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();

修改了@ danya的SO回答

private void copyAssets(String path, String outPath) {
    AssetManager assetManager = this.getAssets();
    String assets[];
    try {
        assets = assetManager.list(path);
        if (assets.length == 0) {
            copyFile(path, outPath);
        } else {
            String fullPath = outPath + "/" + path;
            File dir = new File(fullPath);
            if (!dir.exists())
                if (!dir.mkdir()) Log.e(TAG, "No create external directory: " + dir );
            for (String asset : assets) {
                copyAssets(path + "/" + asset, outPath);
            }
        }
    } catch (IOException ex) {
        Log.e(TAG, "I/O Exception", ex);
    }
}

private void copyFile(String filename, String outPath) {
    AssetManager assetManager = this.getAssets();

    InputStream in;
    OutputStream out;
    try {
        in = assetManager.open(filename);
        String newFileName = outPath + "/" + 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();
        out.flush();
        out.close();
    } catch (Exception e) {
        Log.e(TAG, e.getMessage());
    }

}

准备工作

在src /主/资产 添加名称折叠文件夹

使用

File outDir = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).toString());
copyAssets("fold",outDir.toString());

在外部目录中找到折叠资产内的所有文件和目录

复制所有文件和目录从资产到您的文件夹!

为了更好地复制，使用apache Commons IO

public void doCopyAssets() throws IOException {
    File externalFilesDir = context.getExternalFilesDir(null);

    doCopy("", externalFilesDir.getPath());

}

//这是复制的主要方法

private void doCopy(String dirName, String outPath) throws IOException {

    String[] srcFiles = assets.list(dirName);//for directory
    for (String srcFileName : srcFiles) {
        String outFileName = outPath + File.separator + srcFileName;
        String inFileName = dirName + File.separator + srcFileName;
        if (dirName.equals("")) {// for first time
            inFileName = srcFileName;
        }
        try {
            InputStream inputStream = assets.open(inFileName);
            copyAndClose(inputStream, new FileOutputStream(outFileName));
        } catch (IOException e) {//if directory fails exception
            new File(outFileName).mkdir();
            doCopy(inFileName, outFileName);
        }

    }
}

public static void closeQuietly(AutoCloseable autoCloseable) {
    try {
        if(autoCloseable != null) {
            autoCloseable.close();
        }
    } catch(IOException ioe) {
        //skip
    }
}

public static void copyAndClose(InputStream input, OutputStream output) throws IOException {
    copy(input, output);
    closeQuietly(input);
    closeQuietly(output);
}

public static void copy(InputStream input, OutputStream output) throws IOException {
    byte[] buffer = new byte[1024];
    int n = 0;
    while(-1 != (n = input.read(buffer))) {
        output.write(buffer, 0, n);
    }
}

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

在Kotlin中，这可以用一行完成!

为InputStream添加扩展乐趣

fun InputStream.toFile(to: File){
    this.use { input->
        to.outputStream().use { out->
            input.copyTo(out)
        }
    }
}

然后使用它

MainActivity.kt

assets.open("test.zip").toFile(File(filesDir,"test.zip"))

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))
            }
        }
    }