Spring Boot Tutorial

Introduction

Spring Boot is one of the most popular and most used frameworks for building microservices. Here is a Basic Spring Boot Tutorial with the latest version of Sprint Boot (2.0.5.RELEASE), as of October 2018, which shows you how to build RESTful GET and POST APIs using Spring Boot.

What is Spring Boot?
From their website:
Takes an opinionated view of building production-ready Spring applications. Spring Boot favors convention over configuration and is designed to get you up and running as quickly as possible.
Spring Boot makes it easy to create stand-alone, production-grade Spring based Applications that you can "just run". We take an opinionated view of the Spring platform and third-party libraries so you can get started with minimum fuss. Most Spring Boot applications need very little Spring configuration.
Website: Spring Boot Website

Requirements to Run the Application:

1. Java
2. Maven
3. IDE of your choice

In a few simple steps I will help you to get a Spring Boot Application up and running which you can use as a base to build additional functionalities.

Step 1: Requirements in pom.xml

The following are required in pom.xml:

        
        <parent>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-parent</artifactId>
            <version>2.0.5.RELEASE</version>
        </parent>

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

Here is the full 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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <groupId>com.aj.basicspringboot</groupId>
 <artifactId>BasicSpringBoot</artifactId>
 <version>1.0.0</version>
    
    <parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>2.0.5.RELEASE</version>
 </parent>

 <properties>
        <jdk.version>1.8</jdk.version>
        <java.version>1.8</java.version>
        <packaging>jar</packaging>
 </properties>

 <dependencies>

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

 </dependencies>

 <build>
  <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.0</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
   <plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
   </plugin>
  </plugins>
 </build>
</project>

Step 2: Application class

The application class is the entry point for the Application. The following Annotation is added to this class:

@SpringBootApplication

@SpringBootApplication : Signifies that it is a Spring Boot Application. This annotation is equivalent to using @Configuration, @EnableAutoConfiguration and @ComponentScan with their default attributes.

BasicSpringBootApplication.java

package com.aj.basicspringboot;

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

@SpringBootApplication
public class BasicSpringBootApplication {

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

Step 3: Controller Class for RESTful APIs

Java Class which acts as Rest Controller. In this class I have given examples of how to use:

@RequestMapping
@RequestBody
@PathVariable
@GetMapping - For GET API
@PostMapping - For POST API

PingController.java

package com.aj.basicspringboot.controller;

import com.aj.basicspringboot.domain.PingRequest;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;

import java.util.HashMap;
import java.util.Map;


@RestController
@RequestMapping("/")
public class PingController {

    private static final Logger logger = LoggerFactory.getLogger(PingController.class);

    @GetMapping("ping")
    public ResponseEntity<Map<String, String>> ping() {
        Map<String, String> response = new HashMap<>();
        response.put("message", "pong");
        return new ResponseEntity<>(response, HttpStatus.OK);
    }

    //GET API with path variable
    @GetMapping("ping/{message}")
 public ResponseEntity<Map<String, String>> pingPath(@PathVariable String message) {
  Map<String, String> response = new HashMap<>();
  response.put(message, "pong");
        return new ResponseEntity<>(response, HttpStatus.OK);
 }

    @PostMapping("ping")
    public ResponseEntity<Map<String, String>> send(@RequestBody PingRequest pingRequest) {
        logger.info("Request received is: " + pingRequest );
        Map<String, String> response = new HashMap<>();
        response.put("message", "");
        if("ping".equalsIgnoreCase(pingRequest.getInput())) {
            response.put("message", "pong");
        }
        return new ResponseEntity<>(response, HttpStatus.OK);
    }
}

Project Setup:

For Java Setup, please refer to: Java Setup
For Maven Setup, please refer to: Maven Setup
For Git and Project Setup, please refer to: Git and Project Setup

Run Application:

1. To run application in your IDE use:
Program arguments: src/main/resources/application.yml

2. To run JAR from command prompt:
Build jar by using command:
mvn clean install
Run JAR by using command in Project folder location:
java -jar target\BasicSpringBoot-1.0.0.jar src\main\resources\application.yml

Please note: I have set the server port as 4000 in application.yml

API calls and results:

1. GET API for Ping:

http://localhost:4000/ping

2. GET API for Ping with Path Variable:
http://localhost:4000/ping/message

3. POST API for Ping: http://localhost:4000/ping
JSON Request Body:

  {
    "input": "ping"
  }

Conclusion and GitHub link:

This tutorial gives a basic introduction to writing RESTful APIs using Spring Boot. The code used in this post is available on GitHub.
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