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The J2EE platform service technologies allow applications to access a wide range of services in a uniform manner. This section describes technologies that provide access to databases, transactions, XML processing, naming and directory services, and enterprise information systems.
The JDBC API provides database-independent connectivity between the J2EE platform and a wide range of tabular data sources. JDBC technology allows an application component provider to:
The J2EE platform requires both the JDBC 2.0 Core API (included in the J2SE platform), and the JDBC 2.0 Extension API, which provides row sets, connection naming via JNDI, connection pooling, and distributed transaction support. The connection pooling and distributed transaction features are intended for use by JDBC drivers to coordinate with a J2EE server. Access to databases and enterprise information systems is covered in detail in Chapter 6.
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 J2EE server, and the manager that controls access to the shared resources affected by the transactions.
The Java Transaction Service (JTS) specifies the implementation of a transaction manager that supports JTA and implements the Java mapping of the Object Management Group Object Transaction Service 1.1 specification. A JTS transaction manager provides the services and management functions required to support transaction demarcation, transactional resource management, synchronization, and propagation of information that is specific to a particular transaction instance.
The Java Naming and Directory InterfaceTM (JNDI) API provides naming and directory functionality. It provides applications with methods for performing standard directory operations, such as associating attributes with objects and searching for objects using their attributes. Using JNDI, an application can store and retrieve any type of named Java object.
Because JNDI is independent of any specific implementations, applications can use JNDI to access multiple naming and directory services, including existing naming and directory services such as LDAP, NDS, DNS, and NIS. This allows applications to coexist with legacy applications and systems.
The J2EE Connector architecture is a standard API for connecting the J2EE platform to enterprise information systems, such as enterprise resource planning, mainframe transaction processing, and database systems. The architecture addresses the issues involved when integrating existing enterprise information systems (EIS), such as SAP, CICS, legacy applications, and nonrelational databases, with an EJB server and enterprise applications. The J2EE Connector architecture defines a set of scalable, secure, and transactional mechanisms for integrating an EIS with a J2EE platform. Adhering to the architecture simplifies this integration, enabling J2EE applications to use the strengths of the J2EE platform along with existing data in EISs.
The J2EE Connector architecture:
- Defines system contracts between J2EE-compliant application servers and resource adapters. Resource adapters, which are system libraries specific to an EIS, provide connectivity between J2EE application components and an EIS. Adapters are analogous to JDBC drivers for relational databases.
- Defines a common set of APIs so that Java applications and tools vendors can connect to and use an EIS through its resource adapters.
- Defines a standard packaging and deployment facility for resource adapters to facilitate their deployment in a J2EE environment.
To use the J2EE Connector architecture, an enterprise information system vendor provides a resource adapter for its EIS. The adapter is then either deployed as a separate module in the J2EE server or packaged and deployed along with the J2EE application. The EIS provider develops the resource adapter following the Connector architecture specification; it can be used on all J2EE platforms. Similarly, an application developed using the Connector API is deployable on all J2EE platforms that have the resource adapter for the EIS used by the application.
The Java API for XML Processing (JAXP) technology supports the processing of XML documents using DOM, SAX, and XSLT. JAXP enables applications to parse and transform XML documents independent of a particular XML processing implementation. Depending on the needs of the application, developers have the flexibility to swap between XML processors, such as between high-performance or memory-conservative parsers, with no application code changes.