java 读取网络文件 protocol = http host = null

java中通过ip地址读取文件

public void testReadFile() {
		try {
			URL url = new URL("http://172.31.77.220:8080/data/files/F_000001/F_000001_10743.xlsx");
			URLConnection openConnection = url.openConnection();
			InputStream inputStream = openConnection.getInputStream();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

 protocol = http host = null错误

上述代码写成  URL url = new URL("http:/172.31.77.220:8080/data/files/F_000001/F_000001_10743.xlsx");这样会报这个错误

应该是双斜杠才正确