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