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