这里是一个针对当前Android设备的清理版本，功能方法设计，以便您可以将其复制到AssetsHelper类，例如;)

/**
 * 
 * Info: prior to Android 2.3, any compressed asset file with an
 * uncompressed size of over 1 MB cannot be read from the APK. So this
 * should only be used if the device has android 2.3 or later running!
 * 
 * @param c
 * @param targetFolder
 *            e.g. {@link Environment#getExternalStorageDirectory()}
 * @throws Exception
 */
@TargetApi(Build.VERSION_CODES.GINGERBREAD)
public static boolean copyAssets(AssetManager assetManager,
        File targetFolder) throws Exception {
    Log.i(LOG_TAG, "Copying files from assets to folder " + targetFolder);
    return copyAssets(assetManager, "", targetFolder);
}

/**
 * The files will be copied at the location targetFolder+path so if you
 * enter path="abc" and targetfolder="sdcard" the files will be located in
 * "sdcard/abc"
 * 
 * @param assetManager
 * @param path
 * @param targetFolder
 * @return
 * @throws Exception
 */
public static boolean copyAssets(AssetManager assetManager, String path,
        File targetFolder) throws Exception {
    Log.i(LOG_TAG, "Copying " + path + " to " + targetFolder);
    String sources[] = assetManager.list(path);
    if (sources.length == 0) { // its not a folder, so its a file:
        copyAssetFileToFolder(assetManager, path, targetFolder);
    } else { // its a folder:
        if (path.startsWith("images") || path.startsWith("sounds")
                || path.startsWith("webkit")) {
            Log.i(LOG_TAG, "  > Skipping " + path);
            return false;
        }
        File targetDir = new File(targetFolder, path);
        targetDir.mkdirs();
        for (String source : sources) {
            String fullSourcePath = path.equals("") ? source : (path
                    + File.separator + source);
            copyAssets(assetManager, fullSourcePath, targetFolder);
        }
    }
    return true;
}

private static void copyAssetFileToFolder(AssetManager assetManager,
        String fullAssetPath, File targetBasePath) throws IOException {
    InputStream in = assetManager.open(fullAssetPath);
    OutputStream out = new FileOutputStream(new File(targetBasePath,
            fullAssetPath));
    byte[] buffer = new byte[16 * 1024];
    int read;
    while ((read = in.read(buffer)) != -1) {
        out.write(buffer, 0, read);
    }
    in.close();
    out.flush();
    out.close();
}

轻微修改以上回答复制文件夹递归和适应自定义目的地。

public void copyFileOrDir(String path, String destinationDir) {
    AssetManager assetManager = this.getAssets();
    String assets[] = null;
    try {
        assets = assetManager.list(path);
        if (assets.length == 0) {
            copyFile(path,destinationDir);
        } else {
            String fullPath = destinationDir + "/" + path;
            File dir = new File(fullPath);
            if (!dir.exists())
                dir.mkdir();
            for (int i = 0; i < assets.length; ++i) {
                copyFileOrDir(path + "/" + assets[i], destinationDir + path + "/" + assets[i]);
            }
        }
    } catch (IOException ex) {
        Log.e("tag", "I/O Exception", ex);
    }
}

private void copyFile(String filename, String destinationDir) {
    AssetManager assetManager = this.getAssets();
    String newFileName = destinationDir + "/" + filename;

    InputStream in = null;
    OutputStream out = null;
    try {
        in = assetManager.open(filename);
        out = new FileOutputStream(newFileName);

        byte[] buffer = new byte[1024];
        int read;
        while ((read = in.read(buffer)) != -1) {
            out.write(buffer, 0, read);
        }
        in.close();
        in = null;
        out.flush();
        out.close();
        out = null;
    } catch (Exception e) {
        Log.e("tag", e.getMessage());
    }
    new File(newFileName).setExecutable(true, false);
}

试试这个，它更简单，这将帮助你:

// Open your local db as the input stream
    InputStream myInput = _context.getAssets().open(YOUR FILE NAME);

    // Path to the just created empty db
    String outFileName =SDCARD PATH + YOUR FILE NAME;

    // Open the empty db as the output stream
    OutputStream myOutput = new FileOutputStream(outFileName);

    // transfer bytes from the inputfile to the outputfile
    byte[] buffer = new byte[1024];
    int length;
    while ((length = myInput.read(buffer)) > 0) {
        myOutput.write(buffer, 0, length);
    }
    // Close the streams
    myOutput.flush();
    myOutput.close();
    myInput.close();

对于正在更新到Kotlin的用户:

