Tutorials : Stepping through Jakarta Struts :

Validating your input

I'll finish this introduction to Struts by showing you how to make some simple validations. Let's assume that the user of our form must enter his or her last name, address, sex and age. The simplest way to implement validation is in the ActionForm bean, but you can also do it in the Action class.

Step a: Code the "validate" method in ActionForm

While we're modifying the code, we also add some log messages so we can check the data we receive from the form:

public ActionErrors validate(ActionMapping mapping,
         HttpServletRequest request) {
  // Log the forms data
  servlet.log("Lastname:" + lastName);       
  servlet.log("Address:" + address);       
  servlet.log("Sex:" + sex);       
  servlet.log("Married:" + married);       
  servlet.log("Age:" + age);
  
  // Check for mandatory data
  ActionErrors errors = new ActionErrors();
  if (lastName == null || lastName.equals("")) { 
    errors.add("Last Name", new ActionError("error.lastName"));
  }
  if (address == null || address.equals("")) { 
    errors.add("Address", new ActionError("error.address"));
  }
  if (sex == null || sex.equals("")) { 
    errors.add("Sex", new ActionError("error.sex"));
  }
  if (age == null || age.equals("")) { 
    errors.add("Age", new ActionError("error.age"));
  }
  return errors;
}

The servlet controller will check if the returned ActionErrors object is empty or not. If not empty the controller will return to the page specified by the "input" parameter in the config file. In our example this is the submit.jsp page.

Step b: Define the error message text

The error messages are taken from the ApplicationResources.properties file. The messages are inserted in the jsp-page by using the Struts tag <html:errors/>. In order to have a nice formatting of the messages you must also define two keys called errors.header and errors.footer. This is our ApplicationResources.properties file (note that HTML tags may be included as you like it):

errors.header=<h4>Validation Error(s)</h4><ul>
errors.footer=</ul><hr>

error.lastName=<li>Enter your last name
error.address=<li>Enter your address
error.sex=<li>Enter your sex
error.age=<li>Enter your age

Now restart the servlet container.

Step c: Test the validations

If we don't enter anything in the form we'll get this answer:

Note that age 0-19 is selected as default according to normal HTML selection list practice.

The total picture

Here's a picture that shows how the Struts components work together:

Final remarks

There's a lot more to say about Struts, but having kept my example simple I hope that I have brought forward the basic architecture of Struts. A very important characteristic of this architecture is the loose coupling between modules. There are no hardcoded file names or class names in the controller or in the Action or ActionForm classes.

Another thing is that all text in your pages may be placed in the ApplicationResources.properties file--you may even implement multi-language support using these properties-files.

In my next article I'll dig somewhat deeper into Struts and build a more realistic application that'll keep track of your CD/Video/DVD collection.

Resources

There are a lot of good resources available from the Struts web site. My favorites are these:

• Introduction to Jakarta Struts Framework by Sue Spielman: article 1 - article 2 - article 3
• Struts Tutorial by Stephan Wiesner
• Using Struts by Larry Maturo (pdf file)
• The Struts Kickstart FAQ
• and of course: The Jakarta Struts User Guide

How to Add Java Applets to Your Site

New on the Java Boutique:

New Review:

Time Management Made Easy with the Quartz Enterprise Job Scheduler
Why not just use the Java timer API? This open source scheduling API boasts simplicity, ease-of-integration, a well-rounded feature set, and it's free!

New Applet:

Reverse Complement
Reverse Complement is a simple applet that converts DNA or RNA sequences into three useful formats.

Elsewhere on internet.com:

WebDeveloper Java
Lots of Java information on webdeveloper.com

WDVL Java
Thorough Java resource at the Web Developer's Virtual Library.

ScriptSearch Java
Hundreds of free Java code files to download.

jGuru: Your View of the Java Universe
Customizable portal with online training, FAQs, regular news updates, and tutorials.