J2EE Interview Questions

What is J2EE?

J2EE refers to Java 2 Enterprise Edition. It is used to develop and deploy web-based multi-tier enterprise applications. The J2EE platform combines a range of services, protocols, and application programming interfaces. The J2EE platform includes the capabilities needed to deliver a comprehensive, secure, stable, and fast Java platform at the enterprise level.

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What are the components available in J2EE applications?

The components of the J2EE applications consist of:

• Web-tier components
• Business-tier components
• Client-tier components
• Enterprise Information System software

What do you understand by J2EE client types?

Following are J2EE client types:

• Application clients
• Applets
• Wireless clients, according to Mobile Information Device Profile (MIDP).
• Java Web Start-enabled clients, through the Java Web, Start technology.

What is ORM?

ORM refers to Object-Relational mapping. Objects in a Java class that are mapped to tables in a relational database utilizing the metadata which describes the mapping of objects to the database. It acts by converting data from one representation to the other.

What is JSF?

JSF refers to JavaServer Faces. It is a user interface that designs a framework for Java web applications. It provides a set of user interface components that can be reused, a standard for web applications. JSF uses the MVC design pattern. It stores the form data on the server automatically and specifies the date of the form when it is displayed on the client side.

What is the servlet?

Servlets is one of the server-side components which delivers a powerful mechanism for server-side program development. Servlets is a platform-independent server. Servlets are designed with different protocols in mind; The most common one is HTTP protocols. The servlets uses the classes of java packages javax.servlet.http.HttpSession, javax.servlet.http.HttpServletRequest, javax.servlet, javax.servlet.http.HttpServletResponse. All the servlets are required to implement the Servlet interface that defines the methods of the lifecycle.

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What is a web component?

Java Server Pages technology and Java Servlet components are the web components. Servlet is a component that receives the request sends responses dynamically. JSP pages run like servlets but provide a more natural way to create static content.

What is Hibernate?

Hibernate is an object-relational mapping tool. In hibernate, HQL is used rather than SQL, which saves developers from spending more time on writing native SQL. It has a great association, polymorphism, inheritance, collection, and compositions. This is a great way to persist in the database using Java objects. Hibernate enables you the ability to express queries based on Java criteria.

What is Hashtable?

Hashtable is the same as HashMap, with the exception that Hashtable is synchronized. Hashtable is a synchronized objects cluster in which duplicate values and null values are not permitted.

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) What is a J2EE container?

The interface between the low-level platform and a component with specific features which supports the component is referred to as a container. The application server will maintain control and deliver relevant services through a framework or an interface calls as a container.

J2EE intermediate-level Interview Questions:

) What are structs?

The Struts framework is an MVC architecture that designs large-scale applications. It consists of JSP, Java Servlets, Custom tags, and messages. According to the published standards and the proven design templates, struts help you create a scalable development environment for your application.

) Explain ActionErrors, ActionForm and ActionMapping.

ActionError: ActionErrors is an object that wraps up all the available validation errors. If errors are not found, returns either null or an ActionErrors object with no error message recorded. The default implementation tries to switch to HTTP. Maintaining request parameter mapping and request and return all validation errors if the validation fails; a null or an empty set.

ActionForm: It is a Java bean which brings together one or multiple ActionMappings. A java bean becomes FormBean when extending org.apache.struts.action.ActionForm. The ActionForm object is populated automatically on the server-side with the data entered by the customer from the user interface. ActionForm keeps the session state for the web app.

ActionMapping: When mapping actions, we mention the action class for a specific URL, i.e., the path and various target views, i.e., redirect to which the response to the request will be sent. The ActionMapping is the information which the ActionServlet is aware of regarding mapping a specific request to an instance in a specific Action class. The mapping is passed to the method execute() in the Action class, allowing direct access to that information.

) Explain about MVC on structs?

MVC refers to Model View Controller.

Model: In many applications, the model represents the system's internal state in the form of one or more JavaBeans. 

View: The view is usually built with JavaServer Pages technology. The controller concentrates on receiving customer requests and generating the next stage of the user interface to a suitable View component. 

Controller: The Controller's main component in the framework is an ActionServlet class servlet. The definition of an ActionMappings set sets up this servlet.

) What are the differences between .ear, .jar, and .war files.

.jar files: These files have the .jar extension. The .jar files include accessories files such as property files, libraries, and resources.

.war files: These files have the .war extension. The .war file includes HTML,  javascript, JSP, and other files required for web application development.

.ear files: The .ear file includes the application's EJB modules.

) What is the difference between Save() and Saveorupdate()?

Save(): The purpose of this method in Hibernate is to store an object in the database. It will insert an entry if there is a record, otherwise, it does not.

