    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.lang3;
    018
    019    import java.io.Serializable;
    020    import java.lang.reflect.Array;
    021    import java.lang.reflect.InvocationTargetException;
    022    import java.lang.reflect.Method;
    023
    024    import org.apache.commons.lang3.exception.CloneFailedException;
    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 960138 2010-07-03 00:30:46Z joehni $
    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>Returns the first value in the array which is not <code>null</code>.
    101         * If all the values are <code>null</code> or the array is <code>null</code>
    102         * or empty then <code>null</code> is returned.</p>
    103         *
    104         * <pre>
    105         * ObjectUtils.firstNonNull(null, null)      = null
    106         * ObjectUtils.firstNonNull(null, "")        = ""
    107         * ObjectUtils.firstNonNull(null, null, "")  = ""
    108         * ObjectUtils.firstNonNull(null, "zz")      = "zz"
    109         * ObjectUtils.firstNonNull("abc", *)        = "abc"
    110         * ObjectUtils.firstNonNull(null, "xyz", *)  = "xyz"
    111         * ObjectUtils.firstNonNull(Boolean.TRUE, *) = Boolean.TRUE
    112         * ObjectUtils.firstNonNull()                = null
    113         * </pre>
    114         *
    115         * @param values  the values to test, may be <code>null</code> or empty
    116         * @return the first value from <code>values</code> which is not <code>null</code>,
    117         *  or <code>null</code> if there are no non-null values
    118         */
    119        public static <T> T firstNonNull(T... values) {
    120            if (values != null) {
    121                for (T val : values) {
    122                    if (val != null) {
    123                        return val;
    124                    }
    125                }
    126            }
    127            return null;
    128        }
    129
    130        // Null-safe equals/hashCode
    131        //-----------------------------------------------------------------------
    132        /**
    133         * <p>Compares two objects for equality, where either one or both
    134         * objects may be <code>null</code>.</p>
    135         *
    136         * <pre>
    137         * ObjectUtils.equals(null, null)                  = true
    138         * ObjectUtils.equals(null, "")                    = false
    139         * ObjectUtils.equals("", null)                    = false
    140         * ObjectUtils.equals("", "")                      = true
    141         * ObjectUtils.equals(Boolean.TRUE, null)          = false
    142         * ObjectUtils.equals(Boolean.TRUE, "true")        = false
    143         * ObjectUtils.equals(Boolean.TRUE, Boolean.TRUE)  = true
    144         * ObjectUtils.equals(Boolean.TRUE, Boolean.FALSE) = false
    145         * </pre>
    146         *
    147         * @param object1  the first object, may be <code>null</code>
    148         * @param object2  the second object, may be <code>null</code>
    149         * @return <code>true</code> if the values of both objects are the same
    150         */
    151        public static boolean equals(Object object1, Object object2) {
    152            if (object1 == object2) {
    153                return true;
    154            }
    155            if ((object1 == null) || (object2 == null)) {
    156                return false;
    157            }
    158            return object1.equals(object2);
    159        }
    160
    161        /**
    162         * <p>Gets the hash code of an object returning zero when the
    163         * object is <code>null</code>.</p>
    164         *
    165         * <pre>
    166         * ObjectUtils.hashCode(null)   = 0
    167         * ObjectUtils.hashCode(obj)    = obj.hashCode()
    168         * </pre>
    169         *
    170         * @param obj  the object to obtain the hash code of, may be <code>null</code>
    171         * @return the hash code of the object, or zero if null
    172         * @since 2.1
    173         */
    174        public static int hashCode(Object obj) {
    175            return (obj == null) ? 0 : obj.hashCode();
    176        }
    177
    178        // Identity ToString
    179        //-----------------------------------------------------------------------
    180        /**
    181         * <p>Gets the toString that would be produced by <code>Object</code>
    182         * if a class did not override toString itself. <code>null</code>
    183         * will return <code>null</code>.</p>
    184         *
    185         * <pre>
    186         * ObjectUtils.identityToString(null)         = null
    187         * ObjectUtils.identityToString("")           = "java.lang.String@1e23"
    188         * ObjectUtils.identityToString(Boolean.TRUE) = "java.lang.Boolean@7fa"
    189         * </pre>
    190         *
    191         * @param object  the object to create a toString for, may be
    192         *  <code>null</code>
    193         * @return the default toString text, or <code>null</code> if
    194         *  <code>null</code> passed in
    195         */
    196        public static String identityToString(Object object) {
