Showing posts with label Tag. Show all posts
Showing posts with label Tag. Show all posts

Wednesday, 5 January 2022

Top 20 Apache Struts 2 Interview Questions and Answers

  

Struts 2 is a Java enterprise application framework for constructing web applications. It was created by the Apache Software Foundation. In the year 2006, it was first released. It's written in the Java programming language. It is cross-platform compatible. It is built on the MVC architecture, which is a software design paradigm for creating applications. Struts 2 includes features such as simplified testability, Ajax support, Thread-safety, and Template support, among others.

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Ques. 1): What exactly is Struts2?

Answer:

Apache Struts2 is a Java web application framework that is free source. The OpenSymphony WebWork framework is the foundation for Struts2. It's a significant improvement over Struts1, making it more adaptable, simple to use, and extendable. Action, Interceptors, and Result pages are the three main components of Struts2.

Struts2 offers a variety of options for creating Action classes and configuring them using struts.xml or annotations. For common jobs, we can make our own interceptors. Struts2 includes a large number of tags and makes use of the OGNL expression language. To render result pages, we can design our own type converters. JSPs and FreeMarker templates can be used as result pages.

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Ques. 2): What are some of Struts2's features?

Answer:

Here are some of the fantastic features that can persuade you to use Struts2.

POJO forms and POJO actions − Struts2 has done away with the Action Forms that were an integral part of the Struts framework. With Struts2, you can use any POJO to receive the form input. Similarly, you can now see any POJO as an Action class.

Tag support − Struts2 has improved the form tags and the new tags allow the developers to write less code.

AJAX support − Struts2 has recognised the take over by Web2.0 technologies, and has integrated AJAX support into the product by creating AJAX tags, that function very similar to the standard Struts2 tags.

Easy Integration − Integration with other frameworks like Spring, Tiles and SiteMesh is now easier with a variety of integration available with Struts2.

Template Support − Support for generating views using templates.

Plugin Support − The core Struts2 behaviour can be enhanced and augmented by the use of plugins. A number of plugins are available for Struts2.

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Ques. 3): What's the difference between Struts 1 and Struts 2?

Answer: 

This is a list of the most common Strut 2 interview questions. The action class in Strut 1 is not a POJO, hence it must inherit the abstract class. An action servlet is used as the front controller. Only JSP is used for the component view. A configuration file can be inserted in the WEB-INF directory in section 1. When processing requests, it makes use of the Request Processor class. Actions and models are separated in Strut 1.

The action class in Strut 2 is a POJO, therefore there's no need to inherit any classes or implement any interfaces. For the view component, it has JSP, free-market, and so on. The function controller in strut 2 is the Struts Prepare and Execute filter. In this, a configuration file must be named as struts.xml and placed inside the classes directory. It uses the concept of Interceptors while processing the request. In strut 2, action and models are combined within the action class.

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Ques. 4): In Struct2, What Is The Use Of Struts.properties?

Answer:

This configuration file allows you to override the framework's default behaviour. In fact, all of the properties in the struts.properties configuration file can be defined in the web.xml using the init-param, as well as in the struts.xml configuration file using the constant tag. However, if you prefer to keep things separate and more struts specific, you can create this file in the WEB-INF/classes folder. The default values configured in default.properties, which is included in the struts2-core-x.y.z.jar distribution, will be overridden by the values configured in this file.

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Ques. 5): Explain The Life Cycle Of A Request In Struct2 Application?

Answer :

Following is the life cycle of a request in Struct2 application −

  • User sends a request to the server for requesting for some resource (i.e pages).
  • The FilterDispatcher looks at the request and then determines the appropriate Action.
  • Configured interceptors functionalities applies such as validation, file upload etc.
  • Selected action is executed to perform the requested operation.
  • Again, configured interceptors are applied to do any post-processing if required.
  • Finally the result is prepared by the view and returns the result to the user.

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Ques. 6): What are the inbuilt themes that are provided by strut 2?

Answer:

There are 3 different inbuilt themes:

Simple theme: It is a minimal theme which is having very little content. It means that the text field tag renders the HTML tag without label, validation, error reporting or any other formatting or functionality.

