Java Interview Questions - 26

Java Interview Questions - 26

1.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.

2.What are the core classes of Struts?
Action, ActionForm, ActionServlet, ActionMapping, ActionForward are basic classes of Structs.

3.What is the design role played by Struts?
The role played by Structs 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.

4.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.

5.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.

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

--struts-html.tld
--struts-bean.tld
--struts-logic.tld

7.Who makes the Struts?

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

8.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.

9.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.

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 Struts?

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.

15.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.

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. How you will display validation fail errors on jsp page? - The following tag displays all the errors: < html:errors/ >

20.Why do we need Struts?

Java technologies give developers a serious boost when creating and maintaining applications to meet the demands of today's public Web sites and enterprise intranets. Struts combines Java Servlets, Java ServerPages, custom tags, and message resources into a unified framework. The end result is a cooperative, synergistic platform, suitable for development teams, independent developers, and everyone in between.

21.Who wrote Struts?

There are several active committers to the Struts project, working cooperatively from around the globe. Dozens of individual developers and committers contributed to the Struts 1.x codebase. All interested Java developers are invited to contribute to the project. Struts is a Apache Software Foundation project, with the mission to "provide secure, enterprise-grade server solutions based on the Java Platform that are developed in an open and cooperative fashion".
Struts was created by Craig R. McClanahan and donated to The Apache Software Foundation in May 2000. Craig was the primary developer of both Struts 1.x and Tomcat 4. Tomcat 4 was the basis for the official reference implementation for a servlet 2.3 and JSP 1.2 container.
Craig's current focus is as architect of the Sun Java Studio Creator (formerly Project Rave). Craig also serves as the Specification Lead for JavaServer Faces (JSR-127), and is the Web Layer Architect for the Java2 Enterprise Edition (J2EE) platform as a whole.

22.Does Struts include its own unit tests?

Struts currently has two testing environments, to reflect the fact that some things can be tested statically, and some really need to be done in the environment of a running servlet container.
For static unit tests, we use the JUnit framework. The sources for these tests are in the "src/test" hierarchy in the source repository, and are executed via the "test.junit" target in the top-level build.xml file. Such tests are focused on the low-level functionality of individual methods, are particularly suitable for the static methods in the org.apache.struts.util utility classes. In the test hierarchy, there are also some "mock object" classes (in the org.apache.struts.mock package) so that you can package up things that look like servlet API and Struts API objects to pass in as arguments to such tests.
Another valuable tool is Struts TestCase which provides a useful harness for Action classes that can be used with JUnit or Cactus.

23.If the framework doesn't do what I want, can I request that a feature be added?

First, it's important to remember that Struts is an all-volunteer project. We don't charge anyone anything to use Struts. Committers and other developers work on Struts because they need to use it with their own applications. If others can use it too, that's "icing on the cake". If you submit a patch for a feature that a Committer finds useful, then that Committer may choose to volunteer his or her time to apply the patch. If you just submit an idea without a patch, it is much less likely to be added (since first someone else has to volunteer their time to write the patch).
We are grateful for any patches, and we welcome new ideas, but the best way to see that something gets added to the framework is to do as much of the work as you can, rather than rely on the "kindness of strangers". Worst case, you can apply the patch to your copy of Struts and still use the feature in your own application. (Which is what open source is ~really~ all about.)

24.Why is it called Struts?

It's a reference to struts in the architectural sense, a reminder of the nearly invisible pieces that hold up buildings, houses, and bridges.

25.Do I have to credit Struts on my own website?

You need to credit Struts if you redistribute your own framework based on Struts for other people to use. (See the Apache License for details.) But you do not need to credit Struts just because your web application utilizes the framework. It's the same situation as using the Apache HTTPD server or Tomcat. Not required if its just running your web site.

26.Where can I get a copy of Struts?

The best place to download Struts is at struts.apache.org. The nightly builds are very stable, and recommended as the best place to start today.

27.How do I install Struts?

To develop applications with Struts, you can usually just add the Struts JAR file to your Java development environment. You can then start using the Struts classes as part of your own application. A blank Struts application (in the webapps directory, open struts-blank.war) is provided, which you can just copy to get a quick-start on your own brainchild.
Since the full source code for Struts is available, we also provide complete instructions for compiling your own Struts JAR from scratch. (This is actually easier than it looks!)
Your Struts application can usually be deployed using a standard WAR file. In most cases, you simply deposit the WAR file on your application server, and it is installed automatically. If not, step-by-step installation instructions for various servlet containers are available.