    197            if (object == null) {
    198                return null;
    199            }
    200            StringBuffer buffer = new StringBuffer();
    201            identityToString(buffer, object);
    202            return buffer.toString();
    203        }
    204
    205        /**
    206         * <p>Appends the toString that would be produced by <code>Object</code>
    207         * if a class did not override toString itself. <code>null</code>
    208         * will throw a NullPointerException for either of the two parameters. </p>
    209         *
    210         * <pre>
    211         * ObjectUtils.identityToString(buf, "")            = buf.append("java.lang.String@1e23"
    212         * ObjectUtils.identityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa"
    213         * ObjectUtils.identityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa")
    214         * </pre>
    215         *
    216         * @param buffer  the buffer to append to
    217         * @param object  the object to create a toString for
    218         * @since 2.4
    219         */
    220        public static void identityToString(StringBuffer buffer, Object object) {
    221            if (object == null) {
    222                throw new NullPointerException("Cannot get the toString of a null identity");
    223            }
    224            buffer.append(object.getClass().getName())
    225                  .append('@')
    226                  .append(Integer.toHexString(System.identityHashCode(object)));
    227        }
    228
    229        // ToString
    230        //-----------------------------------------------------------------------
    231        /**
    232         * <p>Gets the <code>toString</code> of an <code>Object</code> returning
    233         * an empty string ("") if <code>null</code> input.</p>
    234         *
    235         * <pre>
    236         * ObjectUtils.toString(null)         = ""
    237         * ObjectUtils.toString("")           = ""
    238         * ObjectUtils.toString("bat")        = "bat"
    239         * ObjectUtils.toString(Boolean.TRUE) = "true"
    240         * </pre>
    241         *
    242         * @see StringUtils#defaultString(String)
    243         * @see String#valueOf(Object)
    244         * @param obj  the Object to <code>toString</code>, may be null
    245         * @return the passed in Object's toString, or nullStr if <code>null</code> input
    246         * @since 2.0
    247         */
    248        public static String toString(Object obj) {
    249            return obj == null ? "" : obj.toString();
    250        }
    251
    252        /**
    253         * <p>Gets the <code>toString</code> of an <code>Object</code> returning
    254         * a specified text if <code>null</code> input.</p>
    255         *
    256         * <pre>
    257         * ObjectUtils.toString(null, null)           = null
    258         * ObjectUtils.toString(null, "null")         = "null"
    259         * ObjectUtils.toString("", "null")           = ""
    260         * ObjectUtils.toString("bat", "null")        = "bat"
    261         * ObjectUtils.toString(Boolean.TRUE, "null") = "true"
    262         * </pre>
    263         *
    264         * @see StringUtils#defaultString(String,String)
    265         * @see String#valueOf(Object)
    266         * @param obj  the Object to <code>toString</code>, may be null
    267         * @param nullStr  the String to return if <code>null</code> input, 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, String nullStr) {
    272            return obj == null ? nullStr : obj.toString();
    273        }
    274
    275        // Min/Max
    276        //-----------------------------------------------------------------------
    277        /**
    278         * Null safe comparison of Comparables.
    279         *
    280         * @param c1  the first comparable, may be null
    281         * @param c2  the second comparable, may be null
    282         * @return
    283         *  <ul>
    284         *   <li>If both objects are non-null and unequal, the lesser object.
    285         *   <li>If both objects are non-null and equal, c1.
    286         *   <li>If one of the comparables is null, the non-null object.
    287         *   <li>If both the comparables are null, null is returned.
    288         *  </ul>
    289         */
    290        public static <T extends Comparable<? super T>> T min(T c1, T c2) {
    291            if (c1 != null && c2 != null) {
    292                return c1.compareTo(c2) < 1 ? c1 : c2;
    293            } else {
    294                return c1 != null ? c1 : c2;
    295            }
    296        }
    297
    298        /**
    299         * Null safe comparison of Comparables.
    300         *
    301         * @param c1  the first comparable, may be null
    302         * @param c2  the second comparable, may be null
    303         * @return
    304         *  <ul>
    305         *   <li>If both objects are non-null and unequal, the greater object.
    306         *   <li>If both objects are non-null and equal, c1.
    307         *   <li>If one of the comparables is null, the non-null object.
