Struts 1.x Interview Questions and Answers -1

Question 1: What is Struts? Why you have used struts in your application or project.

Its is based on MVC pattern which is model view Controller pattern.
Struts is MVC design pattern, it uses Front Controller Pattern and for better flow management

Question 2: What are the main classes which are used in struts application?

Ans 2: Main classes in Struts Framework are:
Action servlet: Front controller class responsible for handling the entire request.
Action class: In Action classes we have the business logic ,call to model(DB) is also done through your action class.
Action Form: it’s a java bean which represents our forms and associated with action mapping. And it also maintains the session state its object is automatically populated on the server side with data entered from a form on the client side.
Action Mapping: using this class we do the mapping between object and Action.
ActionForward: this class in Struts is used to forward the result from controller to destination.

Question 3: How exceptions are handled in Struts application?

Ans: There are two ways of handling exception in Struts:

Programmatically handling: using try {} catch block in code where an exception can come and flow of code is also decided by programmer .its a normal java language concept.

Declarative handling: There are two ways again either we define <global-Exception> tag inside struts-config.XML file

<exception

key=”stock.error.invalidCurrencyType”

path=”/AvailbleCurrency.jsp”

type=”Stock.account.illegalCurrencyTypeException”>
</exception>

Here :
Key: The key represents the key present in MessageResource.properties file to describe the exception.
Type: The class of the exception occurred.
Path: The page where the controls are to be followed is case exception occurred.

Question 4: How validation is performed in struts application?

Ans: In struts validation is performed using validator framework, Validator Framework in Struts consist of two XML configuration files.

1. validator-rules.xml file: which contains the default struts pluggable validator definitions. You can add new validation rules by adding an entry in this file. This was the original beauty of struts which makes it highly configurable.
2. Validation.xml files which contain details regarding the validation routines that are applied to the different Form Beans.

These two configuration files in Struts should be placed somewhere inside the /WEB-INF folder of the application to keep it safe from the client and make it available in Classpath.

<!– Validator plugin –>
<plug-in className=”org.apache.struts.validator.ValidatorPlugIn”>
<set-property
property=”pathnames”
value=”/WEB-INF/validator-rules.xml,/WEB-INF/validation.xml”/>
</plug-in>

Now the next step towards validation is created error messages inside the message resource property file which are used by validator framework.

Message resource Contain:
1. CurrencyConverterForm.fromCurrency = From Currency
2. CurrencyConverterForm.toCurrency=To currency
3. errors.required={0} is required.

Then validation rules are defined in validation.xml for the fields of form on which we want desire validation

Form bean code that extend DynaValidatorForm
Eg;

<form-beans>
<form-bean name=”CurrencyConverterForm” type=”org.apache.struts.validator.DynaValidatorForm”>
<form-property name=”fromCurrency” type=”java.lang.double” />
<form-property name=”toCurrecny” type=”java.lang.double” />
</form-bean>
</form-beans>

Validation.xml file contains

<form-validation>
<formset>
<form name=” CurrencyConverterForm “>
<field property=” fromCurrency ” depends=”required”>
<arg key=” CurrencyConverterForm. fromCurrency “/>
</field>
<field property=” toCurrecny ” depends=”required “>
<arg key=” CurrencyConverterForm.toCurrency “/>
</field>
</form>
</formset>
</form-validation>

To associate more than one validation rule to the property we can specify a comma-delimited list of values. The first rule in the list will be checked first and then the next rule and so on.

Question 5: What is the Difference between DispatchAction and LookupDispatchAction in Struts Framework?

Question 6: How you can retrieve the value which is set in the JSP Page in the case of DynaActionForm?

Ans: DynaActionForm is a subclass of ActionForm that allows the creation of form beans with dynamic sets of properties, without requiring the developer to create a Java class for each type of form bean. DynaActionForm eliminates the need of FormBean class and now the form bean definition can be written into the struts-config.XML file. So, it makes the FormBean declarative and this helps the programmer to reduce the development time.