28.How does Struts work?

Java Servlets are designed to handle requests made by Web browsers. Java ServerPages are designed to create dynamic Web pages that can turn billboard sites into live applications. Struts uses a special Servlet as a switchboard to route requests from Web browsers to the appropriate ServerPage. This makes Web applications much easier to design, create, and maintain.

29.Is Struts compatible with other Java technologies?

Yes. Struts is committed to supporting industry standards. Struts acts as an integrator of Java technologies so that they can be used in the "real world".

30.When do I need "struts.jar" on my classpath?

When you are compiling an application that uses the Struts classes, you must have the "struts.jar" on the classpath your compiler sees -- it does not have to be on your CLASSPATH environment variable.
Why is that an important distinction? Because if you are using a servlet container on your development machine to test your application, the "struts.jar" must not be on your CLASSPATH environment variable when running the container. (This is because each Web application must also have their own copy of the Struts classes, and the container will become confused if it is on the environment path as well.)
There are several general approaches to this issue:
* Use ANT for building your projects -- it can easily assemble classpaths for the compiler. (This is how Struts itself is built, along with Tomcat and most other Java-based projects).
* Use an IDE where you can configure the "class path" used for compilation independent of the CLASSPATH environment variable.
* Use a shell script that temporarily adds struts.jar to the classpath just for compilation, for example javac -classpath /path/to/struts.jar:$CLASSPATH $@

31.Where can I get help with Struts?

The Struts package comes complete with a Users Guide to introduce people to the framework and its underlying technologies. Various components also have their own in-depth Developers Guide, to cover more advanced topics. Comprehensive Javadocs are included along with the full source code. For your convenience, these are bundled together as a self-installing application. The struts-documentation.war is the same bundle that is deployed as the Struts Web site.
The Strut's mailing list is also very active, and welcomes posts from new users. Before posting a new question, be sure to consult the MAILING LIST ARCHIVE and the very excellent How To Ask Questions The Smart Way by Eric Raymond. Please do be sure to turn off HTML in your email client before posting.

32.What's the difference between Struts and Turbine? What's the difference between Struts and Espresso?

If you are starting from scratch, packages like Turbine and Espresso can be very helpful since they try to provide all of the basic services that your team is likely to need. Such services include things like data persistence and logging.
If you are not starting from scratch, and need to hook up your web application to an existing infrastructure, then "plain vanilla" Struts can be a better choice. The core Struts framework does not presuppose that you are using a given set of data persistence, presentation, or logging tools. Anything goes =:0)
Compared to other offerings, Struts endeavors to be a minimalist framework. We try leverage existing technologies whenever we can and provide only the missing pieces you need to combine disparate technologies into a coherent application. This is great when you want to select your own tools to use with Struts. But, if you prefer a more integrated infrastructure, then packages like Turbine or Espresso (which uses Struts) are perfectly good ways to go.
See also
* < http://www.mail-archive.com/struts-user@jakarta.apache.org/msg03206.html >
* < http://www.mail-archive.com/general@jakarta.apache.org/msg00495.html >
* < http://jakarta.apache.org/velocity/ymtd/ymtd.html >

33.Why aren't the Struts tags maintained as part of the Jakarta Taglibs project ?

Development of both products began about the same time. Leading up to the release of 1.0, it was thought better to continue to develop the taglibs alongside the controller. Now that 1.0 is out, the JavaServer Pages Standard Taglib is in active development. Once work on JSTL stabilizes, the Struts taglibs will be revisited. Tags which are not linked directly to the framework may be hosted at Jakarta Taglibs instead.

34.Are the Struts tags XHTML compliant ?

If you use an <html:html xhtml="true> or <html:xhtml/> element on your page, the tags will render as XHTML (since Struts 1.1).

35.Will the Struts tags support other markup languages such as WML  ?

Struts itself is markup neutral. The original Struts taglibs are only one example of how presentation layer components can access the framework. The framework objects are exposed through the standard application, session, and request contexts, where any Java component in the application can make use of them.
Markup extensions that use Struts are available for Velocity and XLST, among others. A new Struts tag library for Java Server Faces is also in development.
For more about using WAP/WML with Struts see the article WAP up your EAserver.

36.What about JSTL and JavaServer Faces ?

JSTL, the JavaServer Standard Tag Library, is a set of JSP tags that are designed to make it easier to develop Web applications. JavaServer Faces (JSF) is a specification for a new technology that promises to make it easier to write MVC applications, both for the Web and for the desktop.
The inventor of Struts, Craig McClanahan, is the specification co-lead for JavaServer Faces (JSR 127), and architect of the reference implemenation as well as Java Studio Creator. Both JSTL and JSF are complementary to Struts.
The mainstay of the Struts framework is the controller components, which can be used with any Java presentation technology. As new technologies become available, it is certain that new "glue" components will also appear to help these technologies work as well with Struts.
Struts originally came bundled with a set of custom JSP tags. Today, several extensions are available to help you use Struts with other popular presentation technologies, like XSLT and Velocity. Likewise, extensions for JSTL and JSF are now available as well.
The JSTL reference implementation is available through the Jakarta Taglibs site. A JSTL taglibs for Struts, Struts-El , is available and distributed with Struts beginning with the 1.1 release.
The JSF specification and reference implementation is available through Sun's The JSF specification and reference implementation is available through Sun's Java ServerFaces page. An early-release JavaServer Faces taglib for Struts, Struts-Faces, is also in early release and available through the nightly build. The Struts Faces taglib is expected to work with any compliant JSF implementation, including MyFaces.

37.Is there a particularly good IDE to use with Struts ?

Struts should work well with any development environment that you would like to use, as well as with any programmers editor. The members of the Struts development team each use their own tools such as Emacs, IDEA, Eclipse, and NetBeans.

38.Why was reload removed from Struts (since 1.1)?

The problem with ReloadAction was that Struts was trying to act like a container, but it couldn't do a proper job of it. For example, you can't reload classes that have been modified, or (portably) add new classes to a running web application (even if the container supported it).
Meanwhile, as Struts 1.1 was being developed, work progressed on things like Tomcat's reload command via the Manager webapp. This feature allows you to quickly reload-on-demand, complete with saving and restoring your session). It started to make even less sense for Struts to half-implement a feature that containers are implementing fully.
A more minor point is that freezing the configuration information at application startup time allows Struts to safely access the mapping information without bothering with synchronization. The "startup-only" strategy creates a modest but real improvement in performance for all users.
So, ReloadAction is not supported since Struts 1.1 for two reasons:
* It never did let you reload everything that you would really want to -- particularly changed classes -- so many people ended up having to reload the webapp anyway.
* Containers are starting to offer reload-on-demand features which does the same thing as the Struts ReloadAction, only better.
* Not supporting ReloadAction lets Struts avoid doing synchronization locks around all the lookups (like figuring out which action to use, or the destination of an ActionForward) so applications can run a little faster.
Of course, if someone came up with an implementation that solved these problems without creating any others, we would not be opposed to including a new ReloadAction.

39.What is a modular application? What does module-relative mean?

Since Struts 1.1, the framework supports multiple application modules. All applications have at least one root, or default, module. Like the root directory in a file system, the default application has no name. (Or is named with an empty string, depending your viewpoint.) Developing an application with only a default module is no different from how applications were developed under Struts 1.0. Since Struts 1.1, you can add additional modules to your application, each of which can have their own configuration files, messages resources, and so forth. Each module is developed in the same way as the default module. Applications that were developed as a single module can added to a multiple module application, and modules can promoted to a standalone application without change. For more about configuring your application to support multiple modules, see Configuring Applications in the User Guide.
But to answer the question =:0), a modular application is a Struts application that uses more than one module. Module-relative means that the URI starts at the module level, rather than at the context level, or the absolute-URL level.
* Absolute URL: http://localhost/myApplication/myModule/myAction.do
* context-relative: /myModule/myAction.do
* module-relative: /myAction.do
The Struts Examples application is a modular application that was assembled from several applications that were created independently.

40.Why are some of the class and element names counter-intuitive?

The framework grew in the telling and, as it evolved, some of the names drifted.
The good thing about a nightly build, is that everything becomes available to the community as soon as it is written. The bad thing about a nightly build is that things like class names get locked down early and then become difficult to change.

41.Why is ActionForm a base class rather than an interface?

