Top 50 Spring Interview Questions and Answers

Spring is a lightweight open-source framework for developing applications using the Java programming language. Also, we can say that Spring is a framework of frameworks since it supports various other frameworks, such as Hibernate, Struts, JSF, etc. Spring is known for its Inversion of Control (IoC) container. This container enables developers to manage and configure Java objects using reflective programming.

Millions of developers across the globe use the Spring framework to develop high-performing and easily testable applications using plain old Java objects (POJOs). The Spring framework lets us use its core features for building any Java application. Moreover, it provides extensions for developing web applications on top of the Java Enterprise Edition (Java EE) platform.

Over the years, the Spring framework has become an increasingly popular choice among Java developers. Since the use of this Spring has increased, the number of job opportunities as a Spring developer has also increased.

If you aim to appear for a Spring developer job interview and look for a quick preparation guide, you are at the right place. This article will familiarize you with some commonly asked Spring interview questions along with their detailed answers.

So, let us get started!

Top Spring Interview Questions and Answers

Here are the top 50 Spring interview questions and answers that can help you prepare better for your next interview. We have categorized Spring interview questions into three different levels, namely beginner, intermediate, and advanced.

Let us start with the beginner-level questions.

Spring Basic Interview Questions

1. What is the Spring framework?

Spring framework is an open-source application framework and inversion of control container for the Java platform. It provides a programming and configuration model for developing state-of-art enterprise Java applications. This framework follows aspect-oriented programming (AOP), Dependency Injection (DI), and POJO to simplify the cumbersome process of developing high-performing enterprise applications.

It can also be thought of as a framework of frameworks since it supports various other frameworks. Besides Java, the Spring framework also supports Kotlin and Groovy programming languages.

2. Can you state the features of the Spring framework?

The following are the salient features of the Spring framework:

• Lightweight: Spring is a lightweight framework due to its small size and it offers enhanced functionality due to its POJO implementation. Also, the POJO implementation does not force the Spring framework to inherit any class or implement any interface.
• Aspect-Oriented Programming (AOP): AOP provides modularity to cross-cutting concerns, such as transaction management, authentication, logging, caching, etc. In other words, AOP enables the separation of cross-cutting concerns from the business logic of an application.
• Transaction Management: It unifies multiple transaction management APIs and coordinates transactions for Java objects. It is generally used in container fewer environments.
• Container: The Spring container develops and manages application objects’ lifecycle and configurations.
• Dependency Injection: This feature of Spring allows developers to create loosely coupled applications, which, in turn, simplifies the process of creating unit tests for these applications. In addition, developers can remove and add components to an application with ease.
• MVC Framework: The Spring MVC framework enables developers to create applications using the model-view-controller (MVC) architectural pattern.
• Data Access and Integration: Spring includes modules that help developers handle transaction processing and data access in an application. These modules include spring-jdbc, spring-orm, spring-oxm, spring-jsx, and spring-tx.

3. List out some advantages of the Spring framework.

The following are the advantages offered by the Spring framework:

• The Spring framework enables us to develop enterprise-level Java applications using POJO.
• Spring is organized in a modular fashion, which involves various modules. We have the choice of using those modules that we want while leaving others.
• Since Spring supports various testing frameworks, like TestNG and JUnit, testing becomes easier and effortless.
• We can use many other frameworks, like Strut, Hibernate, etc., with Spring.

4. What are the different modules of the Spring framework?

There are 20 modules in the Spring framework that are grouped into different layers, such as Core Container, AOP, Data Access/Integration, Web, Test, and Instrumentation.

• Spring Core Container: It is the core of the Spring framework and includes modules, namely Spring Core, Spring Bean, SpEL (Spring Expression Language), and Spring Context.
• Data Access/Integration: It includes modules that support the interaction with databases. The modules in this category include:
  • JDBC (Java DataBase Connectivity)
  • ORM (Object Relational Mapping)
  • OXM (Object XML Mappers)
  • JMS (Java Messaging Service)
  • Transaction
• Web: It supports the creation of web applications and includes modules, namely Web, Web – MVC, Web – Socket, and Web – Portlet.
• Aspect-Oriented Programming (AOP): It enables the implementation of crosscutting concerns. In general, cross-cutting concerns in AOP are the aspects of an application that affect other concerns.
• Instrumentation: It enables class instrumentation and classloader implementations.
• Test: It supports testing applications with JUnit and TestNG.
• Aspects: It supports the integration with AspectJ.
• Messaging: It supports STOMP and an annotation programming model. An annotation programming model is used for processing and routing STOMP messages from WebSocket clients.

