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How to validate through annotations: Struts 2

Hi to all. I've studied some stuff about struts 2 those days so i've learn a lot of new things like this post topic. Normally, what do you do when you want to implement a basic validation on Struts 2? The steps about how to do that are:

• Assure that you're using defaultStack interceptor stack because inside it are workflow and validation interceptors that are responsible of execute validation logic and redirect to appropiate result when validation triggers.
• Define a result named "input" in action's declaration on struts.xml . This is the result where validation must redirect automatically if exists validation errors. If input result is not defined it will give an error of result not found.
• Override validate() method on your action.
• Write your own validation logic inside it, that must add error messages when it fails to properly validation mechanism. For example, if i validate that a field must be a number and greater than 1000, if it doesn't pass the validation it must add a error message using addActionError() or addFieldError() (To follow standards you should use addFieldError() ), like this:

  if (fieldOne == null || fieldOne.equals("")) {
   addFieldError("fieldOne", "Field one must not be empty.");
   }
   if (fieldTwo == null || Integer.valueOf(fieldTwo) < 30) {
   addFieldError("fieldTwo", "Field two must be greater or equal than 30.");
   }

• (Optional) in your jsp you can define <s:fielderror> or <s:actionerror> tags to print your validation messages. As you can guess, <s:fielderror> prints validation errors added with addFieldError() and <s:actionerror> to print action error messages added with addActionError(). To print validation errors from fieldOne and fieldTwo you have to define <s:fielderror> like this:

  <s:fielderror cssClass="cssClassForUllistwithLi" >
   <s:param>fieldOne</s:param>
   <s:param>fieldTwo</s:param>
   </s:fielderror>

• Run your app

This is the basic way. But if you want to validate through annotations is easier and faster, you have to do this:

• The first three bullets from previous list.
• One line before getter method of field that you want to validate, you can use one of the next annotations depending of the kind of validation that you wanna do:
  • RequiredStringValidator
  • RequiredFieldValidator
  • EmailValidator
  • .... You can see the list of validation annotations avaliable >>> HERE IN JAVADOC<<<
• Define the message parameter of annotation, that is like you write addFieldError("fieldOne", "Field one must not be empty") . We can convert our previous example to annotations and it will look like this:

  public void validate() {}
  
  @RequiredStringValidator(message="Field one must not be empty.")
  public String getFieldOne() {...
  
  @IntRangeFieldValidator(message="Field two must be greater or equal than 30.", min="30")
  public String getFieldTwo() {...

That's it!! Even when annotations-way looks better than default validation definition, in some cases is better to do in the default way and in other cases using annotations, none is better than the other. Enjoy it .