第一部分是协议(或称为服务方式)。资源的访问方式？
 
A URL for HTTP (or HTTPS) is normally made up of three or four components: 
  1. A scheme. The scheme identifies the protocol to be used to access the resource on the Internet. It can be HTTP (without SSL) or HTTPS (with SSL).
  2. A host. The host name identifies the host that holds the resource. For example, www.example.com. A server provides services in the name of the host, but hosts and servers do not have a one-to-one mapping. Refer to Host names.

    Host names can also be followed by a port number. Refer to Port numbers. Well-known port numbers for a service are normally omitted from the URL. Most servers use the well-known port numbers for HTTP and HTTPS , so most HTTP URLs omit the port number.

  3. A path. The path identifies the specific resource in the host that the web client wants to access. For example, /software/htp/cics/index.html. 
  4. A query string. If a query string is used, it follows the path component, and provides a string of information that the resource can use for some purpose (for example, as parameters for a search or as data to be processed). The query string is usually a string of name and value pairs; for example, term=bluebird. Name and value pairs are separated from each other by an ampersand (&); for example, term=bluebird&source=browser-search.
The scheme and host components of a URL are not defined as case-sensitive, but the path and query string are case-sensitive. Typically, the whole URL is specified in lowercase.
The components of the URL are combined and delimited as follows: 
scheme://host:port/path?query
scheme :The components of a URL_html
  • The scheme is followed by a colon and two forward slashes.
  • If a port number is specified, that number follows the host name, separated by a colon.
  • The path name begins with a single forward slash.
  • If a query string is specified, it is preceded by a question mark. 
Figure 1. Syntax of an HTTP URL
scheme :The components of a URL_html_02scheme :The components of a URL_ide_03http://host nameIP address:80:port/path component?query string
 
https://www.ibm.com/support/knowledgecenter/SSGMCP_5.3.0/com.ibm.cics.ts.internet.doc/topics/dfhtl_uricomp.html

 

I like to think of the term "scheme" as the region of the URL that indicates the "protocol".

 the scheme
 ┌───┐
 https://www.google.com/
 └───┘
 the specific protocol

URL是URI的一个子集。它是Uniform Resource Locator的缩写，译为“统一资源定位 符”。

通俗地说，URL是Internet上描述信息资源的字符串，主要用在各种WWW客户程序和服务器程序上。

采用URL可以用一种统一的格式来描述各种信息资源，包括文件、服务器的地址和目录等。URL是URI概念的一种实现方式。

URL的一般格式为(带方括号[]的为可选项)：

protocol :// hostname[:port] / path / [;parameters][?query]#fragment

URL的格式由三部分组成： 

①第一部分是协议(或称为服务方式)。

②第二部分是存有该资源的主机IP地址(有时也包括端口号)。

③第三部分是主机资源的具体地址，如目录和文件名等。
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