Saveorupdate():  The purpose of this method in Hibernate is to update the objects with the identifier. If the identifiers are not present, this method will call save(). If the identifier is available, then it will call the update method.

) What is the difference between the load and get method?

load() cannot find the object in the database or cache, an exception is issued, and the load() method will never return null. If the object is not found, the get() method will return null. The load() method can return a proxy in place of a persistent instance, get() does not return a proxy

) What is Spring?

) What is authorization?

Authorization is the process of determining access to a method or resource. It is based on determining the security role of the primary for an authentication request. A security role may be described as a logical grouping of users that is defined by the person assembling the application. A deployer matches the security roles for the security identities. Security identities can be groups or principles in the operational environment.

) What is an authorization constraint?

An authorization rule that determines who is allowed to access the collection of web resources is called an authorization constraint.

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) What is EJB?

EJB refers to Enterprise Java Beans. This is the server-side component that runs in the EJB container and wraps the business logic of the enterprise application.

J2EE Interview Questions for Experienced:

) What is a connector?

The connector is a standard container extension mechanism that delivers connectivity to enterprise information systems. It is unique to an enterprise information system and includes application development tools and a resource adapter for the connectivity of enterprise information systems. The resource adapter is connected to a container by supporting system-level contracts that are defined in the Connector architecture.

) Explain JMS, JTA, and JNDI.

JTA: JTA stands for Java Transaction API. Its purpose is to coordinate and manage transactions across the company's information system.

JNDI: JNDI stands for Java Naming Directory Interface. This is used to access directory services information.

JMS: JMS stands for Java Messaging Service. Its purpose is to receive and send messages using messaging systems.

) What are EDI and EAI?

EDI: EDI stands for Electronic Data Interchange. It is used to exchange data via the value-added network (VAN) that acts as a means of transmission. The installation of EDI is costly and needs customization by exchanging clients. EDI is also based on X12 standards for exchanging documents.

EAI: EAI stands for Enterprise Application Integration. This makes one or multiple applications into one application and needs that data to be transferred to the suitable system at the correct time. For example, during the integration of accounts and sales systems, it is required for sales to send a sales order for accounting for generating an invoice. In addition, accounting has to send a sales invoice to update the data for the sales professionals. This system automatically manages the transaction through the application and removes human mistakes.

) Explain about J2EE tiers.

J2EE includes the following tier:

Client tier: It stands for the browser from which the server gets the requests. In this tier, the interfaces used are the java application, the HTML browser, a non-java application, or an applet.

Middle Tier: This includes an integration tier, a presentation tier, and a business tier. Within the integration tier, the database objects are created. The UI is created at the presentation tier with the help of JSP. The business logic is written at the business tier with the help of EJB.

Backend: It consists of the Enterprise Information System that is used for storing data.

) What is DCOM?

DCOM refers to Distributed Component Object Model. It employs the Object Remote Procedure Call protocol to handle remote objects. The Object Remote Procedure Call is based on Remote Procedure Call and interacts with the runtime services. DCOM supports more than one interface, and components can be built in different programming languages like C, Java, Visual Basics, etc. DCOM is largely used in the Windows platforms.

) What is JRMP?

) What is a Secure Socket Layer?

The technology used for communication between the Web browser and the Web server is referred to as the Secure Socket Layer. Specifically, SSL is a protocol which describes the way algorithms should be used for encryption. The technology creates an encrypted link between the two parties, and this link makes it possible to secure the transmission of sensitive information like credit or debit card information, login credentials, and social security numbers.

) What do you mean by id URL?

URL refers to Uniform Resource Locator. It is the textual reference standard for writing arbitrary information on the World Wide Web. The URL is generally structured as - 

protocol://host/local info

protocol – The protocol allows you to retrieve the object (example: HTTP, FTP)

host – The target host's Internet name.

local info – A String is sent to the protocol handler on the remote host. In most of the cases, this is a filename with an extension.

) What is the JSP directive?

JSP is the process by which metadata information is provided to web containers regarding the JSP file. This metadata is used by the web container during the translation and compilation stages of the JSP lifecycle.

There are three different kinds of JSP directives:

• Include directive
• Page directive
• Taglib directive

) Explain connection pooling?

Connection pooling is an easy concept that is popular for reusing existing connections. This means that if the object connections are well defined and connected already, they may be reused each time there is a need rather than generating a new one.

) What is a J2EE Module?

It is a piece of software that is made up of one/more J2EE components for that similar container type and a deployment descriptor of that type. Into a J2EE application, modules may be assembled or deployed quickly. 

) What is included in the application client module?

An application module includes the class file and a client deployment descriptor. It will be packaged as a JAR file with the extension .jar.

) What is the web module made up of?

