Chapter 6: Enterprise JavaBeans Overview

EJB transaction attribute values

Each EJB component has a transaction attribute that determines how instances of the component participate in transactions. In EAServer, you set the transaction attribute in the Transaction tab of the Component Properties dialog box.

When you design an EJB component, you must decide how the bean will manage transaction demarcation: either programmatically in the business methods, or whether the transaction demarcation will be managed by the container based on the value of the transaction attribute in the deployment descriptor.

A session bean can use either bean-managed transaction demarcation or with container-managed transaction demarcation; you cannot create a session bean where some methods use container-managed demarcation and others use bean-managed demarcation. An entity bean must use container-managed transaction demarcation.

Table 6-1 lists the transaction attribute values. Requires, Supports, Requires New, or Mandatory are the values that specify container-managed transaction demarcation. You can set the Transaction Attribute for the component and for individual methods in the home and remote interfaces. Values set at the method level override the component setting.

**Table 6-1: Transaction attribute values**
Attribute	Description
Not Supported	(The component-level default.) The EJB component's methods never execute as part of a transaction. If the EJB component is activated by a client that has a pending transaction, the EJB component’s work is performed outside the existing transaction. Since entity beans are almost always involved in transactions, this value is not usually used for an entity bean.
Supports	The EJB component can execute in the context of an EAServer transaction, but a transaction is not required to execute the component’s methods. If a method is called by a base client that has a pending transaction, the method’s database work occurs in the scope of the client’s transaction. Otherwise, the EJB component’s database work is done outside of any transaction.
Required	The EJB component always executes in a transaction. Use this option when your EJB component’s database activity needs to be coordinated with other components, so that all components participate in the same transaction.
Requires New	Whenever the EJB component is instantiated, a new transaction begins.
Mandatory	EJB component methods must be called in the context of a pending transaction. If a client calls a method without an open transaction, the EAServer ORB throws an exception.
Never	The component’s methods never execute as part of a transaction, and the component may cannot be called in the context of a transaction. If a client or another component calls the component with an outstanding transaction, EAServer throws an exception.
Bean Managed	(For EJB session beans only.) The EJB component can explicitly begin, commit, and roll back new, independent transactions by using the javax.transaction.UserTransaction interface. Transactions begun by the component execute independently of the client’s transaction. If the component has not begun a transaction, the component’s database work is performed independently of any EAServer transaction.
Default to component	(Method-level default) In the Transactions tab of the Method properties window, choose this option if the method should inherit the transaction attribute set in the component properties.

View this book as PDF