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();

使用AssetManager，它允许读取资产中的文件。然后使用常规的Java IO将文件写入sdcard。

谷歌是你的朋友，搜索一个例子。

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();
}

你可以用Kotlin在几个步骤中做到这一点，在这里我只复制几个文件，而不是所有从资产到我的应用程序文件目录。

private fun copyRelatedAssets() {
    val assets = arrayOf("myhome.html", "support.css", "myscript.js", "style.css")
    assets.forEach {
        val inputStream = requireContext().assets.open(it)
        val nameSplit = it.split(".")
        val name = nameSplit[0]
        val extension = nameSplit[1]
        val path = inputStream.getFilePath(requireContext().filesDir, name, extension)
        Log.v(TAG, path)
    }
}

这是扩展函数，

fun InputStream.getFilePath(dir: File, name: String, extension: String): String {
    val file = File(dir, "$name.$extension")
    val outputStream = FileOutputStream(file)
    this.copyTo(outputStream, 4096)
    return file.absolutePath
}

洛格猫

/data/user/0/com.***.***/files/myhome.html
/data/user/0/com.***.***/files/support.css
/data/user/0/com.***.***/files/myscript.js
/data/user/0/com.***.***/files/style.css

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))
            }
        }
    }

使用这个问题答案中的一些概念，我编写了一个名为assetcopyer的类来简化复制/assets/。它在github上可用，可以通过jitpack.io访问:

new AssetCopier(MainActivity.this)
        .withFileScanning()
        .copy("tocopy", destDir);

详情见https://github.com/flipagram/android-assetcopier。