Spring Boot Interview Questions Spring Boot is an extension of the Spring framework designed to simplify the setup and development of new Spring applications.
It eliminates much of the boilerplate code and configuration typically required in Spring projects, allowing developers to focus on writing business logic instead of configuration.
You can create a Spring Boot application in several ways. The most popular method is to use the Spring Initializr, a web-based tool that allows you to select dependencies and download a pre-configured project. Alternatively, you can set up a Maven or Gradle project manually by adding the necessary dependencies in your build configuration.
Key features of Spring Boot include:
The @SpringBootApplication annotation is a convenience annotation that combines three important annotations:
Starters are a set of convenient dependency descriptors that simplify the inclusion of common libraries in your project. For example, the spring-boot-starter-web includes everything you need to develop a web application, such as Spring MVC, Jackson for JSON processing, and Tomcat as the default embedded server.
You can run a Spring Boot application from the command line using the following command:
mvn spring-boot:runAlternatively, you can build a JAR file and execute it with:
java -jar target/myapp.jarSpring Boot Actuator provides built-in endpoints that help you monitor and manage your application. These endpoints can provide information about application health, metrics, environment properties, and more. You can access these endpoints through HTTP, allowing for easy integration with monitoring tools.
The application.properties file is used to configure application-specific properties such as server port, datasource configurations, and various Spring features. This file enables customization of your application's behavior without altering code.
To connect to a database, you need to define the database connection properties in the application.properties file. For example, to connect to a MySQL database, you would configure it as follows:
spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=root
spring.datasource.password=password
All three annotations are part of the Spring framework's stereotype annotations, but they serve different purposes:
DevTools is a set of tools that enhances the development experience by enabling features such as automatic restarts and hot swapping of code changes. This significantly speeds up the development process, as you can see changes reflected in the application without manually restarting it.
You can manage exceptions globally using the @ControllerAdvice annotation, which allows you to define a centralized exception handling mechanism. Here's an example:
@ControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(Exception.class)
public ResponseEntity<String> handleException(Exception ex) {
return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(ex.getMessage());
}
}
Spring Data JPA is part of the Spring Data project that simplifies the implementation of JPA-based repositories. It provides an easy way to interact with databases by reducing the amount of boilerplate code needed for data access and management. With Spring Data JPA, you can create repository interfaces and use them without writing implementation code.
The @Configuration annotation indicates that a class declares one or more @Bean methods. The Spring container processes these classes to generate bean definitions and manage the lifecycle of these beans within the application context.
To create RESTful web services, you use the @RestController annotation to define a controller and the @RequestMapping annotation to map HTTP requests to handler methods. Here's an example:
@RestController
@RequestMapping("/api")
public class MyController {
@GetMapping("/hello")
public String hello() {
return "Hello, World!";
}
}
The @Autowired annotation allows Spring to automatically inject the required bean into the class. This eliminates the need for manual wiring and makes the code cleaner and easier to manage.
You can configure Spring Security by adding the spring-boot-starter-security dependency to your project and creating a configuration class that extends WebSecurityConfigurerAdapter. Here’s a simple example:
@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
@Override
protected void configure(HttpSecurity http) throws Exception {
http.authorizeRequests()
.anyRequest().authenticated()
.and()
.formLogin();
}
}
The @Value annotation is used to inject property values from the application.properties file into Spring-managed beans. For example:
@Value("${my.custom.property}")
private String myProperty;
You can implement custom error handling by using the @ControllerAdvice annotation along with @ExceptionHandler methods to define how to handle specific exceptions. You can also customize the error response body and status codes.
The @RequestMapping annotation is used to map web requests to specific handler methods. It can handle different HTTP methods (GET, POST, etc.). The @GetMapping annotation is a specialized version of @RequestMapping that specifically handles GET requests. Here’s an example:
@RestController
@RequestMapping("/api")
public class MyController {
@GetMapping("/items")
public List- getItems() {
return itemService.findAll();
}
}
Profiles allow you to segregate parts of your application configuration and make it available only in certain environments. For instance, you can define different application-{profile}.properties files for development, testing, and production, and activate them accordingly.
Spring Boot uses Apache Commons Logging for internal logging but allows you to configure various logging frameworks like Logback, Log4j2, or Java Util Logging. You can configure logging in the application.properties file by setting properties like:
logging.level.root=INFO
logging.file.name=app.log
A Spring Boot Starter Parent is a special starter that serves as a parent in a Maven project. It provides dependency management, versioning, and default configuration for various Spring Boot projects. Using it simplifies your pom.xml file.
Spring is a comprehensive framework for building Java applications, providing a wide range of features for building enterprise-level applications. Spring Boot, on the other hand, is a project within the Spring ecosystem designed to simplify the process of developing new Spring applications by providing auto-configuration and default settings, reducing boilerplate code and configuration complexity.
