Unsafe的使用

1、调用问题

我们直接获取Unsafe，调用其中属性方法时会出现异常：

java.lang.SecurityException: Unsafeat sun.misc.Unsafe.getUnsafe(Unsafe.java:90)at UnsafeTest.main(UnsafeTest.java:5)

异常分析：

Unsafe unsafe = Unsafe.getUnsafe();

上面这行代码出现的异常，获取Unsafe时出现异常，查看getUnsafe()方法如下：

	@CallerSensitivepublic static Unsafe getUnsafe() {Class var0 = Reflection.getCallerClass();if (!VM.isSystemDomainLoader(var0.getClassLoader())) {throw new SecurityException("Unsafe");} else {return theUnsafe;}}

如上getUnsafe()被设计成只能从启动类加载器(Bootstrap Class Loader)加载，所以我们自己直接调用时会出现异常。

2、如何调用

	//引用Unsafe需使用如下反射方式，否则会抛出异常java.lang.SecurityException: Unsafepublic static Unsafe reflectGetUnsafe() throws NoSuchFieldException, IllegalAccessException {Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");theUnsafe.setAccessible(true);//禁止访问权限检查（访问私有属性时需要加上）return (Unsafe) theUnsafe.get(null);}