JavaBeans Component Design Conventions

JavaBeans component design conventions govern the properties of the class and govern the public methods that give access to the properties.

A JavaBeans component property can be:

• Read/write, read-only, or write-only

• Simple, which means it contains a single value, or indexed, which means it represents an array of values

A property does not have to be implemented by an instance variable. It must simply be accessible using public methods that conform to the following conventions:

• For each readable property, the bean must have a method of the form:

  PropertyClass getProperty() { ... }

• For each writable property, the bean must have a method of the form:

  setProperty(PropertyClass pc) { ... }

In addition to the property methods, a JavaBeans component must define a constructor that takes no parameters.

The Duke’s Bookstore application JSP pages bookstore.jsp, bookdetails.jsp, catalog.jsp, and showcart.jsp, all located at tut-install/javaeetutorial5/examples/web/bookstore2/web, use the tut-install/javaeetutorial5/examples/web/bookstore2/src/java/com/sun/bookstore2/database/BookDB.java JavaBeans component.

BookDB provides a JavaBeans component front end to the access object BookDBAO. The JSP pages showcart.jsp and cashier.jsp access the bean tut-install/javaeetutorial5/examples/web/bookstore/src/com/sun/bookstore/cart/ShoppingCart.java, which represents a user’s shopping cart.

The BookDB bean has two writable properties, bookId and database, and three readable properties: bookDetails, numberOfBooks, and books. These latter properties do not correspond to any instance variables but rather are a function of the bookId and database properties.

package database;
public class BookDB {
    private String bookId = "0";
    private BookDBAO database = null;
    public BookDB () {
    }
    public void setBookId(String bookId) {
    this.bookId = bookId;
    }
    public void setDatabase(BookDBAO database) {
    this.database = database;
    }
    public Book getBook() throws
         BookNotFoundException {
        return (Book)database.getBook(bookId);
     }
    public List getBooks() throws BooksNotFoundException {
        return database.getBooks();
    }
    public void buyBooks(ShoppingCart cart)
         throws OrderException {
        database.buyBooks(cart);
    }
    public int getNumberOfBooks() throws BooksNotFoundException {
        return database.getNumberOfBooks();
    }
}