Struts Interview Questions and Answers
Ques 56. Can I have an Action without a form?
Ans. Yes. If your Action does not need any data and it does
not need to make any data available to the view or
controller component that it forwards to, it doesn't need
a form. A good example of an Action with no ActionForm is
the LogoffAction in the struts example application:
<forward name="success" path="/index.jsp"/>
This action needs no data other than the user's session, which
it can get from the Request, and it doesn't need to prepare any
view elements for display, so it does not need a form.
However, you cannot use the <html:form> tag without
an ActionForm. Even if you want to use the <html:form>
tag with a simple Action that does not require input,
the tag will expect you to use some type of ActionForm,
even if it is an empty subclass without any properties.
Ques 57. Can you give me a simple example of using the requiredif Validator rule?Ans. First off, there's an even newer Validator rule called
validwhen, which is almost certainly what you want to use,
since it is much easier and more powerful.
It will be available in the first release after 1.1 ships.
The example shown below could be coded with validwhen as:
Ques 58. When is the best time to validate input?Ans.
This is an excellent question. Let's step back a second and think about a typical mid to large size application. If we start from the back end and work toward the view we have:
1) Database: Most modern databases are going to validate for required fields, duplicate records, security constraints, etc.
2) Business Logic: Here you are going to check for valid data relationships and things that make sense for the particular problem you are triing to solve.
... This is where struts comes into the picture, by now the system should be pretty well bulletproof. What we are going to do is make validation friendlier and informative. Rember it is OK to have duplicate validations...
3) ActionErrors validate(ActionMapping map, HttpServletRequest req) is where you can do your validation and feed back to the view, information required to correct any errors. validate is run after the form has been reset and after the ActionForm properties have been set from corresponding view based input. Also remember you can turn validation off with validate="false" in the action mapping in the struts-config.xml. This is done by returning an ActionErrors collection with messages from your ApplicationResources.properties file.
Here you have access to the request so you can see what kinds of action is being requested to fine tune your validations. The <html:error> tag allows you to dump all errors on your page or a particular error associated with a particular property. The input attribute of the struts-config.xml action allows you to send validation errors to a particular jsp / html / tile page.
Ques 59. How can I avoid validating a form before data is entered?Ans. The simplest way is to have two actions. The first one has the job of setting the form data, i.e. a blank registration screen. The second action in our writes the registration data to the database. Struts would take care of invoking the validation and returning the user to the correct screen if validation was not complete.
The EditRegistration action in the struts example application illustrates this:
< action path="/editRegistration">
When the /editRegistration action is invoked, a registrationForm is created and added to the request, but its validate method is not called. The default value of the validate attribute is true, so if you do not want an action to trigger form validation, you need to remember to add this attribute and set it to false.
Ques 60. How can I create a wizard workflow?Ans. The basic idea is a series of actions with next, back, cancel and finish actions with a common bean. Using a LookupDispatchAction is reccomended as it fits the design pattern well and can be internationalized easily. Since the bean is shared, each choice made will add data to the wizards base of information. A sample of struts-config.xml follows:
<!-- the first screen of the wizard (next action only available) -->
<!-- no validation, since the finish action is not available -->
<!-- the second screen of the wizard (back, next and finish) -->
<!-- since finish action is available, bean should validated, note
validation should not necessarily validate if back action requested, you
might delay validation or do conditional validation -->
<!-- the last screen of the wizard (back, finish and cancel only) -->
The pieces of the wizard are as follows:
forms.MyWizard.java - the form bean holding the information required
actions.MyWizard.java - the actions of the wizard, note the use of LookupDispatchAction allows for one action class with several methods. All the real work will be done in the 'finish' method.
mywizard[x].jsp - the data collection jsp's
mywizarddone.jsp - the 'success' page
mywizardcancel.jsp - the 'cancel' page
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