Java Servlet API allows a software developer to add dynamic content to a Web server using the Java platform. The generated content is commonly HTML, but may be other data such as XML. Servlets are the Java counterpart to dynamic web content technologies such as CGI, PHP or ASP. Servlets can maintain state across many server transactions by using HTTP cookies, session variables or URL rewriting.

The Servlet API, contained in the Java package hierarchy javax.servlet, defines the expected interactions of a web container and a servlet. A web container is essentially the component of a web server that interacts with the servlets. The web container is responsible for managing the lifecycle of servlets, mapping a URL to a particular servlet and ensuring that the URL requester has the correct access rights.

A Servlet is an object that receives requests (ServletRequest) and generates a response (ServletResponse) based on the request. The API package javax.servlet.http defines HTTP subclasses of the generic servlet (HttpServlet) request (HttpServletRequest) and response (HttpServletResponse) as well as an (HttpSession) that tracks multiple requests and responses between the web server and a client. Servlets may be packaged in a WAR file as a Web application.

Moreover, servlets can be generated automatically by JavaServer Pages (JSP), or alternately by template engines such as WebMacro. Often servlets are used in conjunction with JSPs in a pattern called "Model 2", which is a flavor of the model-view-controller pattern.

History

The original servlet specification was created by Sun Microsystems (version 1.0 was finalized in June 1997). Starting with version 2.3, the servlet specification was developed under the Java Community Process. JSR 53 defined both the Servlet 2.3 and JavaServer Page 1.2 specifications. JSR 154 specifies the Servlet 2.4 and 2.5 specifications. As of May 10, 2006, the current version of the servlet specification is 2.5.

In his blog on java.net, Sun veteran and GlassFish lead Jim Driscoll details the history of servlet technology. James Gosling first thought of servlets in the early days of Java, but the concept did not become a product until Sun shipped the Java Web Server product. This was before what is now the Java Platform, Enterprise Edition was made into a specification.

Web containers

A Web container is a computer program that runs Web applications. Web containers are also sometimes called Web engines. Like the other Java APIs, different vendors provide their own implementation. Below is a list of some of the free web containers. (Note that 'free' means that commercial use is free. Some of the commercial containers, e.g. Resin and Orion, make ideal development containers and are also free to use in a server environment for non-profit organizations).

Non-commercial web containers

* Java System Application Server is developed by Sun.
* Apache Tomcat (formerly Jakarta Tomcat) is an open source web container available free of charge under the Apache Software License. It is used in the official reference implementation and has a reputation for being stable.
* Jetty
* Jaminid contains a higher abstraction than servlets.
* Enhydra
* jo!
* Winstone supports specification v2.4, has a focus on minimal configuration and the ability to strip the container down to only what you need.
* tjws spec 2.4, small footprint, modular design
 

Above article originally from wikipedia.org. Above article is available under GNU Free Documentation License.