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The Java EE 6 Tutorial, Volume I

Chapter 26 Introduction to JavaTM EE Supporting Technologies

The Java EE platform includes several technologies and APIs that extend its functionality. These technologies allow applications to access a wide range of services in a uniform manner.

This chapter introduces the following Java EE technologies:

These technologies are explained in greater in subsequent chapters: Chapter 27, Transactions and Chapter 28, Resource Connections.

The following topics are addressed here:

Transactions

A transaction is a series of actions in a Java EE application that must all complete successfully or else all the changes in each action are backed out. Transactions end in either a commit or a rollback.

The Java Transaction API (JTA) allows applications to access transactions in a manner that is independent of specific implementations. JTA specifies standard Java interfaces between a transaction manager and the parties involved in a distributed transaction system: the transactional application, the Java EE server, and the manager that controls access to the shared resources affected by the transactions.

The JTA defines the UserTransaction interface that is used by applications to start, and commit or abort transactions. Application components get a UserTransaction object through a JNDI lookup using the name java:comp/UserTransaction or by requesting injection of a UserTransaction object. A number of interfaces defined by JTA are used by an application server to communicate with a transaction manager, and for a transaction manager to interact with a resource manager.

See the Chapter 27, Transactions chapter for a more detailed explanation. The JTA 1.1 specification is available at http://java.sun.com/javaee/technologies/jta/index.jsp.

Resources

A resource is a program object that provides connections to systems such as database servers and messaging systems.

The Java EE Connector Architecture and Resource Adapters

The Java EE Connector 1.6 architecture enables Java EE components to interact with enterprise information systems (EISs) and EISs to interact with Java EE components. EIS software includes various types of systems: enterprise resource planning (ERP), mainframe transaction processing, and nonrelational databases, among others. Connector architecture simplifies the integration of diverse EISs. Each EIS requires only one implementation of the Connector architecture. Because an implementation adheres to the Connector specification, it is portable across all compliant Java EE servers.

The specification defines the contracts for an application server as well as for resource adapters, which are system-level software drivers for specific EIS resources. These standard contracts provide pluggability between application servers and EISs. The Java EE Connector 1.6 specification defines new system contracts such as Generic Work Context and Security Inflow.

The Java EE Connector 1.6 specification is available at: http://jcp.org/en/jsr/detail?id=322

A resource adapter is a Java EE component that implements the Connector architecture for a specific EIS.

A resource adapter can choose to support the following levels of transactions:

See the Chapter 28, Resource Connections chapter for a more detailed explanation of resource adapters.

Java Message Service

Messaging is a method of communication between software components or applications. A messaging system is a peer-to-peer facility: A messaging client can send messages to, and receive messages from, any other client. Each client connects to a messaging agent that provides facilities for creating, sending, receiving, and reading messages.

The Java Message Service API is a Java API that allows applications to create, send, receive, and read messages. Designed by Sun and several partner companies, the JMS API defines a common set of interfaces and associated semantics that allow programs written in the Java programming language to communicate with other messaging implementations.

The JMS API minimizes the set of concepts a programmer must learn in order to use messaging products but provides enough features to support sophisticated messaging applications. It also strives to maximize the portability of JMS applications across JMS providers in the same messaging domain.

Sun GlassFishTM Enterprise Server v3 implements the Java Message Service (JMS) API by integrating the Sun GlassFish Message Queue software with the Enterprise Server software.

Java DataBase Connectivity (JDBCTM) Software

To store, organize, and retrieve data, most applications use relational databases. Java EE applications access relational databases through the JDBC API.

A JDBC resource (data source) provides applications with a means of connecting to a database. Typically, a JDBC resource is created for each database accessed by the applications deployed in a domain. Transactional access to JDBC resources is available from servlets, JSP pages, and enterprise beans. The connection pooling and distributed transaction features are intended for use by JDBC drivers to coordinate with an application server.

For more information, see DataSource Objects and Connection Pools.