5. What do you understand about Spring IoC Containers?

IoC stands for Inversion of Control. The Spring IoC Container creates objects, assembles their dependencies, configures them, and manages their entire life cycles. It uses Dependency Injection (DI) to manage various components that form an application.

The Spring container receives information about objects either from Java code, a configuration file, or Java Annotations and Java POJO class. We refer to these objects as Spring Beans. We can call the Spring containers the Inversion of Control (IoC) containers because developers do not control Java objects.

6. Enlist the components of the Spring application.

The following are the components of the Spring application:

• Interface: This component defines the functions of a Spring application.
• Bean Class: This class contains properties, setter and getter methods, and functions.
• Spring Aspect Oriented Programming: It offers the functionality to implement cross-cutting concerns.
• Bean Configuration File: This file stores information about classes and the approach to configure those classes.
• User program: It uses the functions defined by the Interface.

7. Can you explain Dependency Injection in Spring?

Spring IoC provides one of the major functions called Dependency Injection (DI). Dependency Injection (DI) enables the Spring container to inject objects into other objects or dependencies.

DI allows us to define how to create objects instead of allowing us to create them directly. The application code does not directly contain connecting services and components, which ensures loose coupling. However, the configuration file stores information about various components and the services that they require. Later, the IoC container connects the components with their appropriate services.

8. What do you understand about the Spring Configuration file?

The Spring configuration file is an XML file that stores information about classes and interfaces along with their dependencies. It describes how these classes are configured and introduced to each other. The Spring configuration file has the .xml extension. Also, the Spring configuration file helps a Spring container to achieve Dependency Injection (DI) and control the life cycle of Spring Beans.

9. What are the types of dependency injection in Spring?

There are two types of Dependency Injection in Spring, namely Constructor-based, and Setter.

• Constructor-based Dependency Injection (CDI): In CDI, Spring will inject the dependency using constructors.
• Setter Dependency Injection (SDI): In SDI, Spring will inject the dependency using setter or getter methods.

10. Can you differentiate between constructor-based injection and setter injection?

The following table differentiates between constructor-based injection and setter injection:

11. Can you list out the types of IoC containers in Spring?

BeanFactory and ApplicationContext interfaces act as Spring IoC containers.

• BeanFactory: As its name suggests, BeanFactory is a factory class that contains a collection of Beans. This class instantiates the Bean as required by a client.

• ApplicationContext: This type of IoC container is built on top of the BeanFactory interface. It provides additional functionalities than BeanFactory, such as message resource handling, the application-layer-specific context for web applications, and integration with Spring’s AOP.

12. How do you use the BeanFactory interface?

The implementation class for the BeanFactory interface is XMLBeanFactory. We need to create an instance of the XMLBeanFactory class to use the BeanFactory interface.

The following lines of code create the instance of the XMLBeanFactory class:

Resource resource = new ClassPathResource("applicationContext.xml"); BeanFactory factory = new XmlBeanFactory(resource);

13. How do you use the ApplicationContext interface?

The implementation class for the ApplicationContext interface is ClassPathXmlApplicationContext .

We need to create an instance of the ClassPathXmlApplicationContext class to use the ApplicationContext interface.

Following is the code for creating the instance of the ClassPathXmlApplicationContext class:

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

14. Can you differentiate between BeanFactory and ApplicationContext?

The below table describes the key difference between BeanFactory and ApplicationContext:

15. State the benefits of Inversion of Control (IoC).

Some significant benefits of Inversion of Control (IoC) are:

• IoC minimizes the amount of code in an application. We do not have to care about how services are created or how we get references to the desired services.
• It makes our application more testable since there is no need for singletons or JNDI lookup mechanisms in unit test cases.
• IoC promotes loose coupling with the least intrusive mechanism and minimal effort.
• It supports Eager instantiation and Lazy loading of services.

