Java tutorial
/** * Copyright (C) 2006 Google Inc. * * Licensed 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 com.google.inject.internal; import com.google.common.base.Function; import com.google.common.base.Joiner; import com.google.common.base.Joiner.MapJoiner; import com.google.common.base.Preconditions; import com.google.common.cache.CacheBuilder; import com.google.common.cache.CacheLoader; import com.google.common.cache.LoadingCache; import com.google.common.collect.ImmutableMap; import com.google.common.collect.Maps; import com.google.inject.BindingAnnotation; import com.google.inject.Key; import com.google.inject.ScopeAnnotation; import com.google.inject.TypeLiteral; import com.google.inject.internal.util.Classes; import com.google.inject.name.Named; import com.google.inject.name.Names; import java.lang.annotation.Annotation; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.reflect.InvocationHandler; import java.lang.reflect.Member; import java.lang.reflect.Method; import java.lang.reflect.Proxy; import java.util.Arrays; import java.util.Collection; import java.util.Map; import javax.inject.Qualifier; /** * Annotation utilities. * * @author crazybob@google.com (Bob Lee) */ public class Annotations { /** * Returns {@code true} if the given annotation type has no attributes. */ public static boolean isMarker(Class<? extends Annotation> annotationType) { return annotationType.getDeclaredMethods().length == 0; } public static boolean isAllDefaultMethods(Class<? extends Annotation> annotationType) { boolean hasMethods = false; for (Method m : annotationType.getDeclaredMethods()) { hasMethods = true; if (m.getDefaultValue() == null) { return false; } } return hasMethods; } private static final LoadingCache<Class<? extends Annotation>, Annotation> cache = CacheBuilder.newBuilder() .weakKeys().build(new CacheLoader<Class<? extends Annotation>, Annotation>() { @Override public Annotation load(Class<? extends Annotation> input) { return generateAnnotationImpl(input); } }); /** * Generates an Annotation for the annotation class. Requires that the annotation is all * optionals. */ public static <T extends Annotation> T generateAnnotation(Class<T> annotationType) { Preconditions.checkState(isAllDefaultMethods(annotationType), "%s is not all default methods", annotationType); return (T) cache.getUnchecked(annotationType); } private static <T extends Annotation> T generateAnnotationImpl(final Class<T> annotationType) { final Map<String, Object> members = resolveMembers(annotationType); return annotationType.cast(Proxy.newProxyInstance(annotationType.getClassLoader(), new Class<?>[] { annotationType }, new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Exception { String name = method.getName(); if (name.equals("annotationType")) { return annotationType; } else if (name.equals("toString")) { return annotationToString(annotationType, members); } else if (name.equals("hashCode")) { return annotationHashCode(annotationType, members); } else if (name.equals("equals")) { return annotationEquals(annotationType, members, args[0]); } else { return members.get(name); } } })); } private static ImmutableMap<String, Object> resolveMembers(Class<? extends Annotation> annotationType) { ImmutableMap.Builder<String, Object> result = ImmutableMap.builder(); for (Method method : annotationType.getDeclaredMethods()) { result.put(method.getName(), method.getDefaultValue()); } return result.build(); } /** Implements {@link Annotation#equals}. */ private static boolean annotationEquals(Class<? extends Annotation> type, Map<String, Object> members, Object other) throws Exception { if (!type.isInstance(other)) { return false; } for (Method method : type.getDeclaredMethods()) { String name = method.getName(); if (!Arrays.deepEquals(new Object[] { method.invoke(other) }, new Object[] { members.get(name) })) { return false; } } return true; } /** Implements {@link Annotation#hashCode}. */ private static int annotationHashCode(Class<? extends Annotation> type, Map<String, Object> members) throws Exception { int result = 0; for (Method method : type.getDeclaredMethods()) { String name = method.getName(); Object value = members.get(name); result += (127 * name.hashCode()) ^ (Arrays.deepHashCode(new Object[] { value }) - 31); } return result; } private static final MapJoiner JOINER = Joiner.on(", ").withKeyValueSeparator("="); private static final Function<Object, String> DEEP_TO_STRING_FN = new Function<Object, String>() { @Override public String apply(Object arg) { String s = Arrays.deepToString(new Object[] { arg }); return s.substring(1, s.length() - 1); // cut off brackets } }; /** Implements {@link Annotation#toString}. */ private static String annotationToString(Class<? extends Annotation> type, Map<String, Object> members) throws Exception { StringBuilder sb = new StringBuilder().append("@").append(type.getName()).append("("); JOINER.appendTo(sb, Maps.transformValues(members, DEEP_TO_STRING_FN)); return sb.append(")").toString(); } /** * Returns true if the given annotation is retained at runtime. */ public static boolean isRetainedAtRuntime(Class<? extends Annotation> annotationType) { Retention retention = annotationType.getAnnotation(Retention.class); return retention != null && retention.value() == RetentionPolicy.RUNTIME; } /** Returns the scope annotation on {@code type}, or null if none is specified. */ public static Class<? extends Annotation> findScopeAnnotation(Errors errors, Class<?