Here basic REST APIs that are needed for Library sytem will be written i.e. CRUD(Create, Retrieve, Update and Delete) REST service on entity Book. As per the specs the Retrieve/ Get method will be available to both Member and Admin, only the representation will differ. For the simplicity of this topic, same representation will be returned in GET call. Different representations will be added once security/roles are added to application since the implementation or calls may differ. Also handling for exception scenarios will be added in later topics.
Code reference: https://github.com/GlueCoders/springboot-guide/releases/tag/rest-with-mvc
Below is the definition of Book, this is the representation that will be mapped to REST responses and requests.
public class Book implements Serializable {
private String title;
private String author;
private int publishedYear;
private List<String> categories;
private String publisher;
private long isbnCode;
}
This class serves as REST layer which will be mapped to HTTP requests.
package org.gluecoders.library.rest;
import org.gluecoders.library.models.Book;
import org.gluecoders.library.services.BookService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import java.util.List;
@RestController()
@RequestMapping(produces = MediaType.APPLICATION_JSON_UTF8_VALUE, path = "/books")
public class Books {
@Autowired
private BookService bookService;
@GetMapping
public ResponseEntity<List<Book>> getAllBooks() {
List<Book> list = bookService.getAllBooks();
return new ResponseEntity<>(list, HttpStatus.OK);
}
@GetMapping("/{isbn}")
public ResponseEntity<Book> getBook(@PathVariable("isbn") long isbnCode) {
Book book = bookService.getBookByISBN(isbnCode);
if(book == null) {
return new ResponseEntity<>(HttpStatus.NOT_FOUND);
}else{
return new ResponseEntity<>(book, HttpStatus.OK);
}
}
@PostMapping
public ResponseEntity<Book> addBook(@RequestBody Book book) {
book = bookService.addBook(book);
return new ResponseEntity<>(book, HttpStatus.CREATED);
}
@DeleteMapping("/{isbn}")
public ResponseEntity deleteBook(@PathVariable("isbn") long isbnCode) {
bookService.deleteBook(isbnCode);
return new ResponseEntity(HttpStatus.OK);
}
}
Let’s go to individual lines :
@RestController - Tells Spring to map the methods of this class to HTTP requests.@RequestMapping - Defines the HTTP path that should be mapped to the controller class.@GetMapping . @PostMapping, @DeleteMapping - These annotations are flavoured @RequestMapping which define HTTP methods as well. These annotations have parameters for HTTP path, Content-Type and Accept parameters.ResponseEntity - This is used to return response body, headers and status code.Below is the interface to be consumed by REST layer in our application.
public interface BookService {
List<Book> getAllBooks();
Book addBook(Book book);
Book getBookByISBN(long isbn);
void deleteBook(long isbn);
}
Below is the default implementation of this interface, which as of now will do nothing but just return null or empty lists as required from signature.
package org.gluecoders.library.services;
import org.gluecoders.library.models.Book;
import org.springframework.stereotype.Component;
import java.util.Collections;
import java.util.List;
@Component
public class DefaultBookService implements BookService {
@Override
public List<Book> getAllBooks() {
return Collections.emptyList();
}
@Override
public Book addBook(Book book) {
return book;
}
@Override
public Book getBookByISBN(long isbn) {
return null;
}
@Override
public void deleteBook(long isbn) {
}
}
@Component is a Spring annotation which creates a instance of the class and registers it in Bean Registry. Anywhere this bean’s instance can be acquired by using @Autowired annotation as shown in REST layer.