The Web module is made up of 

• JSP files(Java Server pages) 
• Graphics Interchange format(GIF) file
• Hypertext Markup Language(HTML) file
• Servlets class files 
• Web deployment descriptor

These files will be packaged as JAR files with the extension .war(Web Archive)

) What is the Enterprise Java Bean module made up of?

The Enterprise Java Bean module is made up of the class files for enterprise beans and the EJB deployment descriptor. These files will be packaged as JAR files with the extension .jar.

) What is the resource adapter module made up of?

The resource adaptor module is made up of Java interfaces, native libraries, classes, resource adaptor deployment description and other documentation. These files will be packaged as JAR files with the extension .rar(resource adapter archive).

) What is meant by an Applet?

It is a component of  J2EE that is commonly executed on the web browser. This  can be executed on a wide range of other devices or applications that accept the applet programming model.

) What do you mean by an applet container?

"Applet container" refers to a container that supports the applet programming model.

) What is meant by a thin Client?

A thin client is a lightweight application interface that will not allow functions like complex business rules execution, database  queries or connection to legacy applications.

) What is meant by deployment descriptor?

The Deployment descriptor is according to Extensible MarkUp Language(XML) that has a .xml extension. It can be used to define the deployment options for a component. J2EE applications and modules have their own deployment descriptors.

) What do you mean by a web container in J2EE?

A web container in J2EE refers to an interface between the low level platform and a component with defined functionality which is intended  to support the functionality.

) What will be the file extension that is used for the Hibernate configuration file and hibernate configuration file?

The file name for the hibernate mapping will be written like filename.hbm.xml.

The file name for the hibernate configuration will be written like filename.hbm.xml.

) How should a Hibernate mapping file in the hibernate configuration file be added?

You can add it quickly using the following code:

) What are the core components of a Multi-tier architecture?

Following are the core components of the Multi tier architecture:

• Presentation Tier: The presentation is displayed using the front-end component included in this tier.
• Resource Layer: The database is accessed through the back-end component included in this tier.
• Business Layer: The business logic of the system is provided by the component included in this tier.

) What do you mean by a backing bean?

Backing bean refers to a Javabeans component that relates to JavaServer Pages and contains JavaServer Faces components. Backing bean outlines the characteristics for the page components as well as methods that process them.

This processing will consist of validation, event handling, processing related to navigation.

) What do you mean by build file?

An XML file with one or more asant targets is referred to as a build file. A target is a list of assignments that a user hopes to complete. A user can specify which target should be executed when asant is started. If no target exists, the  project’s default target is carried out.

) What do you mean by CDATA?

A CDATA is an XML tag that is predefined for character data that denotes "don't interpret these characters." It is comparable to parsed character data (PCDATA), in which the usual XML syntax is followed. CDATA sections will be used to display XML syntax examples.

) What is the difference between JDK and JIT?

A cross-platform software development environment called JDK (Java Development Kit) provides diverse collections of libraries and tools needed to develop applets and  Java programmes. It even comprises JRE, which offers tools and libraries that accept the bytecode execution. JDK is required for creating and executing Java programmes. In contrast, JIT stands for Just In Time Compiler, a module that exists inside the JVM (i.e., inside JRE). In order to reduce the time for compilation, and improving speed, JIT compilers are used to compile some of the portions of bytecode that carry out similarly to machine code at the same time.

) What are the primary interfaces of the Hibernate framework?

• Sessionfactory interface
• Transaction interface
• Session Interface
• Query and Criteria Interface
• Configuration interface

) How do PATH and CLASSPATH differ from each other in relation to J2EE?

• The two most important environmental variables utilised by Java platforms are PATH and CLASSPATH.
• PATH refers to the JDK binaries or native libraries such as java.exe. while, the CLASSPATH variable refers to the Java binaries, like JAR files that include bytecode.
• Regardless of whether Java is installed on the system or not, PATH is a system-level variable. Where as JVM uses CLASSPATH, which is entirely Java-specific, to load the classes needed by running Java programmes.

) What are the phases of servlet life cycle?

Following are the phases of Servlet lifecycle:

• Classloading phase: Servlet’s class file (*.class) will be loaded by web container.
• Instantiation phase: The servlet gets instantiated by calling the default no-arg constructor.
• Initialize phase: init() method will be called only once in the servlet lifetime. Servlet configuration will be assigned to the servlet.  
• Request Handling phase: The servlet spends most of its time in this phase. Services to various requests will be provided by calling service().
• Removal phase: before the Servlet destruction, the destroy() function will be called.  The garbage collection will be carried out later.

Conclusion:

All the above are some of the frequently asked J2EE interview questions gathered by our J2EE Experts. We hope you found these questions helpful. Learning these questions will help you in clearing your interview. If you are searching for any other questions related to J2EE, feel free to comment. We would revert with the answer.