Spring Interview Questions Part: 1

• What is mean by Dependency Injection? Or What do you mean by Inversion of Control?

Dependency injection (DI) is a programming design pattern and architectural model, sometimes also referred to as inversion of control or IOC, although technically speaking, dependency injection specifically refers to an implementation of a particular form of IOC.

Dependancy Injection describes the situation where one object uses a second object to provide a particular capacity. For example, being passed a database connection as an argument to the constructor instead of creating one internally. The term "Dependency injection" is a misnomer, since it is not a dependency that is injected, rather it is a provider of some capability or resource that is injected. There are three common forms of dependency injection: setter-, constructor- and interface-based injection.

Dependency injection is a way to achieve loose coupling. Inversion of control (IOC) relates to the way in which an object obtains references to its dependencies. This is often done by a lookup method. The advantage of inversion of control is that it decouples objects from specific lookup mechanisms and implementations of the objects it depends on. As a result, more flexibility is obtained for production applications as well as for testing.

• What are the modules in Spring?

1. The core container:
   The core container provides the fundamental functionality of the Spring framework. In this module primary component is the BeanFactory, an implementation of the Factory pattern. The BeanFactoryapplies the Inversion of Control (IOC) pattern to separate an application's configuration and dependency specification from the actual application code.
2. Spring context module :
   TThe Spring context is a configuration file that provides context information to the Spring framework. The Spring context includes enterprise services such as e-mail, JNDI, EJB, internalization, validation, scheduling and applications lifecycle events. Also included is support for the integration with templating frameworks such as velocity.
3. Spring AOP module:
   The Spring AOP module allows a software component to be decorated with additional behavior, through its configuration management feature. As a result you can easily AOP-enable any object managed by the Spring framework. The Spring AOP module provides transaction management services for objects in any Spring-based application. With Spring AOP you can incorporate declarative transaction management into your applications without relying on EJB components.
4. Spring DAO module:
   The Spring DAO module provides a JDBC-abstraction layer that reduces the need to do tedious JDBC coding and parsing of database-vendor specific error codes. Also, the JDBC package provides a way to do programmatic as well as declarative transaction management, not only for classes implementing special interfaces, but for all your POJOs (plain old Java objects).
5. Spring ORM module:
   : Spring provides integration with OR mapping tools like Hibernate, JDO and iBATIS. Spring transaction management supports each of these ORM frameworks as well as JDBC.
6. Spring Web module:
   The Web context module provides basic web-oriented integration features builds on top of the application context module, providing contexts for Web-based applications. As a result, the Spring framework supports integration with Jakarta Struts. The Web module also eases the tasks of handling multi-part requests and binding request parameters to domain objects.
7. Spring MVC framework module:
   Spring provides a pluggable MVC architecture. The users have a choice to use the web framework or continue to use their existing web framework. Spring separates the roles of the controller; the model object, the dispatcher and the handler object which makes it easier to customize them. Spring web framework is view agnostic and does not push the user to use only JSPs for the view. The user has the flexibility to use JSPs, XSLT, velocity templates etc to provide the view.

• What is a BeanFactory and XMLBeanFactory?

Bean factory is a container. It configures, instantiates and manages a set of beans. These beans are collaborated with one another and have dependencies among themselves. The reflection of these dependencies are used in configuring data that is used by BeanFactory.

XMLBeanFactory is a bean factory that is loaded its beans from an XML file.

• What are Inner Beans?

A bean inside another bean is known as Inner Bean. They are created and used on the fly, and can not be used outside the enclosing beans. The Id and scope attributes for inner beans are of no use.

• What is DataAccessException?

DataAccessException is an unchecked RuntimeException. These type of exceptions are unforced by users to handle. This exception is used to handle the errors occurring when the details of the database access API in use, such as JDBC.

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