Build an API with Spring Boot

To get started with Spring Boot, navigate to start.spring.io. In the “Search for dependencies” field, select the following:

DevTools: Provides auto-reloading of your application when files change
H2: An in-memory database
JPA: Standard ORM for Java
Rest Repositories: Allows you to expose your JPA repositories as REST endpoints
Web: Spring MVC with Jackson (for JSON), Hibernate Validator, and embedded Tomcat

Open the “server” project in your favorite IDE and run DemoApplication or start it from the command line using ./mvnw spring-boot:run.

Create a com.example.demo.beer package and a Beer.java file in it. This will be the entity that holds your data.

package com.example.demo.beer;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class Beer {

    @Id
    @GeneratedValue
    private Long id;
    private String name;

    public Beer() {}

    public Beer(String name) {
        this.name = name;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Beer{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

Add a BeerRepository class that leverages Spring Data to do CRUD on this entity.

package com.example.demo.beer;

import org.springframework.data.jpa.repository.JpaRepository;

interface BeerRepository extends JpaRepository<Beer, Long> {
}

Add a BeerCommandLineRunner that uses this repository and creates a default set of data.

package com.example.demo.beer;

import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

import java.util.stream.Stream;

@Component
public class BeerCommandLineRunner implements CommandLineRunner {

    private final BeerRepository repository;

    public BeerCommandLineRunner(BeerRepository repository) {
        this.repository = repository;
    }

    @Override
    public void run(String... strings) throws Exception {
        // Top beers from https://www.beeradvocate.com/lists/top/
        Stream.of("Kentucky Brunch Brand Stout", "Good Morning", "Very Hazy", "King Julius",
                "Budweiser", "Coors Light", "PBR").forEach(name ->
                repository.save(new Beer(name))
        );
        repository.findAll().forEach(System.out::println);
    }
}

Rebuild your project and you should see a list of beers printed in your terminal.

Add a @RepositoryRestResource annotation to BeerRepository to expose all its CRUD operations as REST endpoints.

import org.springframework.data.rest.core.annotation.RepositoryRestResource;

@RepositoryRestResource
interface BeerRepository extends JpaRepository<Beer, Long> {
}

Add a BeerController class to create an endpoint that filters out less-than-great beers.

package com.example.demo.beer;

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

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.stream.Collectors;

@RestController
public class BeerController {
    private BeerRepository repository;

    public BeerController(BeerRepository repository) {
        this.repository = repository;
    }

    @GetMapping("/good-beers")
    public Collection<Beer> goodBeers() {

        return repository.findAll().stream()
                .filter(this::isGreat)
                .collect(Collectors.toList());
    }

    private boolean isGreat(Beer beer) {
        return !beer.getName().equals("Budweiser") &&
                !beer.getName().equals("Coors Light") &&
                !beer.getName().equals("PBR");
    }
}