com.google.gson.internal.UnsafeAllocator Maven / Gradle / Ivy
/*
* Copyright (C) 2011 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.gson.internal;
import java.io.ObjectInputStream;
import java.io.ObjectStreamClass;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
/**
* Do sneaky things to allocate objects without invoking their constructors.
*
* @author Joel Leitch
* @author Jesse Wilson
*/
public abstract class UnsafeAllocator {
public abstract T newInstance(Class c) throws Exception;
/**
* Check if the class can be instantiated by Unsafe allocator. If the instance has interface or abstract modifiers
* return an exception message.
* @param c instance of the class to be checked
* @return if instantiable {@code null}, else a non-{@code null} exception message
*/
static String checkInstantiable(Class c) {
int modifiers = c.getModifiers();
if (Modifier.isInterface(modifiers)) {
return "Interfaces can't be instantiated! Register an InstanceCreator "
+ "or a TypeAdapter for this type. Interface name: " + c.getName();
}
if (Modifier.isAbstract(modifiers)) {
return "Abstract classes can't be instantiated! Register an InstanceCreator "
+ "or a TypeAdapter for this type. Class name: " + c.getName();
}
return null;
}
/**
* Asserts that the class is instantiable. This check should have already occurred
* in {@link ConstructorConstructor}; this check here acts as safeguard since trying
* to use Unsafe for non-instantiable classes might crash the JVM on some devices.
*/
private static void assertInstantiable(Class c) {
String exceptionMessage = checkInstantiable(c);
if (exceptionMessage != null) {
throw new AssertionError("UnsafeAllocator is used for non-instantiable type: " + exceptionMessage);
}
}
public static UnsafeAllocator create() {
// try JVM
// public class Unsafe {
// public Object allocateInstance(Class type);
// }
try {
Class unsafeClass = Class.forName("sun.misc.Unsafe");
Field f = unsafeClass.getDeclaredField("theUnsafe");
f.setAccessible(true);
final Object unsafe = f.get(null);
final Method allocateInstance = unsafeClass.getMethod("allocateInstance", Class.class);
return new UnsafeAllocator() {
@Override
@SuppressWarnings("unchecked")
public T newInstance(Class c) throws Exception {
assertInstantiable(c);
return (T) allocateInstance.invoke(unsafe, c);
}
};
} catch (Exception ignored) {
}
// try dalvikvm, post-gingerbread
// public class ObjectStreamClass {
// private static native int getConstructorId(Class c);
// private static native Object newInstance(Class instantiationClass, int methodId);
// }
try {
Method getConstructorId = ObjectStreamClass.class
.getDeclaredMethod("getConstructorId", Class.class);
getConstructorId.setAccessible(true);
final int constructorId = (Integer) getConstructorId.invoke(null, Object.class);
final Method newInstance = ObjectStreamClass.class
.getDeclaredMethod("newInstance", Class.class, int.class);
newInstance.setAccessible(true);
return new UnsafeAllocator() {
@Override
@SuppressWarnings("unchecked")
public T newInstance(Class c) throws Exception {
assertInstantiable(c);
return (T) newInstance.invoke(null, c, constructorId);
}
};
} catch (Exception ignored) {
}
// try dalvikvm, pre-gingerbread
// public class ObjectInputStream {
// private static native Object newInstance(
// Class instantiationClass, Class constructorClass);
// }
try {
final Method newInstance = ObjectInputStream.class
.getDeclaredMethod("newInstance", Class.class, Class.class);
newInstance.setAccessible(true);
return new UnsafeAllocator() {
@Override
@SuppressWarnings("unchecked")
public T newInstance(Class c) throws Exception {
assertInstantiable(c);
return (T) newInstance.invoke(null, c, Object.class);
}
};
} catch (Exception ignored) {
}
// give up
return new UnsafeAllocator() {
@Override
public T newInstance(Class c) {
throw new UnsupportedOperationException("Cannot allocate " + c + ". Usage of JDK sun.misc.Unsafe is enabled, "
+ "but it could not be used. Make sure your runtime is configured correctly.");
}
};
}
}