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

94

Chapter 4 Handling the Client Request: HTTP Request Headers

matically: the servlet needs to explicitly read the request headers to make

use of this information.

GET /search?keywords=servlets+jsp HTTP/1.1

Accept: image/gif, image/jpg, */*

Accept Encoding: gzip

Connection: Keep Alive

Cookie: userID=id456578

Host: www.somebookstore.com

Referer: http://www.somebookstore.com/findbooks.html

User Agent: Mozilla/4.7 [en] (Win98; U)

4.1 Reading Request Headers from 

Servlets

Reading headers is straightforward; just call the 

getHeader

 method of

HttpServletRequest

, which returns a 

String

 if the specified header was

supplied on this request, 

null

 otherwise. Header names are not case sensi 

tive. So, for example, 

request.getHeader("Connection")

 and

request.getHeader("connection")

 are interchangeable.

Although 

getHeader

 is the general purpose way to read incoming head 

ers, there are a couple of headers that are so commonly used that they have

special access methods in 

HttpServletRequest

. I'll list them here, and

remember that Appendix A (Servlet and JSP Quick Reference) gives a sepa 

rate syntax summary. 

getCookies

The 

getCookies

 method returns the contents of the 

Cookie

header, parsed and stored in an array of 

Cookie

 objects. This 

method is discussed more in Chapter 8 (Handling Cookies). 

getAuthType

 and 

getRemoteUser

The 

getAuthType

 and 

getRemoteUser

 methods break the 

Authorization

 header into its component pieces. Use of the 

Authorization

 header is illustrated in Section 4.5 (Restricting 

Access to Web Pages). 

getContentLength

The 

getContentLength

 method returns the value of the 

Content Length

 header (as an 

int

). 

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.