Transfer Object

Remember the Example from the Data Access Object pattern, where we used to send information about books from one object to another. In case just using built-in data-types (such as String, int, ...) a call to saveBook would look like

  dao.saveBook("123456789X", "A Book of Books", "Martha T. Bone");

Now imagine we want to save more information than just isbn, title and author. We could add publisher, price, coverimage, release-date, and even more. The method-call would become rather unreadable.

Furthermore think about a method returning data of a book. Through it is not possible in Java to return more than one value, you would have to make several calls to get all data.

The solution for this problem is the Transfer Object. A Transfer Object is an object encapsulating data. A single method call is now sufficient to send and retrieve the Transfer Object and all included data.

Applicability / Uses

Use the Transfer Object pattern when:

  • the number of calls made by a client to a Data Access Object or Enterprise Bean impacts network performance
  • you want to reduce communication effort when dealing with a lot of small data entities

Related Patterns

  • Data Access Object: A Transfer Object pattern is often used in combination with a Data Access Object pattern.

Structure

UML diagram of the sample code:

UML diagram of the sample code

Sample

In this example we consider an advanced Book.

public class Book {
  private String isbn;
  private String title;
  private String author;
  private String publisher;
  private float price;
  private int pages;
  private Date releaseDate;
  private byte[] coverImage;

  public String getAuthor() {
    return author;
  }

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

  public String getIsbn() {
    return isbn;
  }

  public void setIsbn(String isbn) {
    this.isbn = isbn;
  }

  public String getTitle() {
    return title;
  }

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

  public byte[] getCoverImage() {
    return coverImage;
  }

  public void setCoverImage(byte[] coverImage) {
    this.coverImage = coverImage;
  }

  public int getPages() {
    return pages;
  }

  public void setPages(int pages) {
    this.pages = pages;
  }

  public float getPrice() {
    return price;
  }

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

  public String getPublisher() {
    return publisher;
  }

  public void setPublisher(String publisher) {
    this.publisher = publisher;
  }

  public Date getReleaseDate() {
    return releaseDate;
  }

  public void setReleaseDate(Date releaseDate) {
    this.releaseDate = releaseDate;
  }
}

References / More Info

Data Transfer Object - Wikipedia