Struts Interview Questions with Answers Page I


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1. What is Struts?

1.Struts is a web page development framework and an open source software that helps developers build web applications quickly and easily. Struts combines

Java Servlets, Java Server Pages, custom tags, and message resources into a unified framework. It is a cooperative, synergistic platform, suitable for

development teams, independent developers, and everyone between.


2.The core of the Struts framework is a flexible control layer based on standard technologies like Java Servlets, JavaBeans, ResourceBundles, and XML, as

well as various Jakarta Commons packages. Struts encourages application architectures based on the Model 2 approach, a variation of the classic

Model-View-Controller (MVC) design paradigm. Struts provides its own Controller component and integrates with other technologies to provide the Model and

the View. For the Model, Struts can interact with standard data access technologies, like JDBC and EJB, as well as most any third-party packages, like

Hibernate, iBATIS, or Object Relational Bridge. For the View, Struts works well with JavaServer Pages, including JSTL and JSF, as well as Velocity

Templates, XSLT, and other presentation systems. The Struts framework provides the invisible underpinnings every professional web application needs to

survive. Struts helps you create an extensible development environment for your application, based on published standards and proven design patterns.


3. Struts Frame work is the implementation of Model-View-Controller (MVC) design pattern for the JSP. Struts is maintained as a part of Apache Jakarta

project and is open source. Struts Framework is suited for the application of any size. Latest version of struts can be downloaded from

http://jakarta.apache.org/. We are using jakarta-struts-1.1 and jakarta-tomcat-5.0.4 for this tutorial.


2. How is the MVC design pattern used in Struts framework?

In the MVC design pattern, application flow is mediated by a central Controller. The Controller delegates requests to an appropriate handler. The

handlers are tied to a Model, and each handler acts as an adapter between the request and the Model. The Model represents, or encapsulates, an

application's business logic or state. Control is usually then forwarded back through the Controller to the appropriate View. The forwarding can be

determined by consulting a set of mappings, usually loaded from a database or configuration file. This provides a loose coupling between the View and

Model, which can make an application significantly easier to create and maintain.

Controller--Servlet controller which supplied by Struts itself; View --- what you can see on the screen, a JSP page and presentation components; Model

--- System state and a business logic JavaBeans.


3. Who makes the Struts?

Struts is hosted by the Apache Software Foundation(ASF) as part of its Jakarta project, like Tomcat, Ant and Velocity.


4. Why it called Struts?

Because the designers want to remind us of the invisible underpinnings that hold up our houses, buildings, bridges, and ourselves when we are on stilts.

This excellent description of Struts reflect the role the Struts plays in developing web applications.


5. Do we need to pay the Struts if being used in commercial purpose?

No. Struts is available for commercial use at no charge under the Apache Software License. You can also integrate the Struts components into your own

framework just as if they were written in house without any red tape, fees, or other hassles.


6. What are the core classes of Struts?

Action, ActionForm, ActionServlet, ActionMapping, ActionForward are basic classes of Struts.


7. What is the design role played by Struts?

The role played by Struts is controller in Model/View/Controller(MVC) style. The View is played by JSP and Model is played by JDBC or generic data source

classes. The Struts controller is a set of programmable components that allow developers to define exactly how the application interacts with the user.


8. What configuration files are used in Struts?

ApplicationResources.properties

struts-config.xml

These two files are used to bridge the gap between the Controller and the Model.


9. What helpers in the form of JSP pages are provided in Struts framework?

--struts-html.tld

--struts-bean.tld

--struts-logic.tld


10. Is Struts efficient?

  • The Struts is not only thread-safe but thread-dependent(instantiates each Action once and allows other requests to be threaded through the original object.
  • ActionForm beans minimize subclass code and shorten subclass hierarchies
  • The Struts tag libraries provide general-purpose functionality
  • The Struts components are reusable by the application
  • The Struts localization strategies reduce the need for redundant JSPs
  • The Struts is designed with an open architecture--subclass available
  • The Struts is lightweight (5 core packages, 5 tag libraries)
  • The Struts is open source and well documented (code to be examined easily)
  • The Struts is model neutral


11. How you will enable front-end validation based on the xml in validation.xml?

The < html:javascript > tag to allow front-end validation based on the xml in validation.xml. For example the code: < html:javascript formName=logonForm

dynamicJavascript=true staticJavascript=true / > generates the client side java script for the form logonForm as defined in the validation.xml file. The

< html:javascript > when added in the jsp file generates the client site validation script.


12. What is ActionServlet?

The class org.apache.struts.action.ActionServlet is the called the ActionServlet. In the the Jakarta Struts Framework this class plays the role of

controller. All the requests to the server goes through the controller. Controller is responsible for handling all the requests.


13. How you will make available any Message Resources Definitions file to the Struts Framework Environment?

Message Resources Definitions file are simple .properties files and these files contains 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 / >


14. What is Action Class?

The Action Class is part of the Model and is a wrapper around the business logic. The purpose of Action Class is to translate the HttpServletRequest to

the business logic. To use the Action, we need to Subclass and overwrite the execute() method. In the Action Class all the database/business processing

are done. It is advisable to perform all the database related stuffs in the Action Class. The ActionServlet (commad) passes the parameterized class to

Action Form using the execute() method. The return type of the execute method is ActionForward which is used by the Struts Framework to forward the

request to the file as per the value of the returned ActionForward object.


15. How Struts control data flow?

Struts implements the MVC/Layers pattern through the use of ActionForwards and ActionMappings to keep control-flow decisions out of presentation layer.


16. Write code of any Action Class?

Here is the code of Action Class that returns the ActionForward object.

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.apache.struts.action.Action;

import org.apache.struts.action.ActionForm;

import org.apache.struts.action.ActionForward;

import org.apache.struts.action.ActionMapping;



public class TestAction extends Action

{

public ActionForward execute(

ActionMapping mapping,

ActionForm form,

HttpServletRequest request,

HttpServletResponse response) throws Exception

{

return mapping.findForward(\"testAction\");

}

}


17. What is ActionForm?

An ActionForm is a JavaBean that extends org.apache.struts.action.ActionForm. ActionForm maintains the session state for web application and the

ActionForm object is automatically populated on the server side with data entered from a form on the client side.


18. What is Struts Validator Framework?

Struts Framework provides the functionality to validate the form data. It can be use to validate the data on the users browser as well as on the server

side. Struts Framework emits the java scripts and it can be used validate the form data on the client browser. Server side validation of form can be

accomplished by sub classing your From Bean with DynaValidatorForm class. The Validator framework was developed by David Winterfeldt as third-party

add-on to Struts. Now the Validator framework is a part of Jakarta Commons project and it can be used with or without Struts. The Validator framework

comes integrated with the Struts Framework and can be used without doing any extra settings.


19. Give the Details of XML files used in Validator Framework?

The Validator Framework uses two XML configuration files validator-rules.xml and validation.xml. The validator-rules.xml defines the standard validation

routines, these are reusable and used in validation.xml. to define the form specific validations. The validation.xml defines the validations applied to a

form bean.


20. How you will display validation fail errors on jsp page?

The following tag displays all the errors:

< html:errors/ >


21. Can I use other beans or hashmaps with ActionForms?

Yes. There are several ways that you can use other beans or hashmaps with ActionForms.

  • ActionForms can have other beansor hashmaps as properties
  • "Value Beans" or "Data Transfer Objects" (DTOs) can be used independently of ActionForms to transfer data to the view
  • ActionForms can use Maps to support "dynamic" properties (since Struts 1.1)

ActionForms (a.k.a. "form beans") are really just Java beans (with a few special methods) that Struts creates and puts into session or request scope for

you. There is nothing preventing you from using other beans, or including them in your form beans. Here are some examples:

Collections as properties Suppose that you need to display a pulldown list of available colors on an input form in your application. You can include a

string-valued colorSelected property in your ActionForm to represent the user's selection and a colorOptions property implemented as a Collection (of

strings) to store the available color choices. Assuming that you have defined the getters and setters for the colorSelected and colorOptions properties

in your orderEntryForm form bean, you can render the pulldown list using:

<html:select property="colorSelected">

<html:options property="colorOptions" name="orderEntryForm"/>

</html:select>

The list will be populated using the strings in the colorOptions collection of the orderEntryForm and the value that the user selects will go into the

colorSelected property that gets posted to the subsequent Action. Note that we are assuming here that the colorOptions property of the orderEntryForm has

already been set.

See How can I prepopulate a form? for instructions on how to set form bean properties before rendering edit forms that expect properties to be pre-set.

Independent DTO An Action that retrieves a list of open orders (as an ArrayList of Order objects) can use a DTO independently of any form bean to

transfer search results to the view. First, the Action's execute method performs the search and puts the DTO into the request:

ArrayList results = businessObject.executeSearch(searchParameters);

request.setAttribute("searchResults",results);

Then the view can iterate through the results using the "searchResults" request key to reference the DTO:

<logic:iterate id="order" name="searchResults" type="com.foo.bar.Order">

<tr><td><bean:write name="order" property="orderNumber"/><td>

<td>..other properties...</td></tr>

</logic:iterate>


22. Why do the Struts tags provide for so little formatting?

The Struts tags seem to provide only the most rudimentary functionality. Why is there not better support for date formatting and advanced string

handling?

Three reasons:

First, work started on the JSTL and we didn't want to duplicate the effort.

Second, work started on Java Server Faces, and we didn't want to duplicate that effort either.

Third, in a Model 2 application, most of the formatting can be handled in the ActionForms (or in the business tier), so all the tag has to do is spit out

a string. This leads to better reuse since the same "how to format" code does not need to be repeated in every instance. You can "say it once" in a

JavaBean and be done with it. Why don't the Struts taglibs offer more layout options?

Since the Struts tags are open source, you can extend them to provide whatever additional formatting you may need. If you are interested in a pre-written

taglib that offers more layout options, see the struts-layout taglib.

In the same arena, there is a well regarded contributor taglib that can help you create Menus for your Struts applications.


23. Why does the <html:link> tag URL-encode javascript and mailto links?

The <html:link> tag is not intended for use with client-side references like those used to launch Javascripts or email clients. The purpose of link tag

is to interject the context (or module) path into the URI so that your server-side links are not dependent on your context (or module) name. It also

encodes the link, as needed, to maintain the client's session on the server. Neither feature applies to client-side links, so there is no reason to use

the <html:link> tag. Simply markup the client-side links using the standard tag.


24. Why does the <html:link> tag URL-encode javascript and mailto links?

The <html:link> tag is not intended for use with client-side references like those used to launch Javascripts or email clients. The purpose of link tag

is to interject the context (or module) path into the URI so that your server-side links are not dependent on your context (or module) name. It also

encodes the link, as needed, to maintain the client's session on the server. Neither feature applies to client-side links, so there is no reason to use

the <html:link> tag. Simply markup the client-side links using the standard tag.


25. How can I scroll through list of pages like the search results in google?

Many Struts developers use the Pager from the JSPTags site.


26. How would you display “validation fail” errors on a JSP page?

Following tag displays all the errors: <html:errors/>


27. How can one enable front-end validation based on the xml in validation.xml?

The <html:javascript> tag allows front-end validation based on the xml in validation.xml.

For example the code:

generates the client side JavaScript for the form "logonForm" as defined in the validation.xml file.

The <html:javascript> when added in the JSP file generates the client side validation script.

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