XHTML theme: It is referred to as the default theme used by struts 2 and provides all the basics that a simple theme provides. It adds the other several features like standard two-column table layout for the HTML labels for each of the HTML, validation and error reporting etc.

Css_xhtml theme: This is the theme that provides all the basics that the simple theme provides, and it adds other several features like the standard two-column CSS-based layout and using div tag for HTML struts tags, labels for each of the HTML struts tags and placed according to the CSS style sheet.

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 Ques. 7): What is internationalization and how does it work?

Answer:

This is one of the most common Struts 2 Interview Questions that is asked during an interview. Localization refers to the process of planning and implementing products and services so that they may be easily modified to specific local languages and cultures, whereas internationalization refers to the act of enabling localization.

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Ques. 8): What is the difference between an interceptor and a filter?

Answer:

The interceptors are built around struts 2. It runs for all requests that qualify for a servlet filter front controller and can be customised to run extra interceptors for specific action execution. Interceptor methods can be configured to execute or not to execute using exclude and include methods.

Servlet specifications are used to create the filters. Executes on request and non-configurable method calls if the pattern matches.

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Ques. 9): Explain struts 2's XML-based validation.

Answer:

XML-based validation in Struts 2 adds more validation options, such as email validation, integer range validation, form validation field, expression validation, regex validation, needed validation, string length validation, and necessary string validation, among others. The XML file must be titled 'actionclass'-validation.xml in Struts 2.

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Ques. 10): How Does Validation in Struts 2 Work?

Answer:

When the user clicks the submit button, Struts 2 will run the validate method, and if any of the if statements inside the method are true, Struts 2 will call the addFieldError method. Struts 2 will not proceed to invoke the execute method if any errors have been introduced. The Struts 2 framework, on the other hand, will return input as a result of calling the action.

When validation fails and Struts 2 returns input, the view file is redisplayed by the Struts 2 framework. Because we utilised Struts 2 form tags, the error messages will appear directly above the completed form.

These are the error messages we specified in the call to the addFieldError function. The addFieldError method takes two arguments. The first is the form field name to which the error applies and the second is the error message to display above that form field.

 

Ques. 11): What Types Of Validations Are Available In Xml Based Validation In Struts2?

Answer :

Following is the list of various types of field level and non-field level validation available in Struts2 −

  • date validator
  • double validator
  • email validator
  • expression validator
  • int validator
  • regex validator
  • required validator
  • requiredstring validator
  • stringlength validator
  • url validator

 

Ques. 12):  How Does Struts 2's Interceptor Work?

Answer:

The actual action will be performed by calling invocation.invoke() from the interceptor. So, depending on your needs, you can conduct some pre-processing and some post-processing.

The framework initiates the process by using the invoke method on the ActionInvocation object (). When invoke() is called, ActionInvocation consults its state and performs the next available interceptor. The invoke() method will cause the action to be executed once all of the configured interceptors have been invoked.

 

Ques. 13): What Is Value Stack?

Answer :

The value stack is a set of several objects which keeps the following objects in the provided order −

Temporary Objects − There are various temporary objects which are created during execution of a page. For example the current iteration value for a collection being looped over in a JSP tag.

The Model Object − If you are using model objects in your struts application, the current model object is placed before the action on the value stack.

The Action Object − This will be the current action object which is being executed.

Named Objects − These objects include #application, #session, #request, #attr and #parameters and refer to the corresponding servlet scopes.

 

Ques. 14): What Is The Difference Between Valuestack And OGNL?

Answer:

ValueStack is the storage space where Struts2 stores application data for processing client requests. The information is saved in ActionContext objects that use ThreadLocal to store values that are unique to each request thread.

OGNL (Object-Graph Navigation Language) is a sophisticated Expression Language for manipulating data on the ValueStack. Both interceptors and result pages can use OGNL to access data stored on ValueStack, as shown in the architectural diagram.

 

Ques. 15): What Is The Struts-default Package And How Does It Help?

