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2.2 A Simple Servlet Generating Plain Text

25

3. A directory for infrequently changing servlets in JAR files. 

With the second option above, the class files are placed directly 

in the 

classes

 directory or in subdirectories corresponding to 

their package name. Here, the class files are packaged in a JAR 

file, and that file is then placed in the designated directory. With 

Tomcat, the JSWDK, the Java Web Server, and most other serv 

ers, this directory is 

install_dir/lib

. You must restart the 

server whenever you change files in this directory.

Once you've configured your server, set your 

CLASSPATH

, and placed the

servlet in the proper directory, simply do  

javac HelloWorld.java

  to

compile the servlet. In production environments, however, servlets are fre 

quently placed into packages to avoid name conflicts with servlets written by

other developers. Using packages involves a couple of extra steps that are

covered in Section 2.4 (Packaging Servlets). Also, it is common to use HTML

forms as front ends to servlets (see Chapter 16). To use them, you'll need to

know where to place regular HTML files to make them accessible to the

server. This location varies from server to server, but with the JSWDK and

Tomcat, you place an HTML file in

install_dir/webpages/path/file.html

 and then access it via

http://localhost/path/file.html

 (replace 

localhost

 with the real

hostname if running remotely). A JSP page can be installed anywhere that a

normal HTML page can be.

Invoking the Servlet

With different servers, servlet classes can be placed in a variety of different

locations, and there is little standardization among servers. To invoke servlets,

however, there is a common convention: use a URL of the form

http://host/servlet/ServletName

. Note that the URL refers to 

serv 

let

, singular, even if the real directory containing the servlet code is called

servlets

, plural, or has an unrelated name like 

classes

 or 

lib

. 

Figure 2 1, shown earlier in this section, gives an example with the Web

server running directly on my PC ( localhost  means  the current machine ). 

Most servers also let you register names for servlets, so that a servlet can

be invoked via 

http://host/any path/any file

. The process for doing

this is server specific; check your server's documentation for details. 

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

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