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Application Server
An application server is a server computer in a computer network dedicated to running certain software applications. The term also refers to the software installed on such a computer to facilitate the serving (running) of other applications.
In the latter 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. So far, this shift has not happened on the predicted scale, and serving a GUI-based application over a slow network has presented a number of technical challenges that have not entirely been solved. It remains to be seen if the prediction comes true or whether the late 90s interest turns out to have been a fad.
Following the success of the Java platform, the term application server more often refers to a J2EE application server. WebSphere (IBM) and WebLogic (BEA) are the better known commercial J2EE application servers. 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. As mentioned, the chosen language for these big operations is Java. The Web modules are servlets and JavaServer Pages (JSP) and the business logic is built into Enterprise JavaBeans (EJB) and 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).
Servlets are Java programs that execute in a Web container and are the equivelant of CGI scripts. JSP is a way to create HTML pages by embedding the server logic within the page by using reference so as not to clutter it. HTML coders and Java programmers can work side by side by referencing each other's code within their own. JavaBeans are the independent class components of the Java2 architecture from Sun Microsystems.
Recently with the rising popularity of the .NET platform the term has started to also refer to various offerings, public and commercial from vendors. Some examples are the Base4 Server and Microsoft's Windows Communication Foundation.
Application Servers are referred to as middleware and provide transparency to programmers so they don't have to be concerned with the operating system or the huge array of interfaces required of a modern web based application. There has to be communication with the web in the form of HTML and XML, a link to various kinds of databases, and very likely links to systems and devices ranging from huge and irreplaceable legacy applications to small information devices which could be a link to the atomic clock or even home appliances.
Testing Master is website testing software which provides web application load and stress testing.
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