Spring Boot interview @ Sapient

Hi Friends,

Also go through my other interview posts:

• Interview @ Sirion Labs - Round - 2
• Interview @ Sirion Labs Round - 1
• Java 8 interview Questions - Part - I
• Java Interview @ Aricent - Part - 2

Question 1:

What is the use case of Spring Boot?

Answer:

Spring Boot is used while creating microservices. As with increasing features in our applications, we need to create a separate microservice for each new feature and doing entire setup for this including adding all dependencies will  take time. So, in this scenario, Spring Boot is required.

In a monolithic application, we just do setup and dependency addition only once, so in monolithic application, we don't need spring boot.




Question 2:

What are the steps to use Spring-boot-starter-caching ?

Answer:

Steps for using spring-boot-starter-cache are following:

1). Add dependency: 

    <dependency>
        <groupId> org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-cache </artifactId>
    </dependency>

2). Add @EnableCaching annotation on main Spring Boot Application class.

The @EnableCaching triggers a post-processor that inspects every spring bean for the presence of caching annotations  on public methods. If such an annotation is found, a proxy is automatically created  to intercept the method call and handle the caching behavior accordingly.

The post-processor handles the @Cacheable, @CachePut and @CacheEvict annotations.

Spring boot automatically configures a suitable CacheManager to serve as a provider for the relevant cache.

3). Put @Cacheable and other annotations on methods.

e.g.:

public interface BookRepository{

    Book getByIsbn(String isbn);
}

Use our own implementation if we are not using Spring Data.

public class SimpleBookRepository implements BookRepository{

    @Override
    @Cacheable("books")
    public Book getByIsbn(String isbn){

        return new Book(isbn);
    }

}




Question 3:

What happens when we call SpringApplication.run() method in main class of SpringBoot application?

Answer:

Syntax of the class containing main method looks like code below:

@SpringBootApplication
public class StudentApplication{

    public static void main(String[] args){

        SpringApplication.run(StudentAppplication.class, args);
    }
}

When we run this class as a java application, then our application gets started.

SpringApplication.run() is a static method and it returns an object of ConfigurableApplicationContext.

ConfiguravleApplicationContext ctx = SpringApplication.run(StudentApplication.class, args);

Thus, Spring container gets started once run() method gets called.

Spring container once started is responsible for:

• Creating all objects: This is done by @ComponentScan. Remember @SpringBootApplication is a combination of @ComponentScan + @Configuration + @EnableAutoConfiguration

• Dependency injection

• Managing the lifecycle of all beans

Steps executed under run() method are as follows:

• Application Context is started.

• Using application context, auto discovery occurs: @ComponentScan

• All default configurations are setup.

• An embedded servlet container is started e.g. Tomcat. No need to setup a separate web server. Note: Embedded servlet container is launched  only if the web is mentioned in a dependency.

Question 4:

What are Spring Boot Actuator endpoints?

Answer:

Spring Boot Actuator is used to monitor and manage application usages in production environment without coding and configuration for any of them.


This monitoring and managing information is exposed via REST like endpoint URL's.

Actuator Endpoints:

/env : Returns list of properties in current environment

/health : Returns application health information.

/beans : Returns a complete list of all the Spring beans in the application.

/trace : Returns trace logs [By default the last 100 HTTP requests]

/dump : It performs a thread dump

/metrics : It shows several useful metrics information like JVM memory used, CPU usage , open files and much more.

Note: These endpoints can be explicitly enabled/disabled.
 
If we need to list all endpoints in the browser:
Just run the application and from browser , use localhost:8080/actuator. It will list 2 endpoints by default : info and health

For other endpoints, we need to expose them manually.

Now, if we want to explore health endpoint, then just open localhost:8080/actuator/health URL and it will just display "status" : "UP"

We can enable or disable the endpoint from application.properties file:

management.endpoint.shutdown.enabled = true

By default all the endpoints are enabled except shutdown endpoint.




Question 5:

By default on which port Spring Boot Actuator runs?

Answer:

On port 8080

We can override that setting by adding application.properties file.



Question 6:

Difference between Spring 2 and Spring 5?

Answer:

Below are the differences between Spring 2 and Spring 5 versions:

• JDK Baseline update
• Core framework revision
• Reactive programming model
• Core Container updates
• Testing improvements

Question 7:

What is the difference between @SpringBootApplication and @EnableAutoConfiguration?

Answer:

Following are the differences between @SpringBootApplication and @EnableAutoConfiguration:

Availability : SpringBootApplication was introduced in version 1.2 ,  While EnableAutoConfiguration was introduced in version 1.0

Purpose : @EnableAutoConfiguration enables auto configuration feature of Spring Boot application  which automatically configures things if certain classes are present in classpath e.g. : it can configure Thymeleaf  TemplateResolver and ViewResolver if Thymeleaf is present in the classpath.

On the other hand , @SpringBootApplication does three things.

• It allows us to run the main class as a jar with an embedded container [Web server Tomcat]. 
• It enables java configuration.
• It enables component scanning. 

That's all from this interview.
Hope this post helps everybody in their interviews.
Thanks for reading!!