Spring Interview Questions & Answers

In this blog, we shall discuss some important,Spring interview questions
Spring MVC interview questions & answers, Dependency injection and Spring framework

We shall reflect upon important questions & answers you need to know to kick start your career in the best possible way in the field of Java. So let’s get reading!

Spring Interview Questions and Answers

What are the major features in different versions of Spring Framework?

The Spring Framework has evolved over the years, and each major version brought new features and improvements. Here's an overview of the major features in different versions:

Spring 1.x: The initial versions focused on lightweight container and configuration management.

Spring 2.x: Introduced AOP (Aspect-Oriented Programming), enhanced support for data access, and introduced the Spring MVC framework.

Spring 3.x: Enhanced support for annotation-based configuration, introduced Spring Expression Language (SpEL), and introduced features like REST support and Spring Security.

Spring 4.x: Improved Java 8 support, introduced WebSocket support, and enhanced the Spring Boot project for microservices.

Spring 5.x: Focused on Java 9+ compatibility, introduced the reactive programming model with Spring WebFlux, and added support for Kotlin.

What is a Spring Framework?

The Spring Framework is an open-source application framework for building enterprise-level Java applications.

It provides comprehensive infrastructure support for developing Java applications, addressing various concerns such as dependency injection, transaction management, aspect-oriented programming, and more.

Spring simplifies the development process, promotes best practices, and helps create loosely coupled, highly maintainable, and testable applications.

List the advantages of Spring Framework

Spring offers several advantages for application development:

Dependency Injection: Spring promotes Inversion of Control (IoC) through Dependency Injection, making code more modular and testable.

AOP Support: Spring provides powerful support for Aspect-Oriented Programming, allowing the separation of cross-cutting concerns.

Modular Architecture: It is modular and provides a range of features that can be used individually or in combination.

Declarative Transaction Management: Spring simplifies transaction management through declarative annotations or XML configuration.

Integration with Other Technologies: It seamlessly integrates with various technologies like Hibernate, JPA, REST, and more.

Simplified Unit Testing: Spring's IoC and DI principles make it easy to write unit tests.

Security: Spring Security provides robust security features for authentication and authorization.

Simplified Exception Handling: It simplifies exception handling through a centralized approach.

Support for Reactive Programming: Spring 5 introduced support for reactive programming using Spring WebFlux.

What are the different features of Spring Framework?

The Spring Framework encompasses a wide range of features, including:

Dependency Injection: Inversion of Control (IoC) through DI, making code modular and loosely coupled.

Aspect-Oriented Programming (AOP): Allows for the modularization of cross-cutting concerns.

Spring MVC: A web module for building web applications.

Data Access/Integration: Simplifies database access and integrates with various data sources.

Security: Provides security features for authentication and authorization.

Transaction Management: Declarative transaction management and programmatic support.

Spring Boot: A project that simplifies application setup and development.

Spring Cloud: For building cloud-native applications.

Messaging: Integration with messaging systems like JMS.

Spring Data: Simplifies data access with support for various data stores.

Spring Batch: Supports batch processing and large-scale data processing.

Spring WebFlux: Reactive programming support for building asynchronous, non-blocking applications.

Spring Security: Comprehensive security features for applications.

Spring Web Services: Simplifies the development of web services.

How many modules are there in Spring Framework and what are they?

The Spring Framework is organized into several modules to provide a highly modular and flexible architecture. As of my last knowledge update in September 2021, some of the key modules include:

Core Container: Provides the core functionality, including Dependency Injection and IoC. Key modules within this category are:

• Spring Core
• Spring Beans
• Spring Context

Data Access/Integration: Offers support for data access and integration with various data sources, including databases, messaging systems, and more. Modules include:

• Spring JDBC
• Spring ORM
• Spring Data (for various data stores)
• Spring JMS (Java Messaging Service)
• Spring Transaction

Web: Facilitates web application development. Key modules are:

• Spring Web
• Spring Web MVC
• Spring Web WebSocket

Security: Provides security features for applications. Modules include:

• Spring Security
• Spring Security OAuth

AOP and Instrumentation: Supports Aspect-Oriented Programming and application monitoring:

• Spring AOP
• Spring Instrumentation

Messaging: Integration with messaging systems, particularly JMS:

• Spring Messaging

Testing: Provides utilities and support for testing Spring applications:

• **Spring Test **

Miscellaneous: Includes various modules like Spring Expression Language (SpEL), Spring Core Validation, and others.

What is a Spring configuration file?

A Spring configuration file is an XML or Java-based file that defines the configuration for a Spring application.

It contains information about beans (components), their dependencies, and various settings for the Spring container to manage the application's components.

In XML-based configuration, the file often has the extension ".xml" and includes bean definitions and other configuration details.

In Java-based configuration, you use annotations and Java classes to configure the application, typically through the @Configuration annotation and the @Bean annotation.

What are the different components of a Spring application?

A Spring application typically consists of the following key components:

Beans: These are the fundamental building blocks of a Spring application. Beans are Java objects managed by the Spring container and are defined in the configuration files. They can represent services, data sources, controllers, and more.