> implementation) { return findScopeAnnotation(errors, implementation.getAnnotations()); } /** Returns the scoping annotation, or null if there isn't one. */ public static Class<? extends Annotation> findScopeAnnotation(Errors errors, Annotation[] annotations) { Class<? extends Annotation> found = null; for (Annotation annotation : annotations) { Class<? extends Annotation> annotationType = annotation.annotationType(); if (isScopeAnnotation(annotationType)) { if (found != null) { errors.duplicateScopeAnnotations(found, annotationType); } else { found = annotationType; } } } return found; } /** * Checks for the presence of annotations. Caches results because Android doesn't. */ static class AnnotationChecker { private final Collection<Class<? extends Annotation>> annotationTypes; /** Returns true if the given class has one of the desired annotations. */ private CacheLoader<Class<? extends Annotation>, Boolean> hasAnnotations = new CacheLoader<Class<? extends Annotation>, Boolean>() { public Boolean load(Class<? extends Annotation> annotationType) { for (Annotation annotation : annotationType.getAnnotations()) { if (annotationTypes.contains(annotation.annotationType())) { return true; } } return false; } }; final LoadingCache<Class<? extends Annotation>, Boolean> cache = CacheBuilder.newBuilder().weakKeys() .build(hasAnnotations); /** * Constructs a new checker that looks for annotations of the given types. */ AnnotationChecker(Collection<Class<? extends Annotation>> annotationTypes) { this.annotationTypes = annotationTypes; } /** * Returns true if the given type has one of the desired annotations. */ boolean hasAnnotations(Class<? extends Annotation> annotated) { return cache.getUnchecked(annotated); } } private static final AnnotationChecker scopeChecker = new AnnotationChecker( Arrays.asList(ScopeAnnotation.class, javax.inject.Scope.class)); public static boolean isScopeAnnotation(Class<? extends Annotation> annotationType) { return scopeChecker.hasAnnotations(annotationType); } /** * Adds an error if there is a misplaced annotations on {@code type}. Scoping * annotations are not allowed on abstract classes or interfaces. */ public static void checkForMisplacedScopeAnnotations(Class<?> type, Object source, Errors errors) { if (Classes.isConcrete(type)) { return; } Class<? extends Annotation> scopeAnnotation = findScopeAnnotation(errors, type); if (scopeAnnotation != null) { errors.withSource(type).scopeAnnotationOnAbstractType(scopeAnnotation, type, source); } } /** Gets a key for the given type, member and annotations. */ public static Key<?> getKey(TypeLiteral<?> type, Member member, Annotation[] annotations, Errors errors) throws ErrorsException { int numErrorsBefore = errors.size(); Annotation found = findBindingAnnotation(errors, member, annotations); errors.throwIfNewErrors(numErrorsBefore); return found == null ? Key.get(type) : Key.get(type, found); } /** * Returns the binding annotation on {@code member}, or null if there isn't one. */ public static Annotation findBindingAnnotation(Errors errors, Member member, Annotation[] annotations) { Annotation found = null; for (Annotation annotation : annotations) { Class<? extends Annotation> annotationType = annotation.annotationType(); if (isBindingAnnotation(annotationType)) { if (found != null) { errors.duplicateBindingAnnotations(member, found.annotationType(), annotationType); } else { found = annotation; } } } return found; } private static final AnnotationChecker bindingAnnotationChecker = new AnnotationChecker( Arrays.asList(BindingAnnotation.class, Qualifier.class)); /** * Returns true if annotations of the specified type are binding annotations. */ public static boolean isBindingAnnotation(Class<? extends Annotation> annotationType) { return bindingAnnotationChecker.hasAnnotations(annotationType); } /** * If the annotation is an instance of {@code javax.inject.Named}, canonicalizes to * com.google.guice.name.Named. Returns the given annotation otherwise. */ public static Annotation canonicalizeIfNamed(Annotation annotation) { if (annotation instanceof javax.inject.Named) { return Names.named(((javax.inject.Named) annotation).value()); } else { return annotation; } } /** * If the annotation is the class {@code javax.inject.Named}, canonicalizes to * com.google.guice.name.Named. Returns the given annotation class otherwise. */ public static Class<? extends Annotation> canonicalizeIfNamed(Class<? extends Annotation> annotationType) { if (annotationType == javax.inject.Named.class) { return Named.class; } else { return annotationType; } } }