按照以下步骤避免FileUriExposedExceptions， 假设用户已授予WRITE_EXTERNAL_STORAGE权限，并且您的文件位于assets/pdfs/mypdf.pdf。

private fun openFile() {
    var inputStream: InputStream? = null
    var outputStream: OutputStream? = null
    try {
        val file = File("${activity.getExternalFilesDir(null)}/$PDF_FILE_NAME")
        if (!file.exists()) {
            inputStream = activity.assets.open("$PDF_ASSETS_PATH/$PDF_FILE_NAME")
            outputStream = FileOutputStream(file)
            copyFile(inputStream, outputStream)
        }

        val uri = FileProvider.getUriForFile(
            activity,
            "${BuildConfig.APPLICATION_ID}.provider.GenericFileProvider",
            file
        )
        val intent = Intent(Intent.ACTION_VIEW).apply {
            setDataAndType(uri, "application/pdf")
            addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)
            addFlags(Intent.FLAG_ACTIVITY_NO_HISTORY)
        }
        activity.startActivity(intent)
    } catch (ex: IOException) {
        ex.printStackTrace()
    } catch (ex: ActivityNotFoundException) {
        ex.printStackTrace()
    } finally {
        inputStream?.close()
        outputStream?.flush()
        outputStream?.close()
    }
}

@Throws(IOException::class)
private fun copyFile(input: InputStream, output: OutputStream) {
    val buffer = ByteArray(1024)
    var read: Int = input.read(buffer)
    while (read != -1) {
        output.write(buffer, 0, read)
        read = input.read(buffer)
    }
}

companion object {
    private const val PDF_ASSETS_PATH = "pdfs"
    private const val PDF_FILE_NAME = "mypdf.pdf"
}

这在Kotlin中是一种简洁的方式。

    fun AssetManager.copyRecursively(assetPath: String, targetFile: File) {
        val list = list(assetPath)
        if (list.isEmpty()) { // assetPath is file
            open(assetPath).use { input ->
                FileOutputStream(targetFile.absolutePath).use { output ->
                    input.copyTo(output)
                    output.flush()
                }
            }

        } else { // assetPath is folder
            targetFile.delete()
            targetFile.mkdir()

            list.forEach {
                copyRecursively("$assetPath/$it", File(targetFile, it))
            }
        }
    }

嗨，伙计们，我做了这样的事情。 用于n深度复制文件夹和文件复制。 它允许你复制所有的目录结构从Android资产管理器复制:)

    private void manageAssetFolderToSDcard()
    {

        try
        {
            String arg_assetDir = getApplicationContext().getPackageName();
            String arg_destinationDir = FRConstants.ANDROID_DATA + arg_assetDir;
            File FolderInCache = new File(arg_destinationDir);
            if (!FolderInCache.exists())
            {
                copyDirorfileFromAssetManager(arg_assetDir, arg_destinationDir);
            }
        } catch (IOException e1)
        {

            e1.printStackTrace();
        }

    }


    public String copyDirorfileFromAssetManager(String arg_assetDir, String arg_destinationDir) throws IOException
    {
        File sd_path = Environment.getExternalStorageDirectory(); 
        String dest_dir_path = sd_path + addLeadingSlash(arg_destinationDir);
        File dest_dir = new File(dest_dir_path);

        createDir(dest_dir);

        AssetManager asset_manager = getApplicationContext().getAssets();
        String[] files = asset_manager.list(arg_assetDir);

        for (int i = 0; i < files.length; i++)
        {

            String abs_asset_file_path = addTrailingSlash(arg_assetDir) + files[i];
            String sub_files[] = asset_manager.list(abs_asset_file_path);

            if (sub_files.length == 0)
            {
                // It is a file
                String dest_file_path = addTrailingSlash(dest_dir_path) + files[i];
                copyAssetFile(abs_asset_file_path, dest_file_path);
            } else
            {
                // It is a sub directory
                copyDirorfileFromAssetManager(abs_asset_file_path, addTrailingSlash(arg_destinationDir) + files[i]);
            }
        }

        return dest_dir_path;
    }


    public void copyAssetFile(String assetFilePath, String destinationFilePath) throws IOException
    {
        InputStream in = getApplicationContext().getAssets().open(assetFilePath);
        OutputStream out = new FileOutputStream(destinationFilePath);

        byte[] buf = new byte[1024];
        int len;
        while ((len = in.read(buf)) > 0)
            out.write(buf, 0, len);
        in.close();
        out.close();
    }

    public String addTrailingSlash(String path)
    {
        if (path.charAt(path.length() - 1) != '/')
        {
            path += "/";
        }
        return path;
    }

    public String addLeadingSlash(String path)
    {
        if (path.charAt(0) != '/')
        {
            path = "/" + path;
        }
        return path;
    }

    public void createDir(File dir) throws IOException
    {
        if (dir.exists())
        {
            if (!dir.isDirectory())
            {
                throw new IOException("Can't create directory, a file is in the way");
            }
        } else
        {
            dir.mkdirs();
            if (!dir.isDirectory())
            {
                throw new IOException("Unable to create directory");
            }
        }
    }

最后创建一个Asynctask:

    private class ManageAssetFolders extends AsyncTask<Void, Void, Void>
    {

        @Override
        protected Void doInBackground(Void... arg0)
        {
            manageAssetFolderToSDcard();
            return null;
        }

    }

从你的活动中:

    new ManageAssetFolders().execute();