Top 50+ Spring Boot Interview Question and Answers

Answer: Spring Boot can be defined as a project built on top of the Spring Framework. It renders a faster & more accessible way to configure, run, & set web-based applications. Spring Boot is a module that provides a Rapid Application Development feature to the Spring. It helps to create a stand-alone Spring-based app that can efficiently run as it needs minimal Spring configuration. Spring Boot is a framework for rapid Spring-based application development. It supports auto-configuration & embedded app servers with extensive documentation & community support. Spring Boot is the most popular Java technology to date. Here are some salient features of Spring Boot:

• Starters- It is a set of dependency descriptors that includes relevant dependencies at one go.
• Auto-configuration-It is a way to configure applications based on dependencies present in their classpath automatically.
• Actuator– It helps to access production-ready features like monitoring, security, etc.

Answer:

• Spring Boot creates stand-alone Spring-based applications that can be started using the Java-jar.
• It can easily test web applications using different Embedded HTTP servers like Jetty, Tomcat, etc. Thus, there is no need to deploy WAR files.
• It renders an opinionated ‘starter’ POMs that simplifies your Maven configuration.
• It offers production-ready features such as health checks, metrics, & externalized configuration.
• It eliminates the need for XML configuration.
• It offers a CLI tool for building & testing Spring Boot applications.
• It provides s a large number of plug-ins.
• Spring Boot also minimizes writing multiple boilerplate codes, XML configuration, & annotations.
• It accelerates productivity & reduces development time.

Answer: The following are a few features of Spring Boot:

• Web Development– It is a well-suited Spring module for web app development. We can easily develop a self-contained HTTP server using embedded Jetty, Undertow, or Tomcat. We can deploy the spring-boot-starter-web module to start & run applications quickly.
• SpringApplication- It is a class that provides a convenient way to bootstrap the Spring Application. You can start such an application from THE main method by calling a static run() method.
• Application Events & Listeners- Spring Boot use events to handle a variety of tasks. It enables us to create factories files used to add listeners. One can refer to it by using the ApplicationListener key. It always creates factory files in the META-INF folder like META-INF/spring.factories.
• Admin Support-Spring Boot enables admin-related features for an application. It is used to manage & access an application remotely. One can enable Admin Support by using spring.application.admin.enabled property.
• Externalized Configuration- Spring Boot enables us to externalize our application’s configuration. It allows us to work with the same app in different environments. The application uses YAML files to externalize the configuration.
• Properties Files- Spring Boot renders a rich set of Application Properties. Properties files help to set properties like server-port = 8082 & various others. It helps to organize an application’s properties.
• YAML Support- Spring Boot provides a convenient way to specify a hierarchical configuration. The SpringApplication class automatically supports YAML & proves to be a potent alternative of properties.
• Type-safe Configuration- It has a strong type-safe configuration to validate & govern the application’s configuration. Application configuration is a crucial task that should be type-safe. You can also utilize the annotation provided by this library.
• Logging-Spring Boot uses common logging for all the internal logging. The logging dependencies of Spring Boot are managed by default. One should not change the logging dependencies if there is no need for customization.
• Security- Spring Boot applications are spring bases web applications. So, it is secure by default with basic authentication on all HTTP endpoints. A rich set of Endpoints are available for develop a secure Spring Boot application.

Answer: You can create a Spring Boot project by multiple approaches:

• Spring Initializr
• Spring Boot CLI
• Spring Starter Project Wizard
• Spring Maven Project

Answer: The Spring Initializr is a web-based tool given by the Pivotal Web Service. One can easily generate the Spring Boot project’s structure using Spring Initializr. It provides extensible APIs for creating JVM-based projects. It also offers several options for the project expressed in a metadata model. The metadata model allows you to configure a list of dependencies supported by the JVM & platform versions. It serves its metadata in a well-known way that provides the necessary assistance to third-party clients.

Answer: Spring Boot Annotations are a form of metadata that provides data about the program. Annotations provide a program’s supplementary information. It is not a part of an application we develop & does not directly affect the code’s operation they annotate. Also, it does not change the actions of a compiled program. Spring Boot offers many different annotations that help to configure several things for an application. Annotations provide us metadata about a program which generally includes additional information. Spring Boot has simplified configuration by providing annotations. Spring Boot Annotations is a type of metadata that provides information about the program that is not a part of the program itself. Annotations don’t have any direct effect on a code’s operation. It uses the convention over configuration principle & does not use XML.

Answer: The dependency management in Spring Boot is used to manage dependencies & configuration automatically without needing to specify a version for any dependencies.

Answer: Spring Boot offers a no. of starters that enables us to add jars to the classpath. It has built-in starters the make development easier, quicker, & better. Spring Boot Starters are the dependency descriptors. All the starters in a Spring Boot framework follow a similar naming pattern; spring-boot-starter-*, where * that represents a particular type of application.

Answer: Actuator is a sub-project of the Spring Boot framework. It includes a no. of additional features that help to manage & monitor a Spring Boot application. The actuator endpoints the place wherein the resources live. We can use JMX & HTTP endpoints to manage & monitor Spring Boot applications. You should use an Actuator to get production-ready features in the application.

