Java Spring Boot with example

Example: A simple Spring Boot REST API

Setting up Spring Boot Project: You can create a Spring Boot project using Spring Initializr:
- Visit: Spring Initializr
- Select the following:
  - Project: Maven or Gradle (Maven is common)
  - Language: Java
  - Spring Boot version: Choose the latest stable version
  - Dependencies: Web (Spring Web), Spring Boot DevTools (optional, for automatic reloads)
Download the generated ZIP file, extract it, and open it in your favorite IDE (e.g., IntelliJ IDEA or Eclipse).

Project Structure: The default structure will look like this:

scss
├── src
    ├── main
        ├── java
            └── com
                └── example
                    └── demo
                        ├── DemoApplication.java
                        └── controller
                            └── HelloController.java
├── pom.xml (for Maven) or build.gradle (for Gradle)
└── resources
    ├── application.properties

Writing Code:

DemoApplication.java: This is the entry point for the Spring Boot application. Spring Boot automatically runs this class when you execute the application.

java
package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

HelloController.java: A REST controller that exposes an endpoint.

java
package com.example.demo.controller;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, World!";
    }
}

This HelloController class has a single endpoint /hello that returns "Hello, World!" when accessed via an HTTP GET request.

Application Properties (Optional): You can configure your application using the application.properties file. Here’s a simple configuration to set the server port:
```
properties
server.port=8081
```
Running the Application: Once the code is written, you can run the Spring Boot application:
- From the IDE: Run the DemoApplication.java class as a Java application.
- From the command line:
  - Navigate to the project folder and run:
```
bash
./mvnw spring-boot:run   # For Maven
# or
./gradlew bootRun        # For Gradle
```
Accessing the Application: After the application is running, you can access the REST API by navigating to:
```
Bash
http://localhost:8081/hello
```
The response will be
```
Hello, World!
```

Explanation of Key Concepts:

@SpringBootApplication: This is a convenience annotation that includes:
- @Configuration: Marks the class as a source of bean definitions for the application context.
- @EnableAutoConfiguration: Enables Spring Boot’s auto-configuration mechanism.
- @ComponentScan: Tells Spring to look for other components, configurations, and services in the package where @SpringBootApplication is located.
@RestController: This annotation is a convenience for @Controller and @ResponseBody, indicating that the class will handle HTTP requests and return responses directly (as opposed to rendering views).
@GetMapping: This is used to map HTTP GET requests to the sayHello() method.

Further Improvements:

Adding more endpoints: You can add more methods to your controller to handle different types of requests like POST, PUT, DELETE, etc.
Database Integration: Spring Boot can easily integrate with databases using Spring Data JPA or JDBC.
Security: You can use Spring Security to protect endpoints and manage user authentication and authorization.
Testing: You can write unit and integration tests with Spring Boot’s testing support.

This is a simple introduction to Spring Boot. The framework offers a wide range of features to support web services, REST APIs, batch processing, messaging.

People Who Code | Blog