Top 20 Spring Boot Interview Questions with Answers for Java Developers

Certainly! Here are 20 common Spring Boot interview questions along with their answers:

What is Spring Boot?

Spring Boot is an opinionated framework built on top of the Spring framework that simplifies the development of Java applications. It provides default configurations and conventions, reducing boilerplate code and enabling developers to quickly create production-ready applications.

What are the key features of Spring Boot?

Key features of Spring Boot include:

• Auto-configuration
• Embedded servers
• Starter dependencies
• Actuator
• Production-ready metrics and monitoring
• How does Spring Boot simplify the configuration of a Spring application?
• Spring Boot uses convention over configuration. It provides default configurations based on classpath settings, annotations, and properties files. Developers can override these defaults by providing their own configurations.

What is the difference between Spring and Spring Boot?

Spring is a comprehensive framework that provides various modules for developing enterprise Java applications. Spring Boot is built on top of the Spring framework and focuses on simplifying the configuration and development of Spring applications.

What is the purpose of the @SpringBootApplication annotation?

The @SpringBootApplication annotation is used to indicate the main class of a Spring Boot application. It combines the @Configuration, @EnableAutoConfiguration, and @ComponentScan annotations into a single annotation.

What is Spring Boot Starter?

A Spring Boot Starter is a dependency that includes a set of opinionated dependencies related to a specific feature or functionality. It simplifies dependency management and configuration for that specific feature.

What is the purpose of the application.properties (or application.yml) file in Spring Boot?

The application.properties or application.yml file is used to configure various settings of a Spring Boot application, such as server port, database connection details, logging configuration, etc.

What is the purpose of the Spring Boot Actuator?

Spring Boot Actuator provides production-ready features for monitoring and managing Spring Boot applications. It includes endpoints that expose useful information and metrics about the application, such as health checks, metrics, environment details, and more.

What is the difference between @RestController and @Controller?

The @RestController annotation is a specialized version of @Controller that combines @Controller and @ResponseBody. It is used to build RESTful web services, where the return values of methods are automatically serialized to JSON or XML.

Explain the concept of Spring Boot Auto-configuration.

Spring Boot Auto-configuration automatically configures the Spring application based on the dependencies and the classpath. It analyzes the project's dependencies and, if a specific library is found on the classpath, it automatically configures the necessary beans and settings.

What is the purpose of the @Autowired annotation?

The @Autowired annotation is used to automatically wire (inject) dependencies into a Spring bean. It can be applied to constructors, setter methods, or directly on fields.

What is the Spring Boot starter parent?

The Spring Boot starter parent is a special Maven POM that provides default configurations and dependency management for Spring Boot applications. It simplifies the project's Maven configuration by inheriting common settings.

How can you create a custom starter in Spring Boot?

To create a custom starter, you can follow these steps:

Create a Maven module with a specific naming convention (e.g., spring-boot-starter-{name}).

Define the necessary dependencies and configurations in the module.

Package the module as a JAR and distribute it

10 Tips to Debug Java Program in Eclipse - Examples

 Here is some tips to debug the error in eclipse ide, 

1. Set Breakpoints: Place breakpoints at specific lines of code where you suspect the issue might be occurring. To set a breakpoint, simply click on the left margin of the line you want to break on. For example, if you suspect an error in a method called "calculateTotal", set a breakpoint at the beginning of that method.

2. Step Over (F6): Use the Step Over feature to execute the current line of code and move to the next line without entering into method calls. This allows you to quickly move through the code while observing the variable values. For example, you can use Step Over to examine the flow of execution in a loop.

3. Step Into (F5): Use the Step Into feature to step into a method call and debug the code within that method. This is helpful when you want to investigate the details of a particular method. For example, if you have a method called "calculateTotal", you can use Step Into to see what's happening inside that method.

4. Step Return (Ctrl+Shift+F7): Use the Step Return feature to quickly return from a method call and continue debugging from the caller's perspective. This is useful when you want to skip the internal details of a method and focus on the higher-level flow. For example, if you stepped into a method and realized you want to skip the internal details, you can use Step Return to go back to the calling method.

5. Inspect Variables: While debugging, you can inspect the values of variables by hovering over them or adding them to the Expressions view. This helps you understand the state of the program at specific points in time. For example, if you have a variable called "total" that should contain the sum of two numbers, you can inspect its value to see if it's calculated correctly.

6. Conditional Breakpoints: Eclipse allows you to set breakpoints with conditions. This means the program will only stop at the breakpoint if the specified condition evaluates to true. For example, you can set a conditional breakpoint to pause the program when a variable reaches a certain value.

7. Watch Expressions: Use the Watch Expressions feature to monitor specific variables or expressions during debugging. You can add expressions to the Expressions view, and Eclipse will evaluate and display their values continuously. For example, you can add an expression to watch the length of an array while debugging to ensure it has the expected size.

8. Evaluate Expressions: While debugging, you can evaluate expressions in the Debug perspective using the Display view. This allows you to check the result of a particular expression without modifying the code. For example, if you suspect an arithmetic error, you can evaluate an expression like "2 + 3 * 4" to verify the expected result.

9. Log Messages: Insert log messages at critical points in your code to track the flow and values of variables. Use the logging framework (e.g., log4j or java.util.logging) to log messages with different levels of severity. You can then check the log output to understand what's happening during program execution. For example, you can log a message before and after a particular method call to verify if it's being executed correctly.

10. HerUse the Debug Perspective: Switch to the Debug perspective in Eclipse to access all the debugging features conveniently. The Debug perspective provides a comprehensive set of views and tools specifically designed for debugging. It helps you keep track of breakpoints, variable values, and control flow. Use this perspective to have a dedicated workspace for debugging and improve your efficiency.

These are just a few tips to help you get started with debugging in Eclipse. Remember to practice and experiment with different debugging techniques to become proficient in troubleshooting Java programs.