github.com/keysonZZZ/kmg@v0.0.0-20151121023212-05317bfd7d39/kmgRpc/kmgRpcJava/java/src/com/google/gson/internal/UnsafeAllocator.java (about)

     1  /*
     2   * Copyright (C) 2011 Google Inc.
     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  
    17  package com.google.gson.internal;
    18  
    19  import java.io.ObjectInputStream;
    20  import java.io.ObjectStreamClass;
    21  import java.lang.reflect.Field;
    22  import java.lang.reflect.Method;
    23  
    24  /**
    25   * Do sneaky things to allocate objects without invoking their constructors.
    26   *
    27   * @author Joel Leitch
    28   * @author Jesse Wilson
    29   */
    30  public abstract class UnsafeAllocator {
    31    public abstract <T> T newInstance(Class<T> c) throws Exception;
    32  
    33    public static UnsafeAllocator create() {
    34      // try JVM
    35      // public class Unsafe {
    36      //   public Object allocateInstance(Class<?> type);
    37      // }
    38      try {
    39        Class<?> unsafeClass = Class.forName("sun.misc.Unsafe");
    40        Field f = unsafeClass.getDeclaredField("theUnsafe");
    41        f.setAccessible(true);
    42        final Object unsafe = f.get(null);
    43        final Method allocateInstance = unsafeClass.getMethod("allocateInstance", Class.class);
    44        return new UnsafeAllocator() {
    45          @Override
    46          @SuppressWarnings("unchecked")
    47          public <T> T newInstance(Class<T> c) throws Exception {
    48            return (T) allocateInstance.invoke(unsafe, c);
    49          }
    50        };
    51      } catch (Exception ignored) {
    52      }
    53  
    54      // try dalvikvm, post-gingerbread
    55      // public class ObjectStreamClass {
    56      //   private static native int getConstructorId(Class<?> c);
    57      //   private static native Object newInstance(Class<?> instantiationClass, int methodId);
    58      // }
    59      try {
    60        Method getConstructorId = ObjectStreamClass.class
    61            .getDeclaredMethod("getConstructorId", Class.class);
    62        getConstructorId.setAccessible(true);
    63        final int constructorId = (Integer) getConstructorId.invoke(null, Object.class);
    64        final Method newInstance = ObjectStreamClass.class
    65            .getDeclaredMethod("newInstance", Class.class, int.class);
    66        newInstance.setAccessible(true);
    67        return new UnsafeAllocator() {
    68          @Override
    69          @SuppressWarnings("unchecked")
    70          public <T> T newInstance(Class<T> c) throws Exception {
    71            return (T) newInstance.invoke(null, c, constructorId);
    72          }
    73        };
    74      } catch (Exception ignored) {
    75      }
    76  
    77      // try dalvikvm, pre-gingerbread
    78      // public class ObjectInputStream {
    79      //   private static native Object newInstance(
    80      //     Class<?> instantiationClass, Class<?> constructorClass);
    81      // }
    82      try {
    83        final Method newInstance = ObjectInputStream.class
    84            .getDeclaredMethod("newInstance", Class.class, Class.class);
    85        newInstance.setAccessible(true);
    86        return new UnsafeAllocator() {
    87          @Override
    88          @SuppressWarnings("unchecked")
    89          public <T> T newInstance(Class<T> c) throws Exception {
    90            return (T) newInstance.invoke(null, c, Object.class);
    91          }
    92        };
    93      } catch (Exception ignored) {
    94      }
    95  
    96      // give up
    97      return new UnsafeAllocator() {
    98        @Override
    99        public <T> T newInstance(Class<T> c) {
   100          throw new UnsupportedOperationException("Cannot allocate " + c);
   101        }
   102      };
   103    }
   104  }