浏览器里面能打开，java代码下载的时候返回403错误码，可能是对方的网站中加入了防盗链的功能，可以尝试以下两种解决方案：
1）可以伪装成浏览器访问

HttpURLConnection conn = (HttpURLConnection) u.openConnection();
conn.setConnectTimeout(50000);
conn.setReadTimeout(50000);
conn.addRequestProperty("User-Agent","Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/53.0.2785.143 Safari/537.36");

conn.connect();
System.out.println("状态码："+conn.getResponseCode());

2) 可能是cookie信息缺失，加入网站的cookie

conn.addRequestProperty("cookie","www3.wipo.int");