import java.net.URL;
import java.net.URLConnection;

public class Main {
   public static void main(String[] args) throws Exception {
      int size;
      URL url = new URL("http://www.twle.cn/wp-content/themes/twle/assets/img/newlogo.png");
      URLConnection conn = url.openConnection();
      size = conn.getContentLength();
      if (size < 0)
          System.out.println("无法获取文件大小。");
      else
        System.out.println("文件大小为：" + size + " bytes");
      conn.getInputStream().close();
   }
}

文件大小为：4261 bytes