Entity to DTO mapping in Spring Boot - Mini Project: Build & Apply

Entity to DTO Mapping in Spring Boot

📖 Scenario: You are building a simple Spring Boot application to manage books in a library. The data is stored in an entity class, but you want to send only selected information to the user through a Data Transfer Object (DTO).

🎯 Goal: Learn how to create an entity class, a DTO class, and map data from the entity to the DTO in a clean and simple way.

📋 What You'll Learn

Create a Book entity class with fields id, title, author, and price.

Create a BookDTO class with fields title and author only.

Create a method to convert a Book entity to a BookDTO.

Use the mapping method to create a BookDTO from a Book instance.

💡 Why This Matters

🌍 Real World

In real applications, entities often contain sensitive or extra data not needed by users. DTOs help send only the necessary data, improving security and performance.

💼 Career

Understanding entity to DTO mapping is essential for backend developers working with Spring Boot to build clean, maintainable APIs.

1

Create the Book entity class

Create a class called Book with private fields Long id, String title, String author, and double price. Include public getters and setters for each field.

Spring Boot

// Your code here to create the Book entity class with fields and getters/setters

Need a hint?

Define private fields and generate public getters and setters for each field.

2

Create the BookDTO class

Create a class called BookDTO with private fields String title and String author. Include public getters and setters for these fields.

Spring Boot

public class Book {
    private Long id;
    private String title;
    private String author;
    private double price;

    public Long getId() {
        return id;
    }

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

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

// Your code here to create the BookDTO class with title and author fields and getters/setters

Need a hint?

Define the BookDTO class with only title and author fields and their getters and setters.

3

Create a method to map Book to BookDTO

Inside the BookDTO class, create a public static method called fromEntity that takes a Book object as a parameter and returns a BookDTO object. Copy the title and author values from the Book to the new BookDTO.

Spring Boot

public class Book {
    private Long id;
    private String title;
    private String author;
    private double price;

    public Long getId() {
        return id;
    }

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

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

public class BookDTO {
    private String title;
    private String author;

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    // Your code here to add fromEntity method
}

Need a hint?

Create a static method that creates a new BookDTO, copies title and author from the Book parameter, and returns the DTO.

4

Use the mapping method to create a BookDTO

Create a Book object called book and set its title to "Spring Boot Guide" and author to "John Doe". Then create a BookDTO object called bookDTO by calling BookDTO.fromEntity(book).

Spring Boot

public class Book {
    private Long id;
    private String title;
    private String author;
    private double price;

    public Long getId() {
        return id;
    }

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

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

public class BookDTO {
    private String title;
    private String author;

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public static BookDTO fromEntity(Book book) {
        BookDTO dto = new BookDTO();
        dto.setTitle(book.getTitle());
        dto.setAuthor(book.getAuthor());
        return dto;
    }
}

// Your code here to create book and bookDTO objects

Need a hint?

Create a Book object, set title and author, then create a BookDTO by calling the fromEntity method.