The MVC design pattern is very simple to understand but much more difficult to live with. You just need this little bit of Business Logic in the View logic or you need just that little bit of View logic in the Business tier and pretty soon you have a real mess.
Making ActionForm a class takes advantage of the single inheritance restriction of Java to it makes it more difficult for people to do things that they should not do.
ActionForms implemented as interfaces encourage making the property types match the underlying business tier instead of Strings, which violates one of the primary purposes for ActionForms in the first place (the ability to reproduce invalid input, which is a fundamental user expectation). ActionForms as an interface would also encourage using existing DAO objects as ActionForms by adding ‘implements ActionForm’ to the class. This violates the MVC design pattern goal of separation of the view and business logic.
Since the goal of struts is to enforce this separation, it just makes more sense for Struts to own the ActionForm.
DynaActionForms relieve developers of maintaining simple ActionForms. For near zero maintenance, try Niall Pemberton's LazyActionForm

42.Do ActionForms have to be true JavaBeans?

The utilities that Struts uses (Commons-BeanUtils since 1.1) require that ActionForm properties follow the JavaBean patterns for mutators and accessors (get*,set*,is*). Since Struts uses the Introspection API with the ActionForms, some containers may require that all the JavaBean patterns be followed, including declaring "implements Serializable" for each subclass. The safest thing is to review the JavaBean specification and follow all the prescribed patterns.
Since Struts 1.1, you can also use DynaActionForms and mapped-backed forms, which are not true JavaBeans. For more see ActionForm classes in the User Guide and Using Hashmaps with ActionForms in this FAQ.

43.Can I use multiple HTML form elements with the same name?

Yes. Define the element as an array and Struts will autopopulate it like any other.
private String[] id= {};
public String[] getId() { return this.id; }
public void setItem(String id[]) {this.id = id;}
And so forth

44.Can I use multiple HTML form elements with the same name?

Yes. The issue is that only one action class can be associated with a single form. So the real issue is how do I decode multiple submit types to a single Action class. There is more than one way to achieve this functionality.
The way that is suggested by struts is right out of the javadoc for LookupDispatchAction . Basically, LookupDispatchAction is using the keys from ApplicationProperties.resources as keys to a map of actions available to your Action class. It uses reflection to decode the request and invoke the proper action. It also takes advantage of the struts <html:submit> tags and is straight forward to implement.
You can roll your own with JavaScript events and javascript:void (document.forms["myform"].submit) on any html element. This gives you control of how you want your page to look. Again you will have to decode the expected action in the execute method of your action form if you choose this route.

45.Why doesn't the focus feature on the <html:form> tag work in every circumstance?

Unfortunately, there is some disagreement between the various browsers, and different versions of the same browser, as to how the focus can be set. The <html:form> tag provides a quick and easy JavaScript that will set the focus on a form for most versions of most browsers. If this feature doesn't work for you, then you should set the focus using your own JavaScript. The focus feature is a convenient "value-add" -- not a core requirement of the tag. If you do come up with a JavaScript that provides the final solution to this project, please post your patch to this Bugzilla ticket.

46.Why are my checkboxes not being set from ON to OFF?

A problem with a checkbox is that the browser will only include it in the request when it is checked. If it is not checked, the HTML specification suggests that it not be sent (i.e. omitted from the request). If the value of the checkbox is being persisted, either in a session bean or in the model, a checked box can never unchecked by a HTML form -- because the form can never send a signal to uncheck the box. The application must somehow ascertain that since the element was not sent that the corresponding value is unchecked.
The recommended approach for Struts applications is to use the reset method in the ActionForm to set all properties represented by checkboxes to null or false. The checked boxes submitted by the form will then set those properties to true. The omitted properties will remain false. Another solution is to use radio buttons instead, which always submit a value.
It is important to note that the HTML specification recommends this same behavior whenever a control is not "successful". Any blank element in a HTML form is not guaranteed to submitted. It is therefor very important to set the default values for an ActionForm correctly, and to implement the reset method when the ActionForm might kept in session scope.

47.Can't I just create some of my JavaBeans in the JSP using a scriptlet?

Struts is designed to encourage a Model 2/MVC architecture. But there is nothing that prevents you from using Model 1 techniques in your JavaServer Pages, so the answer to the question is "Yes, you can".
Though, using Model 1 techniques in a Struts application does go against the grain. The approach recommended by most Struts developers is to create and populate whatever objects the view may need in the Action, and then forward these through the request. Some objects may also be created and stored in the session or context, depending on how they are used.
Likewise, there is nothing to prevent you from using scriptlets along with JSP tags in your pages. Though, many Struts developers report writing very complex scriplet-free applications and recommend the JSP tag approach to others.
For help with Model 1 techniques and scriptlets, you might consider joining the Javasoft JSP-interest mailing list, where there are more people still using these approaches.