Answer:

Struts-default is an abstract package that specifies all of the Struts2 interceptors as well as the most widely used interceptor stack. To prevent having to configure interceptors twice, it's best to extend this package while configuring our application package. This is provided to assist developers by making the work of configuring interceptor and result pages in our application a lot easier.

 

Ques. 16): What Is The Purpose Of @after Annotation?

Answer :

The @After annotation marks a action method that needs to be called after the main action method and the result was executed. Return value is ignored.

public class Employee extends ActionSupport{

   @After

   public void isValid() throws ValidationException {

      // validate model object, throw exception if failed

   }

   public String execute() {

      // perform secure action

      return SUCCESS;

   }

}

 

Ques. 17): What Is The Purpose Of @before Annotation?

Answer :

The @Before annotation marks a action method that needs to be called before the main action method and the result was executed. Return value is ignored.

public class Employee extends ActionSupport{

   @Before

   public void isAuthorized() throws AuthenticationException {

      // authorize request, throw exception if failed

   }

   public String execute() {

      // perform secure action

      return SUCCESS;

   }

}

 

Ques. 18): What Is The Difference Between Using An Action Interface And Using An Actionsupport Class For Our Action Classes, And Which Would You Prefer?

Answer:

To develop our action classes, we can use the Action interface. This interface only has one function, execute(), which we must implement. The main advantage of utilising this interface is that it includes some constants that can be used on result pages, such as SUCCESS, ERROR, NONE, INPUT, and LOGIN.

The ActionSupport class implements the Action interface by default, as well as interfaces for Validation and i18n support. Action, Validateable, ValidationAware, TextProvider, and LocaleProvider are all implemented by the ActionSupport class. To implement field level validation login in our action classes, we can override the validate() method of the ActionSupport class.

Depending on the requirements, we can use any of the approaches to create struts 2 action classes, my favorite is ActionSupport class because it helps in writing validation and i18n logic easily in action classes.

 

Ques. 19): How Do We Get Servlet Api Requests, Responses, Httpsessions, and Other Objects Into Action Classes?

Answer:

Servlet API components such as Request, Response, and Session are not directly accessible through Struts2 action classes. However, in some action classes, such as checking the HTTP method or adding cookies in the response, these accesses are required.

As a result, the Struts2 API exposes a number of *Aware interfaces through which we can access these objects. Struts2 API injects Servlet API components into action classes using dependency injection. SessionAware, ApplicationAware, ServletRequestAware, and ServletResponseAware are some of the most essential Aware interfaces.

 

Ques. 20): Is Struts2 Interceptors And Action Thread Safe?

Answer:

Because an object is instantiated for each request to process, Struts2 Action classes are thread safe.

Because Struts2 interceptors are singleton classes that launch a new thread to handle the request, they are not thread safe, and we must construct them carefully to avoid any shared data concerns.

 

 

 

Thursday, 30 December 2021

Top 20 Apache Tapestry Interview Questions and Answers

 

                Do you want to succeed in the Apache Tapestry and advance your career? Then, on this page, we will offer you with the complete set of Apache Tapestry job Interview Questions and Answers. Apache Tapestry is a Java-based open source web framework. It's a web framework that's built around components. Apache Tapestry is a framework for building extremely scalable web applications. Many top firms offer Apache Tapestry jobs in a variety of positions. In the Java programming language, there are more opportunities for experienced workers. Job hunting may be difficult and exhausting, especially if you don't know how to apply, where to look, or how to prepare for job interviews. To minimise any misunderstanding, we've framed Apache tapestry job interview questions and answers to help you prepare for your interview.

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Ques. 1): How do I run multiple Tapestry applications in the same web application?

Answer:

Multiple Tapestry 5 apps are not supported; there is only one place to identify the application root package, therefore configuring multiple filters into multiple directories isn't an option.

Tapestry 5 did not include support for numerous Tapestry applications in the same web application (it needlessly complicated Tapestry 4). Given how disjointed Tapestry 5 pages are, there doesn't appear to be a benefit to doing so... and, if it were possible, there would be a considerable drawback in terms of memory use.

