Unsafe

### 如何使用Unsafe类呢？

• 方式一：通过Unsafe提供的工厂方法。
  Unsafe unsafe = Unsafe.getUnsafe(); 通过这样的方式获得Unsafe的实力会抛出异常信息，因为在unsafe的源码中会有对安全性的检查

  public static Unsafe getUnsafe() {
       Class cc = sun.reflect.Reflection.getCallerClass(2);
       if (cc.getClassLoader() != null)
           throw new SecurityException("Unsafe");
       return theUnsafe;
   }

Exception in thread "main" java.lang.SecurityException: Unsafe
    at sun.misc.Unsafe.getUnsafe(Unsafe.java:68)
    at org.wk.core.concurrent.InitUnsafe.main(InitUnsafe.java:12)

• 方式二：通过反射的方式。
  因为在开源版本的Unsafe.java中声明了一个实例域，所以我们可以通过反射的方式来获得这个域。

  private static final Unsafe theUnsafe = new Unsafe();

//使用方法
private static Unsafe getUnsafeInstance() throws SecurityException,           NoSuchFieldException, IllegalArgumentException,           IllegalAccessException {
           NoSuchFieldException, IllegalArgumentException,
           IllegalAccessException 
       Field theUnsafeInstance = Unsafe.class.getDeclaredField("theUnsafe");
       theUnsafeInstance.setAccessible(true);
       return (Unsafe) theUnsafeInstance.get(Unsafe.class);
   }

• 事例

private static Unsafe unsafe = null;
static {
    try {
        Class<?> clazz = Unsafe.class;
        Field f;
        f = clazz.getDeclaredField("theUnsafe");
        f.setAccessible(true);
        unsafe = (Unsafe) f.get(clazz);
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (SecurityException e) {
        e.printStackTrace();
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
    }
}

• 结束