如何在后台使用服务下载文件？

Question

我正在制作一个 Android 库应用程序，可以下载和显示特殊文件。现在我需要编写一个在后台下载文件的服务！有服务样品吗？

我想将文件保存在SD中，因为用户可以更新应用程序并且不应该错过下载的文件。

如果您对此有建议或意见，请写信给我。

Answer 1

try {
    URL url = new URL("url from apk file is to be downloaded");
    HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
    urlConnection.setRequestMethod("GET");
    urlConnection.setDoOutput(true);
    urlConnection.connect();

    File sdcard = Environment.getExternalStorageDirectory();
    File file = new File(sdcard, "filename.ext");

    FileOutputStream fileOutput = new FileOutputStream(file);
    InputStream inputStream = urlConnection.getInputStream();

    byte[] buffer = new byte[1024];
    int bufferLength = 0;

    while ( (bufferLength = inputStream.read(buffer)) > 0 ) {
        fileOutput.write(buffer, 0, bufferLength);
    }
    fileOutput.close();

} catch (MalformedURLException e) {
        e.printStackTrace();
} catch (IOException e) {
        e.printStackTrace();
}
}

权限：要写入外部存储，您需要添加此权限：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

注意：您可以使用上面的代码下载文件并保存在SD卡中。您可以使用 AsysnTask 或 thread 在后台运行此代码。

Answer 2

这是另一个示例：

try {
        //set the download URL, a url that points to a file on the internet
        //this is the file to be downloaded
        URL url = new URL("http://somewhere.com/some/webhosted/file");

        //create the new connection
        HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();

        //set up some things on the connection
        urlConnection.setRequestMethod("GET");
        urlConnection.setDoOutput(true);

        //and connect!
        urlConnection.connect();

        //set the path where we want to save the file
        //in this case, going to save it on the root directory of the
        //sd card.
        File SDCardRoot = Environment.getExternalStorageDirectory();
        //create a new file, specifying the path, and the filename
        //which we want to save the file as.
        File file = new File(SDCardRoot,"somefile.ext");

        //this will be used to write the downloaded data into the file we created
        FileOutputStream fileOutput = new FileOutputStream(file);

        //this will be used in reading the data from the internet
        InputStream inputStream = urlConnection.getInputStream();

        //this is the total size of the file
        int totalSize = urlConnection.getContentLength();
        //variable to store total downloaded bytes
        int downloadedSize = 0;

        //create a buffer...
        byte[] buffer = new byte[1024];
        int bufferLength = 0; //used to store a temporary size of the buffer

        //now, read through the input buffer and write the contents to the file
        while ( (bufferLength = inputStream.read(buffer)) > 0 ) {
                //add the data in the buffer to the file in the file output stream (the file on the sd card
                fileOutput.write(buffer, 0, bufferLength);
                //add up the size so we know how much is downloaded
                downloadedSize += bufferLength;
                //this is where you would do something to report the prgress, like this maybe
                updateProgress(downloadedSize, totalSize);

        }
        //close the output stream when done
        fileOutput.close();

//catch some possible errors...
} catch (MalformedURLException e) {
        e.printStackTrace();
} catch (IOException e) {
        e.printStackTrace();
}