EJB - Entity Beans III | Java Tips Blog

EJB - Entity Beans III

4 April 2008

This post is in continuation of EJB - Entity Beans II. Do read that one first. This post continues to address requirements about declaring primary keys for Entity beans.

A primary key class must meet the following requirements:

- class must be serializable
- access control modifier of the class must be public.
- all fields must be declared as public.
- fields must be a subset of the bean’s persistent fields.
- public default constructor is a must
- class should implement the hashCode() and equals(Object other) methods

Lets take an example. The example class has a composite primary key.

public class PurchaseOrderKey implements java.io.Serializable {
 
  public String productModel;
  public String vendorId;
 
  public PurchaseOrderKey() { };
 
  public boolean equals(Object other) {
 
    if (other instanceof PurchaseOrderKey) {
      return (productModel.equals(
          ((PurchaseOrderKey)other).productModel) &&
          vendorId.equals(
          ((PurchaseOrderKey)other).vendorId));
    }
    return false;
  }
 
  public int hashCode() {
    return productModel.concat(vendorId).hashCode();
  }
}