Top Spring Interview Questions That You Should Know Before Your Next Interview

Section I: Spring Interview Questions and Answers for Freshers

Let’s begin by looking at some of the most frequently-asked spring interview questions for freshers. If you’re a beginner, knowing the answer to these questions will help you face your interview more confidently. For experienced candidate, these will serve to brush-up your basics, but we’ll deal with more advanced questions that you’re more likely to get asked in the next section. So stay tuned. 

1. What is Spring?

Open-source and lightweight, Spring is one of the world’s most widely-employed application development frameworks for Java EE (Enterprise Edition). Although the Spring Framework's core features can be applied to develop any Java-based app, its extensions are commonly used for developing web applications. Spring facilitates easily testable, high-performing, reusable code.

2. What are the advantages of using the Spring Framework?

The key advantages of using Spring are: 

• Lightweight and Powerful − Spring is a lightweight and powerful framework that streamlines the common issues in enterprise Java. Spring Framework’s basic version is only 2MB.
• IOC (Inversion of Control) − Developers can easily achieve loose-coupling in Spring by using the Inversion of Control (IoC) technique. The objects provide their dependencies, rather than looking for, or creating dependent objects.
• AOP (Aspect-Oriented Programming) − The Spring Framework supports AOP (Aspect-Oriented Programming), and it separates system services from business logic, enabling cohesive development. 
• MVC (Model-View-Controller) − Spring’s MVC architecture provides a Model-View-Controller pattern, along with ready components, which developers can use to build loosely-coupled and flexible web applications. The Model-View-Controller architecture splits the critical aspects of an application, such as the UI logic, input logic, and business logic, while allowing loose-coupling among these elements.
• Transaction Management − The Spring Framework provides excellent support for transaction implementations, which can scale up or down to JTA-based distributed global transactions, or local transactions via a single database. 
• Exception Handling − The Spring Framework offers a handy API for translating technology-oriented exceptions into unchecked, consistent exceptions.

3. What is a configuration file in Spring?

A configuration file in the Spring Framework is an Extensible Markup Language (XML) data file. XML files contain the information of ‘classes’, and it describes how classes can be introduced and configured with each other.

4. What is (DI) Dependency Injection?

Dependency Injection (DI) is an architectural pattern via which IoC (Inversion of Control) is implemented.  DI is a technique in software programming that makes the classes independent of their dependencies. Dependency Injection achieves this by decoupling object usage from its development. The process of injecting objects or connecting objects is performed by the IoC container instead of the objects themselves.

5. What are beans in Spring?

Beans are the backbone, or the core objects, of an application, that are assembled, instantiated, and controlled by IoC container in the Spring Framework. Beans are built using configuration metadata supplied to the IoC container,  which is typically in the ‘XML <bean/> definitions’ format.

6. How to apply the configuration metadata in Spring Container?

There are three important techniques to apply the configuration metadata in the Spring Container, which include: 

• Java-based configurations
• Annotation-based configurations
• XML-based configurations 

Section II: Spring Interview Questions and Answers for Experienced Developers

If you’re someone who has a bit of experience in the sphere of web development, this section is exclusively for you. Here’s a list of some of the most frequently-asked spring interview questions for experienced developers.

7. Can you list the various modules within the Spring framework?

The Spring framework incorporates the following modules:

• Web-Portlet 
• Web-Struts 
• Web-Servlet
• Web module
• Transaction module
• JMS (Java Messaging Service) 
• OXM module
• ORM module
• JDBC module
• Expression Language 
• Context module
• Bean module
• Core module

8. What are some major advantages of Spring IOC?

The significant benefits of Spring IOC are:

• Spring IOC reduces the code density in applications.
• It offers users an easy way to test their applications, as Spring IOC does not need any JNDI or singleton lookups in test cases.
• Loose-coupling can be promoted with the least intrusive mechanisms and minimum effort. 
• Spring IOC container supports Lazy Loading and Eager Instantiation.

9. What are IoC Containers in Spring?

IoC (Inversion of Control) Containers are at the core of the Spring framework.  IoC Containers play the vital role of creating objects, wiring them together, configuring them, and managing their entire lifecycle from formation till destruction. Also known as a DI (Dependency Injection) Container, it furthermore, injects dependencies into the class.

10. What are the different types of Spring IoC containers? 

Spring IoC containers are classified into: 

• BeanFactory Container − The BeanFactory Container provides critical support for Dependency Injection (DI). it is a preferred option where resources are constrained, such as an applet-based application or mobile devices. 
• ApplicationContext Container − The ApplicationContext Container brings enterprise-specific functionalities, for instance, adding capabilities for resolving text-based messages from the properties file or publishing application events.

11. Can you give a BeanFactory implementation example?

A commonly used implementation of BeanFactory is the Class XmlBeanFactory. It reads configuration metadata and utilizes it to produce a totally-configured application or system. 

12. Tell us about the common ApplicationContext implementations.

The three most common ApplicationContext implementations are: 

• FileSystemXmlApplicationContext − The FileSystemXmlApplicationContext container loads beans definitions from XML files. Here, developers will have to specify the entire path of  XML configuration files to the Spring Constructor.
• ClassPathXmlApplicationContext − The ClassPathXmlApplicationContext container also loads beans definitions from XML files, but here, developers do not have to specify the entire path of XML configuration files. Instead, they will have to set the CLASSPATH correctly.
• WebXmlApplicationContext − The WebXmlApplicationContext container loads XML files with all beans definitions from within web applications.

Hopefully, the above spring interview questions and answers will help you prepare for the next Spring interviews that you will be attending.

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