Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.

Chapter

ne of the keys to creating effective servlets is understanding how to

manipulate the HyperText Transfer Protocol (HTTP). Getting a

O

thorough grasp of this protocol is not an esoteric, theoretical topic,

but rather a practical issue that can have an immediate impact on the perfor 

mance and usability of your servlets. This chapter discusses the HTTP infor 

mation that is sent from the browser to the server in the form of request

headers. It explains each of the HTTP 1.1 request headers, summarizing how

and why they would be used in a servlet. The chapter also includes three

detailed examples: listing all request headers sent by the browser, reducing

download time by encoding the Web page with gzip when appropriate, and

establishing password based access control for servlets. 

Note that HTTP request headers are distinct from the form data dis 

cussed in the previous chapter. Form data results directly from user input

and is sent as part of the URL for 

GET

 requests and on a separate line for

POST

 requests. Request headers, on the other hand, are indirectly set by the

browser and are sent immediately following the initial 

GET

 or 

POST

 request

line. For instance, the following example shows an HTTP request that

might result from submitting a book search request to a servlet at

http://www.somebookstore.com/search

. The request includes the head 

ers 

Accept

, 

Accept Encoding

, 

Connection

, 

Cookie

, 

Host

, 

Referer

, and

User Agent

, all of which might be important to the operation of the serv 

let, but none of which can be derived from the form data or deduced auto 

93