UnsafeAllocator.java revision 5a7820356e68a977711afc854d6cd71296c56391 
1/*
2 * Copyright (C) 2012 The Android Open Source Project
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.dexmaker.mockito;
18
19import java.io.ObjectInputStream;
20import java.io.ObjectStreamClass;
21import java.lang.reflect.Field;
22import java.lang.reflect.Method;
23
24/**
25 * Do sneaky things to allocate objects without invoking their constructors.
26 * This is like objenesis but it works on Android. Derived from Gson's
27 * UnsafeAllocator.
28 */
29abstract class UnsafeAllocator {
30    public abstract <T> T newInstance(Class<T> c) throws Exception;
31
32    public static UnsafeAllocator create() {
33        // try JVM
34        // public class Unsafe {
35        //   public Object allocateInstance(Class<?> type);
36        // }
37        try {
38            Class<?> unsafeClass = Class.forName("sun.misc.Unsafe");
39            Field f = unsafeClass.getDeclaredField("theUnsafe");
40            f.setAccessible(true);
41            final Object unsafe = f.get(null);
42            final Method allocateInstance = unsafeClass.getMethod("allocateInstance", Class.class);
43            return new UnsafeAllocator() {
44                @Override
45                @SuppressWarnings("unchecked")
46                public <T> T newInstance(Class<T> c) throws Exception {
47                    return (T) allocateInstance.invoke(unsafe, c);
48                }
49            };
50        } catch (Exception ignored) {
51        }
52
53        // try dalvikvm, pre-gingerbread
54        // public class ObjectInputStream {
55        //   private static native Object newInstance(
56        //     Class<?> instantiationClass, Class<?> constructorClass);
57        // }
58        try {
59            final Method newInstance = ObjectInputStream.class
60                    .getDeclaredMethod("newInstance", Class.class, Class.class);
61            newInstance.setAccessible(true);
62            return new UnsafeAllocator() {
63                @Override
64                @SuppressWarnings("unchecked")
65                public <T> T newInstance(Class<T> c) throws Exception {
66                    return (T) newInstance.invoke(null, c, Object.class);
67                }
68            };
69        } catch (Exception ignored) {
70        }
71
72        // try dalvikvm, post-gingerbread
73        // public class ObjectStreamClass {
74        //   private static native int getConstructorId(Class<?> c);
75        //   private static native Object newInstance(Class<?> instantiationClass, int methodId);
76        // }
77        try {
78            Method getConstructorId = ObjectStreamClass.class
79                    .getDeclaredMethod("getConstructorId", Class.class);
80            getConstructorId.setAccessible(true);
81            final int constructorId = (Integer) getConstructorId.invoke(null, Object.class);
82            final Method newInstance = ObjectStreamClass.class
83                    .getDeclaredMethod("newInstance", Class.class, int.class);
84            newInstance.setAccessible(true);
85            return new UnsafeAllocator() {
86                @Override
87                @SuppressWarnings("unchecked")
88                public <T> T newInstance(Class<T> c) throws Exception {
89                    return (T) newInstance.invoke(null, c, constructorId);
90                }
91            };
92        } catch (Exception ignored) {
93        }
94
95        // give up
96        return new UnsafeAllocator() {
97            @Override
98            public <T> T newInstance(Class<T> c) {
99                throw new UnsupportedOperationException("Cannot allocate " + c);
100            }
101        };
102    }
103}