LANG-1067: Add a reflection-based variant of DiffBuilder

src/main/java/org/apache/commons/lang3/builder/ReflectionDiffBuilder.java

@@ -0,0 +1,140 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.lang3.builder;
+
+import static org.apache.commons.lang3.reflect.FieldUtils.readField;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+
+import org.apache.commons.lang3.ClassUtils;
+import org.apache.commons.lang3.reflect.FieldUtils;
+
+/**
+ * <p>
+ * Assists in implementing {@link Diffable#diff(Object)} methods.
+ * </p>
+ * <p>
+ * All non-static, non-transient fields (including inherited fields)
+ * of the objects to diff are discovered using reflection and compared
+ * for differences.
+ * </p>
+ * 
+ * <p>
+ * To use this class, write code as follows:
+ * </p>
+ * 
+ * <pre>
+ * public class Person implements Diffable&lt;Person&gt; {
+ *   String name;
+ *   int age;
+ *   boolean smoker;
+ *   ...
+ *   
+ *   public DiffResult diff(Person obj) {
+ *     // No need for null check, as NullPointerException correct if obj is null
+ *     return new ReflectionDiffBuilder(this, obj, ToStringStyle.SHORT_PREFIX_STYLE)
+ *       .build();
+ *   }
+ * }
+ * </pre>
+ * 
+ * <p>
+ * The {@code ToStringStyle} passed to the constructor is embedded in the
+ * returned {@code DiffResult} and influences the style of the
+ * {@code DiffResult.toString()} method. This style choice can be overridden by
+ * calling {@link DiffResult#toString(ToStringStyle)}.
+ * </p>
+ * @see Diffable
+ * @see Diff
+ * @see DiffResult
+ * @see ToStringStyle
+ * @since 3.6
+ */
+public class ReflectionDiffBuilder implements Builder<DiffResult> {
+
+    private final Object left;
+    private final Object right;
+    private final DiffBuilder diffBuilder;
+
+    /**
+     * <p>
+     * Constructs a builder for the specified objects with the specified style.
+     * </p>
+     * 
+     * <p>
+     * If {@code lhs == rhs} or {@code lhs.equals(rhs)} then the builder will
+     * not evaluate any calls to {@code append(...)} and will return an empty
+     * {@link DiffResult} when {@link #build()} is executed.
+     * </p>
+     * @param <T>
+     *            type of the objects to diff
+     * @param lhs
+     *            {@code this} object
+     * @param rhs
+     *            the object to diff against
+     * @param style
+     *            the style will use when outputting the objects, {@code null}
+     *            uses the default
+     * @throws IllegalArgumentException
+     *             if {@code lhs} or {@code rhs} is {@code null}
+     */
+    public <T> ReflectionDiffBuilder(final T lhs, final T rhs, final ToStringStyle style) {
+        this.left = lhs;
+        this.right = rhs;
+        diffBuilder = new DiffBuilder(lhs, rhs, style);
+    }
+
+    @Override
+    public DiffResult build() {
+        if (left.equals(right)) {
+            return diffBuilder.build();
+        }
+
+        appendFields(left.getClass());
+        return diffBuilder.build();
+    }
+
+    private void appendFields(final Class<?> clazz) {
+        for (final Field field : FieldUtils.getAllFields(clazz)) {
+            if (accept(field)) {
+                try {
+                    diffBuilder.append(field.getName(), readField(field, left, true),
+                            readField(field, right, true));
+                } catch (final IllegalAccessException ex) {
+                    //this can't happen. Would get a Security exception instead
+                    //throw a runtime exception in case the impossible happens.
+                    throw new InternalError("Unexpected IllegalAccessException: " + ex.getMessage());
+                }
+            }
+        }
+    }
+
+    private boolean accept(final Field field) {
+        if (field.getName().indexOf(ClassUtils.INNER_CLASS_SEPARATOR_CHAR) != -1) {
+            return false;
+        }
+        if (Modifier.isTransient(field.getModifiers())) {
+            return false;
+        }
+        if (Modifier.isStatic(field.getModifiers())) {
+            return false;
+        }
+        return true;
+    }
+
+}

