Chapter 6. Generating the Server Response: HTTP Status Codes

Chapter 6. Generating the Server Response: HTTP Status Codes

Topics in This Chapter

  • Format of the HTTP response

  • How to set status codes

  • What the status codes are good for

  • Shortcut methods for redirection and error pages

  • A servlet that redirects users to browser-specific pages

  • A front end to various search engines

As we saw in the previous chapter, a request from a browser or other client consists of an HTTP command (usually GET or POST ), zero or more request headers (one or more in HTTP 1.1, since Host is required), a blank line, and, only in the case of POST requests , some query data. A typical request looks like the following.

 GET /servlet/  SomeName  HTTP/1.1 Host: ...  Header2  : ... ...  HeaderN  :  (Blank Line)  

When a Web server responds to a request, the response typically consists of a status line, some response headers, a blank line, and the document. A typical response looks like this:

 HTTP/1.1 200 OK Content-Type: text/html  Header2  : ... ...  HeaderN  : ...  (Blank Line)  <!DOCTYPE ...> <HTML> <HEAD>...</HEAD> <BODY> ... </BODY></HTML> 

The status line consists of the HTTP version ( HTTP/1.1 in the preceding example), a status code (an integer; 200 in the example), and a very short message corresponding to the status code ( OK in the example). In most cases, the headers are optional except for Content-Type , which specifies the MIME type of the document that follows . Although most responses contain a document, some don't. For example, responses to HEAD requests should never include a document, and various status codes essentially indicate failure or redirection (and thus either don't include a document or include only a short error-message document).

Servlets can perform a variety of important tasks by manipulating the status line and the response headers. For example, they can forward the user to other sites; indicate that the attached document is an image, Adobe Acrobat file, or HTML file; tell the user that a password is required to access the document; and so forth. This chapter summarizes the most important status codes and describes what can be accomplished with them; the following chapter discusses the response headers.

Core Servlets and JavaServer Pages (Vol. 1.Core Technologies)
Core Servlets and Javaserver Pages: Core Technologies, Vol. 1 (2nd Edition)
ISBN: 0130092290
EAN: 2147483647
Year: 2002
Pages: 194

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