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2.6 The Servlet Life Cycle

37

1. You can add support for other services later by adding 

doPut

, 

doTrace

, etc., perhaps in a subclass. Overriding 

service

directly precludes this possibility.

2. You can add support for modification dates by adding a 

get 

LastModified

 method. If you use 

doGet

, the standard 

ser 

vice

 method uses the 

getLastModified

 method to set 

Last Modified

 headers and to respond properly to conditional 

GET

 requests (those containing an 

If Modified Since

header). See Section 2.8 (An Example Using Servlet Initializa 

tion and Page Modification Dates) for an example.

3. You get automatic support for 

HEAD

 requests. The system just 

returns whatever headers and status codes 

doGet

 sets, but omits 

the page body. 

HEAD

 is a useful request method for custom 

HTTP clients. For example, link validators that check a page for 

dead hypertext links often use 

HEAD

 instead of 

GET

 in order to 

reduce server load.

4. You get automatic support for 

OPTIONS

 requests. If a 

doGet

method exists, the standard 

service

 method answers 

OPTIONS

requests by returning an 

Allow

 header indicating that 

GET

, 

HEAD

, 

OPTIONS

, and 

TRACE

 are supported.

5. You get automatic support for 

TRACE

 requests. 

TRACE

 is a 

request method used for client debugging: it just returns the 

HTTP request headers back to the client.

Core Tip

If your servlet needs to handle both 

GET

 and 

POST

 identically, have your 

doPost

 method call 

doGet

, or vice versa. Don't override 

service

directly.

The doGet, doPost, and doXxx Methods

These methods contain the real meat of your servlet. Ninety nine percent of

the time, you only care about 

GET

 and/or 

POST

 requests, so you override

doGet

 and/or 

doPost

. However, if you want to, you can also override 

doDe 

lete

 for 

DELETE

 requests, 

doPut

 for 

PUT

, 

doOptions

 for 

OPTIONS

, and 

doT 

race

 for 

TRACE

. Recall, however, that you have automatic support for

OPTIONS

 and 

TRACE

, as described in the previous section on the 

service

method. Note that there is no 

doHead

 method. That's because the system

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