Java tutorial
/* * 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; import java.lang.annotation.Annotation; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.util.Arrays; import org.apache.commons.lang3.builder.ToStringBuilder; import org.apache.commons.lang3.builder.ToStringStyle; /** * <p>Helper methods for working with {@link Annotation} instances.</p> * * <p>This class contains various utility methods that make working with * annotations simpler.</p> * * <p>{@link Annotation} instances are always proxy objects; unfortunately * dynamic proxies cannot be depended upon to know how to implement certain * methods in the same manner as would be done by "natural" {@link Annotation}s. * The methods presented in this class can be used to avoid that possibility. It * is of course also possible for dynamic proxies to actually delegate their * e.g. {@link Annotation#equals(Object)}/{@link Annotation#hashCode()}/ * {@link Annotation#toString()} implementations to {@link AnnotationUtils}.</p> * * <p>#ThreadSafe#</p> * * @since 3.0 * @version $Id$ */ public class AnnotationUtils { /** * A style that prints annotations as recommended. */ private static final ToStringStyle TO_STRING_STYLE = new ToStringStyle() { /** Serialization version */ private static final long serialVersionUID = 1L; { setDefaultFullDetail(true); setArrayContentDetail(true); setUseClassName(true); setUseShortClassName(true); setUseIdentityHashCode(false); setContentStart("("); setContentEnd(")"); setFieldSeparator(", "); setArrayStart("["); setArrayEnd("]"); } /** * {@inheritDoc} */ @Override protected String getShortClassName(final java.lang.Class<?> cls) { Class<? extends Annotation> annotationType = null; for (final Class<?> iface : ClassUtils.getAllInterfaces(cls)) { if (Annotation.class.isAssignableFrom(iface)) { @SuppressWarnings("unchecked") // OK because we just checked the assignability final Class<? extends Annotation> found = (Class<? extends Annotation>) iface; annotationType = found; break; } } return new StringBuilder(annotationType == null ? "" : annotationType.getName()).insert(0, '@') .toString(); } /** * {@inheritDoc} */ @Override protected void appendDetail(final StringBuffer buffer, final String fieldName, Object value) { if (value instanceof Annotation) { value = AnnotationUtils.toString((Annotation) value); } super.appendDetail(buffer, fieldName, value); } }; /** * <p>{@code AnnotationUtils} instances should NOT be constructed in * standard programming. Instead, the class should be used statically.</p> * * <p>This constructor is public to permit tools that require a JavaBean * instance to operate.</p> */ public AnnotationUtils() { } //----------------------------------------------------------------------- /** * <p>Checks if two annotations are equal using the criteria for equality * presented in the {@link Annotation#equals(Object)} API docs.</p> * * @param a1 the first Annotation to compare, {@code null} returns * {@code false} unless both are {@code null} * @param a2 the second Annotation to compare, {@code null} returns * {@code false} unless both are {@code null} * @return {@code true} if the two annotations are {@code equal} or both * {@code null} */ public static boolean equals(final Annotation a1, final Annotation a2) { if (a1 == a2) { return true; } if (a1 == null || a2 == null) { return false; } final Class<? extends Annotation> type = a1.annotationType(); final Class<? extends Annotation> type2 = a2.annotationType(); Validate.notNull(type, "Annotation %s with null annotationType()", a1); Validate.notNull(type2, "Annotation %s with null annotationType()", a2); if (!type.equals(type2)) { return false; } try { for (final Method m : type.getDeclaredMethods()) { if (m.getParameterTypes().length == 0 && isValidAnnotationMemberType(m.getReturnType())) { final Object v1 = m.invoke(a1); final Object v2 = m.invoke(a2); if (!memberEquals(m.getReturnType(), v1, v2)) { return false; } } } } catch (final IllegalAccessException ex) { return false; } catch (final InvocationTargetException ex) { return false; } return true; } /** * <p>Generate a hash code for the given annotation using the algorithm * presented in the {@link Annotation#hashCode()} API docs.</p> * * @param a the Annotation for a hash code calculation is desired, not * {@code null} * @return the calculated hash code * @throws RuntimeException if an {@code Exception} is encountered during * annotation member access * @throws IllegalStateException if an annotation method invocation returns * {@code null} */ public static int hashCode(final Annotation a) { int result = 0; final Class<? extends Annotation> type = a.annotationType(); for (final Method m : type.getDeclaredMethods()) { try { final Object value = m.invoke(a); if (value == null) { throw new IllegalStateException(String.format("Annotation method %s returned null", m)); } result += hashMember(m.getName(), value); } catch (final RuntimeException ex) { throw ex; } catch (final Exception ex) { throw new RuntimeException(ex); } } return result; } /** * <p>Generate a string representation of an Annotation, as suggested by * {@link Annotation#toString()}.