Java如何实现下载文件的几种方式

URL url = new URL("https://example.com/file.txt");
URLConnection connection = url.openConnection();
InputStream inputStream = connection.getInputStream();
FileOutputStream fileOutputStream = new FileOutputStream("file.txt");
byte[] buffer = new byte[1024];
int len;
while ((len = inputStream.read(buffer)) > 0) {
    fileOutputStream.write(buffer, 0, len);
}

HttpClient client = HttpClientBuilder.create().build();
HttpGet request = new HttpGet("https://example.com/file.txt");
HttpResponse response = client.execute(request);
HttpEntity entity = response.getEntity();
InputStream inputStream = entity.getContent();
FileOutputStream fileOutputStream = new FileOutputStream("file.txt");
byte[] buffer = new byte[1024];
int len;
while ((len = inputStream.read(buffer)) > 0) {
    fileOutputStream.write(buffer, 0, len);
}

URL url = new URL("https://example.com/file.txt");
URLConnection connection = url.openConnection();
connection.setDoInput(true);
connection.connect();
InputStream inputStream = connection.getInputStream();
FileOutputStream fileOutputStream = new FileOutputStream("file.txt");
byte[] buffer = new byte[1024];
int len;
while ((len = inputStream.read(buffer)) > 0) {
    fileOutputStream.write(buffer, 0, len);
}

Path path = Paths.get("file.txt");
FileChannel fileChannel = FileChannel.open(path, StandardOpenOption.WRITE);
SocketChannel socketChannel = SocketChannel.open();
socketChannel.connect(new InetSocketAddress("example.com", 80));
ByteBuffer buffer = ByteBuffer.allocate(1024);
while ((len = socketChannel.read(buffer)) > 0) {
    fileChannel.write(buffer, 0, len);
}