Answer: The Thymeleaf is an open-source library in Java, licensed under the Apache License 2.0. It is a HTML5/XHTML/XML template engine. Thymeleaf is a server-side, Java template engine for servlet-based web & non-web environments. It is ideal for modern-day HTML5 JVM web development & provides full integration with Spring. It applies a set of transformations to the template files to display text or data produced by an application. It is an ideal-fit for serving XHTML/HTML5 in web applications. Thymeleaf provides a well-formed way of creating templates. It is based on XML attributes & tags. The XML tags define the execution of predefined logic on the Document Object Model rather than explicitly writing the logic as code inside the template.

Answer: Spring Boot JPA is a specification for managing relational data in Java applications. It enables us to persist & access data between Java class/object & relational database. JPA is a set of interfaces that follows ORM (Object-Relation Mapping). It also renders a runtime EntityManager API for processing transactions & queries on the objects against a database. It uses JPQL, an object-oriented, platform-independent query language. It covers three areas:

• Java Persistence API;
• Object-Relational metadata, and;
• API defined in the persistence package.

Answer: RestController annotation in Spring is a convenience annotation that is annotated with @Controller & @ResponseBody. It is applied to a class to mark as a request handler. Spring @RestController annotation creates RESTful web services with Spring MVC &manages the mapping request data to a defined request handler method. Once the data handler generates a response body from the handler method, it converts it to XML or JSON response.

Answer: Spring is a framework that provides various features which make web app development easier. Its features include data binding, dependency injection, data access, aspect-oriented programming, and many others. Over the years, Spring is getting more complex, which is why app configuration is becoming more intimidating. This is where Spring Boot comes in handy by simplifying Spring app configuration.Spring & Spring Boot’s key difference is the former is of an unopinionated view while the latter has an opinionated view of the libraries & platform. Following are two major benefits of Spring Boot:

• It automatically configures applications based on the artifacts; it finds on the classpath.
• It provides non-functional features such as security or health checks, common to every application in production.

Answer: Spring Initializr is a convenient way to build a Spring Boot project. Go to the Spring Initializr site, select a dependency management tool, either Gradle or Maven, a language (Kotlin, Java, or Groovy), a packaging scheme (War or Jar), version & dependencies, then download the project. It creates a skeleton project & saves the setup time so we can concentrate on adding the business logic.

Answer: Spring Boot offers support for external configuration. It allows us to run the same application in different environments. We can use the environment variables, YAML files, properties files, command-line option arguments, & system properties to specify configuration properties.

Answer: Spring Profiles enables users to register beans based on their profile (test, prod, dev). When an application is running in DEVELOPMENT, some beans can be loaded; when an application is running in PRODUCTION, some other beans can be loaded. The Swagger documentation will be enabled only for the environment & disabled for all the others. It is done by using Spring Profiles. Spring Profiles enables users to map beans & components to specific profiles like the Development (dev) profile, Test profile, or Production (prod) profile. In Spring Boot, @Profile annotation helps to map components & beans to a certain profile. Developers can also set-up profiles by using the SpringApplication; i.e,  SpringApplication.setAdditionalProfiles(“dev”).

Answer: There are numerous stages of developing the RAD model: designing, analyzing, building, and testing. Let’s take a look at its various phases: Stage 1: Business Modeling- The business model for the product under development is designed in terms of the flow & distribution of information between various business channels. Complete business analysis is performed to find an information for business, how it can be obtained, processed, & derived. Stage 2: Data Modeling- During this stage, all the gathered information is analyzed. Through analysis, the information is categorized into different groups that a company can utilize. Thereon, the quality of each data group is examined & given an accurate description. The relationship between groups of data & their usefulness is also defined in the Business Modeling step established during this phase. Stage 3: Process Modeling- In this step, all the groups of gathered information during Data Modeling are converted into usable information. The modeling stage change, optimize, & define a set of data. Any descriptions for removing, adding, or changing the data objects are also created during the modeling phase. Stage 4: Application Generation- During this stage, all the gathered information is coded, and the system uses that information to create the prototype. The data models created are then turned to actual prototypes that are tested in the following step. Stage 5: Testing & Turnover- This step reduces the overall time in testing the created prototypes. Each model is tested separately to find & quickly adapt the components to make the most effective product. Since most elements have already been examined previously, there are no significant problems with the prototype.

Answer: RAD stands for Rapid Application Development. It is a software development process that uses minimal planning for rapid prototyping. A prototype refers to a working model functionally equivalent to the component of a product. In the RAD model, the functional modules are built-in parallel as prototypes and integrated to make a complete product for faster product delivery. As there is no detailed preplanning, it simplifies to incorporate changes within the development process. RAD follows an incremental & iterative model with small teams of domain experts, developers, customer representatives, & other IT resources working progressively on their prototype & component. An essential aspect for a RAD model to be successful is to ensure that the prototypes developed are reusable. The RAD model has the following phases:

• Business Modeling
• Data Modeling
• Process Modeling
• Application Generation
• Testing & Turnover

Answer: DevTools in Spring Boot boosts the productivity of developers. So, one doesn’t need to redeploy an application every time any changes are made. It enables the developer to reload changes without needing to restart the server.

Answer:

• @RequestMapping– Developers use this annotation for mapping web requests onto handler methods in the request-handling classes. The process is known as routing.
• @RestController- Developers use this annotation to build RESTful web services by utilizing the Model–View–Controller of Spring. The @RestController maps the request data to specified request handler methods. Once the handler method generates a response body, this annotation modifies it to JSON or XML response.