For Example, we have a CurrencyConverterForm and we don’t want a java class.
CurrencyConverterForm has properties fromCurrency, toCurrency

Step 1 : In the struts-config.xml file, declare the form bean

<form-bean name=” CurrencyConverterForm ”
type=”org.apache.struts.action.DynaActionForm”>
<form-property name=” fromCurrency ” type=”java.lang.String”/>
<form-property name=” toCurrency ” type=”java.lang. String “/>
</form-bean>

Step 2 : Add action mapping in the struts-config.xml file:

<action path=”/convertCurrency” type=”com.techfaq.action.ConvertCurrencyAction”
name=” CurrencyConverterForm ”
scope=”request”
validate=”true”
input=”/pages/ currencyConverterform.jsp”>

<forward name=”success” path=”/jsp/success.jsp”/>
<forward name=”failure” path=”/jsp/error.jsp” />

</action>

Step 3 : In the Action class.

public class ConvertCurrencyAction extends Action
{
public ActionForward execute(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception{

DynaActionForm currencyConverterForm = (DynaActionForm)form;

// by this way we can retrieve the value which is set in the JSP Page

String fromCurrency = (String) currencyConverterForm.get(“fromCurrency “);
String toCurrency = (String) currencyConverterForm.get(“toCurrency “);
return mapping.findForward(“success”);
}
}
}

Step 4 : In the JSP page

<html:text property=” fromCurrency ” size=”30″ maxlength=”30″/>
<html:text property=” toCurrency ” size=”30″ maxlength=”30″/>

Question 7: what the Validate () and reset () method does?

Ans: This is one of my personal favorite Struts interview questions. validate(): validate method is Used to validate properties after they have been populated, and this , method is Called before FormBean is passed to Action. Returns a collection of ActionError as ActionErrors. Following is the method signature for the validate() method.

public ActionErrors validate(ActionMapping mapping, HttpServletRequest request) {

ActionErrors errors = new ActionErrors();
if ( StringUtils.isNullOrEmpty(username) && StringUtils.isNullOrEmpty(password)){
errors.add(ActionErrors.GLOBAL_ERROR, new ActionError(“error.usernamepassword.required”));
}
return errors;
}

reset(): reset() method is called by Struts Framework with each request that uses the defined ActionForm. The purpose of this method is to reset all of the ActionForm’s data members prior to the new request values being set.

Example :
public void reset(ActionMapping mapping, HttpServletRequest request) {
this.password = null;
this.username = null;
}

Set null for every request.

Question 8: How you will make available any Message Resources Definitions file to the Struts Framework Environment?

Ans: Message Resources Definitions file are simple .properties files and these files contain the messages that can be used in the struts project. Message Resources Definitions files can be added to the struts-config.xml file through < message-resources / > tag. Example: < message-resources parameter= MessageResources / >

Message resource definition files can available to the struts environment in two ways
1. using web.xml as
<servlet>
<servlet-name>action<servlet-name>
servlet-class>org.apache.struts.action.ActionServlet<servlet-class>
<init-param>
<param-name>application<param-name>
<param-value>resource.Application<param-value>
</servlet>

2.
<message-resource key=”myResorce” parameter=”resource.Application” null=”false”>

Question 9: What configuration files are used in Struts?

Ans: ApplicationResources.properties and struts-config.xml these two files are used to between the Controller and the Model.

Struts flow and architecture

1) A request comes in from a Java Server Page into the ActionServlet.
2) The ActionServlet having already read the struts-config.xml file knows which form bean relates to this JSP, and delegates work to the validate method of that form bean.

3) The form bean performs the validate method to determine if all required fields have been entered, and performs whatever other types of field validations that need to be performed.

4) If any required field has not been entered, or any field does not pass validation, the form bean generates ActionErrors, and after checking all fields returns back to the ActionServlet.

5) The ActionServlet checks the ActionErrors that were returned from the form beans validate method to determine if any errors have occurred. If errors have occurred, it returns to the originating JSP displaying the appropriate errors.

6) If no errors occurred in the validate method of the form bean, the ActionServlet passes control to the appropriate Action class.

7) The Action class performs any necessary business logic, and then forwards to the next appropriate action (probably another JSP).

   

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