java将一个文件夹下面的子文件夹拷贝到另一个路径下面

你可以使用 Java 的文件操作类 File 来实现文件夹的拷贝。具体实现步骤如下：

1. 定义两个 File 类型的对象，分别表示源文件夹和目标文件夹。

File sourceFolder = new File("源文件夹路径");
File targetFolder = new File("目标文件夹路径");

2. 判断源文件夹是否存在，如果不存在则无法进行拷贝。

if (!sourceFolder.exists()) {
    System.out.println("源文件夹不存在");
    return;
}

3. 创建目标文件夹。如果目标文件夹已经存在，则无需创建。

if (!targetFolder.exists()) {
    targetFolder.mkdir();
}

4. 遍历源文件夹下的所有子文件夹，将每个子文件夹拷贝到目标文件夹下。

File[] subFolders = sourceFolder.listFiles(File::isDirectory);
for (File subFolder : subFolders) {
    String subFolderName = subFolder.getName();
    File targetSubFolder = new File(targetFolder, subFolderName);
    targetSubFolder.mkdir(); // 创建目标子文件夹
    copyFolder(subFolder, targetSubFolder); // 递归拷贝子文件夹
}

5. 如果源文件夹下还有子文件夹，则递归拷贝子文件夹。

private static void copyFolder(File sourceFolder, File targetFolder) {
    File[] files = sourceFolder.listFiles();
    for (File file : files) {
        if (file.isDirectory()) {
            String subFolderName = file.getName();
            File targetSubFolder = new File(targetFolder, subFolderName);
            targetSubFolder.mkdir();
            copyFolder(file, targetSubFolder);
        } else {
            File targetFile = new File(targetFolder, file.getName());
            try (InputStream in = new FileInputStream(file);
                 OutputStream out = new FileOutputStream(targetFile)) {
                byte[] buffer = new byte[1024];
                int length;
                while ((length = in.read(buffer)) > 0) {
                    out.write(buffer, 0, length);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

完整代码如下所示：

import java.io.*;

public class CopyFolderDemo {

    public static void main(String[] args) {
        File sourceFolder = new File("源文件夹路径");
        File targetFolder = new File("目标文件夹路径");
        if (!sourceFolder.exists()) {
            System.out.println("源文件夹不存在");
            return;
        }
        if (!targetFolder.exists()) {
            targetFolder.mkdir();
        }
        File[] subFolders = sourceFolder.listFiles(File::isDirectory);
        for (File subFolder : subFolders) {
            String subFolderName = subFolder.getName();
            File targetSubFolder = new File(targetFolder, subFolderName);
            targetSubFolder.mkdir();
            copyFolder(subFolder, targetSubFolder);
        }
    }

    private static void copyFolder(File sourceFolder, File targetFolder) {
        File[] files = sourceFolder.listFiles();
        for (File file : files) {
            if (file.isDirectory()) {
                String subFolderName = file.getName();
                File targetSubFolder = new File(targetFolder, subFolderName);
                targetSubFolder.mkdir();
                copyFolder(file, targetSubFolder);
            } else {
                File targetFile = new File(targetFolder, file.getName());
                try (InputStream in = new FileInputStream(file);
                     OutputStream out = new FileOutputStream(targetFile)) {
                    byte[] buffer = new byte[1024];
                    int length;
                    while ((length = in.read(buffer)) > 0) {
                        out.write(buffer, 0, length);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

注意，上述代码中的 "源文件夹路径" 和 "目标文件夹路径" 需要替换成实际的文件夹路径。