Handler+urlConnection的文件下载

handler发消息到消息队列，循环器取消息给handler处理

DownloadActivity

class DownloadActivity : AppCompatActivity() {

    private val DOWNLOAD_MESSAGE_CODE = 100001
    private val DOWNLOAD_MESSAGE_FAIL_CODE = 100002
    val APP_URL =
        "http://download.sj.qq.com/upload/connAssitantDownload/upload/MobileAssistant_1.apk"
    private val mHandler = MyHandler(this)

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_download)
        /**
         * 主线程  -- > start
         * 点击按键 |
         * 发起下载 |
         * 开启子线程做下载 |
         * 下载过程中通知主线程 |  -- > 主线程更新进度条
         */
        button2.setOnClickListener {
            thread {
                download(APP_URL)
            }
        }
    }

    private fun download(appUrl: String) {
        try {
            val url = URL(appUrl)
            val urlConnection = url.openConnection()
            val inputStream = urlConnection.getInputStream()
            //获取文件的总长度
            val contentLength = urlConnection.contentLength
            val downloadFolderName =
                Environment.getExternalStorageDirectory()
                    .toString() + File.separator + "imooc" + File.separator
            val file = File(downloadFolderName)
            if (!file.exists()) {
                file.mkdir()
            }
            val fileName = downloadFolderName + "imooc.apk"
            val apkFile = File(fileName)
            if (apkFile.exists()) {
                apkFile.delete()
            }
            var downloadSize = 0
            val bytes = ByteArray(1024)
            var length: Int
            val outputStream: OutputStream = FileOutputStream(fileName)
            while (inputStream.read(bytes).also { length = it } != -1) {
                outputStream.write(bytes, 0, length)
                downloadSize += length
                //update UI
                val message = Message.obtain()
                message.obj = downloadSize * 100 / contentLength
                message.what = DOWNLOAD_MESSAGE_CODE
                mHandler.sendMessage(message)
            }
            inputStream.close()
            outputStream.close()
        } catch (e: MalformedURLException) {
            notifyDownloadFaild()
            e.printStackTrace()
        } catch (e: IOException) {
            notifyDownloadFaild()
            e.printStackTrace()
        }
    }

    private fun notifyDownloadFaild() {
        val message = Message.obtain()
        message.what = DOWNLOAD_MESSAGE_FAIL_CODE
        mHandler.sendMessage(message)
    }

    class MyHandler(activity: DownloadActivity) : Handler() {
        private val weakReference = WeakReference(activity)
        @SuppressLint("SetTextI18n")
        override fun handleMessage(msg: Message) {
            super.handleMessage(msg)
            val activity = weakReference.get()
            when (msg.what) {
                activity?.DOWNLOAD_MESSAGE_CODE -> {
                    activity.progressBar.progress = (msg.obj as Int)
                    activity.text666.text = ((msg.obj as Int).toString())+"%"
                }
                activity?.DOWNLOAD_MESSAGE_FAIL_CODE -> {
                }
            }
        }
    }
}