Container: The Spring container is responsible for managing the beans and their lifecycle. It handles aspects like dependency injection, bean instantiation, and configuration management.

Configuration: Spring applications can be configured using XML-based configuration files or Java-based configuration classes. These files define how beans are created, wired together, and configured.

Aspect: Spring supports Aspect-Oriented Programming (AOP), which allows you to modularize cross-cutting concerns and apply aspects to various parts of the application.

Modules: Spring provides a range of modules and libraries for specific functionalities like data access, security, and web development.

What are the various ways of using Spring Framework?

There are several ways to use the Spring Framework in your applications:

XML Configuration: Configuring Spring beans and components using XML-based configuration files.

Java Configuration: Using Java-based configuration with annotations like @Configuration and @Bean to define beans and their relationships.

Spring Boot: Leveraging the Spring Boot framework for rapid application development, which simplifies configuration and setup.

Dependency Injection: Applying Dependency Injection in standalone Java applications or within enterprise applications.

Spring MVC: Building web applications using the Spring MVC framework for web development.

Spring Data: Utilizing Spring Data for simplified data access and integration with various data sources.

Spring Security: Integrating Spring Security for application security, authentication, and authorization.

Spring Cloud: Building cloud-native and microservices-based applications with Spring Cloud.

Spring MVC Interview Questions and Answers

What is the Spring MVC framework?

The Spring MVC (Model-View-Controller) framework is a component of the Spring Framework that provides a structured approach to developing web applications. It follows the MVC architectural pattern, separating the application into three main components:

Model: Represents the application's data and business logic.

View: Handles the presentation and user interface.

Controller: Manages the flow of data between the Model and the View and processes user requests.

Spring MVC simplifies the development of web applications by providing features like URL mapping, request handling, form processing, and support for view technologies.

What are the benefits of Spring MVC framework over other MVC frameworks?

Spring MVC offers several advantages over other MVC frameworks:

Integration: Seamlessly integrates with other Spring modules like Spring Security, Spring Data, and Spring Boot.

Customization: Provides extensive customization options for request mapping, exception handling, and view resolution.

Testability: Simplifies unit testing of controllers and other components due to its modular and decoupled design.

Flexibility: Supports various view technologies, including JSP, Thymeleaf, and FreeMarker, allowing developers to choose the most suitable option.

Interceptors: Offers interceptors to perform pre- and post-processing tasks, such as logging, security checks, and auditing.

RESTful Capabilities: Supports the development of RESTful web services and APIs in addition to traditional web applications.

Community and Ecosystem: Benefits from a large and active Spring community and a wealth of resources, documentation, and third-party libraries.

What is the Model in Spring MVC?

In Spring MVC, the "Model" represents the application's data and business logic. It is a part of the Model-View-Controller (MVC) architectural pattern.

The Model contains the information that needs to be displayed or processed by the application. This information is typically stored in Java objects or POJOs (Plain Old Java Objects).

The Model is responsible for encapsulating data and making it available to the View for rendering. It can also handle business logic, data retrieval from databases, and any other operations necessary to prepare data for presentation.

The Model is separate from the View and Controller, ensuring a clear separation of concerns in the application.

In Spring MVC, you can pass data to the Model using methods and then make this data accessible to the View for rendering, allowing you to display dynamic content in your web applications.

What are the types of Spring MVC Dependency Injection?

In Spring MVC, you can use the following types of Dependency Injection:

Constructor Injection: Dependencies are injected through the constructor of the controller or any other Spring-managed bean.

Setter Injection: Dependencies are set using setter methods on the controller or other components, making them optional and allowing for dynamic changes.

Field Injection: Dependencies can be injected directly into fields, although this approach is generally less recommended compared to constructor or setter injection.

Method Parameter Injection: In Spring MVC, you can inject dependencies directly into controller methods by using annotations like @RequestParam, @PathVariable, and @ModelAttribute to retrieve request parameters or objects.

What is the importance of the web.xml in Spring MVC?

The web.xml file in a Spring MVC application plays a crucial role in configuring the Servlet container, particularly when using traditional Servlet-based Spring MVC. It serves the following purposes:

DispatcherServlet Configuration: It defines the DispatcherServlet, which is the entry point for Spring MVC requests. The web.xml specifies the URL patterns for which the DispatcherServlet is responsible.

Spring Context Configuration: The web.xml may specify the location of the Spring application context configuration files, allowing Spring to initialize the application context.

However, it's important to note that in modern Spring Boot-based applications, the web.xml is not required as Spring Boot handles many of these configurations automatically.

How is the root application context in Spring MVC loaded?

In a Spring MVC application, there are typically two application contexts:

Root Application Context: This context contains beans that are shared across the entire application, such as services, data sources, and business logic. It is loaded when the application starts and is typically defined in the web.xml using the ContextLoaderListener.

Servlet-specific Application Context: Each DispatcherServlet has its own context containing controller beans and other web-specific configurations. This context is loaded when the DispatcherServlet is initialized.

