Java Enterprise Best Practices

Use Business Interfaces

Because the bean implementation class does not inherit from the bean interface, it’s a fairly common error to get a mismatch in business method signatures between the implementation and the interface. Typically, you would have to package and deploy the EJBs to see the error. Needless to say, this can be very frustrating at times, especially because most of these errors are simple typos or missed method parameters.

One common practice is to use business interfaces to enforce compile-time checks. To do this, create a new interface that contains only business methods of your bean, and let both the remote/local bean interface and the implementation class inherit from it. However, even though this method will work for all types of beans (CMP, BMP, local, or remote), there are some inconveniences when dealing with remote beans. Namely, because remote bean interfaces must throw RemoteException, you are also forced to do this in your business interface. Also, a minor inconvenience is that all method parameters must be Serializable .

Example 2-2 shows the key interfaces for a remote bean.

Example 2-2. The order interfaces and implementation

// Business interface public interface Order { public int getQuantity( ) throws RemoteException; public void setQuantity (int quantity) throws RemoteException; public double getPricePerItem( ) throws RemoteException; public void setPricePerItem (double price) throws RemoteException; public double getTotalPrice( ) throws RemoteException; ...