16. List out some common implementations of the ApplicationContext interface.

There are three common implementations of the ApplicationContext interface, as described below:

• FileSystemXmlApplicationContext: With this container, we can load XML-based Spring configuration files from the file system or a URL. We can use the Java code to get the application context. The possible use cases for this container are standalone environments and test harnesses.
• ClassPathXmlApplicationContext: With this container, we can load XML configuration from the classpath. It is also used for test harnesses.
• WebXmlApplicationContext: With this container, we can use the XML-based configuration in web applications.

Intermediate-Level Spring Interview Questions

17. What do you understand about Spring Beans?

Spring beans are the objects that are the backbone of an application, and they are managed by the Spring IoC container. The Spring IoC container is responsible for instantiating, configuring, wiring, and managing beans. They are created using the configuration metadata that is provided by the users to the container.

18. List out the set of properties that make up a bean definition.

The following are the properties that make up a bean definition:

• class: It specifies the bean class required to create a bean. It is a mandatory attribute.
• name: It defines the bean identifier uniquely. We use the Id or/and name to specify the bean identifier in the XML-based configuration metadata.
• scope: This attribute defines the scope of objects created from a specific bean definition.
• constructor-arg: It injects the dependencies.
• properties: This attribute is also used to inject dependencies.
• Autowiring mode: It is also used to inject dependencies.
• lazy-initialization method: This attribute tells the IoC container to create a bean instance when it is requested, instead of creating it at the beginning.
• initialization method: It calls a callback on the bean just after the IoC container sets all the necessary properties on it.
• destruction method: This attribute calls a callback when the container containing the bean is destroyed.

19. How will you provide configuration metadata to Spring?

There are three ways to provide configuration metadata to Spring, as described below:

• XML-based configuration: The configuration files specify the dependencies and services required by a bean, which are in the XML format. They contain multiple bean definitions and application-specific configuration options.
• Annotation-based configuration: We can configure the bean into the component class by using annotations on the relevant class, method, or field declaration rather than using XML to describe bean wiring. We need to enable annotation wiring in the Spring configuration file before using it since it is turned off by default.
• Java-based configuration: Java-based configuration support includes two key features, namely @Configuration annotated classes and @Bean annotated methods. The @Bean annotation works analogously to the <bean/> element. The @Configuration classes allow us to specify inter-bean dependencies by calling other @bean methods in the same class.

20. How many bean scopes does the Spring framework support?

The Spring framework supports the following five bean scopes:

• Singleton: It scopes a single bean definition to a single object instance per Spring IoC Container.

• • Prototype: It scopes a single bean definition to any number of object instances.
  • Request: It scopes a single bean definition to the lifecycle of a single HTTP request. It is valid only in the context of a web-aware Spring ApplicationContext.

• Session: It scopes a single bean definition to the lifecycle of a single HTTP session. It is valid only in the context of a web-aware Spring ApplicationContext.

• Global-session: It scopes a single bean definition to the lifecycle of a single global HTTP session. It is valid only in the context of a web-aware Spring ApplicationContext.

21. What does bean definition contain?

The configuration metadata contains the information about Spring definition, which requires the container to know the following things:

• How to create a bean?
• The details of a bean’s lifecycle.
• Dependencies of a bean.

22. What is the default scope of bean in the Spring framework?

The default scope of bean in the Spring framework is Singleton.

23. Can you explain bean wiring?

Bean wiring or wiring is the process of combining beans with the Spring container. It is essential to tell the container what beans are required and how it should use dependency injection to wire or tie them together.

24. Explain the bean life cycle in the Spring Bean Factory Container.

The life cycle of a bean in the Spring Bean Factory Container is as follows:

• Firstly, the Spring container instantiates the bean in the XML file from the bean’s definition.
• Using the dependency injection, Spring populates all the properties of the bean, as specified in the bean definition.
• If the bean implements the BeanNameAware interface, the factory calls the setBeanName() method and passes the bean’s id to it.
• If the bean implements the BeanFactoryAware interface, the factory class calls the setBeanName() method and passes the instance of itself.
• The preProcessBeforeInitialization() methods are called if there are any BeanPostProcessors associated with the bean.
• The init-method is called if it is specified for the bean.
• Finally, the postProcessAfterInitialization() methods are called if there are any BeanPostProcessors associated with the bean.

25. Explain bean Autowiring.

Bean autowiring implies that the Spring container can autowire the relationships between collaborating beans. In other words, bean autowiring signifies that it is possible to let Spring automatically resolve collaborators or other beans for a particular bean by inspecting the contents of the BeanFactory without using the <constructor-arg> and <property> elements.

26. Explain different modes of autowiring.

To use autowiring for dependency injection, there are five different modes to instruct the Spring container, as described below:

• no: It is a default mode and indicates no autowiring. In this mode, we should use an explicit bean reference for wiring.
• byName: This mode injects the object dependency according to the name of a bean. The Spring container looks in the XML configuration file for the properties of the beans having the autowire attribute set to byName. It then matches and wires its properties with the bean defined by the same name in the XML configuration file.
• byType: This mode injects object dependency according to type. The Spring container looks in the XML configuration file for the properties of the beans having the autowire attribute set to byType. It then matches and wires a property of its type that matches with exactly one of the beans’ names in the XML configuration file. It throws a fatal exception if it matches with more than one beans’ name.
• constructor: It injects the object dependency by calling the class’s constructor.
• autodetect: The Spring container first tries to autowire by using the constructor mode. If it does not work, it tries autowiring using the byType mode.

27. How can you inject Java Collection in Spring?

The following are the four types of collection configuration elements to inject Java Collection in Spring:

• list: This collection helps in wiring, i.e., injecting a list of values, and allows duplicates.
• set: This collection helps in wiring a set of values without any duplicates.
• map: This collection helps in wiring a collection of name-value pairs, where name and value can be of any type.
• props: This collection helps in wiring a collection of name-value pairs, where name and value both are Strings.

All these configuration elements are enclosed in '< >.'

28. Can you explain the limitations of autowiring?

The following are the limitations of autowiring:

• Overriding possibility: We can specify dependencies using <constructor-arg> and <property> settings that can override autowiring.
• Primitive data types: We cannot autowire simple properties, such as primitives, Strings, and Classes.
• Confusing nature: It is good practice to adopt explicit wiring instead of autowiring because autowiring is less precise.

29. What do you understand about Spring Boot?

Spring Boot is an open-source Java-based framework that lets us develop standalone and enterprise-grade Spring-based applications that we can ‘just run’ with the need for a very few Spring configurations. It is built on top of the Spring framework and provides it with the Rapid Application Development (RAD) feature. In short, we can state that Spring Boot is the combination of Spring Framework and Embedded servers.

30. List out the features of Spring Boot.

The following are the salient features of Spring Boot:

• Web Development: Spring Boot is an ideal framework for developing web applications. We can use Tomcat, Jetty, or Undertow to create a self-contained HTTP server.
• SpringApplication: It is a class that provides a convenient way to bootstrap a Spring application. We can start this application from the main method by calling the static run() method.
• Application Events and Listeners: Spring Boot handles a wide variety of tasks using events. Also, we can create factory files to add listeners and refer to them by using the ApplicationListener key.
• Admin Support: We can enable admin-related features for a Spring boot application using spring.application.admin.Enabled property. It enables us to access and manage an application remotely.
• Externalized Configuration: We can externalize our configuration to work with the same application in different environments.
• Properties Files: It consists of a rich set of application properties.
• YAML Support: With YAML support, we can specify the hierarchical configuration. The SpringApplication class automatically supports YAML.
• Type-safe Configuration: Spring Boot provides a strong type-safe configuration to manage and validate the configuration of an application.
• Logging and Security: Spring Boot manages logging dependencies by default. It uses common logging for all internal logging. Applications developed using Spring Boot are secure by default with basic authentication on all HTTP endpoints.

