The ShoppingCart domain object represents a customer's shopping cart. The ShoppingCart manages the items a customer wants to buy and the customer's billing information, so the ShoppingCart needs to know when a customer opts into the automatic renewal.

To implement the automatic renewal, extend the ShoppingCart domain object to hold an autoBill property. This property denotes whether or not a customer has selected the automatic renewal feature.

1. Navigate to the ext-core project in extensions/core directory.
2. In the the ext-core project's com.extensions.domain package, found under the src/main/java directory, create a new package named shoppingcart.
3. In com.extensions.domain.shoppingcart, create a new interface named ExtShoppingCart and add the following code:

                     CoreTutorial3/ext-core/src/main/java/com/extensions/domain/shoppingcart/ExtShoppingCart.java
   package com.extensions.domain.shoppingcart;
   
   import com.elasticpath.domain.shoppingcart.ShoppingCart;
   
   /**
    * Extends ShoppingCart interface by adding 'AutoBill' methods.
    */
   public interface ExtShoppingCart extends ShoppingCart {
   	/**
   	 * Checks whether this order has been set as an auto bill order.
   	 *
   	 * @return true in case the order is of type auto bill
   	 */
   	boolean isAutoBill();
   
   	/**
   	 * Sets auto bill flag on this order.
   	 *
   	 * @param autoBill the auto bill flag
   	 */
   	void setAutoBill(boolean autoBill);
   }
                  

4. In com.extensions.domain.shoppingcart, create a new package named impl
5. In com.extensions.domain.shoppingcart.impl, create a new class named ExtShoppingCartImpl and add the following code:

                     CoreTutorial3/ext-core/src/main/java/com/extensions/domain/shoppingcart/impl/ExtShoppingCartImpl.java
   package com.extensions.domain.shoppingcart.impl;
   
   import com.extensions.domain.shoppingcart.ExtShoppingCart;
   
   import com.elasticpath.domain.shoppingcart.impl.ShoppingCartImpl;
   
   /**
    * Extends 'ShoppingCartImpl' to enable shopping cart to save 'autoBill' value.
    */
   public class ExtShoppingCartImpl extends ShoppingCartImpl implements ExtShoppingCart {
   
   	/**
   	 * Serial version id.
   	 */
   	public static final long serialVersionUID = 5000000001L;
   
   	private boolean autoBill;
   
   	/**
   	 * Returns whether automatic renewal and billing is enabled for this order.
   	 *
   	 * @return true if automatic renewal and billing is enabled.
   	 */
   	public boolean isAutoBill() {
   		return this.autoBill;
   	}
   
   	/**
   	 * Sets whether automatic renewal and billing is enabled for this order.
   	 *
   	 * @param autoBill true to enable automatic renewal and billing
   	 */
   	public void setAutoBill(final boolean autoBill) {
   		this.autoBill = autoBill;
   	}
   }
                  

The Order domain object represents a customer's order. Elastic Path creates the Order object as the customer completes checkout and saves the Order in the database as a record of the customer's purchase.

To save the autoBill property in the database, you need to extend the Order domain object to have an autoBill property:

1. In the ext-core project's com.extensions.domain package, create a new package named order.
2. In com.extensions.domain.order, create an interface named ExtOrder and add the following code:

                     CoreTutorial3/ext-core/src/main/java/com/extensions/domain/order/ExtOrder.java
   package com.extensions.domain.order;
   
   import com.elasticpath.domain.order.Order;
   
   /**
    * Extends Order interface by adding 'AutoBill' methods.
    */
   public interface ExtOrder extends Order {
   
   	/**
   	 * Returns whether automatic renewal and billing is enabled for this order.
   	 *
   	 * @return true if automatic renewal and billing is enabled.
   	 */
   	boolean isAutoBill();
   
   	/**
   	 * Sets whether automatic renewal and billing is enabled for this order.
   	 *
   	 * @param autoBill true to enable automatic renewal and billing
   	 */
   	void setAutoBill(boolean autoBill);
   }
                  

3. In com.extensions.domain.order, create a new package named impl
4. In com.extensions.domain.order.impl, create a new class named ExtOrderImpl and add the following code:

                     CoreTutorial3/ext-core/src/main/java/com/extensions/domain/order/impl/ExtOrderImpl.java
   package com.extensions.domain.order.impl;
   
   import javax.persistence.Basic;
   import javax.persistence.Column;
   import javax.persistence.DiscriminatorValue;
   import javax.persistence.Entity;
   import javax.persistence.PrimaryKeyJoinColumn;
   import javax.persistence.Table;
   
   import com.extensions.domain.order.ExtOrder;
   
   import com.elasticpath.domain.order.impl.OrderImpl;
   
   /**
    * Implementation of Order extension interface.
    */
   @Entity
   @Table(name = ExtOrderImpl.TABLE_NAME)
   @DiscriminatorValue("extOrder")
   @PrimaryKeyJoinColumn(name = "UIDPK", referencedColumnName = "UIDPK")
   public class ExtOrderImpl extends OrderImpl implements ExtOrder {
   	/**
   	 * Serial version id.
   	 */
   	public static final long serialVersionUID = 5000000092L;
   
   	/**
   	 * Table to which ExtOrderImpl objects will be persisted.
   	 */
   	public static final String TABLE_NAME = "TORDEREXT";
   
   	private boolean autoBill;
   
   	/**
   	 * Checks whether this order has been set as an auto bill order.
   	 *
   	 * @return true in case the order is of type auto bill
   	 */
   	@Basic
   	@Column(name = "AUTOBILL")
   	public boolean isAutoBill() {
   		return autoBill;
   	}
   
   	/**
   	 * Sets auto bill flag on this order.
   	 *
   	 * @param autoBill the auto bill flag
   	 */
   	public void setAutoBill(final boolean autoBill) {
   		this.autoBill = autoBill;
   	}
   
   	/**
   	 * Returns <code>true</code> if this order is equal to the given object.
   	 *
   	 * @param obj the given object
   	 * @return <code>true</code> if this order is equal to the given object
   	 */
   	@Override
   	public boolean equals(final Object obj) {
   		if (!(obj instanceof ExtOrder)) {
   			return false;
   		}
   
   		// check if unextended objects are equal
   		if (!super.equals(obj)) {
   			return false;
   		}
   
   		// compare object id
   		if (this == obj) {
   			return true;
   		}
   
   		// make sure autobill properties are equal
   		ExtOrder other = (ExtOrder) obj;
   		if (this.isAutoBill() == other.isAutoBill()) {
   			return true;
   		}
   
   		return false;
   	}
   
   	@Override
   	public int hashCode() {
   		int code = super.hashCode();
   		if (isAutoBill()) {
   			return code + 1;
   		}
   		return code;
   	}
   }
                  

As mentioned above, the Order object is created at checkout and is saved in the database as a record of the customer's purchase. To save the autoBill value as part of the Order, the Order needs to get the autoBill value from the ShoppingCart.

In core, there is a service layer class for handling additional actions before, during, or after the checkout process is complete. You'll overwrite a method of this service to pass the autoBill value from the ShoppingCart to Order.

1. In the ext-core project's com.extensions package, create a new package named service.shoppingcart.impl.
2. In com.extensions.service.shoppingcart.impl, create a new class named ExtCheckoutEventHandlerImpl and add the following code:

                     CoreTutorial3/ext-core/src/main/java/com/extensions/service/shoppingcart/impl/ExtCheckoutEventHandlerImpl.java
   package com.extensions.service.shoppingcart.impl;
   
   import java.util.Collection;
   
   import com.extensions.domain.order.ExtOrder;
   import com.extensions.domain.shoppingcart.impl.ExtShoppingCartImpl;
   
   import com.elasticpath.domain.order.Order;
   import com.elasticpath.domain.order.OrderPayment;
   import com.elasticpath.domain.shoppingcart.ShoppingCart;
   import com.elasticpath.service.shoppingcart.impl.AbstractCheckoutEventHandlerImpl;
   
   /**
    * Defines a handler to deal with checkout events.
    */
   public class ExtCheckoutEventHandlerImpl extends AbstractCheckoutEventHandlerImpl {
   
   	/**
   	 * This event occurs after a checkout has been processed but before the order has been persisted.
   	 * This event occurs between preCheckout and postCheckout.
   	 *
   	 * @param shoppingCart the shopping cart being checked out
   	 * @param orderPayment information about the method of payment
   	 * @param order the order object resulting from the checkout
   	 */
   	public void preCheckoutOrderPersist(final ShoppingCart shoppingCart,
   			final Collection<OrderPayment> orderPayment, final Order order) {
   		((ExtOrder) order).setAutoBill(((ExtShoppingCartImpl) shoppingCart).isAutoBill());
   	}
   }
                  

Before the Commerce Engine core will use your extended Order, ShoppingCart and CheckoutEventHandler classes, you need to redefine some Java Bean definitions in your core extension's ep-core-plugin.xml:

• In ext-core/src/main/resources/META-INF/conf/ep-core-plugin.xml, insert the following bean definitions before the </beans> tag:

                    CoreTutorial3/ext-core/src/main/resources/META-INF/conf/ep-core-plugin.xml
  	<bean id="order" class="com.extensions.domain.order.impl.ExtOrderImpl" scope="prototype"/commerce-legacy/>
  	<bean id="shoppingCart" class="com.extensions.domain.shoppingcart.impl.ExtShoppingCartImpl" scope="prototype"/commerce-legacy/>
  
  	<bean id="autoBillEventHandler"
  			class="com.extensions.service.shoppingcart.impl.ExtCheckoutEventHandlerImpl">
  	</bean>
  
  	<util:list id="checkoutEventHandlers">
  		<ref bean="autoBillEventHandler"/commerce-legacy/>
  	</util:list>