48.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.

49.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.

50.Why does the option tag render selected=selected instead of just selected?

Attribute minimization (that is, specifying an attribute with no value) is a place where HTML violates standard XML syntax rules. This matters a lot for people writing to browsers that support XHTML, where doing so makes the page invalid. It's much better for Struts to use the expanded syntax, which works the same on existing browsers interpreting HTML, and newer browsers that expect XHTML-compliant syntax. Struts is following the behavior recommended by the XHTML specification

51.Do I have to use JSPs with my application?

The short answer to this question is: No, you are not limited to JavaServer Pages.
The longer answer is that you can use any type of presentation technology which can be returned by a web server or Java container. The list includes but is not limited to:
* JavaServer Pages,
* HTML pages,
* WML files,
* Java servlets,
* Velocity templates, and
* XML/XLST
Some people even mix and match apparently unrelated technologies, like PHP, into the same web application.

52.What's the best way to deal with migrating a large application from Struts to JSF? Is there any tool support that can help?

This is a complicated task depending on your Struts application. Because the two frameworks have different goals, there are some challenges. Migrate your response pages first. Keep the Struts controller and place and forward to JSF pages. Then you can configure Struts forwards to go through the Faces servlet. Consider looking at the Struts-Faces framework from Apache. See the framework chapter in JSF in Action.

53.What are the two types of validations supported by Validator FrameWork?

validator Framework is used for form data validation. This framework provides two types of validations:
Client Side validation on user’s browser
Server side validation

54. What are the steps of Struts Installation?

In order to use Struts framework, we only need to add Struts.Jar file in our development environment. Once jar file is available in the CLASSPATH, we can use the framework and develop Strut based applications.

55. What’s declarative exception handling in Struts?

When logic for exception handling is defined in struts-config.xml or within the action tag, it’s known as declarative exception handling in Struts.

56. What’s the difference between validation.xml and validator-rules.xml files in Struts Validation framework?

In Validation.xml, we define validation rules for any specific Java bean while in validator-rules.xml file, standard and generic validation rules are defined.

57.How can we display all validation errors to user on JSP page?

To display all validation errors based on the validation rules defined in validation.xml file, we use <html:errors /> tag in our JSP file.

58.Which configuration file is used for storing JSP configuration information in Struts?

For JSP configuration details, Web.xml file is used.

59. What’s the purpose of Execute method of action class?

Execute method of action class is responsible for execution of business logic. If any processing is required on the user’s request, it’s performed in this method. This method returns actionForward object which routes the application to appropriate page.

60.How duplicate form submission can be controlled in Struts?

In Struts, action class provides two important methods which can be used to avoid duplicate form submissions.
saveToken() method of action class generates a unique token and saves it in the user’s session. isTokenValid() method is used then used to check uniqueness of tokens.

61. In Struts, how can we access Java beans and their properties?

Bean Tag Library is a Struts library which can be used for accessing Java beans.

62.What’s the significance of logic tags in Struts?

Use of logic tags in Struts helps in writing a clean and efficient code at presentation layer without use of scriptlets.

63. What are the two scope types for formbeans?

1. Request Scope: Formbean values are available in the current request only
2. Session Scope: Formbean values are available for all requests in the current session.

64.How can we group related actions in one group in Struts?

To group multiple related actions in one group, we can use DispatcherAction class.

65. When should we use SwtichAction?

The best scenario to use SwitchAction class is when we have a modular application with multiple modules working separately. Using SwitchAction class we can switch from a resource in one module to another resource in some different module of the application.

66. What’s the difference between Jakarta Struts and Apache Struts? Which one is better to use?

Both are same and there is no difference between them.

67. What’s the use of Struts.xml configuration file?

Struts.xml file is one the key configuration files of Struts framework which is used to define mapping between URL and action. When a user’s request is received by the controller, controller uses mapping information from this file to select appropriate action class.

68. What’s the use of reset method of ActionForm class?

reset method of actionForm class is used to clear the values of a form before initiation of a new request.

69. What are disadvantages of Struts?

Although Struts have large number of advantages associated, it also requires bigger learning curve and also reduces transparency in the development process.
Struts also lack proper documentation and for many of its components, users are unable to get proper online resources for help.

