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186

Chapter 8 Handling Cookies

Placing Cookies in the Response Headers

The cookie is inserted into a 

Set Cookie

 HTTP response header by means

of the 

addCookie

 method of 

HttpServletResponse

. The method is called

addCookie

, not 

setCookie

, because any previously specified 

Set Cookie

headers are left alone and a new header is set. Here s an example: 

Cookie userCookie = new Cookie("user", "uid1234");

userCookie.setMaxAge(60*60*24*365); // 1 year

response.addCookie(userCookie);

Reading Cookies from the Client

To send cookies to the client, you create a 

Cookie

, then use 

addCookie

 to

send a 

Set Cookie

 HTTP response header. To read the cookies that come

back from the client, you call 

getCookies

 on the 

HttpServletRequest

. This

call returns an array of 

Cookie

 objects corresponding to the values that came in

on the 

Cookie

 HTTP request header. If there are no cookies in the request,

getCookies

 returns 

null

. Once you have this array, you typically loop down it,

calling 

getName

 on each 

Cookie

 until you find one matching the name you

have in mind. You then call 

getValue

 on the matching 

Cookie

 and finish with

some processing specific to the resultant value. This is such a common process

that Section 8.5 presents two utilities that simplify retrieving a cookie or cookie

value that matches a designated cookie name.

8.4 Examples of Setting and 

Reading Cookies

Listing 8.1 and Figure 8 1 show the 

SetCookies

 servlet, a servlet that sets

six cookies. Three have the default expiration date, meaning that they should

apply only until the user next restarts the browser. The other three use 

set 

MaxAge

 to stipulate that they should apply for the next hour, regardless of

whether the user restarts the browser or reboots the computer to initiate a

new browsing session. 

Listing 8.2 shows a servlet that creates a table of all  the cookies sent to

it in the request. Figure 8 2 shows this servlet immediately after the

SetCookies

 servlet is visited. Figure 8 3 shows it after 

SetCookies

 is vis 

ited then the browser is closed and restarted. 

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

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