    308         *   <li>If both the comparables are null, null is returned.
    309         *  </ul>
    310         */
    311        public static <T extends Comparable<? super T>> T max(T c1, T c2) {
    312            if (c1 != null && c2 != null) {
    313                return c1.compareTo(c2) >= 0 ? c1 : c2;
    314            } else {
    315                return c1 != null ? c1 : c2;
    316            }
    317        }
    318
    319        /**
    320         * Clone an object.
    321         *
    322         * @param <T> the type of the object
    323         * @param o the object to clone
    324         * @return the clone if the object implements {@link Cloneable} otherwise <code>null</code>
    325         * @throws CloneFailedException if the object is cloneable and the clone operation fails
    326         * @since 3.0
    327         */
    328        public static <T> T clone(final T o) {
    329            if (o instanceof Cloneable) {
    330                final Object result;
    331                if (o.getClass().isArray()) {
    332                    final Class<?> componentType = o.getClass().getComponentType();
    333                    if (!componentType.isPrimitive()) {
    334                        result = ((Object[])o).clone();
    335                    } else {
    336                        int length = Array.getLength(o);
    337                        result = Array.newInstance(componentType, length);
    338                        while (length-- > 0) {
    339                            Array.set(result, length, Array.get(o, length));
    340                        }
    341                    }
    342                } else {
    343                    try {
    344                        final Method clone = o.getClass().getMethod("clone");
    345                        result = clone.invoke(o);
    346                    } catch (final NoSuchMethodException e) {
    347                        throw new CloneFailedException("Cloneable type "
    348                            + o.getClass().getName()
    349                            + " has no clone method", e);
    350                    } catch (final IllegalAccessException e) {
    351                        throw new CloneFailedException("Cannot clone Cloneable type "
    352                            + o.getClass().getName(), e);
    353                    } catch (final InvocationTargetException e) {
    354                        throw new CloneFailedException("Exception cloning Cloneable type "
    355                            + o.getClass().getName(), e.getCause());
    356                    }
    357                }
    358                @SuppressWarnings("unchecked")
    359                final T checked = (T)result;
    360                return checked;
    361            }
    362
    363            return null;
    364        }
    365
    366        /**
    367         * Clone an object if possible. This method is similar to {@link #clone(Object)}, but will
    368         * return the provided instance as the return value instead of <code>null</code> if the instance
    369         * is not cloneable. This is more convenient if the caller uses different
    370         * implementations (e.g. of a service) and some of the implementations do not allow concurrent
    371         * processing or have state. In such cases the implementation can simply provide a proper
    372         * clone implementation and the caller's code does not have to change.
    373         *
    374         * @param <T> the type of the object
    375         * @param o the object to clone
    376         * @return the clone if the object implements {@link Cloneable} otherwise the object itself
    377         * @throws CloneFailedException if the object is cloneable and the clone operation fails
    378         * @since 3.0
    379         */
    380        public static <T> T cloneIfPossible(final T o) {
    381            final T clone = clone(o);
    382            return clone == null ? o : clone;
    383        }
    384
    385        // Null
    386        //-----------------------------------------------------------------------
    387        /**
    388         * <p>Class used as a null placeholder where <code>null</code>
    389         * has another meaning.</p>
    390         *
    391         * <p>For example, in a <code>HashMap</code> the
    392         * {@link java.util.HashMap#get(java.lang.Object)} method returns
    393         * <code>null</code> if the <code>Map</code> contains
    394         * <code>null</code> or if there is no matching key. The
    395         * <code>Null</code> placeholder can be used to distinguish between
    396         * these two cases.</p>
    397         *
    398         * <p>Another example is <code>Hashtable</code>, where <code>null</code>
    399         * cannot be stored.</p>
    400         */
    401        public static class Null implements Serializable {
    402            /**
    403             * Required for serialization support. Declare serialization compatibility with Commons Lang 1.0
    404             *
    405             * @see java.io.Serializable
    406             */
    407            private static final long serialVersionUID = 7092611880189329093L;
    408
    409            /**
    410             * Restricted constructor - singleton.
    411             */
    412            Null() {
    413                super();
    414            }
    415
    416            /**
    417             * <p>Ensure singleton.</p>
    418             *
    419             * @return the singleton value
    420             */
    421            private Object readResolve() {
    422                return ObjectUtils.NULL;
    423            }
    424        }
    425
    426    }