Question

我正在使用一个设置，其中一个线程设置许多线程（服务），一起运行它们以模拟系统的运行，然后在最后加入它们并处理终止等。我的测试运行为其中一项服务，并通过JMS与其他人进行通信。对于我的一个测试，我需要访问另一个线程中包含的私有变量。我无法将其他线程中运行的代码更改为添加访问器方法或让它通过JMS发送变量。由于框架设置的方式，我也没办法将对我想要访问的服务的引用传递到我的测试服务中。

我知道我包含我需要访问的类的线程的名称，我可以通过枚举正在运行的线程来获取对线程的引用，但我不知道如何从中获取任何东西线程一旦我得到它。

我是否有某种方法可以使用反射或其他技术来获取另一个线程中的类的引用？

编辑：以下是我所处的情况示例：

import java.lang.reflect.Field;

public class Runner
{
    /**
     * Pretend this is my test class.
     */
    public static void main( String[] args )
    {
        // this is how my test starts up the system and runs the test
        runTest( TestService.class );
    }

    /**
     * Instantiate the test service and start up all of the threads in the
     * system. Doesn't return until test has completed.
     * 
     * @param testServiceClass
     *            the class that will run the test
     */
    static void runTest( Class<? extends Service> testServiceClass )
    {
        try
        {
            // setup the services
            Service testService =
                    testServiceClass.getConstructor( new Class<?>[] { String.class } )
                            .newInstance( "test service" );

            FixedService fixedService = new FixedService( "fixed service" );

            // start the services
            testService.start();
            fixedService.start();

            // wait for testService to signal that it is done
            System.out.println( "Started threads" );
            while ( !testService.isDone() )
            {
                try
                {
                    Thread.sleep( 1000 );
                }
                catch ( InterruptedException e )
                {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            // stop the fixed service
            fixedService.stop();
            System.out.println( "TestService done, fixed service told to shutdown" );
        }
        catch ( Exception e )
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    /**
     * I cannot modify this class. Handling of thread start is similar to real
     * system.
     */
    abstract static class Service implements Runnable
    {
        protected boolean isDone = false;
        protected boolean stop = false;
        private Thread thisServiceThread;

        public Service( String name )
        {
            thisServiceThread = new Thread( this, name );
        }

        public boolean isDone()
        {
            return isDone;
        }

        public void start()
        {
            thisServiceThread.start();
        }

        public void stop()
        {
            this.stop = true;
        }
    }

    /**
     * I can modify this class. This is the class that actually runs my test.
     */
    static class TestService extends Service
    {
        public TestService( String name )
        {
            super( name );
        }

        @Override
        public void run()
        {
            System.out.println( "TestService: started" );

            // TODO: How can I access FixedService.getMe from where without
            // modifying FixedService?
            try
            {
                Field field = FixedService.class.getDeclaredField( "getMe" );
                field.setAccessible( true );
                System.out.println( field.get( null ) );
            }
            catch ( SecurityException e )
            {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            catch ( NoSuchFieldException e )
            {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            catch ( IllegalArgumentException e )
            {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            catch ( IllegalAccessException e )
            {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            System.out.println( "TestService: done" );
            isDone = true;
        }

    }

    /**
     * I cannot modify this class. This is part of the system being tested.
     */
    static class FixedService extends Service
    {
        private boolean getMe = false;

        public FixedService( String name )
        {
            super( name );
        }

        @Override
        public void run()
        {
            System.out.println( "FixedService: started" );

            // don't stop until signaled to do so
            while ( !stop )
            {
                try
                {
                    Thread.sleep( 1000 );
                }
                catch ( InterruptedException e )
                {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }

            System.out.println( "FixedService: gotMe? " + getMe );

            System.out.println( "FixedService: done" );
            isDone = true;
        }
    }
}

Answer 1

正如Hemal Pandya所说，如果你想真正阅读或操纵这个领域，你将需要服务对象，而不仅仅是类。

假设您需要的Object是线程上设置的Runnable，那么可能会有一些非常脏的反射黑客攻击。您必须使用私有成员访问hack从线程获取target字段，然后再次使用它来访问runnable本身所需的字段。

以下是一些示例代码。请注意，我并没有真正考虑线程同步问题（尽管我不确定是否可以正确同步此类访问）

import java.lang.reflect.Field;

public class SSCCE {
    static class T extends Thread {
        private int i;

        public T(int i) {
            this.i = i;
        }

        @Override
        public void run() {
            while(true) {
                System.out.println("T: " + i);
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    // ignore
                }
            }
        }
    }

    static class R implements Runnable {
        private int i;

        public R(int i) {
            this.i = i;
        }

        @Override
        public void run() {
            while(true) {
                System.out.println("R: " + i);
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    // ignore
                }
            }
        }
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        Thread t1 = new T(1);
        Thread t2 = new Thread(new R(2));

        t1.start();
        t2.start();

        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            // ignore
        }

        setI(t1,3);
        setI(t2,4);
    }

    static void setI(Thread t, int newVal) {
        // Secret sauce here...
        try {
            Field fTarget = Thread.class.getDeclaredField("target");
            fTarget.setAccessible(true);
            Runnable r = (Runnable) fTarget.get(t);

            // This handles the case that the service overrides the run() method
            // in the thread instead of setting the target runnable
            if (r == null) r = t;

            Field fI = r.getClass().getDeclaredField("i");
            fI.setAccessible(true);
            fI.setInt(r, newVal);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

Answer 2

不是Thread而是Object，你必须得到变量。尝试提出控制线程和受控线程的小代码示例，它将变得更加清晰。

访问私人会员很容易。

编辑：使用Map到Thread.getId()的{{1}}。如果要检查线程，请确定runnable，并使用反射。由于同步问题，您可能无法获得最新值。

跨线程反思

2 个答案: