Java ExecutorService如何實現任務優先級

在Java中，ExecutorService本身并不直接支持任務的優先級。但是，你可以通過使用PriorityBlockingQueue和自定義的ThreadFactory來實現任務優先級。

以下是一個簡單的示例，展示了如何使用PriorityBlockingQueue和自定義的ThreadFactory實現任務優先級：

1. 首先，創建一個實現了Runnable接口的任務類，并在其中添加一個priority字段來表示任務的優先級。

public class PriorityTask implements Runnable, Comparable<PriorityTask> {
    private int priority;
    private Runnable task;

    public PriorityTask(int priority, Runnable task) {
        this.priority = priority;
        this.task = task;
    }

    public int getPriority() {
        return priority;
    }

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

    @Override
    public int compareTo(PriorityTask other) {
        return Integer.compare(other.priority, this.priority);
    }
}

2. 創建一個自定義的ThreadFactory，用于創建具有優先級的線程。

import java.util.concurrent.ThreadFactory;

public class PriorityThreadFactory implements ThreadFactory {
    private int counter = 0;

    @Override
    public Thread newThread(Runnable r) {
        Thread t = new Thread(r, "PriorityThread-" + counter++);
        t.setDaemon(false);
        t.setPriority(Thread.NORM_PRIORITY);
        return t;
    }
}

3. 創建一個ExecutorService，使用PriorityBlockingQueue作為任務隊列，并使用自定義的ThreadFactory創建線程。

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.PriorityBlockingQueue;

public class PriorityExecutorService {
    public static void main(String[] args) {
        PriorityBlockingQueue<Runnable> queue = new PriorityBlockingQueue<>();
        ExecutorService executorService = new Executors.newFixedThreadPool(5, new PriorityThreadFactory());

        executorService.submit(new PriorityTask(3, () -> System.out.println("Task 3")));
        executorService.submit(new PriorityTask(1, () -> System.out.println("Task 1")));
        executorService.submit(new PriorityTask(2, () -> System.out.println("Task 2")));

        executorService.shutdown();
    }
}

在這個示例中，我們創建了一個PriorityExecutorService類，它使用PriorityBlockingQueue作為任務隊列，并使用自定義的PriorityThreadFactory創建線程。我們提交了三個具有不同優先級的任務。當你運行這個程序時，你會看到任務按照優先級順序執行。