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7.2 HTTP 1.1 Response Headers and Their Meaning

145

setContentType

This method sets the 

Content Type

 header and is used by the 

majority of servlets. See Section 7.5 (Using Servlets to Generate 

GIF Images) for an example of its use.

setContentLength

This method sets the 

Content Length

 header, which is useful 

if the browser supports persistent (keep alive) HTTP 

connections. See Section 7.4 for an example.

addCookie

This method inserts a cookie into the 

Set Cookie

 header. 

There is no corresponding 

setCookie

 method, since it is 

normal to have multiple 

Set Cookie

 lines. See Chapter 8 for a 

discussion of cookies.

sendRedirect

As discussed in the previous chapter, the 

sendRedirect

method sets the 

Location

 header as well as setting the status 

code to 302. See Section 6.3 (A Front End to Various Search 

Engines) for an example.

7.2 HTTP 1.1 Response Headers 

and Their Meaning

Following is a summary of the HTTP 1.1 response headers. A good under 

standing of these headers can increase the effectiveness of your servlets, so

you should at least skim the descriptions to see what options are at your dis 

posal. You can come back to get details when you are ready to make use of

the capabilities. Note that Appendix A (Servlet and JSP Quick Reference)

presents a brief summary of these headers for use as a reminder.

These headers are a superset of those permitted in HTTP 1.0. For addi 

tional details on these headers, see the HTTP 1.1 specification, given in RFC

2616. There are a number of places the official RFCs are archived on line;

your best bet is to start at 

http://www.rfc editor.org/

 to get a current

list of the archive sites. Header names are not case sensitive, but are tradi 

tionally written with the first letter of each word capitalized.

Be cautious in writing servlets whose behavior depends on response head 

ers that are only available in HTTP 1.1, especially if your servlet needs to run

on the WWW  at large,  rather than on an intranet many older browsers

support only HTTP 1.0. It is best to explicitly check the HTTP version with

request.getRequestProtocol

 before using new headers.

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

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