src/test/java/org/apache/commons/lang3/builder/ReflectionDiffBuilderTest.java

@@ -0,0 +1,131 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.lang3.builder;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+
+public class ReflectionDiffBuilderTest {
+
+    private static final ToStringStyle SHORT_STYLE = ToStringStyle.SHORT_PREFIX_STYLE;
+
+    @SuppressWarnings("unused")
+    private static class TypeTestClass implements Diffable<TypeTestClass> {
+        private ToStringStyle style = SHORT_STYLE;
+        private boolean booleanField = true;
+        private boolean[] booleanArrayField = {true};
+        private byte byteField = (byte) 0xFF;
+        private byte[] byteArrayField = {(byte) 0xFF};
+        private char charField = 'a';
+        private char[] charArrayField = {'a'};
+        private double doubleField = 1.0;
+        private double[] doubleArrayField = {1.0};
+        private float floatField = 1.0f;
+        private float[] floatArrayField = {1.0f};
+        int intField = 1;
+        private int[] intArrayField = {1};
+        private long longField = 1L;
+        private long[] longArrayField = {1L};
+        private short shortField = 1;
+        private short[] shortArrayField = {1};
+        private Object objectField = null;
+        private Object[] objectArrayField = {null};
+        private static int staticField;
+        private transient String transientField;
+
+        @Override
+        public DiffResult diff(final TypeTestClass obj) {
+            return new ReflectionDiffBuilder(this, obj, style).build();
+        }
+
+        @Override
+        public int hashCode() {
+            return HashCodeBuilder.reflectionHashCode(this, false);
+        }
+
+        @Override
+        public boolean equals(final Object obj) {
+            return EqualsBuilder.reflectionEquals(this, obj, false);
+        }
+    }
+
+    @SuppressWarnings("unused")
+    private static class TypeTestChildClass extends TypeTestClass {
+        String field = "a";
+    }
+
+    @Test
+    public void test_no_differences() {
+        final TypeTestClass firstObject = new TypeTestClass();
+        final TypeTestClass secondObject = new TypeTestClass();
+
+        final DiffResult list = firstObject.diff(secondObject);
+        assertEquals(0, list.getNumberOfDiffs());
+    }
+
+    @Test
+    public void test_primitive_difference() {
+        final TypeTestClass firstObject = new TypeTestClass();
+        firstObject.charField = 'c';
+        final TypeTestClass secondObject = new TypeTestClass();
+
+        final DiffResult list = firstObject.diff(secondObject);
+        assertEquals(1, list.getNumberOfDiffs());
+    }
+
+    @Test
+    public void test_array_difference() {
+        final TypeTestClass firstObject = new TypeTestClass();
+        firstObject.charArrayField = new char[] { 'c' };
+        final TypeTestClass secondObject = new TypeTestClass();
+
+        final DiffResult list = firstObject.diff(secondObject);
+        assertEquals(1, list.getNumberOfDiffs());
+    }
+
+    @Test
+    public void test_transient_field_difference() {
+        final TypeTestClass firstObject = new TypeTestClass();
+        firstObject.transientField = "a";
+        final TypeTestClass secondObject = new TypeTestClass();
+        firstObject.transientField = "b";
+
+        final DiffResult list = firstObject.diff(secondObject);
+        assertEquals(0, list.getNumberOfDiffs());
+    }
+
+    @Test
+    public void test_no_differences_inheritance() {
+        final TypeTestChildClass firstObject = new TypeTestChildClass();
+        final TypeTestChildClass secondObject = new TypeTestChildClass();
+
+        final DiffResult list = firstObject.diff(secondObject);
+        assertEquals(0, list.getNumberOfDiffs());
+    }
+
+    @Test
+    public void test_difference_in_inherited_field() {
+        final TypeTestChildClass firstObject = new TypeTestChildClass();
+        firstObject.intField = 99;
+        final TypeTestChildClass secondObject = new TypeTestChildClass();
+
+        final DiffResult list = firstObject.diff(secondObject);
+        assertEquals(1, list.getNumberOfDiffs());
+    }
+}