java - 为什么新的 Java Logger 在这里无法一致工作？

Question

请注意大多数其他调用 Logger 调用是如何工作的，以及所有 System.out.println() 是如何工作的，但请有人向我解释为什么 stop() 和 destroy() 中的 >Logger.info() 调用永远不会与日志的其余部分一起打印，因为这些函数显然正在运行! ？对于 java12，甚至 destroy() 也不会显示。这是一个错误吗？我使用它是否很奇怪，还是什么？

package test;
import java.util.logging.Logger;

public class Test {
    private static Logger LOGGER = Logger.getLogger(Test.class.getCanonicalName());

    public static void main(String[] args) {
        System.out.println("main()");
        LOGGER.info("main()");
        new Test();
    }

    private Test() {
        LOGGER.info("Test()");
        System.out.println("Test()");
        Runtime.getRuntime().addShutdownHook(new ShutdownThread());
    }

    public void shutdown() throws Exception {
        LOGGER.info("shutdown()");
        System.out.println("shutdown()");
        stop();
        destroy();
    }

    public void stop() throws Exception {
        LOGGER.info("stop()");
        System.out.println("stop()");
    }

    public void destroy() {
        LOGGER.info("destroy()");
        System.out.println("destroy()");
    }

    class ShutdownThread extends Thread {
        ShutdownThread() {
            super("app-shutdown-hook");
        }

        @Override
        public void run() {
            try {
                shutdown();
            } catch (Exception e) {
                e.printStackTrace();
            }
            System.out.println("Bye! 🙇‍♂️👋🖖");
        }
    }
}

使用 java 10 和 java 11 (OpenJDK) 的输出:

main()
Mar 14, 2020 1:53:59 PM test.Test main
INFO: main()
Mar 14, 2020 1:53:59 PM test.Test <init>
INFO: Test()
Test()
Mar 14, 2020 1:53:59 PM test.Test shutdown
INFO: shutdown()
shutdown()
stop()
destroy()
Bye! 🙇‍♂️👋🖖

使用 java 12 (OpenJDK) 输出:

main()
Mar 14, 2020 2:17:13 PM test.Test main
INFO: main()
Mar 14, 2020 2:17:13 PM test.Test <init>
INFO: Test()
Test()
shutdown()
stop()
destroy()
Bye! 🙇‍♂️👋🖖

Answer 1

此问题隐藏在:JDK-8161253 - LogManager$Cleaner() can prevent logging in other shutdown hooks .

每张票:

As a workaround to creating a custom shutdown hook you can create a custom handler and install it on the root logger. The first action of the LogManager$Cleaner is to close all the installed handlers on the logger. Once the cleaner calls the close on the custom handler you can then do one of the following:

1. 在处理程序内更干净地运行关闭代码。
2. 使用 Thread API 找到您的自定义关闭 Hook 并加入它。

这是解决方案#1:

import java.util.logging.Handler;
import java.util.logging.LogRecord;
import java.util.logging.Logger;

public class Test {
    private static Logger LOGGER = Logger.getLogger(Test.class.getCanonicalName());

    public static void main(String[] args) {
        System.out.println("main()");
        LOGGER.info("main()");
        new Test();
    }

    private Test() {
        LOGGER.info("Test()");
        System.out.println("Test()");
        addShutdownHandler();
    }

    private void addShutdownHandler() {
        Logger root = Logger.getLogger("");
        Handler[] handlers = root.getHandlers();

        for(Handler h : handlers) {
            if (h.getClass() == ShutdownHandler.class) {
                return;
            }
        }

        for(Handler h : handlers) {
            root.removeHandler(h);
        }

        root.addHandler(new ShutdownHandler());

        for(Handler h : handlers) {
            root.addHandler(h);
        }
    }

    public void shutdown() throws Exception {
        LOGGER.info("shutdown()");
        System.out.println("shutdown()");
        stop();
        destroy();
    }

    public void stop() throws Exception {
        LOGGER.info("stop()");
        System.out.println("stop()");
    }

    public void destroy() {
        LOGGER.info("destroy()");
        System.out.println("destroy()");
    }

    class ShutdownHandler extends Handler {
        ShutdownHandler() {
        }

        @Override
        public void close() {
            final Thread t = Thread.currentThread();
            final String old = t.getName();
            t.setName("app-shutdown-hook");
            try {
                shutdown();
                System.out.println("Bye! 🙇‍♂️👋🖖");
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                t.setName(old);
            }
        }

        @Override
        public void flush() {
        }

        @Override
        public void publish(LogRecord r) {
            isLoggable(r);
        }
    }
}

解决方案 #2 变得很棘手，因为我们无法确保从一个关闭 Hook 启动了另一个关闭 Hook 。如果您想使用 Thread::join，这意味着需要额外的编码。因此，为了解决这个问题，我们只需使用 Future API:

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
import java.util.logging.ErrorManager;
import java.util.logging.Handler;
import java.util.logging.LogRecord;
import java.util.logging.Logger;

public class Test {
    private static Logger LOGGER = Logger.getLogger(Test.class.getCanonicalName());

    public static void main(String[] args) {
        System.out.println("main()");
        LOGGER.info("main()");
        new Test();
    }

    private Test() {
        LOGGER.info("Test()");
        System.out.println("Test()");
        addShutdownHandler();
    }

    private void addShutdownHandler() {
        Logger root = Logger.getLogger("");
        Handler[] handlers = root.getHandlers();

        for(Handler h : handlers) {
            if (h.getClass() == CleanerJoin.class) {
                return;
            }
        }

        for(Handler h : handlers) {
            root.removeHandler(h);
        }

        root.addHandler(new CleanerJoin());

        for(Handler h : handlers) {
            root.addHandler(h);
        }
    }

    public void shutdown() throws Exception {
        LOGGER.info("shutdown()");
        System.out.println("shutdown()");
        stop();
        destroy();
    }

    public void stop() throws Exception {
        LOGGER.info("stop()");
        System.out.println("stop()");
    }

    public void destroy() {
        LOGGER.info("destroy()");
        System.out.println("destroy()");
    }

    class ShutdownTask implements Callable<Void> {
        ShutdownTask() {
        }

        @Override
        public Void call() throws Exception {
            shutdown();
            System.out.println("Bye! 🙇‍♂️👋🖖");
            return null;
        }
    }

    class CleanerJoin extends Handler {
        private final FutureTask<Void> sdt = new FutureTask<>(new ShutdownTask());

        CleanerJoin() {
            Runtime.getRuntime().addShutdownHook(new Thread(sdt, "app-shutdown-hook"));
        }


        @Override
        public void close() {
            boolean interrupted = false;
            try {
                for(;;) {
                    try { //Could use LogManager to lookup timeout values and use a timed join.
                        sdt.get();
                        break;
                    } catch (ExecutionException e) {
                        reportError("Shutdown hook failed.", e, ErrorManager.CLOSE_FAILURE);
                        break;
                    } catch (InterruptedException retry) {
                        interrupted = true;
                    }
                }
            } finally {
                if (interrupted) {
                    Thread.currentThread().interrupt();
                }
            }
        }

        @Override
        public void flush() {
        }

        @Override
        public void publish(LogRecord r) {
            isLoggable(r);
        }
    }
}