An application server is a software framework that provides both facilities to create web applications and a server environment to run them.
Most Application Server Frameworks contain a comprehensive service layer model. An application server acts as a set of components accessible to the software developer through an API defined by the platform itself. For Web applications, these components are usually performed in the same running environment as their web server(s), and their main job is to support the construction of dynamic pages. However, many application servers target much more than just Web page generation: they implement services like clustering, fail-over, and load-balancing, so developers can focus on implementing the business logic.
In the case of Java application servers, the server behaves like an extended virtual machine for running applications, transparently handling connections to the database on one side, and, often, connections to the Web client on the other.
Other uses of the term may refer to the services that a server makes available or the computer hardware on which the services run.
The term was originally used when discussing early client–server systems to differentiate servers that contain application logic SQL services and middleware servers as distinct from other types of data-servers.
In the late 2000s, because of the ubiquity of the web-browser as an application deployment strategy, there is a mistaken belief that the term refers to a web application environment. However, web applications are within the scope of application-server technologies.
Java application servers
Java Platform, Enterprise Edition or Java EE (was J2EE) defines the core set of API and features of Java Application Servers.
The Web modules include servlets and JavaServer Pages. Enterprise JavaBeans (EJB) are used to manage transactions. According to the J2EE blueprints the business logic of an application resides in Enterprise JavaBeans - a modular server component providing many features, including declarative transaction management, and improving application scalability.
Some Java Application Servers leave off many Java EE features like EJB and Java Message Service (JMS) including Tomcat from Apache, and Jetty from Eclipse Foundation. Their focus is more on Java Servlets and JavaServer Pages.
There are many open source Java application servers that support Java EE including JOnAS from Object Web, WildFly (formerly JBoss AS) from JBoss (division of Red Hat), Geronimo from Apache, TomEE from Apache, Resin Java Application Server from Caucho Technology, Blazix from Desiderata Software, Enhydra Server from Enhydra.org, and GlassFish from Oracle.
Commercial Java application servers have been dominated by WebLogic Application Server by Oracle, WebSphere Application Server from IBM and the open source JBoss Enterprise Application Platform (JBoss EAP) by Red Hat.
A Java Server Page (JSP) executes in a web container. 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.
The application servers mentioned above mainly serve web applications, and services via RMI, EJB, JMS and SOAP. Some application servers target networks other than web-based ones: Session Initiation Protocol servers, for instance, target telephony networks.
Microsoft positions their middle-tier applications and services infrastructure in the Windows Server operating system and the .NET Framework technologies in the role of an application server. The Windows Application Server role includes Internet Information Services (IIS) to provide web server support, the .NET Framework to provide application support, ASP.NET to provide server side scripting, COM+ for application component communication, Message Queuing for multithreaded processing, and the Windows Communication Foundation (WCF) for application communication.
- Mono (a cross platform open-source implementation of .NET supporting nearly all its features, with the exception of Windows OS-specific features), sponsored by Novell, Inc., licensed under GPL
- Base4 Application Server, an open source project
- TNAPS Application Server, freeware application server, developed by TN LLC
- cc Devnet Data Access Server, A generic application server for building native Windows Desktop, iOS and Android applications..
PHP application servers
PHP application servers are used for running and managing PHP applications.
Zend Server, built by Zend Technologies, provides application server functionality for the PHP-based applications.
appserver.io, built by TechDivision GmbH is a multithreaded application server for PHP written in PHP.
Open-source application servers also come from other vendors, such as Appaserver.
Non-Java offerings have no formal interoperability specifications on par with the Java Specification Request. As a result, interoperability between non-Java products is poor compared to that of Java EE based products.
Mobile application servers
A mobile app server is mobile middleware that makes back-end systems accessible to mobile applications to support Mobile application development. Much like a web server that stores, processes and delivers web pages to clients, a mobile app server bridges the gap from existing infrastructure to mobile devices.
Although most standards-based infrastructure (including SOAs ) are designed to connect to any independent of any vendor, product or technology, most enterprises have trouble connecting back-end systems to mobile applications, because mobile devices add the following technological challenges:
- Limited resources – mobile devices have limited power and bandwidth
- Intermittent connectivity – cellular service and wifi coverage is often not continuous
- Difficult to secure – mobility and BYOD make it hard to secure mobile devices
The purpose of a mobile application server is to build on existing infrastructure to accommodate mobile devices.
Core capabilities of a mobile application services include
- Data routing– data is packaged in smaller (REST) objects with some business logic to minimize demands on bandwidth and battery
- Orchestration– transactions and data integration across multiple sources
- Authentication service– secure connectivity to back-end systems is managed by the mobile middleware
- Off-line support– allows users to access and use data even though device is not connected
- Security– data encryption, device control, SSL, call logging
Mobile application servers vs. application servers vs. web servers
Mobile application servers, Application servers, and web servers serve similar purposes: they are a piece of middleware that connects back-end systems to the users that need to access them, but the technology in each of the three differs. Application servers - developed before the ubiquity of web-based applications - expose back-end business logic through various protocols, sometimes including HTTP, and manage security, transaction processing, resource pooling, and messaging. When web-based applications grew in popularity, application servers did not meet the needs of developers, and the web server was created to fill the gap.
Web servers provide the caching and scaling functionality demanded by web access and not provided by application servers. They convert requests to static content, and serve only HTTP content. Over time, application servers and web servers have morphed from two previously distinct categories, blended features, and arguably have merged.
Mobile application servers are on a similar path. The emergence of mobile devices presents the need for functionality not anticipated by the developers of traditional application server developers, and mobile application servers fill this gap. They take care of the security, data management and off-line requirements not met by existing infrastructure, and present content exclusively in REST.
Over time, these three categories may fully merge and be available in a single product, but the root functions differ.
A mobile application server can be deployed :
- On premises
- Private cloud
- Platform as a service (PaaS)
- Akula from Verivo
- KonyOne from Kony
- MobileFirst Server from IBM
- Unifiedpush Server
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.Centralized configurationChanges to the application configuration, such as a move of database server, or system settings, can take place centrally.SecurityA 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.PerformanceBy 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.Transaction SupportA 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.