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

2.7 An Example Using Initialization Parameters

39

in languages (such as ones named after letters of the alphabet) where it is

easy to read or write off the ends of arrays, make illegal typecasts, or have

dangling pointers due to memory reclamation errors. Besides, even Java

technology won't prevent someone from tripping over the power cable run 

ning to the computer. So, don't count on 

destroy

 as the only mechanism for

saving state to disk. Activities like hit counting or accumulating lists of cookie

values that indicate special access should also proactively write their state to

disk periodically.

2.7 An Example Using 

Initialization Parameters

Listing 2.8 shows a servlet that reads the 

message

 and 

repeats

 initialization

parameters when initialized. Figure 2 5 shows the result when 

message

 is

Shibboleth

, 

repeats

 is 

5

, and the servlet is registered under the name

ShowMsg

. Remember that, although servlets read init parameters in a stan 

dard way, developers set init parameters in a server specific manner. Please

refer to your server documentation for authoritative details. Listing 2.9 shows

the configuration file used with Tomcat to obtain the result of Figure 2 5,

Listing 2.10 shows the configuration file used with the JSWDK, and Figures

2 6 and 2 7 show how to set the parameters interactively with the Java Web

Server. The result is identical to Figure 2 5 in all three cases.

Because the process of setting init parameters is server specific, it is a good

idea to minimize the number of separate initialization entries that have to be

specified. This will limit the work you need to do when moving servlets that

use init parameters from one server to another. If you need to read a large

amount of data, I recommend that the init parameter itself merely give the

location of a parameter file, and that the real data go in that file. An example

of this approach is given in Section 4.5 (Restricting Access to Web Pages),

where the initialization parameter specifies nothing more than the location of

the password file.

Core Approach

For complex initializations, store the data in a separate file and use the init 

parameters to give the location of that file.

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

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