Servlets - What is Servlet?

What is Java Servlet?

A Servlet is a Java-based server-side web technology. As the name implies, it serves a client request and receives a response from the server.

Technically speaking, a Servlet is a Java class in Java EE that conforms to the Java Servlet API, a protocol by which a Java class may respond to requests. They are not tied to a specific client-server protocol, but are most often used with the HTTP protocol. Therefore, the word "Servlet" is often used in the meaning of "HTTP Servlet". Thus, a software developer may use a servlet to add dynamic content to a Web server using the Java platform.

Servlet is a server-side programming language that is used to create the dynamic web page. Servet technology is robust and scalable as it uses the java language. Before Servlet, CGI (Common Gateway Interface) scripting language was used as a server-side programming language. But there were many disadvantages of this technology. We have discussed these disadvantages below.

There are many interfaces and classes in the servlet API such as Servlet, GenericServlet, HttpServlet, ServletRequest, ServletResponse etc.

Servlet can be described in many ways, depending on the context.

·         Servlet is a technology i.e. used to create web application.

·         Servlet is an API that provides many interfaces and classes including documentations.

·         Servlet is an interface that must be implemented for creating any servlet.

·         Servlet is a class that extend the capabilities of the servers and respond to the incoming request. It can respond to any type of requests.

·         Servlet is a web component that is deployed on the server to create dynamic web page.

To deploy and run a Servlet, a Web container must be used. A Web container (also known as a Servlet 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.

The servlet API, contained in the Java package hierarchy javax.servlet, defines the expected interactions of the Web container and a servlet.

A Servlet is an object that receives a request and generates a response based on that request. The basic servlet package defines Java objects to represent servlet requests and responses, as well as objects to reflect the servlet's configuration parameters and execution environment. The package javax.servlet.http defines HTTP-specific subclasses of the generic servlet elements, including session management objects that track multiple requests and responses between the Web server and a client. Servlets may be packaged in a WAR file as a Web application.

Servlets can be generated automatically from JavaServer Pages (JSP) by the JavaServer Pages compiler. The difference between Servlets and JSP is that Servlets typically embed HTML inside Java code, while JSPs embed Java code in HTML. While the direct usage of Servlets to generate HTML (as shown in the example below) has become rare, the higher level MVC web framework in Java EE (JSF) still explicitly uses the Servlet technology for the low level request/response handling via the FacesServlet. A somewhat older usage is to use servlets in conjunction with JSPs in a pattern called "Model 2", which is a flavor of the model-view-controller pattern.