You can run Tapestry 4 and Tapestry 5 apps side by side (the package names are different for this reason), but they have no knowledge of each other and are unable to interact directly. This is just like the way you could have a single WAR with multiple servlets; the different applications can only communicate via URLs, or shared state in the HttpSession.

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Ques. 2): Tapestry focuses on the wrong field in my form, how do I fix that?

Answer:

Tapestry usually determines which field in your form should receive initial emphasis by giving a FieldFocusPriority to each field as it renders, which translates to the following logic:

There is an error in the first field.

Alternatively, the first mandatory field

Alternatively, the first field

Due to a variety of reasons beyond Tapestry's control, its choices may not always be exactly what you desire, necessitating the use of an override. The data is kept track of in the JavaScriptSupport environment. It's simply a matter of injecting the component to get its client id, then notifying JavaScriptSupport of your override.

Here's an example

 <t:textfield t:id="email" t:mixins="OverrideFieldFocus" .../>

The OverrideFieldFocus mixin forces the email field to be the focus field, regardless.

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Ques. 3): Is Tapestry A Jsp Tag Library?

Answer :

Tapestry is not a JSP tag library; it is based on the servlet API but does not make use of JSPs. It has its own rendering engine and HTML template format. Tapestry now offers a simple JSP tag library in release 3.0, allowing JSP pages to link to Tapestry pages.

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Ques. 4): I Have A Form With A Submit Button. On The Form And The Submit Button Are Two Separate Listeners. Which Is Invoked First?

Answer :

While the shape encounters your button at some time throughout the rewind, the button's listener must be called. The form's submitListener must be called after the shape has completed its rewind, therefore different listeners were called in either scenario. Note that this could mean that the listener for a button can be called before the form has'submitted' all of its values; it all depends on where your input fields are in relation to your button.

 

Ques. 5): Is There A Wysiwyg Editor For Tapestry, Or An Ide Plugin?

Answer :

Tapestry currently lacks a WYSIWYG editor; nonetheless, the nature of Tapestry allows existing editors to function reasonably well (Tapestry additions to the HTML markup are virtually invisible to a WYSIWYG editor). Spindle is a Tapestry plugin for the Eclipse IDE, which is free and open-source. Tapestry apps, pages, and components may now be created using wizards and editors.

 

Ques. 6): How Is The Performance Of Tapestry?

Answer :

Other testing (recorded in the Tapestry discussion boards) coincides with my own testing, which was published in the September 2001 issue of the Java Report: Although plain JSPs have a minor advantage in demo applications, performance curves for equal Tapestry and JSP applications with a database or application server backend are identical. Consider the performance of your Java developers rather than the performance of Tapestry.

 

Ques. 7): What’s The Lifecycle Of A Form Submit?

Answer :

Events will trigger in the following order:

initialize()

pageBeginRender()

formListenerMethod()

pageBeginRender()

The form "rewind" cycle is simply a render cycle with the output buffered and scraped instead of being written to the servlet output stream. The second pageBeginRender() is called while the page is being rendered. To distinguish between these two render cycles, use requestCycle.isRewinding().

 

Ques. 8): Does Tapestry Work With Other Other Application Servers Besides Jboss?

Answer :

Yes, of course! For the turn-key demonstrations, JBoss is free and convenient. In less than a minute, you can download Tapestry and JBoss and have a real J2EE application running! JBoss configuration scripts are specific to a specific release of JBoss, which must be 3.0.6. Tapestry apps, on the other hand, are completely container agnostic... Tapestry is unconcerned with the servlet container it's in, and it doesn't even require an EJB container.

 

Ques. 9): Can I Use The Same Component Multiple Times In One Template?

Answer:

No – but you can copy the definition of a component pretty easily.

<component id=”valueInsert” type=”Insert” >

 <binding name=”value” expression=”getValueAt( rowIndex, columnIndex )” />

 </component>

<component id=”valueInsert1″ copy-of=”valueInsert”/>

 <component id=”valueInsert2″ copy-of=”valueInsert”/>

 <component id=”valueInsert3″ copy-of=”valueInsert”/>

 <component id=”valueInsert4″ copy-of=”valueInsert”/>

 

Ques. 10): Why is @script required in Apache Tapestry?

