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A JSR330 style dependency injection solution
package org.osgl.inject.util;
/*-
* #%L
* OSGL Genie
* %%
* Copyright (C) 2017 OSGL (Open Source General Library)
* %%
* 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.
* #L%
*/
import java.lang.annotation.Annotation;
import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
/**
* Provides utility methods to deal with annotations.
*/
public class AnnotationUtil {
/**
* Return declared annotation with type `annoClass` from
* an {@link AnnotatedElement}.
*
* @param annotatedElement
* the annotated element (could be class, method or field)
* @param annoClass
* the annotation class
* @param
* the generic type of the annotation class
* @return
* the annotation instance or `null` if not found
*/
public static T declaredAnnotation(
AnnotatedElement annotatedElement,
Class annoClass
) {
Annotation[] aa = annotatedElement.getDeclaredAnnotations();
if (null == aa) {
return null;
}
for (Annotation a : aa) {
if (annoClass.isInstance(a)) {
return (T) a;
}
}
return null;
}
/**
* Returns the {@link Annotation} tagged on another annotation instance.
*
* @param annotation
* the annotation instance
* @param tagClass
* the expected annotation class
* @param
* the generic type of the expected annotation
* @return
* the annotation tagged on annotation of type `tagClass`
*/
public static T tagAnnotation(Annotation annotation, Class tagClass) {
Class c = annotation.annotationType();
for (Annotation a : c.getAnnotations()) {
if (tagClass.isInstance(a)) {
return (T) a;
}
}
return null;
}
/**
* Create an annotation instance from annotation class.
*
* @param clazz
* the annotation class
* @param
* the generic type of the annoation
* @return
* the annotation instance
*/
@SuppressWarnings("unchecked")
public static T createAnnotation(final Class clazz) {
return (T) Proxy.newProxyInstance(clazz.getClassLoader(), new Class[]{clazz, Annotation.class}, new SimpleAnnoInvocationHandler(clazz));
}
/**
* Generate a hash code for the given annotation using the algorithm
* presented in the {@link Annotation#hashCode()} API docs.
*
* @param a
* the Annotation for a hash code calculation is desired, not `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 `null`
*/
public static int hashCode(Annotation a) {
int result = 0;
Class type = a.annotationType();
for (Method m : type.getDeclaredMethods()) {
try {
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 (RuntimeException ex) {
throw ex;
} catch (Exception ex) {
throw new RuntimeException(ex);
}
}
return result;
}
/**
* 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
*/
static int hashMember(String name, Object value) {
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 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(Class componentType, 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);
}
}