Como construir uma API Rest com Spring Boot usando MySQL e JPA

package com.rest.API;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class ApiApplication {
public static void main(String[] args) {
      SpringApplication.run(ApiApplication.class, args);
   }
}

1. Aplicativo Spring
2. Aplicativo SpringBoot

1. @Componente — Diz ao compilador que a classe a seguir é um componente que deve ser incluído ao compilar todo o aplicativo.
2. @ComponentScan — Este faz o Scan de quais pacotes vamos usar na seguinte classe Java.
3. @EnableAutoConfiguration — permite que o mecanismo de autoconfiguração do Spring Boot importe módulos importantes para que o Spring Boot seja executado.

Vamos criar um modelo para nossos dados

package com.rest.API.model;
import javax.persistence.*;
import javax.validation.constraints.NotBlank;
@Entity
@Table(name = "books")
public class Book {
    @Id
    @GeneratedValue
    private Long id;
@NotBlank
    private String book_name;
@NotBlank
    private String author_name;
@NotBlank
    private String isbn;
public Book(){
        super();
    }
public Book(Long id, String book_name, String author_name, String isbn) {
        super();
        this.id = id;
        this.book_name = book_name;
        this.author_name = author_name;
        this.isbn=isbn;
    }
public Long getId() {
        return id;
    }
public void setId(Long id) {
        this.id = id;
    }
public String getBook_name() {
        return book_name;
    }
public void setBook_name(String book_name) {
        this.book_name = book_name;
    }
public String getAuthor_name() {
        return author_name;
    }
public void setAuthor_name(String author_name) {
        this.author_name = author_name;
    }
public String getIsbn() {
        return isbn;
    }
public void setIsbn(String isbn) {
        this.isbn = isbn;
    }
}

Criando o repositório

package com.rest.API.repository;
import com.rest.API.model.Book;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
@Repository
public interface BookRepository extends JpaRepository<Book, Long> {
}

.findAll() - to get All datas
.save()    - to save the got Data
.delete()  - to delete the data

Criando controlador e tratamento de exceção

package com.rest.API.controller;

import com.rest.API.exception.BookNotFoundException;
import com.rest.API.model.Book;
import com.rest.API.repository.BookRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import org.springframework.http.ResponseEntity;
import javax.validation.Valid;
import java.util.List;

@RestController
public class BookController {

@Autowired
    BookRepository bookRepository;

// Get All Notes
    @GetMapping("/books")
    public List<Book> getAllNotes() {
        return bookRepository.findAll();
    }

// Create a new Note
    @PostMapping("/books")
    public Book createNote(@Valid @RequestBody Book book) {
        return bookRepository.save(book);
    }

// Get a Single Note
    @GetMapping("/books/{id}")
    public Book getNoteById(@PathVariable(value = "id") Long bookId) throws BookNotFoundException {
        return bookRepository.findById(bookId)
                .orElseThrow(() -> new BookNotFoundException(bookId));
    }

// Update a Note
    @PutMapping("/books/{id}")
    public Book updateNote(@PathVariable(value = "id") Long bookId,
                           @Valid @RequestBody Book bookDetails) throws BookNotFoundException {

Book book = bookRepository.findById(bookId)
                .orElseThrow(() -> new BookNotFoundException(bookId));

book.setBook_name(bookDetails.getBook_name());
        book.setAuthor_name(bookDetails.getAuthor_name());
        book.setIsbn(bookDetails.getIsbn());

Book updatedBook = bookRepository.save(book);

return updatedBook;
    }

// Delete a Note
    @DeleteMapping("/books/{id}")
    public ResponseEntity<?> deleteBook(@PathVariable(value = "id") Long bookId) throws BookNotFoundException {
        Book book = bookRepository.findById(bookId)
                .orElseThrow(() -> new BookNotFoundException(bookId));

bookRepository.delete(book);

return ResponseEntity.ok().build();
    }
}

1. RestController: Esta anotação é usada para denotar cada método na classe anotada como Objeto de Domínio.

Criando uma NotFoundException se não houver tal book_id

package com.rest.API.exception;
public class BookNotFoundException extends Exception {
private long book_id;
public BookNotFoundException(long book_id) {
        super(String.format("Book is not found with id : '%s'", book_id));
        }
}

Conectando com banco de dados MySql

## Spring DATASOURCE (DataSourceAutoConfiguration & DataSourceProperties)
spring.datasource.url = jdbc:mysql://localhost:3306/library
spring.datasource.username = root //normally put your MySQL username 
spring.datasource.password = YOUR_MYSQL_PASSWORD
## Hibernate Properties
# The SQL dialect makes Hibernate generate better SQL for the chosen database
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQL5InnoDBDialect
# Hibernate ddl auto (create, create-drop, validate, update)
spring.jpa.hibernate.ddl-auto = update