热部署

热加载：在不重启jvm前提下 实现类的动态替换

MyObject object = (MyObject)
    myClassReloadingFactory.newInstance("com.jenkov.MyObject");

Remember, a class can only be loaded once by the same ClassLoader instance（一个类加载器不能加载同一个类两次 如果想要reload一个类 需要一个新的类加载器完成这个功能）

Notice how the MyObject class is referenced in the code, as the type of the object variable. This causes the MyObject class to be loaded by the same class loader that loaded the class this code is residing in.
If the myClassReloadingFactory object factory reloads the MyObject class using a different class loader than the class the above code resides in, you cannot cast the instance of the reloaded MyObject class to the MyObject type of the object variable. （同一个类由不同的类加载器加载 将会被视为不同的类）Since the two MyObject classes were loaded with different class loaders, the are regarded as different classes, even if they have the same fully qualified class name. Trying to cast an object of the one class to a reference of the other will result in a ClassCastException.

两种解决办法

MyObjectInterface object = (MyObjectInterface)
    myClassReloadingFactory.newInstance("com.jenkov.MyObject");

MyObjectSuperclass object = (MyObjectSuperclass)
    myClassReloadingFactory.newInstance("com.jenkov.MyObject");

一个简单的实现例子

public static void main(String[] args) throws
    ClassNotFoundException,
    IllegalAccessException,
    InstantiationException {

    ClassLoader parentClassLoader = MyClassLoader.class.getClassLoader();
    MyClassLoader classLoader = new MyClassLoader(parentClassLoader);
    Class myObjectClass = classLoader.loadClass("reflection.MyObject");

    AnInterface2 object1 =
            (AnInterface2) myObjectClass.newInstance();

    MyObjectSuperClass object2 =
            (MyObjectSuperClass) myObjectClass.newInstance();

    //create new class loader so classes can be reloaded.
    classLoader = new MyClassLoader(parentClassLoader);
    myObjectClass = classLoader.loadClass("reflection.MyObject");

    object1 = (AnInterface2) myObjectClass.newInstance();
    object2 = (MyObjectSuperClass) myObjectClass.newInstance();

}

参考

http://tutorials.jenkov.com/java-reflection/dynamic-class-loading-reloading.html#dynamicreloading