001 /*
002 * Copyright (C) 2005 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package com.google.common.reflect;
018
019 import static com.google.common.base.Preconditions.checkArgument;
020 import static com.google.common.base.Preconditions.checkNotNull;
021
022 import com.google.common.annotations.Beta;
023
024 import java.lang.reflect.InvocationHandler;
025 import java.lang.reflect.Proxy;
026
027 /**
028 * Static utilities relating to Java reflection.
029 *
030 * @since 12.0
031 */
032 @Beta
033 public final class Reflection {
034
035 /**
036 * Returns the package name of {@code cls} according to the Java Language Specification (section
037 * 6.7). Unlike {@link Class#getPackage}, this method only parses the class name, without
038 * attempting to define the {@link Package} and hence load files.
039 */
040 public static String getPackageName(Class<?> cls) {
041 return getPackageName(cls.getName());
042 }
043
044 /**
045 * Returns the package name of {@code classFullName} according to the Java Language Specification
046 * (section 6.7). Unlike {@link Class#getPackage}, this method only parses the class name, without
047 * attempting to define the {@link Package} and hence load files.
048 */
049 public static String getPackageName(String classFullName) {
050 int lastDot = classFullName.lastIndexOf('.');
051 if (lastDot < 0) {
052 return "";
053 } else {
054 return classFullName.substring(0, lastDot);
055 }
056 }
057
058 /**
059 * Ensures that the given classes are initialized, as described in
060 * <a href="http://java.sun.com/docs/books/jls/third_edition/html/execution.html#12.4.2">
061 * JLS Section 12.4.2</a>.
062 *
063 * <p>WARNING: Normally it's a smell if a class needs to be explicitly initialized, because static
064 * state hurts system maintainability and testability. In cases when you have no choice while
065 * inter-operating with a legacy framework, this method helps to keep the code less ugly.
066 *
067 * @throws ExceptionInInitializerError if an exception is thrown during
068 * initialization of a class
069 */
070 public static void initialize(Class<?>... classes) {
071 for (Class<?> clazz : classes) {
072 try {
073 Class.forName(clazz.getName(), true, clazz.getClassLoader());
074 } catch (ClassNotFoundException e) {
075 throw new AssertionError(e);
076 }
077 }
078 }
079
080 /**
081 * Returns a proxy instance that implements {@code interfaceType} by
082 * dispatching method invocations to {@code handler}. The class loader of
083 * {@code interfaceType} will be used to define the proxy class. To implement
084 * multiple interfaces or specify a class loader, use
085 * {@link Proxy#newProxyInstance}.
086 *
087 * @throws IllegalArgumentException if {@code interfaceType} does not specify
088 * the type of a Java interface
089 */
090 public static <T> T newProxy(
091 Class<T> interfaceType, InvocationHandler handler) {
092 checkNotNull(interfaceType);
093 checkNotNull(handler);
094 checkArgument(interfaceType.isInterface());
095 Object object = Proxy.newProxyInstance(
096 interfaceType.getClassLoader(),
097 new Class<?>[] { interfaceType },
098 handler);
099 return interfaceType.cast(object);
100 }
101
102 private Reflection() {}
103 }