Android Retrofit下载文件

abstract class DownloadObserver(var url: String) : DisposableObserver<ResponseBody>() {

    override fun onComplete() {}

    override fun onNext(responseBody: ResponseBody) {
        val fileName = url.substring(url.lastIndexOf("/"), url.length)
        val dirPath = Environment.getExternalStorageDirectory().absolutePath + "/" + MyApp.mContext.packageName
        val dirFile = File(dirPath)
        if (!dirFile.exists() && !dirFile.isDirectory) {
            dirFile.mkdirs()
        }
        val file = File("$dirPath/$fileName")
        val inputStream = responseBody.byteStream()
        val buffer = ByteArray(1024 * 4)
        var fos: FileOutputStream? = null
        var sum = 0
        var len = 0
        val off = 0
        try {
            fos = FileOutputStream(file)
            while (inputStream.read(buffer).apply { len = this } > 0)