java多线程拷贝指定文件夹下的文件（不考虑子文件夹，只考虑当层文件夹下的文件），单个线程拷贝单个文件。原文件夹名、目标文件名由用户输入。所有线程完成工作后，输出“文件夹内文件拷贝完成”的消息

在Java中，你可以通过`java.util.concurrent.ExecutorService`和`java.io.File`类来实现这个功能。首先，你需要创建一个`CopyTask`类，该类包含一个具体的拷贝方法，它会接收源文件路径和目标文件路径作为参数。然后，你可以创建一个`CopyWorker`类，继承自`Thread`，并在run()方法中实例化并执行`CopyTask`。

import java.io.File;
import java.io.IOException;

class CopyTask {
    private String sourceFilePath;
    private String targetFilePath;

    public CopyTask(String source, String target) {
        this.sourceFilePath = source;
        this.targetFilePath = target;
    }

    public void copyFile() throws IOException {
        File srcFile = new File(sourceFilePath);
        File dstFile = new File(targetFilePath);
        if (srcFile.exists()) {
            try (InputStream in = new FileInputStream(srcFile);
                 OutputStream out = new FileOutputStream(dstFile)) {
                byte[] buffer = new byte[1024];
                int length;
                while ((length = in.read(buffer)) > 0) {
                    out.write(buffer, 0, length);
                }
                System.out.println("Copied " + srcFile.getName() + " to " + dstFile.getAbsolutePath());
            }
        } else {
            System.err.println("Source file not found: " + srcFile.getAbsolutePath());
        }
    }
}

class CopyWorker extends Thread {
    private final CopyTask task;

    public CopyWorker(CopyTask task) {
        this.task = task;
    }

    @Override
    public void run() {
        try {
            task.copyFile();
        } catch (IOException e) {
            System.err.println("Error copying file: " + e.getMessage());
        }
    }
}

public class Main {
    public static void main(String[] args) {
        // 获取用户输入的源目录和目标目录
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the source folder path: ");
        String source = scanner.nextLine();
        System.out.print("Enter the target folder path: ");
        String target = scanner.nextLine();

        // 创建CopyTasks列表
        List<CopyTask> tasks = new ArrayList<>();
        File folder = new File(source);
        for (File file : folder.listFiles()) { // 只处理当前层级的文件
            tasks.add(new CopyTask(file.getAbsolutePath(), target + "/" + file.getName()));
        }

        ExecutorService executor = Executors.newFixedThreadPool(tasks.size()); // 使用固定大小线程池
        for (CopyTask task : tasks) {
            executor.execute(task);
        }

        executor.shutdown(); // 关闭线程池

        try {
            executor.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS); // 等待所有任务完成
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }

        System.out.println("Files copied successfully.");
    }
}