How to compile and run your servlets

General information

Servlets are Java programs. As for a regular Java program, the source code for a servlet class MyServlet is in a file MyServlet.java. When a servlet is compiled, the result of the complilation is a file MyServlet.class.

The servlets run by a program called TOMCAT. TOMCAT runs on birch.wellesley.edu and uses the port 8080. Servlets are orgainzed into web applications. A web application may include Java classes, Java .jar files, images, and so on. To access a servlet, one needs to specify the application to which the servlet belongs. For instance, if you type


http://birch.wellesley.edu:8080/examples/servlet/MySession1

in your browser, this you are accessing a servlet MySession1 in the web application examples.

When a request for a servlet is made, TOMCAT checks if the servlet with this class is already running. If the servlet is already running and its class has not changed since the last access, then the request is forwarded to the servlet. If its class has changed or the servlet is not running, then its class is started.

The structure of a web application.

A web application is a directory which includes several subdirectories with standard names. The ones that we will be using are:

images, which contains .gif and .jpg files used by the servlets. See the "ice cream shop with graphics" example here to see how to use an image in a servlet.
WEB-INF, which contains:
- subdirectory classes for all java classes used in the application. They include all the servlet classes and other Java classes used by the servlets. For instance, the web application examples contains, among others, files IceCream1.class and KillSession.class (the two servlets in the ice cream shop application), and also the file Order.class (the java class used by these servlets). Even though you may put .java files in this directory, they don't have to be there. You will copy your servlet classes into this directory
- subdirectory lib for all .jar files used in the application. Your application has mckoidb.jar file in its lib directory. Once a .jar file is placed in this directory, all servlets can automatically access it.
- a file web.xml: the file that describes your web application. In this assignment we don't need to do anything with this file, but we might need to modify it in the future.

Note that subdirectory servlets in a web application directory has nothing to do with the classes of servlets. You will not need to access it.

A web application with your project login name has been created for each project group. The directory is /etc/tomcat3/conf/jakarta-tomcat-3.3a/webapps/myproj on birch.wellesley.edu. Instead of myproj you will use your project login name.

How to write and compile your servlet

Suppose you are writing a servlet MyGreatServlet. You write the Java code for the servlet in the file MyGreatServlet.java in your account on puma. If it's using other java classes, write each public class in its own file, for instance MyHelperClass.java.

To compile the servlet, type


javacee MyGreatServlet.java

If it uses other classes, you can compile them all together as


javacee MyGreatServlet.java MyHelperClass.java

or separately. Files MyGreatServlet.class and MyHelperClass.class will be created if the compilation is successful.

Servlets are supported in Java 2 Enterprise Edition (J2EE). So far you have been working with Java 2 Standard Edition. javacee is a variation of the Java compiler javac which includes J2EE libraries. Note that the abbreviation javacee exists only on puma (including puma hosts, s.a. lion, tiger, etc.) and on birch, but not on other Wellesley machines and not outside of Wellesley.

How to run your servlet

After the servlet has successfully compiled, you need to copy it to your web application to run.

To "run" your servlet, you need to copy its class(es) to the directory /etc/tomcat3/conf/jakarta-tomcat-3.3a/webapps/myproj/WEB-INF/classes on birch. Actually, your puma account is accessible on birch with the same password as on puma. Files are shared between puma and birch, so all your file changes on puma will immediately take affect on birch, too.

To copy the class files, you need to:

Connect to birch using ssh. For instance:


ssh birch

will connect you to birch with your current login name. You may get the following warning:


The authenticity of host 'birch (149.130.13.127)' can't be established.
RSA key fingerprint is ...
Are you sure you want to continue connecting (yes/no)?

Type yes (all three letters).

You will be prompted for your password. After you type it in, you will be logged in to your home directory on birch. If needed, change the directory to the one where the class files are.
Copy the files by the following command:
```
cp MyGreatServlet.class /etc/tomcat3/conf/jakarta-tomcat-3.3a/webapps/myproj/WEB-INF/classes/.
```
Instead of MyGreatServlet.class use the name of your servlet, and instead of myproj use the login name of your project.
Type in
```
http://birch.wellesley.edu:8080/myproj/servlet/MyGreatServlet
```
in your browser (you may omit .wellesley.edu) to test your servlet. Copy other classes used by the servlet if they have been recompiled.
If your servlet is already running, you need to reload it to test it. Reloading may cause an error message if a form parameter has changed. If this happens, reload the servlet again.

If you are working on a servlet, you might want to keep the ssh connection open while you are working so that you don't need to log in every time you need to copy a file.

This page has been created and is maintained by Elena Machkasova
Comments and suggestions are welcome at emachkas@wellesley.edu

Spring Semester 2002