Java 图片下载方法：使用 HttpURLConnection 和 FileOutputStream

public void downloadImage(File downloadDir, String imageUrl, String fileName) {

File outputFile = new File(downloadDir, fileName);

try {

    URL url = new URL(imageUrl);
    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    conn.setRequestMethod("GET");
    conn.connect();

    InputStream inputStream = conn.getInputStream();
    FileOutputStream outputStream = new FileOutputStream(outputFile);

    byte[] buffer = new byte[4096];
    int bytesRead = -1;
    while ((bytesRead = inputStream.read(buffer)) != -1) {
        outputStream.write(buffer, 0, bytesRead);
    }

    outputStream.close();
    inputStream.close();

    Log.d("Download", 'Image saved at: ' + outputFile);

} catch (IOException e) {
    Log.e("Download", 'Error downloading image', e);
}

Snackbar.make(view, '输入框为空', Snackbar.LENGTH_LONG)
        .setAction("Action", null).show();

}