Lunanbay JSP HowTo

There are two parts to JSP, setting it up and then doing things with it.

Setting up JSP

Assuming you have set your servlet engine, say, Tomcat up and there isn't already a context for your area then you need to consider how your area is going to fit into your Cyberspace. That is to say you need to give your context a subdirectory from somewhere in your URL's domain. For example, http://yourhost.example.com/my-space/foo.jsp where the contents of /my-space are now going to be served by your servlet engine. The root of the tree needn't be / but can be anywhere, eg. http://yourhost.example.com/some/sub/directory/my-space

Next you need to tell Tomcat it is going to be serving up this piece of Cyberspace. Inside a Host tag you need to add something like

Note that path="/my-space" is your Cyberspace directory and docBase="..." is your physical filesystem directory.

Next you need to tell Apache to ask Tomcat the answer when someone asks for something in my-space. You need to add to your httpd.conf something like:

Finally, you need to restart both Apache and Tomcat.

Doing Things with JSP

Having setup the JSP area you need to put something into your JSP file. There are a number of examples here:

Show the Date

A simple example might be to print the current date:

Note the two expressions in bold. The first page directive is the equivalent of a Java import statement. The second is a shorthand notation to allow the evaluation of variables as strings within the HTML.

The output of this page looks something like this.

Show the HTTP headers

Another example might be to display the values of the headers passed to the JSP:

Note the <% and %> elements which introduce arbitrary expanses of Java. request and out are JSP built-ins.

The output of this page looks something like this.

Simple Bean

Another example might be to store information in a Bean to be retrieved later. A Bean requires a supporting Java class with a very formulaic layout.

Supposing we have a series of web pages, the first lets the user enter a number, the second lets the user select a number to add to the first, then final page displays the sum of the two. For the server to persist the value for the lifetime of the session, using a bean, we need to write a Java program to manipulate our number.

First, though, a form (/my-space/bean-form1.jsp) to read in a number:

Note that the input variable is called number which is important for the supporting Java class.

Next, we need to write the supporting Java class.

The most important thing to note here is the get and set methods where the rest of the method name is a capitalised version of the name of the form field that the JSP files manipulate. In the JSP forms we'll be manipulating a field called number hence we have two methods: getNumber and setNumber (note the capital N).

Note also that the Bean manipulates the object as a string (presumably as the underlying HTML form only uses strings).

Having compiled the Java you need to add the class file to somewhere where the servlet engine can find it. Assuming you installed as per the instructions above you would copy the class file to the directory /the/path/to/my-space/WEB-INF/classes (ie. your docBase plus /WEB-INF/classes).

In particular, you would probably have put your Bean into the com.example package -- because that's your domain -- in which case you'd put the class file into the directory /the/path/to/my-space/WEB-INF/classes/com/example. If you do that then in the subsequent examples where you access the Bean you should set the class attribute to be class="com.example.Bean".
In particular you can do this by invoking javac -d /the/path/to/my-space/WEB-INF/classes

Next you need to write a form (/my-space/bean-form2.jsp) to, say, print out the current value then ask the user to input another value to be added to it:

There are a few things to note:

• the first line (...:useBean...) introduces an instance of Bean identified as formData
• the scope of the instance is the entire session
• the second line (...:setProperty...) indicates that all the parameters (property="*") should be set in the bean identified by formBean. This will use the set methods.
• subsequently, we can call the get methods for the bean on our instance formData, eg. formData.getNumber ()
• we pass the second number as a different value (obviously!), in this case otherNumber

Finally, do something similar to print out the sum of the two numbers (/my-space/bean-form3.jsp):

The only point to note is the mechanism to access the value of otherNumber, that is request.getParameter ("otherNumber").

You can invoke the whole sequence here

Talk To Your MySQL DB

Suppose you have set up your test_user identified by their test_password with access to your test_table in your test_db.

You'll want to make MM.MySQL 2.0.8, Mark Matthews JDBC Driver for MySQL, available in your CLASSPATH -- probably by putting it in the lib directory of your Tomcat distribution, thus making it available for all your JSP contexts.

Then you'll want to write code along the following lines:

Note the two lines for initiating a new instance of the MySQL driver and then creating a connection to the database.

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