</p> * * @param a the annotation of which a string representation is desired * @return the standard string representation of an annotation, not * {@code null} */ public static String toString(final Annotation a) { final ToStringBuilder builder = new ToStringBuilder(a, TO_STRING_STYLE); for (final Method m : a.annotationType().getDeclaredMethods()) { if (m.getParameterTypes().length > 0) { continue; //wtf? } try { builder.append(m.getName(), m.invoke(a)); } catch (final RuntimeException ex) { throw ex; } catch (final Exception ex) { throw new RuntimeException(ex); } } return builder.build(); } /** * <p>Checks if the specified type is permitted as an annotation member.</p> * * <p>The Java language specification only permits certain types to be used * in annotations. These include {@link String}, {@link Class}, primitive * types, {@link Annotation}, {@link Enum}, and single-dimensional arrays of * these types.</p> * * @param type the type to check, {@code null} * @return {@code true} if the type is a valid type to use in an annotation */ public static boolean isValidAnnotationMemberType(Class<?> type) { if (type == null) { return false; } if (type.isArray()) { type = type.getComponentType(); } return type.isPrimitive() || type.isEnum() || type.isAnnotation() || String.class.equals(type) || Class.class.equals(type); } //besides modularity, this has the advantage of autoboxing primitives: /** * Helper method for generating a hash code for a member of an annotation. * * @param name the name of the member * @param value the value of the member * @return a hash code for this member */ private static int hashMember(final String name, final Object value) { final int part1 = name.hashCode() * 127; if (value.getClass().isArray()) { return part1 ^ arrayMemberHash(value.getClass().getComponentType(), value); } if (value instanceof Annotation) { return part1 ^ hashCode((Annotation) value); } return part1 ^ value.hashCode(); } /** * Helper method for checking whether two objects of the given type are * equal. This method is used to compare the parameters of two annotation * instances. * * @param type the type of the objects to be compared * @param o1 the first object * @param o2 the second object * @return a flag whether these objects are equal */ private static boolean memberEquals(final Class<?> type, final Object o1, final Object o2) { if (o1 == o2) { return true; } if (o1 == null || o2 == null) { return false; } if (type.isArray()) { return arrayMemberEquals(type.getComponentType(), o1, o2); } if (type.isAnnotation()) { return equals((Annotation) o1, (Annotation) o2); } return o1.equals(o2); } /** * Helper method for comparing two objects of an array type. * * @param componentType the component type of the array * @param o1 the first object * @param o2 the second object * @return a flag whether these objects are equal */ private static boolean arrayMemberEquals(final Class<?> componentType, final Object o1, final Object o2) { if (componentType.isAnnotation()) { return annotationArrayMemberEquals((Annotation[]) o1, (Annotation[]) o2); } if (componentType.equals(Byte.TYPE)) { return Arrays.equals((byte[]) o1, (byte[]) o2); } if (componentType.equals(Short.TYPE)) { return Arrays.equals((short[]) o1, (short[]) o2); } if (componentType.equals(Integer.TYPE)) { return Arrays.equals((int[]) o1, (int[]) o2); } if (componentType.equals(Character.TYPE)) { return Arrays.equals((char[]) o1, (char[]) o2); } if (componentType.equals(Long.TYPE)) { return Arrays.equals((long[]) o1, (long[]) o2); } if (componentType.equals(Float.TYPE)) { return Arrays.equals((float[]) o1, (float[]) o2); } if (componentType.equals(Double.TYPE)) { return Arrays.equals((double[]) o1, (double[]) o2); } if (componentType.equals(Boolean.TYPE)) { return Arrays.equals((boolean[]) o1, (boolean[]) o2); } return Arrays.equals((Object[]) o1, (Object[]) o2); } /** * Helper method for comparing two arrays of annotations. * * @param a1 the first array * @param a2 the second array * @return a flag whether these arrays are equal */ private static boolean annotationArrayMemberEquals(final Annotation[] a1, final Annotation[] a2) { if (a1.length != a2.length) { return false; } for (int i = 0; i < a1.length; i++) { if (!equals(a1[i], a2[i])) { return false; } } return true; } /** * Helper method for generating a hash code for an array. * * @param componentType the component type of the array * @param o the array * @return a hash code for the specified array */ private static int arrayMemberHash(final Class<?> componentType, final Object o) { if (componentType.equals(Byte.TYPE)) { return Arrays.hashCode((byte[]) o); } if (componentType.equals(Short.TYPE)) { return Arrays.hashCode((short[]) o); } if (componentType.equals(Integer.TYPE)) { return Arrays.hashCode((int[]) o); } if (componentType.equals(Character.TYPE)) { return Arrays.hashCode((char[]) o); } if (componentType.equals(Long.TYPE)) { return Arrays.hashCode((long[]) o); } if (componentType.equals(Float.TYPE)) { return Arrays.hashCode((float[]) o); } if (componentType.equals(Double.TYPE)) { return Arrays.hashCode((double[]) o); } if (componentType.equals(Boolean.TYPE)) { return Arrays.hashCode((boolean[]) o); } return Arrays.hashCode((Object[]) o); } }