70. What’s the use of resourcebundle.properties file in Struts Validation framework?

resourcebundle.properties file is used to define specific error messages in key value pairs for any possible errors that may occur in the code.
This approach helps to keep the code clean as developer doesn’t need to embed all error messages inside code.

71. Can I have html form property without associated getter and setter formbean methods?

For each html form property, getter and setter methods in the formbean must be defined otherwise application results in an error.

72. How many servlet controllers are used in a Struts Application?

Struts framework works on the concept of centralized control approach and the whole application is controlled by a single servlet controller. Hence, we require only one servlet controller in a servlet application.

73. Which model components are supported by Struts?

Struts support all types of models including Java beans, EJB, CORBA. However, Struts doesn’t have any in-built support for any specific model and it’s the developer’s choice to opt for any model.

74. When it’s useful to use IncludeAction?

IncludeAction is action class provided by Struts which is useful when an integration is required between Struts and Servlet based application.

75. Is Struts thread safe?

Yes Struts are thread safe. In Struts, a new servlet object is not required to handle each request; rather a new thread of action class object is used for each new request.

76. What are the benefits of Struts framework?

Struts is based on MVC and hence there is a good separation of different layers in Struts which makes Struts applications development and customization easy. Use of different configuration files makes Struts applications easily configurable. Also, Struts is open source and hence, cost effective.

77. What steps are required to for an application migration from Struts1 to Struts2?

Following Steps are required for Struts1 to Struts2 migration:
Move Struts1 actionForm to Struts2 POJO.
Convert Struts1 configuration file (struts-config.xml) to Struts2 configuration file (struts.xml)

78. How properties of a form are validated in Struts?

For validation of populated properties, validate() method of ActionForm class is used before handling the control of formbean to Action class.

79. What configuration changes are required to use resource files in Struts?

Resource files (.properties files) can be used in Struts by adding following configuration entry in struts-config.xml file:
<message-resources parameter=”com.login.struts.ApplicationResources”/>

80. How nested beans can be used in Struts applications?

Struts provide a separate tag library (Nested Tag Library) for this purpose. Using this library, we can nest the beans in any Struts based application.

81. What are the Core classes of Struts Framework?

Following are the core classes provided by Struts Framework:
Action Class
ActionForm Class
ActionMapping Class
ActionForward Class
ActionServlet Class

82. When should be opt for Struts Framework?

Struts should be used when any or some of the following conditions are true:
A highly robust enterprise level application development is required.
A reusable, highly configurable application is required.
A loosely coupled, MVC based application is required with clear segregation of different layers.

83. Why ActionServlet is singleton in Struts?

In Struts framework, actionServlet acts as a controller and all the requests made by users are controlled by this controller. ActionServlet is based on singleton design patter as only one object needs to be created for this controller class. Multiple threads are created later for each user request.

84.What are Callback interfaces?

These interfaces are used in the application to receive a notification when some object events occur. Like when an object is loaded, saved or deleted. There is no need to
implement callbacks in hibernate applications, but they’re useful for implementing certain kinds of generic functionality.

85. What are Extension interfaces?

When the built-in functionalities provided by hibernate is not sufficient enough, it provides a way so that user can include other interfaces and implement those interfaces
for user desire functionality. These interfaces are called as Extension interfaces.

86. What are the Extension interfaces that are there in hibernate?

There are many extension interfaces provided by hibernate.
 1.ProxyFactory interface - used to create proxies
 2.ConnectionProvider interface – used for JDBC connection management
 3.TransactionFactory interface – Used for transaction management
 4.Transaction interface – Used for transaction management
 5.TransactionManagementLookup interface – Used in transaction management.
 6.Cahce interface – provides caching techniques and strategies
 7.CacheProvider interface – same as Cache interface
 8.ClassPersister interface – provides ORM strategies
 9.IdentifierGenerator interface – used for primary key generation
 10.Dialect abstract class – provides SQL support

87. What are different environments to configure hibernate?

There are mainly two types of environments in which the configuration of hibernate
application differs.
i. Managed environment – In this kind of environment everything from database connections, transaction boundaries, security levels and all are defined. An example of
this kind of environment is environment provided by application servers such as JBoss, Weblogic and WebSphere. ii. Non-managed environment – This kind of environment provides a basic
configuration template. Tomcat is one of the best examples that provide this kind of environment.

