英文:
URI and double slashes
问题
java.net.URI.create("localhost:8080/foo") // 正常工作
java.net.URI.create("127.0.0.1:8080/foo") // 抛出异常
java.net.URI.create("//127.0.0.1:8080/foo") // 正常工作
双斜杠是否在主机为IP地址时是必需的？我浏览了URI的RFC - https://www.rfc-editor.org/rfc/rfc3986，但没有找到相关内容。
英文:
java.net.URI.create("localhost:8080/foo") // Works
java.net.URI.create("127.0.0.1:8080/foo") // Throws exception
java.net.URI.create("//127.0.0.1:8080/foo") // Works
Is double slash required for when you have the host as an IP Address? I glanced through the RFC for URI - https://www.rfc-editor.org/rfc/rfc3986. But could not find anything pertaining to this.
答案1
得分: 5
java.net.URI.create 使用的语法 在 RFC 2396 中有描述。
java.net.URI.create("localhost:8080/foo")
这并不会产生异常，但是该 URI 会以一种您可能不太预期的方式进行解析。它的 scheme（而不是主机！）被设置为 localhost，而 8080/foo 不是端口 + 路径，而是一个 scheme-specific part。因此，这实际上无法正常工作。
java.net.URI.create("//localhost:8080/foo")
会将 URL 解析为没有 scheme 的 net_path 语法元素（详见 RFC 2396）。
以下是来自 RFC 2396 的相关语法摘录：
URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ]
// 这是 'localhost:8080/foo' 的解析方式：
absoluteURI = scheme ":" ( hier_part | opaque_part )
relativeURI = ( net_path | abs_path | rel_path ) [ "?" query ]
...
// 这是 '//127.0.0.1:8080/foo' 的解析方式：
net_path = "//" authority [ abs_path ]
...
// Scheme 必须以字母开头，
// 因此 'localhost' 被解析为 scheme，但 '127' 不会：
scheme = alpha *( alpha | digit | "+" | "-" | "." )
一个正确的方法是：
java.net.URI.create("http://localhost:8080/foo")
英文:
java.net.URI.create uses the syntax described in RFC 2396.
java.net.URI.create("localhost:8080/foo")
This doesn't produce an exception, but the URI is parsed in a way which you probably don't expect. Its scheme (not host!) is set to localhost, and the 8080/foo isn't port + path, but a scheme-specific part. So this doesn't really work.
java.net.URI.create("//localhost:8080/foo")
parses the URL without scheme, as a net_path grammar element (see RFC 2396 for details).
Here's the relevant grammar excerpt from the RFC 2396:
URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ]
// This is how 'localhost:8080/foo' is parsed:
absoluteURI = scheme ":" ( hier_part | opaque_part )
relativeURI = ( net_path | abs_path | rel_path ) [ "?" query ]
...
// This is how '//127.0.0.1:8080/foo' is parsed:
net_path = "//" authority [ abs_path ]
...
// Scheme must start with a letter,
// hence 'localhost' is parsed as a scheme, but '127' isn't:
scheme = alpha *( alpha | digit | "+" | "-" | "." )
One proper way would be:
java.net.URI.create("http://localhost:8080/foo")
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