10 advanced Spring Boot interview questions and answers for 2023

The main differences between Spring and Spring Boot are as follows:

Spring –

• It is a lightweight framework used to build enterprise applications.
• It is also a dependency injection framework that requires setting the server explicitly.
• There is no support for the in-memory database.

Spring Boot –

• It is built on top of the Spring framework and is widely used to build REST APIs.
• Its prominent feature is Autoconfiguration and provides embedded servers like Tomcat and Jetty etc.
• It supports in-memory databases like H2 and creates a production-ready code.

Spring Boot provides a default embedded server that runs on port 8080. It is also possible to change the port as per your preference. You can use any of the following ways to change the default server in Spring Boot –

• Using application.properties file – It is the easiest and fastest way to overwrite the default port value. Use the server.port property to do so. For instance, if you want to change the port from 8080 to 8081, then your code would look like – server.port=8081
• Programmatically – You can also set the server.port on the SpringApplication instance in the main @SpringBootApplication class.
• Using command line parameter - You can also set server.port as a Java command argument whenever you run the application as a jar file. Follow the command to do so – java -jar -Dserver.port=8081 myspringbootproject.jar

When working on enterprise-level application development, developers typically deal with multiple environments, for example, Dev, QA, Test, Prod, etc. Dealing with multiple environments means the application needs different configurations in different environments. Spring Profiles allows you to set the right configurations on the right environments by offering a way to separate parts of the application configuration and making it only available for particular environments.

So instead of maintaining the configurations programmatically, you can keep profile-specific properties in separate files, such as - application-{profile}.properties

You can replace “profile” with whatever environment you need. For instance, if it is a development profile, then it would look like – application-development.properties

You can define properties into a file called application.properties, which is used to keep ‘N’ number of properties in a single file. You can create the application.properties file manually or utilize Spring Initializer to create it. Make sure your file exists under src/main/resources, and Spring Boot will automatically load and configure it accordingly.

Dependency injection is the fundamental aspect that provides dependencies of another object. In simpler terms, a class uses specific functionalities of another class. There are mainly three types of dependency injection –

• Setter injection – Dependent object will be injected to the target object by calling the setter method.
• Constructor injection – Dependent object will be injected to the target object by calling the target constructor.
• Field injection - Dependent object will be injected to the target object by calling Reflection API. IoC container is Spring Boot is used to automatically implement dependency injections by managing the object creation and its lifetime.

Some of the basic annotations offered by Spring Boot are –

• Basic setup – @SpringBootApplications @Configuration @ComponentScan @EnableAutoConfiguration

• Request Responses – @GetMapping @RequestMapping @RequestParam

• Request Responses – @Component @Service @Repository @Controller @RestController

• Request Responses – @SpringBootTest @MockBean @Validated

• Misc – @Bean @ConditionalOnJava

Spring Boot Starters were built to address the issue of doing dependency management manually. It enables easy and rapid development by offering convenient dependency management providers to be used in the application. There are 50+ Spring Boot Starters are available, here are some of them -

• spring-boot-starter
• spring-boot-starter-jdbc
• spring-boot-starter-web
• spring-boot-starter-data-jpa
• spring-boot-starter-security
• spring-boot-starter-aop
• spring-boot-starter-test
• spring-boot-starter-mail

HTTP/2 (or h2) is a major revision of the HTTP network protocol that conveys push, multiplexing streams, and frame control to the web. It aims to eliminate many of the drawbacks of the first HTTP version while making applications faster, simpler, and more robust.

Spring Boot allows you to enable HTTP/2 support easily. You can do so by following this code: server.http2.enabled=true

Thymeleaf is a server-side Java template engine that provides a stylish and well-informed way of building templates. You can use Thymeleaf by adding spring-boot-starter-thymeleaf dependency in the application’s pom.xml file. Follow the code to do so -

Spring Boot Actuator enables developers to monitor and manage when the applications are in the production environment. Follow the code to use Actuator in Spring Boot -