31. State the advantages of using Spring Boot for application development.

The following are the advantages of using Spring Boot for application development:

• We can create standalone applications using Spring Boot and start using java.jar since it does not require configuring WAR files.
• It provides pinpointed ‘started’ POMs to Maven configuration.
• Spring Boot ensures fast and easy development of Spring-based applications.
• Applications developed using Spring Boot do not require XML configuration.
• Spring Boot provides an auto-configuration feature, i.e., it automatically configures an application based on the dependencies present in the classpath.

32. State the differences between Spring and Spring Boot.

The below table highlights the key differences between Spring and Spring Boot:

33. What does @SpringBootApplication annotation do?

The @SpringBootApplication annotation eliminates the need for using the three annotations, namely @Configuration, @EnableAutoConfiguration, and @ComponentScan. We can simply use a single @SpringBootApplication annotation to enable the following three features:

• @EnableAutoConfiguration: It enables Spring Boot’s auto-configuration feature.
• @ComponentScan: It enables @Component scan on the package where an application is located.
• @Configuration: It enables us to use extra beans in the context or import additional configuration classes.

34. What do you know about Spring Boot Dependency Management?

Spring Boot Dependency Management implies automatic management of configurations and dependencies. Every release of Spring Boot provides a list of supported dependencies. This list of dependencies is available as part of Bills of Materials, and we use it with Maven. We do not have to specify the version of dependencies in our configuration since Spring Boot manages itself. When we update the Spring Boot version, Spring Boot automatically updates all dependencies consistently.

35. Can you enlist the possible sources of external configuration?

The external configuration feature of Spring Boot enables us to run the same application in different environments. The following are the three different sources of external configurations:

• Command-line Properties: Spring Boot takes command-line arguments, converts them into properties, and adds them to the set of environment properties.
• Application Properties: Spring Boot searches for its YAML file or application properties file in an application’s current directory, classpath root, or config directory to load the properties.
• Profile-specific Properties: Spring Boot loads properties from the application-{profile}.properties file or its YAML file.

Spring Advanced Interview Questions

36. How can you disable a specific auto-configuration class?

We can disable a specific auto-configuration class by using the exclude attribute of @EnableAutoConfiguration. The example for disabling a specific auto-configuration class is given below:

@EnableAutoConfiguration(exclude = {TechGeekBuzzAutoConfiguration.class})

If the class is not specified in the classpath, we can specify the fully qualified name using the excludeName attribute of the @EnableAutoConfiguration annotation.

37. What do you understand about Annotation-based container configuration?

We can configure the dependency injection using annotations starting from Spring 2.5. Therefore, instead of using XML to describe a bean wiring, we can move the bean configuration into the component class by annotating the relevant class, method, or field declaration. Annotation wiring is turned off by default in the Spring container. We need to enable annotation wiring in the Spring configuration file by enabling the <context:annotation-config/> element to use annotation-based wiring.

38. What do you understand about the Spring MVC framework?

Spring MVC is a Java-based framework that follows the model-view-controller architectural pattern. It provides ready-to-use components to develop loosely coupled and flexible web applications. The MVC pattern separates the different aspects of an application, such as input logic, business logic, and UI logic.

The Spring MVC framework allows the use of the MVC architecture with the help of the DispatcherServlet. DispatcherSevrlet is a class that receives requests and maps them to appropriate resources, such as controllers, models, and views. A model contains the data of an application, a controller controls the business logic of an application, and a view provides the visual representation of the data stored in the model.

39. List out the advantages of the Spring MVC framework.

The advantages of the Spring MVC framework are:

• Lightweight: The Spring MVC framework uses a lightweight servlet container to develop and deploy web applications. Also, it supports POJO applications, which makes the Spring MVC framework more lightweight.
• Rapid Development: This framework facilitates faster and parallel application development.
• Flexible Mapping: It provides specific annotations that easily redirect the page.
• Adaptable Controllers: The Spring MVC framework enables us to use any one of the parameter annotations, such as @RequestParam, @RequestHeader, and @PathVariable, to define the required number of the controller method signature.
• Separate Roles: Every component of the Spring MVC framework has its role or functionality.

