如何使用getExternalCacheDir()在应用程序的缓存下创建子文件夹？

import android.content.Context;
import java.io.File;

public class CacheHelper {
    public static File getSubFolder(Context context, String folderName) {
        // 获取外部缓存目录
        File externalCacheDir = context.getExternalCacheDir();
        
        if (externalCacheDir != null) {
            // 创建子文件夹
            File subFolder = new File(externalCacheDir, folderName);
            
            // 如果子文件夹不存在，则创建它
            if (!subFolder.exists()) {
                subFolder.mkdirs(); // 使用 mkdirs() 而不是 mkdir() 以确保所有父目录都被创建
            }
            
            return subFolder;
        } else {
            // 处理外部存储不可用的情况
            throw new IllegalStateException("External storage is not available.");
        }
    }
}

import android.os.Environment;

public boolean isExternalStorageWritable() {
    String state = Environment.getExternalStorageState();
    return Environment.MEDIA_MOUNTED.equals(state);
}

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

import android.Manifest;
import android.content.pm.PackageManager;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

public void requestPermissionsIfNeeded(Activity activity) {
    if (ContextCompat.checkSelfPermission(activity, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(activity, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_CODE);
    }
}