Many information systems, from mainframe transaction processing environments like CICS to the stored procedures of a DBMS, provide for the server-side execution of business processes. Running business logic on a server can improve security, manageability, performance and reusability. With the explosive growth of intranets and the Internet, developers need a rich, flexible server to host their business applications: a server that complements the content from databases and Web servers.

As a platform, Java raises the bar for application servers. A Java application server marries the benefits of a robust, scalable application server with the expressive power and dynamism of the Java platform.

Java application servers can unite the technologies of the Web, database, and network-ready software components. Functionally, a Java application server is a runtime environment for enterprise business logic that exposes a set of Java APIs to developers, controls the life-cycle of application components, and provide various services, such as state management, database connection pooling and transaction coordination. Business logic can be organized as a combination of Java servlets for efficient CGI-style Web integration, JavaBeans components, and Enterprise JavaBeans (EJB) components.

Java application servers have arisen from products as diverse as Web servers, Object Request Brokers, Rapid Application Development tools, Transaction Processing (TP) monitors. But basically the CORBA technology is the foundation on which many Java application server technology came out. Even some Java application servers have been written in 100% Java from the scratch.

The architectural significance of the Java application server is that it maps remote services and components to a rich local runtime environment in a way that is independent of the underlying middleware and consistent across platforms and implementations. Though the implementation language is Java, it is entirely possible to map components created with other languages and component models into the Java environment and vice versa.

This mapping is straightforward in the case of Java and CORBA components as Java provides both a CORBA-to-Java mapping (the Java IDL compiler) and a Java-to-CORBA mapping (RMI over IIOP). There are mappings available between various CORBA object services and their Java equivalents. For example, CORBA Naming Service with Java Naming and Directory Interface (JNDI) and CORBA Transaction Service with Java Transaction Service (JTS). Also there are enhancements to make CORBA's IIOP equivalent with Java Remote Invocation Protocol (JRMP) and vice versa. Thus, applications running under a Java application server can integrate easily with CORBA-based applications. Also Java developers get a higher-level API for calling remote EJBs and this is better than a client application calls on CORBA objects through their IDL-defined interfaces.

There are Java application servers in the market that can export Java business objects as COM objects. Enterprise JavaBeans and other Java objects can be automatically wrapped as COM components for easy importation into Microsoft Windows-compatible development tools, such as Visual Basic, Visual C++, and Active Server Pages (ASP). Thus for a Microsoft developer, the invocation mechanism of a remote Java component is same as the invocation mechanism for COM components. Java application servers can eliminate the integration barriers between server-side Java components and the broad array of client environments, such as web browsers, Java clients and Microsoft applications.

The other way is also possible. There are tools and application servers that helps users to automatically wrap their COM business components with Java components that can be remotely accessed from any Java platform. To the Java developer, COM business components are then invoked like any other remote Java object provided it has to be instantiated within a COM runtime environment like Windows OS. Thus Java application server provides what other two products lack and is set to blossom in the days ahead in developing and deploying mission-critical, scalable, reliable, flexible, enterprise-level, robust, distributed applications.

Java application servers reduce the complexity of developing enterprise applications. Before the advent of technologies like Enterprise JavaBeans, developers had to worry about making server-side business objects persistent, finding them over the network, their security, isolating them from sharing conflicts, protecting them from failures, managing their life cycle, and ensuring their scalability and availability. Java application servers themselves take care all these enterprise system features and hence helps the developers to concentrate on coding the business logic alone.

Enterprises look to Java application servers to separate their business logic from their middleware. Mixing the two, as being found in traditional client/server applications, complicates application maintenance, portability, scalability and interoperability. With the support of Enterprise JavaBeans technology and other Java-based enterprise-related services, Java applications can be developed independently of the underlying middleware. Thus, using a Java application server, an EJB component can be built with Java RMI, deployed in a CORBA environment, and then reused with Microsoft DCOM, all without making any change to the application. Thus Java application servers deliver on the promise of reuse of business logic on the server.

Nowadays, Java application servers are available from a variety of vendors on almost all platforms, they can thereby meet growing application demands. Also the product vendors have to consistently implement the set of interfaces found in the Java application server specification. Also some vendors developer their application servers to be good and efficient for simple Web-based applications while some application servers are fit for developing and deploying mission-critical, complex, distributed applications that are transaction-aware across multiple back-end systems. Thus there are products that can be differentiated on the basis of their Quality of Service (QOS). As it is being proved beyond any doubt that Java is an elegant appropriate language for coding server-side applications, there is a lot of scope for efficient and robust products like Java application servers in the days ahead.

The list of applications that need the services of Java application servers is growing rapidly. Currently there are hundreds of enterprises and organizations world-wide using Java application server technology for their customer self-service, e-commerce, supply-chain and distribution channel management. Also they are being applied for converting currently available business applications, such as Enterprise Resource Planning (ERP) systems to Web-based applications.

The Fortune 1000 companies started to make use of the benefits being offered by Enterprise JavaBeans to provide superior customer service through the integration of different applications, such as customer management, billing and support tracking. Enterprise JavaBeans along with other enterprise services are being used to define a higher-level view of the customer. Also Java application server maintains a very high level of security for the deployed applications using SSL and HTTPS technologies. Both firewalls and authorization have been integrated with these application servers to ensure a very high protection to the business logic code and corporate data. Thus Java application servers are all set to flourish for deploying mission-critical, scalable server-side computing applications for the betterment of not only to fortune companies but also to meet the advanced requirements of customers.

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