The Spring Boot CLI (Command Line Interface) is a tool that allows you to run Groovy scripts. It simplifies the development process by enabling rapid prototyping and testing of Spring Boot applications with minimal setup.
Dependencies can be added in Spring Boot by including them in your pom.xml file (for Maven) or build.gradle file (for Gradle). Each dependency can be defined within the respective section to automatically download the necessary libraries.
Spring Boot Starter Projects are a set of convenient dependency descriptors that aggregate common libraries needed for specific tasks, such as web development or data access, making it easier to include multiple dependencies with a single starter.
You can customize the default server port in Spring Boot by adding the line server.port=8081 (or your desired port) to the application.properties file, allowing the application to run on the specified port.
@RestController is a specialized version of the @Controller annotation that automatically serializes the response body to JSON or XML. In contrast, @Controller is used when you need to return views, typically in a web application.
To serve static content in Spring Boot, place your static files (HTML, CSS, JavaScript) in the src/main/resources/static directory. Spring Boot will automatically serve these files at the root URL of your application.
The CommandLineRunner interface allows you to execute code after the Spring application has started. It is useful for tasks like initializing data, executing startup logic, or running checks upon application start.
An Application Listener is a component that listens for specific events within the application context, allowing you to execute custom logic in response to these events, such as when the application starts or stops.
To create custom configuration in Spring Boot, define a class annotated with @Configuration and include @Bean methods within it to declare the beans you want to manage. This allows you to provide specific configurations for your application components.
Spring Profiles allow you to group configuration properties and beans into separate profiles, enabling you to activate specific configurations based on the environment (e.g., development, testing, production) in which the application is running.
To use Spring Boot with a NoSQL database, you can include specific Spring Data modules, such as Spring Data MongoDB or Spring Data Cassandra, by adding their dependencies to your project and configuring them in your application.properties file.
You can schedule tasks in Spring Boot by using the @Scheduled annotation. You need to enable scheduling by adding @EnableScheduling to your configuration class, then you can define methods to run periodically.
Auto-Configuration in Spring Boot automatically configures your application based on the libraries and dependencies present in the classpath, minimizing the need for manual configurations and speeding up development.
You can secure a Spring Boot application by using Spring Security. You will need to add the spring-boot-starter-security dependency and then configure authentication and authorization rules within a configuration class.
@Transactional is an annotation used to define transaction boundaries at the method or class level, while @EnableTransactionManagement is an annotation used to enable Spring's annotation-driven transaction management features in your application context.
HTTP status codes are standardized three-digit codes returned by a server in response to a client request, indicating the result of the request. Common examples include 200 (OK), 404 (Not Found), and 500 (Internal Server Error).
You can handle validation in Spring Boot using JSR-303/JSR-380 annotations such as @Valid, @NotNull, and @Size on model fields. Spring will automatically enforce these validations during data binding.
Spring Boot Starter Test is a starter dependency that simplifies the setup of testing Spring Boot applications. It includes libraries like JUnit, Mockito, and Spring Test, making it easier to write unit and integration tests.
You can enable CORS in a Spring Boot application by creating a configuration class that implements WebMvcConfigurer and overriding the addCorsMappings method to define allowed origins and paths.
Spring Boot Actuator provides production-ready features to monitor and manage Spring Boot applications. It exposes various endpoints that can provide health checks, metrics, and application information.
To implement a custom error page in Spring Boot, create an error.html file in the src/main/resources/templates directory. This page will be rendered for any error status codes defined in your application.
@Bean is an annotation used to declare a bean explicitly in a configuration class, while @Component is a stereotype annotation that indicates a class is a Spring-managed component, allowing for component scanning to find it automatically.
You can externalize configuration in Spring Boot using properties files, YAML files, environment variables, or command-line arguments. This allows you to manage application settings without changing the code.
@SpringBootTest is an annotation used for integration testing in Spring Boot. It loads the full application context and enables Spring Boot features, allowing you to test your application as a whole.
You can create a REST client in Spring Boot using RestTemplate or WebClient. These classes allow you to make HTTP requests to external APIs and handle responses conveniently.
Spring Boot DevTools is a set of tools that enhances the development experience by providing features like automatic restarts, live reload, and improved logging, which help developers see changes in real-time without restarting the application manually.
You can configure caching in Spring Boot by adding the spring-boot-starter-cache dependency and using the @EnableCaching annotation in your configuration class. You can then use caching annotations like @Cacheable, @CachePut, and @CacheEvict in your methods.
Spring Cloud is a collection of tools for building distributed systems, and it complements Spring Boot by providing features like service discovery, configuration management, and circuit breakers, enabling easier microservices development.
You can monitor your Spring Boot application in production using Spring Boot Actuator for health checks and metrics, and integrate with external monitoring solutions like Prometheus and Grafana to visualize and analyze application performance.