Java Web Services: Up and Running, 2nd Edition

Review of HTTP Requests and Responses

The next section has a REST-style sample service whose URL is:

http://localhost:8080/predictions/

If this URL is typed into a browser’s window, the browser generates a request similar to:

GET /predictions/ HTTP/1.1
User-Agent: Mozilla/5.0 (X11; Linux x86_64) Chrome/24.0.1312.56
Host: localhost:8080
Accept: text/html

The browser parses the entered URL into these parts, with clarifications below:

• GET /predictions/ HTTP/1.1

  This is the HTTP request start line:

  • GET is the HTTP method (verb).
  • /predictions/ is the URI (resource’s name).
  • HTTP/1.1 is the HTTP version that the requester is using.

• User-Agent: Mozilla/5.0 (X11; Linux x86_64) Chrome/24.0

  Immediately after the start line come the HTTP request header elements or headers for short. Each element is a key/value pair with a colon (:) separating the key on the left from the value on the right. In this element, User-Agent is the key, and everything to the right of the colon is the value. Chrome is the browser used in this request, and Mozilla/5.0 specifies a browser compatibility type. The User-Agent information also includes the operating system in use, 64-bit Linux. Of interest here is that key User-Agent captures the intended meaning: it is the application (agent) that a user employs to make a request.

• Host: localhost:8080

  In localhost:8080, the network address of the machine that hosts the resource is to the left of the colon; the port number, in this case 8080, is to the right. In this example, ...