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An application server is a software engine that delivers applications to client computers or devices. Moreover, an application server should handle most, if not all, of the business logic and data access of the application. The main benefits of application server technology are ease of application development and centralization.

Although the term application server applies to all platforms, it has become heavily identified with the Sun Microsystems J2EE platform; however, it has also come to encompass servers of web-based applications, such as integrated platforms for e-commerce, content management systems, affiliate management systems and occasionally, even applied to simplistic web-site page builders. The paradigm is more similar to mainframe based applications than traditional client-server.

Contents 1 Common features 2 History 3 Java application servers 4 Other platforms 5 Advantages of application servers 6 See also

Application server products typically bundle middleware to enable applications to intercommunicate with dependent applications, like web servers, database management systems, and chart programs. Some application servers also provide an API, making them operating system independent.

Portals are a very common application server mechanism by which organizations can manage information. They provide a single point of entry for all users, they can access Web services transparently from any device, and they are highly flexible. Portals can work inside or outside of the organization, and they can attach themselves to any part of it.

This term is widely used as a buzzword in the following fields:

• Distributed computing — denoting a computer running some part of a distributed computation task
• Software components — denoting a "component farm", which is a computer loaded with software components, ready to answer calls for usage
• Web services — denoting a machine running applications which will answer interface calls over HTTP in an XML format

In the later part of the 1990s, it was thought that a massive shift over to centrally served applications was likely, and that the desktop PC would be replaced by lightweight network computers. This would have been a return to the much older model of computing as it was done in the 1960s, with a large, very expensive central computer being accessed by multiple users using dumb terminals. The difference now was the widespread use of the graphical user interface (GUI). Certain products, such as Citrix's WinFrame, became quite popular, allowing standard Windows software to be run on an NT server, and accessed from a wide variety of clients, including non-Windows platforms such as Mac and Unix. Currently, the trend is to deliver applications via a browser (see Appaserver) or other Internet device.

Following the success of the Java platform, the term application server sometimes refers to a J2EE application server. WebLogic Server (BEA), JBoss (Red Hat), WebSphere (IBM), JRun (Adobe) and Oracle OC4J (Oracle Corporation) are the better known commercial J2EE application servers. GlassFish, an open source Application Server from Sun, is the first to provide a robust, commercial, compatible Java EE 5 implementation.

The JOnAS application server, developed by the ObjectWeb consortium, is the first non-commercial, open source application server to have reached the official certification of compliance with J2EE. The programming language used is Java. The web modules are servlets and JavaServer Pages (JSP), and business logic is built into Enterprise JavaBeans (EJB). The Java 2 Platform, Enterprise Edition (J2EE) provides standards for containing the web components. Tomcat from Apache and JOnAS from ObjectWeb are typical of containers to put these modules into. Both organizations provide the code freely and openly (open source).

A JSP is a Servlet from Java that executes in a web container--the Java equivalent of CGI scripts. JSPs are a way to create HTML pages by embedding references to the server logic within the page. HTML coders and Java programmers can work side by side by referencing each other's code from within their own. JavaBeans are the independent class components of the Java2 architecture from Sun Microsystems.

The application servers mentioned above mainly serve Web applications. Some application servers are targeting networks other than the Web. This is the case of SIP servers, which target telephony networks.

The term application server has also been applied to various non-J2EE and non-Java offerings. For example, with the rising popularity of .NET, Microsoft can claim to deliver an application server. Additional open source and commercial application servers are available from other vendors. Some examples are Appaserver, Base4, Concept, and Zope.

Data and code integrity 

By centralizing business logic on an individual or small number of server machines, updates and upgrades to the application for all users can be guaranteed. There is no risk of old versions of the application accessing or manipulating data in an older, incompatible manner.

Centralized configuration 

Changes to the application configuration, such as a move of database server, or system settings, can be done centrally.

Security 

A central point through which access to data and portions of the application itself can be managed is considered a security benefit, devolving responsibility for authentication away from the potentially insecure client layer without exposing the database layer.

Performance 

By limiting the network traffic to presentation layer traffic, it is perceived that the client-server model improves the performance of large applications in heavy usage environments.

Total Cost of Ownership (TCO) 

The above benefits combined are considered to represent a cost saving to a company. In practice, however, the technical challenges of writing software that conforms to that paradigm combined with the need for software distribution to distribute client code somewhat negate these benefits.

• Server
• Client-server
• Standalone server
• Comparison of application servers See this article for a list of web application servers listed by programming language.