""
    283         * ObjectUtils.toString("bat", "null")        = "bat"
    284         * ObjectUtils.toString(Boolean.TRUE, "null") = "true"
    285         * </pre>
    286         *
    287         * @see StringUtils#defaultString(String,String)
    288         * @see String#valueOf(Object)
    289         * @param obj  the Object to <code>toString</code>, may be null
    290         * @param nullStr  the String to return if <code>null</code> input, may be null
    291         * @return the passed in Object's toString, or nullStr if <code>null</code> input
    292         * @since 2.0
    293         */
    294        public static String toString(Object obj, String nullStr) {
    295            return obj == null ? nullStr : obj.toString();
    296        }
    297
    298        // Min/Max
    299        //-----------------------------------------------------------------------
    300        /**
    301         * Null safe comparison of Comparables.
    302         *
    303         * @param c1  the first comparable, may be null
    304         * @param c2  the second comparable, may be null
    305         * @return
    306         *  <ul>
    307         *   <li>If both objects are non-null and unequal, the lesser object.
    308         *   <li>If both objects are non-null and equal, c1.
    309         *   <li>If one of the comparables is null, the non-null object.
    310         *   <li>If both the comparables are null, null is returned.
    311         *  </ul>
    312         */
    313        public static Object min(Comparable c1, Comparable c2) {
    314            return (compare(c1, c2, true) <= 0 ? c1 : c2);
    315        }
    316
    317        /**
    318         * Null safe comparison of Comparables.
    319         *
    320         * @param c1  the first comparable, may be null
    321         * @param c2  the second comparable, may be null
    322         * @return
    323         *  <ul>
    324         *   <li>If both objects are non-null and unequal, the greater object.
    325         *   <li>If both objects are non-null and equal, c1.
    326         *   <li>If one of the comparables is null, the non-null object.
    327         *   <li>If both the comparables are null, null is returned.
    328         *  </ul>
    329         */
    330        public static Object max(Comparable c1, Comparable c2) {
    331            return (compare(c1, c2, false) >= 0 ? c1 : c2);
    332        }
    333
    334        /**
    335         * Null safe comparison of Comparables.
    336         * {@code null} is assumed to be less than a non-{@code null} value.
    337         *
    338         * @param c1  the first comparable, may be null
    339         * @param c2  the second comparable, may be null
    340         * @return a negative value if c1 < c2, zero if c1 = c2
    341         * and a positive value if c1 > c2
    342         * @since 2.6
    343         */
    344        public static int compare(Comparable c1, Comparable c2) {
    345            return compare(c1, c2, false);
    346        }
    347
    348        /**
    349         * Null safe comparison of Comparables.
    350         *
    351         * @param c1  the first comparable, may be null
    352         * @param c2  the second comparable, may be null
    353         * @param nullGreater if true <code>null</code> is considered greater
    354         * than a Non-<code>null</code> value or if false <code>null</code> is
    355         * considered less than a Non-<code>null</code> value
    356         * @return a negative value if c1 < c2, zero if c1 = c2
    357         * and a positive value if c1 > c2
    358         * @see java.util.Comparator#compare(Object, Object)
    359         * @since 2.6
    360         */
    361        public static int compare(Comparable c1, Comparable c2, boolean nullGreater) {
    362            if (c1 == c2) {
    363                return 0;
    364            } else if (c1 == null) {
    365                return (nullGreater ? 1 : -1);
    366            } else if (c2 == null) {
    367                return (nullGreater ? -1 : 1);
    368            }
    369            return c1.compareTo(c2);
    370        }
    371
    372        /**
    373         * Clone an object.
    374         *
    375         * @param o the object to clone
    376         * @return the clone if the object implements {@link Cloneable} otherwise <code>null</code>
    377         * @throws CloneFailedException if the object is cloneable and the clone operation fails
    378         * @since 2.6
    379         */
    380        public static Object clone(final Object o) {
    381            if (o instanceof Cloneable) {
    382                final Object result;
    383                if (o.getClass().isArray()) {
    384                    final Class componentType = o.getClass().getComponentType();
    385                    if (!componentType.isPrimitive()) {
    386                        result = ((Object[])o).clone();
    387                    } else {
    388                        int length = Array.getLength(o);
    389                        result = Array.newInstance(componentType, length);
    390                        while (length-- > 0) {
    391                            Array.set(result, length, Array.get(o, length));
    392                        }
    393                    }
    394                } else {
    395                    try {
    396                        result = MethodUtils.invokeMethod(o, "clone", null);
    397                    } catch (final NoSuchMethodException e) {
    398                        throw new CloneFailedException("Cloneable type "
    399                            + o.getClass().getName()
    400                            + " has no clone method", e);
    401                    } catch (final IllegalAccessException e) {
    402                        throw new CloneFailedException("Cannot clone Cloneable type "
    403                            + o.getClass().getName(), e);
    404                    } catch (final InvocationTargetException e) {
    405                        throw new CloneFailedException("Exception cloning Cloneable type "
    406                            + o.getClass().getName(), e.getTargetException());
    407                    }
    408                }
    409                return result;
    410            }
    411
    412            return null;
    413        }
    414
    415        /**
    416         * Clone an object if possible. This method is similar to {@link #clone(Object)}, but will
    417         * return the provided instance as the return value instead of <code>null</code> if the instance
    418         * is not cloneable. This is more convenient if the caller uses different
    419         * implementations (e.g. of a service) and some of the implementations do not allow concurrent
    420         * processing or have state. In such cases the implementation can simply provide a proper
    421         * clone implementation and the caller's code does not have to change.
    422         *
    423         * @param o the object to clone
    424         * @return the clone if the object implements {@link Cloneable} otherwise the object itself
    425         * @throws CloneFailedException if the object is cloneable and the clone operation fails
    426         * @since 2.6
    427         */
    428        public static Object cloneIfPossible(final Object o) {
    429            final Object clone = clone(o);
    430            return clone == null ? o : clone;
    431        }
    432
    433        // Null
    434        //-----------------------------------------------------------------------
    435        /**
    436         * <p>Class used as a null placeholder where <code>null</code>
    437         * has another meaning.</p>
    438         *
    439         * <p>For example, in a <code>HashMap</code> the
    440         * {@link java.util.HashMap#get(java.lang.Object)} method returns
    441         * <code>null</code> if the <code>Map</code> contains
    442         * <code>null</code> or if there is no matching key. The
    443         * <code>Null</code> placeholder can be used to distinguish between
    444         * these two cases.</p>
    445         *
    446         * <p>Another example is <code>Hashtable</code>, where <code>null</code>
    447         * cannot be stored.</p>
    448         */
    449        public static class Null implements Serializable {
    450            /**
    451             * Required for serialization support. Declare serialization compatibility with Commons Lang 1.0
    452             *
    453             * @see java.io.Serializable
    454             */
    455            private static final long serialVersionUID = 7092611880189329093L;
    456
    457            /**
    458             * Restricted constructor - singleton.
    459             */
    460            Null() {
    461                super();
    462            }
    463
    464            /**
    465             * <p>Ensure singleton.</p>
    466             *
    467             * @return the singleton value
    468             */
    469            private Object readResolve() {
    470                return ObjectUtils.NULL;
    471            }
    472        }
    473
    474    }