URI.getHost() returns 空
URI.getHost() returns null
这会打印出 null:
System.out.println(new URI("http://a.1a/").getHost());
但这会打印出 a.1a:
System.out.println(new URL("http://a.1a/").getHost());
如果所有 URL 都是 URI（但并非所有 URI 都是 URL），则具有主机组件的有效 URL 不应也具有相同的主机组件（而不是 null) 作为 URI？
查看 Javadoc：
https://docs.oracle.com/javase/8/docs/api/java/net/URI.html:
Returns: The host component of this URI, or null if the host is undefined"
好的，为什么您的特定 URI ("http://a.1a/") 的主机部分未定义？查看 RFC：
https://www.ietf.org/rfc/rfc2396.txt
Hostnames take the form described in Section 3 of [RFC1034] and
Section 2.1 of [RFC1123]: a sequence of domain labels separated by
".", each domain label starting and ending with an alphanumeric
character and possibly also containing "-" characters. The rightmost
domain label of a fully qualified domain name will never start > with a digit... To actually be "Uniform" as a resource
locator, a URL hostname should be a fully qualified domain name.
这会打印出 null:
System.out.println(new URI("http://a.1a/").getHost());
但这会打印出 a.1a:
System.out.println(new URL("http://a.1a/").getHost());
如果所有 URL 都是 URI（但并非所有 URI 都是 URL），则具有主机组件的有效 URL 不应也具有相同的主机组件（而不是 null) 作为 URI？
查看 Javadoc：
https://docs.oracle.com/javase/8/docs/api/java/net/URI.html:
Returns: The host component of this URI, or null if the host is undefined"
好的，为什么您的特定 URI ("http://a.1a/") 的主机部分未定义？查看 RFC：
https://www.ietf.org/rfc/rfc2396.txt
Hostnames take the form described in Section 3 of [RFC1034] and
Section 2.1 of [RFC1123]: a sequence of domain labels separated by
".", each domain label starting and ending with an alphanumeric
character and possibly also containing "-" characters. The rightmost domain label of a fully qualified domain name will never start > with a digit... To actually be "Uniform" as a resource locator, a URL hostname should be a fully qualified domain name.