code: /*
   * 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 tools.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> T newInstance(Class<T> c) throws Exception;
  
    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> T newInstance(Class<T> 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> T newInstance(Class<T> 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> T newInstance(Class<T> c) throws Exception {
            assertInstantiable(c);
            return (T) newInstance.invoke(null, c, Object.class);
          }
        };
      } catch (Exception ignored) {
      }
  
      // give up
      return new UnsafeAllocator() {
        @Override
        public <T> T newInstance(Class<T> c) {
          throw new UnsupportedOperationException("Cannot allocate " + c);
        }
      };
    }
  
    /**
     * Check if the class can be instantiated by unsafe allocator. If the instance has interface or abstract modifiers
     * throw an {@link java.lang.UnsupportedOperationException}
     * @param c instance of the class to be checked
     */
    static void assertInstantiable(Class<?> c) {
      int modifiers = c.getModifiers();
      if (Modifier.isInterface(modifiers)) {
        throw new UnsupportedOperationException("Interface can't be instantiated! Interface name: " + c.getName());
      }
      if (Modifier.isAbstract(modifiers)) {
        throw new UnsupportedOperationException("Abstract class can't be instantiated! Class name: " + c.getName());
      }
    }
  }
  