Sending Book objects

Rather than plain strings, we would like to send and receive all the information about a book in one go. To do this, we will create a Data Transfer Object (DTO) class, which will be automatically turned to JSON by Micronaut so long as we annotate it as @Serdeable and follow certain conventions.

Writing the Book DTO

Note: the name Serdeable comes from “serialisable + deserialisable”. Serialisation is the process of turning an in-memory object into a stream of bytes that you can send over the network or save into a file (e.g. by representing it as JSON). Deserialisation is the reverse process of reading a stream of bytes and turning it into an in-memory object.

Create a new dto subpackage inside uk.ac.york.cs.eng2.books, and create a Book class inside it. Annotate it with @Serdeable, to indicate to Micronaut that you want to serialise and deserialise it to/from JSON:

@Serdeable
public class Book {
}

For this example, let’s track the title and the full name of the author, and an integer id. We will need to define them as properties to be serialised and deserialised. There are several ways to do it (see the docs). For this practical, we will use a pair of getter and setter methods.

For instance, to track the title:

• Add a private String title field to Book.
• Add a public getTitle() method that returns the value of the title field.
• Add a public setTitle(String newTitle) method that changes the value of the title field.

Do the same for the author and the id.

Note: in IntelliJ, you can usually write just the fields, and then use “Code - Generate” to have it producer the getter and setter methods.

Using the Book DTO

Go back to our BooksController. Rename the getTitles() method to getBooks(), change the @Get("/titles") to just @Get, and have it return a List<Book>. Change the code so that it creates a few Book objects instead of just using strings.

Once you’re done with the changes, run the application as before, and try out the endpoint through the Swagger UI. If you expand GET /books and scroll down to the “Example Value”, you’ll notice that it now shows a JSON object:

[
  {
    "id": 0,
    "title": "string",
    "author": "string"
  }
]

Click on “Try it out” and then “Execute” to run your endpoint and check that it works as intended. You should get an HTTP 200 OK response like this one:

[
  {
    "id": 1,
    "title": "Title 1",
    "author": "Author 1"
  },
  {
    "id": 2,
    "title": "Title 2",
    "author": "Author 2"
  }
]