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LearnRemember   SPRING





Spring Starters

Spring Boot is the fastest way to start building Spring-based applications. You can start generating a project from Spring Initializr: https://start.spring.io You can also start the project using Spring CLI: 
 
spring init \
    --boot-version=4.0.0 \
    --dependencies=web \
    --group-id=com.example \
    --artifact-id=demoapp \
    --name=DemoApp \
    --package-name=com.example \
    --description="Sample Spring Boot Demo" \
    --build=maven \
    demoapp

Generate Project Structure 

 
demoapp/
├─ mvnw
├─ pom.xml
├─ src/main/java/com/example/DemoApp.java
├─ src/main/resources/application.properties
└─ src/test/java/com/example/DemoAppTests.java

Pom

The application build configuration is defined in pom.xml 
 
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
    https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>quick_start</artifactId>
    <version>0.0.1</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

Demo Application 

 
/**
 * SPRING BOOT - QUICK START
 * *
 * Spring Boot sits on top of the Spring Framework  removes much of the boilerplate, 
 * letting us build production-ready application quickly.
 * 
 * Spring Boot is the fastest way to start building Spring-based applications. 
 * You can start generating a project from Spring Initializr: 
 *      https://start.spring.io
 * 
 * POM:
 * *
 * The application build configuration is defined in pom.xml
 * Build and run the application using Maven.
 * Test the application with embedded Apache Tomcat server.
 * 
 * mvn package
 * mvn spring-boot:run
 * curl http://localhost:8080/hello    OR
 *
 * java -jar .\target\demo-0.0.1.jar
 * curl http://localhost:8080/hello
 *      # Hello World
 */

package com.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@RestController
public class DemoApp {
    public static void main(String[] args) {
        SpringApplication.run(DemoApp.class, args);
    }

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

Starter

A starter in Spring Boot is a preconfigured set of dependencies. Starters remove the need to manually manage dozen of individual dependencies. This is the starter used to build REST APIs and web applications with Spring Boot. 
 
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
This is the most common starter in Spring Boot because it enables: 
 
REST controllers (@RestController)
JSON serialization/deserialization
Embedded web server (Tomcat)
Spring MVC infrastructure

Started example 

 
/**
 * STARTERS - SPRING BOOT
 * *
 * A starter in Spring Boot is a preconfigured set of dependencies.
 * Starters remove the need to manually manage dozen of individual dependencies.
 * 
 * You include one dependency and automatically get:
 *  - All required libraries
 *  - Matching, compatible versions
 *  - Auto-configuration that works
 * 
 * Starter used to build REST APIs and web application:
 * 
 *   <dependency>
 *      <groupId>org.springframework.boot</groupId>
 *      <artifactId>spring-boot-starter-web</artifactId>
 *   </dependency>
 * 
 * This enables:
 *  - REST controllers (@RestController)
 *  - JSON (serialization/deserialization)
 *  - Embeded web server (Tomcat)
 *  - Spring MVC infrastructure
 * 
 * This code show how Spring Boot automatically enables JSON 
 * serialization using Jackson - without adding Jackson manually.
 * 
 * mvn spring-boot:run
 * curl http://localhost:8080/user
 *      {"name":"Ana","age":30}
 */

package com.example;

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

@RestController
public class StarterExample {
    
    @GetMapping("/user")
    public User getUser() {
        return new User("Ana", 30);
    }
}

/**
 * Simple data model (POJO - Plain Old Java Object).
 * Jackson, provided by starter, automatically serializes this class 
 * to JSON when returned from a controller.
 */
class User {
    private String name;
    private int age;

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() { return name; }
    public int getAge() { return age; }
}

Run 

 
mvn spring-boot:run
curl http://localhost:8080/user
{"name":"Ana","age":30}




References: