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 */
017package org.apache.commons.lang3.builder;
018
019import static org.apache.commons.lang3.reflect.FieldUtils.readField;
020
021import java.lang.reflect.Field;
022import java.lang.reflect.Modifier;
023
024import org.apache.commons.lang3.ClassUtils;
025import org.apache.commons.lang3.reflect.FieldUtils;
026
027/**
028 * <p>
029 * Assists in implementing {@link Diffable#diff(Object)} methods.
030 * </p>
031 * <p>
032 * All non-static, non-transient fields (including inherited fields)
033 * of the objects to diff are discovered using reflection and compared
034 * for differences.
035 * </p>
036 *
037 * <p>
038 * To use this class, write code as follows:
039 * </p>
040 *
041 * <pre>
042 * public class Person implements Diffable&lt;Person&gt; {
043 *   String name;
044 *   int age;
045 *   boolean smoker;
046 *   ...
047 *
048 *   public DiffResult diff(Person obj) {
049 *     // No need for null check, as NullPointerException correct if obj is null
050 *     return new ReflectionDiffBuilder(this, obj, ToStringStyle.SHORT_PREFIX_STYLE)
051 *       .build();
052 *   }
053 * }
054 * </pre>
055 *
056 * <p>
057 * The {@code ToStringStyle} passed to the constructor is embedded in the
058 * returned {@code DiffResult} and influences the style of the
059 * {@code DiffResult.toString()} method. This style choice can be overridden by
060 * calling {@link DiffResult#toString(ToStringStyle)}.
061 * </p>
062 * @see Diffable
063 * @see Diff
064 * @see DiffResult
065 * @see ToStringStyle
066 * @since 3.6
067 */
068public class ReflectionDiffBuilder implements Builder<DiffResult> {
069
070    private final Object left;
071    private final Object right;
072    private final DiffBuilder diffBuilder;
073
074    /**
075     * <p>
076     * Constructs a builder for the specified objects with the specified style.
077     * </p>
078     *
079     * <p>
080     * If {@code lhs == rhs} or {@code lhs.equals(rhs)} then the builder will
081     * not evaluate any calls to {@code append(...)} and will return an empty
082     * {@link DiffResult} when {@link #build()} is executed.
083     * </p>
084     * @param <T>
085     *            type of the objects to diff
086     * @param lhs
087     *            {@code this} object
088     * @param rhs
089     *            the object to diff against
090     * @param style
091     *            the style will use when outputting the objects, {@code null}
092     *            uses the default
093     * @throws IllegalArgumentException
094     *             if {@code lhs} or {@code rhs} is {@code null}
095     */
096    public <T> ReflectionDiffBuilder(final T lhs, final T rhs, final ToStringStyle style) {
097        this.left = lhs;
098        this.right = rhs;
099        diffBuilder = new DiffBuilder(lhs, rhs, style);
100    }
101
102    @Override
103    public DiffResult build() {
104        if (left.equals(right)) {
105            return diffBuilder.build();
106        }
107
108        appendFields(left.getClass());
109        return diffBuilder.build();
110    }
111
112    private void appendFields(final Class<?> clazz) {
113        for (final Field field : FieldUtils.getAllFields(clazz)) {
114            if (accept(field)) {
115                try {
116                    diffBuilder.append(field.getName(), readField(field, left, true),
117                            readField(field, right, true));
118                } catch (final IllegalAccessException ex) {
119                    //this can't happen. Would get a Security exception instead
120                    //throw a runtime exception in case the impossible happens.
121                    throw new InternalError("Unexpected IllegalAccessException: " + ex.getMessage());
122                }
123            }
124        }
125    }
126
127    private boolean accept(final Field field) {
128        if (field.getName().indexOf(ClassUtils.INNER_CLASS_SEPARATOR_CHAR) != -1) {
129            return false;
130        }
131        if (Modifier.isTransient(field.getModifiers())) {
132            return false;
133        }
134        return !Modifier.isStatic(field.getModifiers());
135    }
136
137}