How to do it...

1. The very first thing that we will need to do is add a new dependency to build.gradle with the spring-boot-starter-web starter to get us all the necessary libraries for web-based functionality. The following code snippet is what it will look like:

dependencies { 
  compile("org.springframework.boot:spring-boot-starter-data-jpa") 
  compile("org.springframework.boot:spring-boot-starter-jdbc") 
  compile("org.springframework.boot:spring-boot-starter-web") 
  runtime("com.h2database:h2") 
  runtime("mysql:mysql-connector-java")
  testCompile("org.springframework.boot:spring-boot-starter-test") 
} 

1. Next, we will need to create a Spring controller that will be used to handle the web requests for the catalog data in our application. Let's start by creating a new package structure to house our controllers so that we have our code nicely grouped by its appropriate purposes. Create a package folder called controllers in the src/main/java/com/example/bookpub directory from the root of our project.
2. As we will be exposing the book data, let's create the controller class file called BookController in our newly created package with the following content:

@RestController 
@RequestMapping("/books") 
public class BookController { 
  @Autowired 
  private BookRepository bookRepository; 
 
  @RequestMapping(value = "", method = RequestMethod.GET) 
  public Iterable<Book> getAllBooks() { 
    return bookRepository.findAll(); 
  } 
 
  @RequestMapping(value = "/{isbn}", method =  
    RequestMethod.GET) 
  public Book getBook(@PathVariable String isbn) { 
    return bookRepository.findBookByIsbn(isbn); 
  } 
} 

1. Start the application by running ./gradlew clean bootRun.
2. After the application has started, open the browser and go to http://localhost:8080/books and you should see a response: [].