An application server, in an n-tier software architecture, serves an API to expose business logic and business processes for use by third-party applications.
The term can refer to:
1. the services that a server makes available
2. the computer hardware on which the services run
3. the software framework used to host the services (such as JBoss application server or Oracle Application Server)
Java application servers :
Following the success of the Java platform, the term application server sometimes refers to a J2EE or Java EE 5 application server. Some of the better-known Java Enterprise Edition application servers include:
* WebSphere Application Server and WebSphere Application Server Community Edition (IBM)
* Sybase Enterprise Application Server (Sybase Inc)
* WebLogic Server (Oracle)
* JBoss (Red Hat)
* JRun (Adobe Systems)
* Apache Geronimo (Apache Software Foundation)
* Oracle OC4J (Oracle)
* Sun Java System Application Server (based on GlassFish Application Server)(Sun Microsystems)
* SAP Netweaver AS (ABAP/Java) (SAP)
* Glassfish Application Server (open source)
The web modules include servlets and JavaServer Pages. Business logic resides in Enterprise JavaBeans (EJB-3 and later). The Hibernate project offers an EJB-3 container implementation for the JBoss application server. Tomcat from Apache and JOnAS from ObjectWeb exemplify typical containers which can store these modules.
A Java Server Page (JSP) (a servlet from Java) executes in a web container — the Java equivalent of CGI scripts. JSPs provide 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 Java architecture from Sun Microsystems.
The application servers mentioned above mainly serve web applications. Some application servers target networks other than web-based ones: Session Initiation Protocol servers, for instance, target telephony networks.
Microsoft platform :
Microsoft has contributed the .NET Framework to the world of application servers. .NET technology includes the Windows Communication Foundation, .NET Remoting, ADO.NET, and ASP.NET among several other components. It works with (or depends upon) other Microsoft products, such as Microsoft Message Queuing and Internet Information Services.
Zend platform :
Zend offers an application server called Zend Server — used for running and managing PHP applications.
Other platforms :
Open-source application servers also come from other vendors. Examples include Appaserver, Base4, Zope and Spring Framework.
Non-Java offerings have no formal interoperability specifications on a par with the Java Specification Request. As a result, interoperability between non-Java products is poor compared to that of Java EE based products. To address these shortcomings, specifications for enterprise application integration and service-oriented architecture were designed[by whom?] to connect the many different products. These specifications include Business Application Programming Interface, Web Services Interoperability, and Java EE Connector Architecture.
Advantages of application servers :
Data and code integrity
By centralizing business logic on an individual server or on a 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.
Changes to the application configuration, such as a move of database server, or system settings, can take place centrally.
A central point through which service-providers can manage access to data and portions of the application itself counts as a security benefit, devolving responsibility for authentication away from the potentially insecure client layer without exposing the database layer.
By limiting the network traffic to performance-tier traffic the client-server model improves the performance of large applications in heavy usage environments.
Total Cost of Ownership (TCO)
In combination, the benefits above may result in cost savings to an organization developing enterprise applications. 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.
A transaction represents a unit of activity in which many updates to resources (on the same or distributed data sources) can be made atomic (as an indivisible unit of work). End-users can benefit from a system-wide standard behaviour, from reduced time to develop, and from reduced costs. As the server does a lot of the tedious code-generation, developers can focus on business logic.