The root application context is loaded using the ContextLoaderListener in the web.xml. Here's an example:

This listener initializes the root context and loads beans defined in files like applicationContext.xml.

How does the Spring MVC flow look like? In other words, how does a DispatcherServlet know what Controller needs to be called when there is an incoming request to the Spring MVC?

The Spring MVC flow involves several steps when a request is made:

Incoming Request: A client (e.g., a web browser) sends a request to the application.

DispatcherServlet: The request is first received by the DispatcherServlet, which is the front controller in Spring MVC.

Handler Mapping: The DispatcherServlet consults the configured "Handler Mapping" to determine which controller should handle the request based on the URL mapping.

Controller Execution: The selected controller (a Spring bean) processes the request, typically by invoking a method on the controller class.

Model Preparation: The controller prepares a model (data to be displayed) and returns a logical view name.

View Resolver: The logical view name is resolved to an actual view (e.g., a JSP or Thymeleaf template) by a "View Resolver."

View Rendering: The view is rendered with the model data.

Response to Client: The generated view is sent back as the response to the client.

The configuration of handler mappings, view resolvers, and controller classes is typically done in the Spring configuration files or using annotations.

Where does the access to the model from the view come from?

The access to the model from the view in Spring MVC comes from the model that the controller prepares.

In the Spring MVC flow, after a controller processes a request and performs business logic, it populates the model with data.

The model is typically a Model or ModelMap object provided as a method parameter or by returning a ModelAndView or ModelMap instance.

For example, in a controller method:

@RequestMapping("/example")
public String example(Model model) {
// Populate the model with data
model.addAttribute("message", "Hello, Spring MVC!");
return "exampleView"; // The logical view name
}

In the associated view (e.g., a JSP or Thymeleaf template), you can access the data from the model using expressions like ${message} to display the value in the HTML output.

The model acts as an intermediary between the controller and the view, allowing the view to access and render the data provided by the controller.

Why do we need BindingResults?

BindingResult is a class in Spring MVC that is used to handle validation and binding errors. It is typically used in conjunction with form handling and validation. Here's why it's needed:

Error Handling: BindingResult is used to capture and report validation errors that occur during the data binding process, such as type mismatches or format errors in form fields.

Prevent Exception: It helps prevent exceptions from being thrown when validation fails, allowing you to handle errors gracefully and display error messages to the user.

Keep Processing: It enables the controller to continue processing and return to the view with error information, rather than terminating due to validation errors.

Does Spring MVC provide validation support?

Yes, Spring MVC provides robust validation support through the use of the javax.validation API (Bean Validation) and custom validation logic. You can perform validation in Spring MVC as follows:

Annotation-Based Validation: Use annotations like @NotNull, @Size, and custom annotations on model attributes to validate input.

Custom Validator: Implement custom validator classes that implement the Validator interface to define your validation logic.

@Valid Annotation: Use the @Valid annotation to trigger automatic validation of nested objects within your model.

Error Messages: Spring MVC allows you to bind error messages to your views to display validation errors to the user.

What is autowiring in Spring? What are the autowiring modes?

Autowiring in Spring is a mechanism that allows Spring to automatically inject dependencies into Spring beans without the need for explicit configuration in XML or Java code.

Autowiring simplifies the configuration process by reducing the amount of boilerplate code. There are several autowiring modes in Spring:

No Autowiring (default): No autowiring is used, and you must specify dependencies explicitly using elements or @Autowired annotations.

Autowire by Type: Spring automatically matches and injects a property if the type of the property matches exactly one bean in the application context.

Autowire by Name: The property name must match the name of a bean in the application context for autowiring to occur.

Autowire by Qualifier: This mode is similar to "by Type," but if multiple candidates are found, you can use the @Qualifier annotation to specify which bean to inject.

Autowire by Constructor: Spring will attempt to autowire constructor arguments, matching them by type if possible.

What are the different bean scopes in Spring?

Spring provides several bean scopes that control the lifecycle and visibility of beans:

Singleton (default): There is only one instance of the bean in the Spring container. All requests for the bean result in the same instance.

Prototype: A new instance of the bean is created every time it is requested.

Request: The bean is created once per HTTP request. This scope is only applicable in a web application context.

Session: The bean is created once per HTTP session. Like the request scope, this is also specific to web applications.

Global Session: Similar to the session scope but applies to global HTTP sessions when using Portlet-based web applications.

Application: The bean is created once for the entire lifecycle of the application context.

Custom Scopes: You can define custom scopes to meet specific application requirements.

In which scenario, will you use singleton and prototype scope?

Singleton Scope: You typically use the Singleton scope when you want a single instance of a bean to be shared by multiple parts of your application.

For example, you might use Singleton for services or components that should be stateless and shared among various clients. This is the default scope.

Prototype Scope: You would use the Prototype scope when you want a new instance of a bean every time it is requested. This is suitable for objects that should have their own state and should not be shared.

For example, when working with HTTP session-specific data, it's common to use Prototype scope. Each user session gets its own instance of a Prototype-scoped bean to maintain session-specific state.

The choice between Singleton and Prototype depends on the specific requirements of your application and the behavior you want for your beans.