Answer:

The script framework is a useful tool for grouping scripts into components. It delivers the benefits of components to scripts. It may now be utilised as a component without having to bother about renaming field names or rewiring the fields and scripts. All you have to do now is declare the component and you're ready to go. It is true that another layer of abstraction must be acquired, but once learned, it is extremely powerful. And, to tell you the truth, there isn't much to it.

The script framework is required since form element/field names are produced automatically by the framework. As a result, you write your script in XML, assigning these names to variables, and relying on the framework to deliver the correct names at runtime. Further, you can request that the framework include extra objects that will aid in the creation of your script.

 

Ques. 11): When a form is submitted, why does Tapestry send a redirect?

Answer:

This is a variant of the Post/Redirect/Get strategy. It ensures that if a user resubmits the resultant page after an operation that alters server-side state, such as a form submission, the operation is not repeated; instead, only the results of the operation, reflecting the updated server-side state, are re-rendered.

This has the unwelcome consequence of requiring any data required to produce the answer to persist between the event request (the form submission) and the render request; this frequently necessitates the use of @Persist annotations on fields.

 

Ques. 12): When I utilise an HTML object like &nbsp; in my template, why do I get a SAXParseException?

Answer:

Tapestry reads your templates using a regular SAX parser. This means that your templates must be well-formed, with balanced open and close tags, quoted attribute values, and defined entities. The simplest method to do this is to include a DOCTYPE at the top of your template:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"

   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

Part of the DOCTYPE is the declaration of entities such as &nbsp;.

You can also use the numeric version: &#160; This is the exact same character and will render in the browser identically. When no doctype is present, Tapestry adds an XHTML doctype; this ensures that common HTML entities behave properly.

 

Ques. 13): When I submit a form, I get an error message that says "Tapestry is undefined." Why?

Answer:

This client-side mistake is obvious, yet it can be difficult to resolve. It implies your browser was unable to correctly load the tapestry.js file. Why, exactly, is the question? It could be for a variety of causes, some of which are listed below:

Check to see if 'tapestry.js' is present in the head section of your HTML page.

Tapestry generates a single URL to get all the JS files if the tapestry.combine-scripts configuration parameter is set to true. This can sometimes result in long URLs that browsers are unable to get. Set the sign to false and see what happens.

If you use jQuery in conjunction with Tapestry's prototype, the '$' selection used by both will clash. Put jQuery on top of the stack and enable the jQuery.noConflict mode in this scenario.

Also, if you've added a custom or third-party JS library to the stack and it's causing the JavaScript parsing to fail, look at the JavaScript syntax in that library.

If you used a programme to compress your JavaScript libraries, it's possible that you'll get JavaScript syntax issues, so make sure it works with all of the JavaScript files unpacked.

 

Ques. 14): Do I have to specify both id and t:id for Zone components?

Answer:

The Zone component's examples (in the Component Reference) always give both id and t:id, which is definitely a good thing.

In general, the client-side id (the id attribute) will be the same as the Tapestry component id if you don't define it (t:id).

There are, however, numerous exceptions to this rule. It's possible that the Zone is rendering inside a Loop (in which case, each rendering will have a unique client side id). A random unique id is added into the id if the Zone is rendering as part of a partial page render. Tapestry component ids in nested components can potentially clash in other situations.

 

Ques. 15): When rendering an empty Zone, why do I get the exception "The produced content did not include any components that allow for the positioning of the concealed form field's element."?

Answer:

Tapestry must write a hidden input element with information needed when the form is submitted as part of its form processing. Because the content of a Zone can be altered or erased, a hidden field separate from the rest of the enclosing form is established solely for the Zone.

At the same time, Tapestry wants to position the <input> field in a valid location, and HTML defines some constraints for that; an input field must appear inside a <p> or <div> element. If your zone is initially empty, there's no place to put the hidden element, and Tapestry will complain.

