在java.net.http.HttpClient上使用授权的解决方案:

HttpClient client = HttpClient.newHttpClient();

HttpRequest request = HttpRequest.newBuilder()
        .GET()
        .header("Accept", "application/json")
        // .header("Authorization", "Basic ci5raG9kemhhZXY6NDdiYdfjlmNUM=") if you need
        .uri(URI.create("https://jira.google.ru/secure/attachment/234096/screenshot-1.png"))
        .build();

HttpResponse<InputStream> response = client.send(request, HttpResponse.BodyHandlers.ofInputStream());

try (InputStream in = response.body()) {
    Files.copy(in, Paths.get(target + "screenshot-1.png"), StandardCopyOption.REPLACE_EXISTING);
}

总结(并以某种方式润色和更新)之前的答案。以下三种方法实际上是等效的。(我添加了明确的超时，因为我认为这是必须的。没有人希望下载在连接丢失时永远冻结。)

public static void saveUrl1(final Path file, final URL url,
    int secsConnectTimeout, int secsReadTimeout))
    throws MalformedURLException, IOException {

    // Files.createDirectories(file.getParent()); // Optional, make sure parent directory exists
    try (BufferedInputStream in = new BufferedInputStream(
         streamFromUrl(url, secsConnectTimeout,secsReadTimeout));
         OutputStream fout = Files.newOutputStream(file)) {

            final byte data[] = new byte[8192];
            int count;
            while((count = in.read(data)) > 0)
                fout.write(data, 0, count);
        }
}

public static void saveUrl2(final Path file, final URL url,
    int secsConnectTimeout, int secsReadTimeout))
    throws MalformedURLException, IOException {

    // Files.createDirectories(file.getParent()); // Optional, make sure parent directory exists
    try (ReadableByteChannel rbc = Channels.newChannel(
             streamFromUrl(url, secsConnectTimeout, secsReadTimeout)
        );
        FileChannel channel = FileChannel.open(file,
             StandardOpenOption.CREATE,
             StandardOpenOption.TRUNCATE_EXISTING,
             StandardOpenOption.WRITE)
        ) {

        channel.transferFrom(rbc, 0, Long.MAX_VALUE);
    }
}

public static void saveUrl3(final Path file, final URL url,
    int secsConnectTimeout, int secsReadTimeout))
    throws MalformedURLException, IOException {

    // Files.createDirectories(file.getParent()); // Optional, make sure parent directory exists
    try (InputStream in = streamFromUrl(url, secsConnectTimeout,secsReadTimeout) ) {
        Files.copy(in, file, StandardCopyOption.REPLACE_EXISTING);
    }
}

public static InputStream streamFromUrl(URL url,int secsConnectTimeout,int secsReadTimeout) throws IOException {
    URLConnection conn = url.openConnection();
    if(secsConnectTimeout>0)
        conn.setConnectTimeout(secsConnectTimeout*1000);
    if(secsReadTimeout>0)
        conn.setReadTimeout(secsReadTimeout*1000);
    return conn.getInputStream();
}

我没有发现明显的差异，在我看来都是对的。它们既安全又高效。(速度的差异似乎无关紧要——我从本地服务器写入180 MB到SSD磁盘的时间大约在1.2到1.5秒之间波动)。它们不需要外部库。所有这些都可以使用任意大小和(根据我的经验)HTTP重定向。

此外，如果没有找到资源(通常是404错误)，所有抛出FileNotFoundException，如果DNS解析失败则抛出java.net.UnknownHostException;其他IOException对应传输过程中的错误。

简单使用有一个问题:

org.apache.commons.io.FileUtils.copyURLToFile(URL, File)

如果你需要下载和保存非常大的文件，或者在一般情况下，如果你需要自动重试以防连接断开。

在这种情况下，我建议使用Apache HttpClient以及org.apache.commons.io.FileUtils。例如:

GetMethod method = new GetMethod(resource_url);
try {
    int statusCode = client.executeMethod(method);
    if (statusCode != HttpStatus.SC_OK) {
        logger.error("Get method failed: " + method.getStatusLine());
    }
    org.apache.commons.io.FileUtils.copyInputStreamToFile(
        method.getResponseBodyAsStream(), new File(resource_file));
    } catch (HttpException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
    method.releaseConnection();
}

这可以读取互联网上的文件，并将其写入文件。

import java.net.URL;
import java.io.FileOutputStream;
import java.io.File;

public class Download {
    public static void main(String[] args) throws Exception {
         URL url = new URL("https://www.google.com/images/branding/googlelogo/1x/googlelogo_color_272x92dp.png");  // Input URL
         FileOutputStream out = new FileOutputStream(new File("out.png"));  // Output file
         out.write(url.openStream().readAllBytes());
         out.close();
    }
}

更简单的非阻塞I/O用法:

URL website = new URL("http://www.website.com/information.asp");
try (InputStream in = website.openStream()) {
    Files.copy(in, target, StandardCopyOption.REPLACE_EXISTING);
}

当使用Java 7+时，使用以下方法从Internet下载文件并将其保存到某个目录:

private static Path download(String sourceURL, String targetDirectory) throws IOException
{
    URL url = new URL(sourceURL);
    String fileName = sourceURL.substring(sourceURL.lastIndexOf('/') + 1, sourceURL.length());
    Path targetPath = new File(targetDirectory + File.separator + fileName).toPath();
    Files.copy(url.openStream(), targetPath, StandardCopyOption.REPLACE_EXISTING);

    return targetPath;
}

文档在这里。