88. What is the file extension you use for hibernate mapping file?

The name of the file should be like this : filename.hbm.xml
The filename varies here. The extension of these files should be “.hbm.xml”. This is just a convention and it’s not mandatory. But this is the best practice to follow this
extension.

89. What do you create a SessionFactory?

Configuration cfg = new Configuration();
cfg.addResource("myinstance/MyConfig.hbm.xml");
cfg.setProperties( System.getProperties() );
SessionFactory sessions = cfg.buildSessionFactory();
First, we need to create an instance of Configuration and use that instance to refer to the location of the configuration file. After configuring this instance is used to create the
SessionFactory by calling the method buildSessionFactory().

90. What is meant by Method chaining?

Method chaining is a programming technique that is supported by many hibernate interfaces. This is less readable when compared to actual java code. And it is not mandatory to use this format. Look how a SessionFactory is created when we use method
chaining.
SessionFactory sessions = new Configuration()
.addResource("myinstance/MyConfig.hbm.xml")
.setProperties( System.getProperties() )
.buildSessionFactory();

91. What does hibernate.properties file consist of?

This is a property file that should be placed in application class path. So when the Configuration object is created, hibernate is first initialized. At this moment the
application will automatically detect and read this hibernate.properties file.
hibernate.connection.datasource = java:/comp/env/jdbc/AuctionDB
hibernate.transaction.factory_class = net.sf.hibernate.transaction.JTATransactionFactory
hibernate.transaction.manager_lookup_class = net.sf.hibernate.transaction.JBossTransactionManagerLookup
hibernate.dialect = net.sf.hibernate.dialect.PostgreSQLDialect

92. What should SessionFactory be placed so that it can be easily accessed?

As far as it is compared to J2EE environment, if the SessionFactory is placed in JNDI then it can be easily accessed and shared between different threads and various components that are hibernate aware.
You can set the SessionFactory to a JNDI by configuring a property hibernate.session_factory_name in the hibernate.properties file.

93. What are POJOs?

POJO stands for plain old java objects. These are just basic JavaBeans that have defined setter and getter methods for all the properties that are there in that bean. Besides they
can also have some business logic related to that property. Hibernate applications works efficiently with POJOs rather then simple java classes.

94. What is object/relational mapping metadata?

ORM tools require a metadata format for the application to specify the mapping between classes and tables, properties and columns, associations and foreign keys, Java types and
SQL types. This information is called the object/relational mapping metadata. It defines the transformation between the different data type systems and relationship
representations.

95. What is Attribute Oriented Programming?

XDoclet has brought the concept of attribute-oriented programming to Java. Until JDK 1.5, the Java language had no support for annotations; now XDoclet uses the Javadoc tag
format (@attribute) to specify class-, field-, or method-level metadata attributes. These attributes are used to generate hibernate mapping file automatically when the application
is built. This kind of programming that works on attributes is called as Attribute Oriented Programming.

96. What are the different methods of identifying an object?

There are three methods by which an object can be identified.
i. Object identity –Objects are identical if they reside in the same memory location
in the JVM. This can be checked by using the = = operator.
ii. Object equality – Objects are equal if they have the same value, as defined by the equals( ) method.
Classes that don’t explicitly override this method inherit the implementation defined by java.lang.Object, which compares object identity.
iii. Database identity – Objects stored in a relational database are identical if they represent the same row or, equivalently, share the same table and primary key value.

97. What are the different approaches to represent an inheritance hierarchy?

i. Table per concrete class.
ii. Table per class hierarchy.
iii. Table per subclass.

98. What are managed associations and hibernate associations?

Associations that are related to container management persistence are called managed associations. These are bi-directional associations. Coming to hibernate associations,
these are unidirectional.

99. What are the different levels of ORM quality?

There are four levels defined for ORM quality.
i. Pure relational
ii. Light object mapping
iii. Medium object mapping
iv. Full object mapping

100. What is a pure relational ORM?

The entire application, including the user interface, is designed around the relational
model and SQL-based relational operations.

101. What is a meant by light object mapping?

The entities are represented as classes that are mapped manually to the relational tables. The code is hidden from the business logic using specific design patterns. \
This approach is successful for applications with a less number of entities, or applications with common, metadata-driven data models. This approach is most known to all.

102. What is a meant by medium object mapping?

The application is designed around an object model. The SQL code is generated at build time. And the associations between objects are supported by the persistence mechanism,
and queries are specified using an object-oriented expression language. This is best suited  



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