SimpleTest.java

import sun.misc.Unsafe;

import java.nio.*;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;

import java.security.AccessController;
import java.security.PrivilegedExceptionAction;

public class SimpleTest3
{
  public static final Unsafe UNSAFE;
  public static final long BYTE_BUFFER_ADDRESS_FIELD_OFFSET;

  static {
    Unsafe unsafe = null;
    try {
      Constructor<Unsafe> unsafeConstructor = Unsafe.class.getDeclaredConstructor();
      unsafeConstructor.setAccessible(true);
      unsafe = unsafeConstructor.newInstance();

      Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
      theUnsafe.setAccessible(true);
      unsafe = (Unsafe) theUnsafe.get(null);

      BYTE_BUFFER_ADDRESS_FIELD_OFFSET = unsafe.objectFieldOffset(Buffer.class.getDeclaredField("address"));
    } catch (final Exception ex) {
      throw new RuntimeException(ex);
    }

    UNSAFE = unsafe;
  }

  public static long address(final ByteBuffer buffer)
  {
    if (!buffer.isDirect())
      throw new IllegalArgumentException("buffer.isDirect() must be true");
    return UNSAFE.getLong(buffer, BYTE_BUFFER_ADDRESS_FIELD_OFFSET);
  }

  public static void main(String[] args)
  {
    ByteBuffer byteBuffer = ByteBuffer.allocateDirect(128);
    assert byteBuffer.isDirect() == true;

    long addressOffset = address(byteBuffer);
    System.out.println("addressOffset=" + addressOffset);

    UNSAFE.putInt(null, addressOffset + 0, 42);
    if (UNSAFE.getInt(null, addressOffset + 0) == 42)
      System.out.println("The magic of unsafe.");
  }
}