16.2 Requirements and Qualities

What are some of the goals of Sun Microsystems in developing the J2EE/EJB specification? How are these goals reflected in the qualities of the J2EE/EJB architecture?

THE WEB AND J2EE

In response to the increasing demands of Internet-enabled business systems, more and more enterprise information systems are constructed using distributed object technology. These systems require scalability, high performance, portability, and security. They need to handle large volumes of requests generated by the Internet community and must be able to respond to these requests in a timely fashion.

For many e-business organizations, the most challenging thing right now is a successful Web site. Successful sites attract large volumes of hits, and large volumes of hits stress the site software, as mentioned in Chapter 13. On the Internet, it is not uncommon for sites to receive millions or many millions of accesses daily. Such numbers might not be too frightening if user requests are spread out evenly during the day, but this is often not the case. Requests often arrive in bursts, which place greater demands on Web site software.

In fact, industry folklore is rife with stories of e-business sites failing under unexpected client surges. For example, the Wimbledon Tennis tournament experienced almost 1 billion Web accesses in 1999, with 420,000 hits per minute (7,000 per second) during one match. Bear in mind, that the Internet is currently used by only a small portion of the globe's population; things have just started.

In this sense, then, the Internet has forever changed the requirements for enterprise software systems. The very nature of the Internet brings new pressures to bear on applications that are not commonly experienced by traditional networked information systems. The impact of quality attribute requirements, such as manageability, scalability, security, and availability, are radically increased when applications are exposed to potentially limitless numbers of concurrent users. Table 16.1 describes the quality requirements that any Web-based application must fulfill.

Table 16.1. Typical Web-Based Application Quality Attribute Requirements

Quality	Requirement
Scalability	System should support variations in load without human intervention
Availability/ Reliability	System should provide 24/7 availability with very small downtime periods
Security	System should authenticate users and protect against unauthorized access to data
Usability	Different users should be able to access different content in different forms
Performance	Users should be provided with responsive systems

Sun Microsystems, in developing J2EE, aimed to provide a basis for technology that supports the construction of such systems. In particular, as part of the J2EE specification, EJB aims to

• provide a component-based architecture for building distributed object-oriented business applications in Java. EJBs make it possible to build distributed applications by combining components developed with tools from different vendors.

• make it easier to write applications. Application developers do not have to deal with low-level details of transaction and state management, multi-threading, and resource pooling.

More specifically, the EJB architecture does the following:

• Addresses the development, deployment, and runtime aspects of an enterprise application's life cycle

• Defines the contracts that enable tools from multiple vendors to develop and deploy components that can interoperate at runtime

• Interoperates with other Java APIs

• Provides interoperability between enterprise beans and non-Java applications

• Interoperates with CORBA

J2EE makes it possible to re-use Java components in a server-side infrastructure. With appropriate component assembly and deployment tools, the aim is to bring the ease of programming associated with GUI-builder tools (like Visual Basic) to building server applications. And, by providing a standard framework for J2EE products based on a single language (Java), J2EE component-based solutions are, in theory at least, product independent and portable between the J2EE platforms provided by various vendors.

Thus, in addition to the core requirements given in Table 16.1, Sun added a set of requirements that address the activities of a programming team. These additional quality attribute requirements are listed in Table 16.2.

Table 16.2. Sun's Quality Attribute Requirements for J2EE

Quality Attribute	Requirement
Portability	J2EE should be able to be implemented with minimal work on a variety of computing platforms
Buildability	Application developers should be provided with facilities to manage common services such as transactions, name services, and security
Balanced Specificity	Detailed enough to provide meaningful standard for component developers, vendors, and integrators, but general enough to allow vendor-specific features and optimizations
Implementation Transparency	Provide complete transparency of implementation details so that client programs can be independent of object implementation details (server-side component location, operating system, vendor, etc.)
Interoperability	Support interoperation of server-side components implemented on different vendor implementations; allow bridges for interoperability of the J2EE platform to other technologies such as CORBA and Microsoft component technology
Evolvability	Allow developers to incrementally adopt different technologies
Extensibility	Allow incorporation of relevant new technologies as they are developed