关于使用ContextClassLoader遇到的问题

/**
 * Thread.currentThread().setContextClassLoader
 * 如果父线程加载了某个class, 那么子线程也可以使用该class
 */
public class Test2 {
    public static void main(String[] args) throws InterruptedException {
        ClassLoader ccl = Thread.currentThread().getContextClassLoader();
        MyClassLoader classLoader = new MyClassLoader();
            classLoader.setClassFile(new File("D:\\UserService3Impl.class"));
            Thread.currentThread().setContextClassLoader(classLoader);
            try {
                classLoader.loadClass("com.sample.mybatis.service.impl.UserService3Impl");
            } catch (Exception e) {
                e.printStackTrace();
            }
        Thread thread = new Thread(() -> {
            try {
                Class<?> userClass = Thread.currentThread().getContextClassLoader().loadClass("com.sample.mybatis.service.impl.UserService3Impl");
                System.out.println(userClass);
                UserService3 userObj = (UserService3)userClass.newInstance();
                System.out.println(Thread.currentThread().getName() + " ==> " + userObj.getUserNo());
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
         thread.start();
    }
}

/**
 * Thread.currentThread().setContextClassLoader
 * 如果子线程加载了某个class, 那么父线程不能共享到该class
 */
public class Test4 {
    public static void main(String[] args) throws Exception {
        Thread thread = new Thread(() -> {
            try {
                MyClassLoader classLoader = new MyClassLoader();
                classLoader.setClassFile(new File("D:\\UserService3Impl.class"));
                Thread.currentThread().setContextClassLoader(classLoader);
                try {
                    classLoader.loadClass("com.sample.mybatis.service.impl.UserService3Impl");
                } catch (Exception e) {
                    e.printStackTrace();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
        thread.start();
        thread.join();
        Class<?> userClass = Thread.currentThread().getContextClassLoader().loadClass("com.sample.mybatis.service.impl.UserService3Impl");
        System.out.println(userClass);
        UserService3 userObj = (UserService3) userClass.newInstance();
        System.out.println(Thread.currentThread().getName() + " ==> " + userObj.getUserNo());
    }
}

/**
 * 如果两个线程不是父子线程， 线程之间不会共享加载过的class
 */
public class Test3 {
    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(() -> {
            MyClassLoader classLoader = new MyClassLoader();
            classLoader.setClassFile(new File("D:\\UserService3Impl.class"));
            Thread.currentThread().setContextClassLoader(classLoader);
            Class<?> userClass = null;
            try {
                userClass = classLoader.loadClass("com.sample.mybatis.service.impl.UserService3Impl");
                System.out.println(userClass);
                UserService3 userObj = (UserService3) userClass.newInstance();
                System.out.println(Thread.currentThread().getName() + " ==> " + userObj.getUserNo());
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
        thread.start();
        thread.join();
        Thread thread2 = new Thread(() -> {
            try {
                Class<?> userClass = Thread.currentThread().getContextClassLoader().loadClass("com.sample.mybatis.service.impl.UserService3Impl");
                System.out.println(userClass);
                UserService3 userObj = (UserService3) userClass.newInstance();
                System.out.println(Thread.currentThread().getName() + " ==> " + userObj.getUserNo());
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
        thread2.start();
    }
}

ClassLoader ccl = Thread.currentThread().getContextClassLoader(); //取出
try {
    MyClassLoader classLoader = new MyClassLoader();
    classLoader.setClassFile(new File("D:\\UserService3Impl.class"));
    Thread.currentThread().setContextClassLoader(classLoader); //设置
    //其他逻辑。。。
}finally {
    Thread.currentThread().setContextClassLoader(ccl); //还原
}