The solution is simple: just add a <div> element to the body of the zone. This ensures that there's a place for the hidden input field.  An empty <div> element (even one containing a hidden form field) will not affect page layout.

 

Ques. 16): Why is it necessary for me to provide an interface for my services? Why can't I simply use the class?

Answer:

To begin with, you can do just this, but you will lose some of the functionality provided by Tapestry's IoC container.

Tapestry will be able to provide functionality for your service around the core service implementation as a result of the split. This is accomplished by using proxies, which are Java classes that implement the service interface. The proxy's methods will eventually call the methods of your service implementation.

One of the most important functions of proxies is to encapsulate the life cycle of a service: most services are singletons that are built just once. Just in time refers to the moment you call a method. What's going on is that the life cycle proxy (the object that gets injected into pages, components or other service implementations) checks on each method invocation to see if the actual service exists yet. If not, it instantiates and configures it (using proper locking to ensure thread safety), then delegates the method invocation to the service.

If you bind a service class (not a service interface and class), then the service is fully instantiated the first time it is injected, rather than at that first method invocation. Further, you can't use decorations or method advice on such a service. The life cycle proxy (the object injected into pages, components, and other service implementations) examines each method invocation to determine if the actual service has been created yet. If it isn't already instantiated and configured (with suitable locking to ensure thread safety), it delegated method invocation to the service.

When you bind a service class (rather than a service interface and class), the service is fully instantiated the first time it is injected, rather than when the first method is invoked. Furthermore, such a service does not allow for the use of decorations or technique suggestions.

The final reason for the service interface / implementation split is to nudge you towards always coding to an interface, which has manifest benefits for code structure, robustness, and testability.

 

Ques. 17): How do I make my service startup with the rest of the application, rather than lazily?

Answer:

Tapestry services are designed to be lazy; they are only fully realized when needed: when the first method on the service interface is invoked.

Sometimes a service does extra work that is desirable at application startup: examples may be registering message handlers with a JMS implementation, or setting up indexing. Since the service's constructor (or @PostInjection methods) are not invoked until the service is realized.

The solution is the @EagerLoad annotation; service implementation classes marked with this annotation are loaded when the Registry is first startup, rather than lazily.

 

Ques. 18): How can I dynamically add new components to an existing page?

Answer:

You don't, to put it succinctly. The long answer is that you don't have to in order to achieve the desired behaviour.

High scalability is one of Tapestry's core values; it can be expressed in a variety of ways, reflecting scalability concerns both within a single server and across a cluster of servers.

Although you code Tapestry pages and components as if they were ordinary POJOs (Plain Old Java Objects — Tapestry doesn't require you to extend any base classes or implement any special interfaces), they behave more like a traditional servlet when deployed by Tapestry: a single instance of each page serves requests from multiple threads. In the background,

 

Ques. 19): What this means is that any incoming request must be handled by a single page instance. Therefore, Tapestry enforces the concept of static structure, dynamic behavior.

Answer:

 Beyond simple conditionals and loops, Tapestry offers a variety of options for varying what content is presented. When rendering a page, you can "drag in" components from other pages (other FAQs will expand on this concept). The idea is that, while the structure of a Tapestry page is quite strict, the order in which the page's components render does not have to be top to bottom.

 

Ques. 20): Why do my images and stylesheets end up with a weird URLs like /assets/meta/zeea17aee26bc0cae/layout/layout.css?

Answer:

The servlet container isn't used by Tapestry to serve static assets (images, stylesheets, flash movies, etc.). Tapestry, on the other hand, handles the requests and streams assets to the browser.

The content of the assets will be compressed using GZIP (if the client supports compression, and the content is compressible). Tapestry will also add an expires header to the content in the future. This means the browser will not ask for the file again, resulting in a significant reduction in network traffic.

The strange hex string is a fingerprint; it's a hash code calculated from the asset's real content. If the asset changes, a new fingerprint will be created, as well as a new path and (immutable) resource. This approach, combined with a far-future expires header also provided by Tapestry, ensures that clients aggressively cache assets as they navigate your site, or even between visits.