40. What do you know about DispatcherServlet?

DispatcherServlet is responsible for handling all HTTP requests and responses, and it is the core of the Spring MVC framework. Besides handling HTTP requests and responses, it also:

• Seamlessly integrates with the IoC container and enables us to use every feature of the Spring framework.
• Receives the entry of handler mapping from the configuration and forwards the request to the controller. Later, the controller responds with the object of the Model and View. The DispatchServlet then checks the configuration file for the entry of the view resolver and calls the specified view component.

41. What is WebApplicationContext?

The WebApplicationContext is an extension of the plain ApplicationContext. It is used in web applications and provides features to deal with web components, such as view resolvers, controllers, etc. Each ServletDispatcher is associated with one WebApplication Context and a single web application can have multiple WebApplicationContext to handle requests.

42. Can you explain DAO support in Spring?

DAO stands for Data Access Object. The DAO support in Spring allows us to work with database technologies like Hibernate, JDO, JPA, or JDBC quickly and consistently. Also, it enables us to switch between the aforementioned technologies easily and effortlessly. We can even code without worrying too much about catching exceptions specific to each technology.

43. Enlist the classes present in the JDBC API.

The following is the list of classes present in the JDB API:

• JdbcTemplate
• SimpleJdbcTemplate
• NamedParameterJdbcTemplate
• SimpleJdbcInsert
• SimpleJdbcCall

44. How can we access Hibernate using Spring?

We can access Hibernate using Spring using the following two methods:

• Inversion of Control (IoC) with a Hibernate Template and a callback.
• Extending HibernateDAOSupport and applying an AOP Interceptor node.

45. What do you understand about Aspect in AOP?

An Aspect in aspect-oriented programming is a class that implements enterprise application concerns, which cross-cuts multiple classes. One of the best examples of cross-cutting concerns in J2EE applications is Transaction Management. There are two ways to implement aspects in the Spring framework.

• We can use a normal class configured through Spring XML configuration.
• We can Spring AspectJ integration to define a class as Aspect using the @Aspect annotation.

46. Explain Joinpoint.

A joinpoint is a specific point during the execution of a program , such as the handling of an exception, execution of methods, or changing object variable values. In AOP, a joinpoint is always the execution of a method.

47. What is Advice? Explain the types of advices in Spring AOP.

An action taken by Aspect for a specific joinpoint is called Advice. The following are the different types of advices in Spring AOP:

• Before: We can configure this type of Advice using the @Before annotation mark. They execute before a joinpoint method executes.
• After returning: We can configure this type of Advice using the @AfterReturning annotation mark. They execute after a joinpoint method executes.
• After throwing: We can configure this type of Advice using the @AfterThrowing annotation mark. They execute only if a joinpoint method exits by throwing an exception.
• After (finally): We can configure this type of Advice using the @After annotation mark. They execute after a joinpoint method, irrespective of the method’s normal exit or exceptional return.
• Around: We can configure this type of Advice using the @Around annotation mark. They execute after and before a joinpoint method executes.

48. List out different implementations of AOP.

There are three different implementations of AOP, as listed below:

• Spring AOP
• Apache AspectJ
• JBoss AOP

49. Explain the terms Proxy and Weaving in Spring.

Proxy: When we create an object after applying advice to a target object, it is referred to as Proxy. The target object and the proxy object in the case of client objects are the same.

Weaving: It is the process of linking an aspect with other application types or objects to create an advised object.

50. Differentiate between Spring AOP and AspectJ AOP.

The following table describes the significant differences between Spring AOP and AspectJ AOP:

Conclusion

So that was all about the top Spring interview questions and answers. Spring is a lightweight Java framework used widely for creating feature-rich Java-based applications. It offers a rich set of features, including aspect-oriented programming, MVC framework, dependency injection, container, and transaction management.

Applications developed using the Spring framework are highly scalable and fast. Therefore, the Spring framework is the first choice of developers for building enterprise-grade applications. Today, this framework has become an essential skill for any Java developer role.

If you are appearing for any Java developer job interview, this article is a perfect guide to brush up on your knowledge of the Spring framework.

This article covers the most commonly asked Spring interview questions along with their detailed answers. Going through these Spring interview questions will help you ace your next interview.

All the best!

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