URI 和双斜杠

URI and double slashes

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

当您将主机作为 IP 地址时,是否需要双斜杠?我浏览了 URI 的 RFC - https://www.rfc-editor.org/rfc/rfc3986。但是找不到与此相关的任何内容。

java.net.URI.create uses the syntax described in RFC 2396.

java.net.URI.create("localhost:8080/foo")   

这不会产生异常,但 URI 的解析方式可能出乎您的意料。它的方案(不是主机!)设置为localhost8080/foo不是端口+路径,而是scheme-specific部分。所以这真的行不通。

java.net.URI.create("//localhost:8080/foo")   

将没有方案的 URL 解析为 net_path 语法元素(有关详细信息,请参阅 RFC 2396)。

这是 RFC 2396 中的相关语法摘录:

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 | "+" | "-" | "." )

一个正确的方法是:

java.net.URI.create("http://localhost:8080/foo")