package unsafe;

import org.junit.Before;

import org.junit.Test;

import sun.misc.Unsafe;

import java.io.File;

import java.io.FileInputStream;

import java.lang.reflect.Constructor;

import java.lang.reflect.Field;

import java.lang.reflect.Method;

/**

* Created by 李恒名 on 2017/6/20.

*/

public class UnsafeTest {

private Unsafe unsafe;

@Before

public void before() throws Exception {

Field f = Unsafe.class.getDeclaredField("theUnsafe");

f.setAccessible(true);

unsafe = (Unsafe) f.get(null);

}

/**

* 通过反射Constructor获得Unsafe的实例对象

*

* @throws Exception

*/

@Test

public void test1() throws Exception {

Constructor<Unsafe> constructor = Unsafe.class.getDeclaredConstructor();

constructor.setAccessible(true);

Unsafe unsafe = constructor.newInstance();

System.out.println(unsafe);

}

/**

* 通过反射Field获得Unsafe的实例对象

*

* @throws Exception

*/

@Test

public void test2() throws Exception {

Field f = Unsafe.class.getDeclaredField("theUnsafe");

f.setAccessible(true);

Unsafe unsafe = (Unsafe) f.get(null);

System.out.println(unsafe);

}

/**

* 通过Unsafe的defineClass方法在内存中创建一个Class对象

*

* @throws Exception

*/

@Test

public void test3() throws Exception {

//读取Class文件

File file = new File("E:\\classes\\Test.class");

FileInputStream input = new FileInputStream(file);

byte[] data = new byte[(int) file.length()];

input.read(data);

input.close();

//创建Class对象

//Class clazz = unsafe.defineClass("Test", data, 0, data.length);//这个方法在Java 8 没了。

Class clazz = unsafe.defineClass("Test", data, 0, data.length, null, null);

//通过反射创建示例调用方法

Object instance = clazz.newInstance();

Method method = clazz.getMethod("say", null);

method.invoke(instance);//Hello

}

/**

* 通过Unsafe的allocateInstance方法创建一个类的实例

*

* @throws Exception

*/

@Test

public void test4() throws Exception {

//通过Unsafe创建实例

TestClass instanceByUnsafe = (TestClass) unsafe.allocateInstance(TestClass.class);

instanceByUnsafe.printValue();//0

//通过反射创建实例

//TestClass instanceByReflect = TestClass.class.newInstance();//该方法只能实例化拥有公开无参构造器的类

Constructor<TestClass> constructor = TestClass.class.getDeclaredConstructor();

constructor.setAccessible(true);//访问私有构造

TestClass instanceByReflect = constructor.newInstance();//创建实例

instanceByReflect.printValue();//1

}

@Test

public void test5() throws Exception {

unsafe.allocateMemory(Long.MAX_VALUE);//java.lang.OutOfMemoryError

}

@Test

public void test6() throws Exception {

Object lock = new Object();

//注掉下面这行代码则抛出java.lang.IllegalMonitorStateException

unsafe.monitorEnter(lock);

lock.wait(1000);

System.out.println("Hello World");

unsafe.monitorExit(lock);

}

}