要監控Java ThreadPoolExecutor的狀態，您可以使用以下方法：

1. 繼承ThreadPoolExecutor類并重寫其beforeExecute()和afterExecute()方法。在這些方法中，您可以記錄線程池的狀態信息，例如活動線程數、任務隊列大小等。

import java.util.concurrent.*;

public class CustomThreadPoolExecutor extends ThreadPoolExecutor {

    public CustomThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
    }

    @Override
    protected void beforeExecute(Thread t, Runnable r) {
        System.out.println("線程 " + t.getName() + " 開始執行任務 " + r.toString());
        super.beforeExecute(t, r);
    }

    @Override
    protected void afterExecute(Runnable r, Throwable t) {
        System.out.println("線程 " + Thread.currentThread().getName() + " 結束執行任務 " + r.toString());
        super.afterExecute(r, t);
    }

    public static void main(String[] args) {
        CustomThreadPoolExecutor executor = new CustomThreadPoolExecutor(3, 5, 60, TimeUnit.SECONDS, new LinkedBlockingQueue<>(10));
        for (int i = 0; i < 20; i++) {
            executor.execute(new Task("任務 " + i));
        }
        executor.shutdown();
    }
}

class Task implements Runnable {
    private String name;

    public Task(String name) {
        this.name = name;
    }

    @Override
    public void run() {
        // 執行任務邏輯
    }
}

2. 使用Java Management Extensions (JMX)監控線程池狀態。JMX提供了一種標準方法來監控和管理Java應用程序。要使用JMX監控ThreadPoolExecutor，您需要啟用JMX代理并在代碼中注冊MBean。

首先，創建一個實現ThreadPoolExecutor的類，并重寫newTaskFor()方法以返回一個實現了RunnableScheduledFuture接口的自定義任務類。然后，創建一個MBean類，用于暴露線程池的狀態信息。最后，在主類中注冊MBean并啟動JMX代理。

import java.util.concurrent.*;
import javax.management.*;
import javax.management.remote.*;

public class ThreadPoolExecutorWithJMX extends ThreadPoolExecutor {

    public ThreadPoolExecutorWithJMX(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
    }

    @Override
    protected <T> RunnableScheduledFuture<T> newTaskFor(Callable<T> callable) {
        return new CustomScheduledFutureTask<>(callable);
    }

    public static void main(String[] args) throws Exception {
        ThreadPoolExecutorWithJMX executor = new ThreadPoolExecutorWithJMX(3, 5, 60, TimeUnit.SECONDS, new LinkedBlockingQueue<>(10));
        MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
        ObjectName name = new ObjectName("com.example:type=ThreadPoolExecutor");
        mbs.registerMBean(executor, name);

        // 提交任務并監控線程池狀態
        for (int i = 0; i < 20; i++) {
            executor.execute(new Task("任務 " + i));
        }

        // 關閉線程池
        executor.shutdown();

        // 連接到JMX代理并獲取線程池狀態信息
        JMXServiceURL url = new JMXServiceURL("service:jmx:rmi:///jndi/rmi://localhost:1099/jmxrmi");
        JMXConnector jmxConnector = JMXConnectorFactory.connect(url);
        JMXServiceConnection connection = jmxConnector.getMBeanConnection();
        AttributeList attributes = connection.getAttributes(name, new String[]{"activeCount", "corePoolSize", "maximumPoolSize", "taskCount", "queueCapacity"});
        for (Object attr : attributes) {
            System.out.println(attr);
        }
    }
}

class CustomScheduledFutureTask<T> extends FutureTask<T> implements RunnableScheduledFuture<T> {
    public CustomScheduledFutureTask(Callable<T> callable) {
        super(callable);
    }

    @Override
    public void run() {
        super.run();
    }
}

class Task implements Runnable {
    private String name;

    public Task(String name) {
        this.name = name;
    }

    @Override
    public void run() {
        // 執行任務邏輯
    }
}

運行上述代碼后，您可以使用JConsole或VisualVM等工具連接到JMX代理，然后查看線程池的狀態信息，如活動線程數、核心線程數、最大線程數、任務隊列容量等。