1/*
2 * Copyright (C) 2005 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.reflect;
18
19import static com.google.common.base.Preconditions.checkArgument;
20import static com.google.common.base.Preconditions.checkNotNull;
21
22import com.google.common.annotations.Beta;
23
24import java.lang.reflect.InvocationHandler;
25import java.lang.reflect.Proxy;
26
27/**
28 * Static utilities relating to Java reflection.
29 *
30 * @since 12.0
31 */
32@Beta
33public final class Reflection {
34
35  /**
36   * Returns the package name of {@code clazz} according to the Java Language Specification (section
37   * 6.7). Unlike {@link Class#getPackage}, this method only parses the class name, without
38   * attempting to define the {@link Package} and hence load files.
39   */
40  public static String getPackageName(Class<?> clazz) {
41    return getPackageName(clazz.getName());
42  }
43
44  /**
45   * Returns the package name of {@code classFullName} according to the Java Language Specification
46   * (section 6.7). Unlike {@link Class#getPackage}, this method only parses the class name, without
47   * attempting to define the {@link Package} and hence load files.
48   */
49  public static String getPackageName(String classFullName) {
50    int lastDot = classFullName.lastIndexOf('.');
51    return (lastDot < 0) ? "" : classFullName.substring(0, lastDot);
52  }
53
54  /**
55   * Ensures that the given classes are initialized, as described in
56   * <a href="http://java.sun.com/docs/books/jls/third_edition/html/execution.html#12.4.2">
57   * JLS Section 12.4.2</a>.
58   *
59   * <p>WARNING: Normally it's a smell if a class needs to be explicitly initialized, because static
60   * state hurts system maintainability and testability. In cases when you have no choice while
61   * inter-operating with a legacy framework, this method helps to keep the code less ugly.
62   *
63   * @throws ExceptionInInitializerError if an exception is thrown during
64   *   initialization of a class
65   */
66  public static void initialize(Class<?>... classes) {
67    for (Class<?> clazz : classes) {
68      try {
69        Class.forName(clazz.getName(), true, clazz.getClassLoader());
70      } catch (ClassNotFoundException e) {
71        throw new AssertionError(e);
72      }
73    }
74  }
75
76  /**
77   * Returns a proxy instance that implements {@code interfaceType} by
78   * dispatching method invocations to {@code handler}. The class loader of
79   * {@code interfaceType} will be used to define the proxy class. To implement
80   * multiple interfaces or specify a class loader, use
81   * {@link Proxy#newProxyInstance}.
82   *
83   * @throws IllegalArgumentException if {@code interfaceType} does not specify
84   *     the type of a Java interface
85   */
86  public static <T> T newProxy(
87      Class<T> interfaceType, InvocationHandler handler) {
88    checkNotNull(handler);
89    checkArgument(interfaceType.isInterface(), "%s is not an interface", interfaceType);
90    Object object = Proxy.newProxyInstance(
91        interfaceType.getClassLoader(),
92        new Class<?>[] { interfaceType },
93        handler);
94    return interfaceType.cast(object);
95  }
96
97  private Reflection() {}
98}
99