In this tutorial we discuss about Java Servlet API and its main packages, interfaces and available classes for developing web components.
There are three types of applications available they are:
1.Stand-alone applications.
2.Web based applications.
3.Mobile based applications.
We can develop stand-alone applications by using JSE Edition of java whereas Web applications can be developed using JEE Edition of java (Older) or You can refer to the Jakarta Edition (New).
The servlet API consists of two main packages, we can develop servlet by using these packages. They are as follows.
- jakarta.servlet package
- jakarta.servlet.http package
Servlet API consists of many classes and interfaces which are used to create servlets which are then deployed in webserver that can be accessed from any device.
Servlet is simply a piece of java code that runs on a web server. How a servlet can be created, accessed and all the operations that can be performed on a servlet is described by the Servlet API.
1. jakarta.servlet package
Jakarta.servlet package contains several classes and interfaces that describe and define about the link between a servlet class and a run time environment which is provided by the servlet container. We can use this jakarta.servlet package to develop protocol independent servlets (Generic Servlets).
Important Interfaces available in jakarta.servlet package:
Interface | Description |
|---|---|
| Servlet | Consisting of methods that all servlets should implement |
| ServletConfig | An Object of servlet configuration can be used by the web container send the data to servlet at the time of initialization |
| ServletConnection | It gives the information about the connection made to the Servlet container |
| ServletContext | It defines a group of methods that a Servlet is used to communicate with its web container |
| ServletRegitration | Interface through which every servlet must be configured further |
| ServletRequest | It provides an object to send the client request information to a servlet |
| ServletResponse | It provides an object to assist a servlet in sending the response to the client |
| RequestDispatcher | It is used to dispatch a servlet request to another servlet |
| Filter | A filter is an object that performs tasks either the request to a resource or on the response from a resource or both |
| FilterChain | It is an object that is provided by the Servlet container to the developer to give a view of filtered request for a resource |
| FilterConfig | A filter configuration object is used by the servlet to information of a filter during Initialization |
| FilterRegistration | It is an interface through which a filter may be further configured |
Important Classes in jakarta.servlet package:
| Class | Description |
|---|---|
| GenericServlet | It implements Servlet and defines a generic, independent Servlet |
| ServletInputStream | It provides an input stream for receiving binary related data from a client |
| ServletOutputStream | It provides an output stream for sending the binary data to the client |
| ServeltRequestWrapper | It implements ServletRequest Interface and provide a convenient implementation to adapt the request of a servlet |
| ServletResponseWrapper | It implements ServletResponse Interface and provide a convenient implementation to adapt the response of a servlet |
| GenericFilter | It implements Filter and defines a generic, independent filter |
| ServletContextEvent | This is the Event class for notifications about changes to servlet context of a web application |
| ServletRequestEvent | Event of this kind indicate life cycle events for a servlet request |
| ServletRequestAttributeEvent | This is the event class for notifications about the attributes of servlet request in an application |
Exceptions in jakarta.servlet package:
| Exception | Description |
|---|---|
| ServletException | It gives a servlet exception whenever a servlet find difficulty in processing our request |
| UnavailableException | It is an Exception that a servlet or a filter throw to indicate that it is temporarily or permanently unavailable |
2. jakarta.servlet.http
jakarta.servlet.http package consists of various classes and interfaces that define and describe the link between a servlet class which is running under HTTP (Hyper Text Transfer Protocol) and a run time environment which is provided by the Servlet container. jakarta.servlet.http package is used to develop Http based servlets.
Important Interfaces in jakarta.servlet.http package:
| Interface | Description |
|---|---|
| HttpServletRequest | It extends the ServletRequest Interface to provide the request information for Http Servlets |
| HttpServletResponse | It extends the ServletResponse Interface to provide the response information for Http Servlets |
| HttpSession | It provides a way to identify a user across more than one page request |
| WebConnection | It is an interface that encapsulates the connection for an upgrade request. |
Important Classes in jakarta.servlet.http package
| Class | Description |
|---|---|
| Cookie | This simply creates a cookie, a small amount of information which is sent by a servlet to a web browser. This information is saved by the browser and later sent back to the server |
| HttpServlet | It is an abstract class which extends GenericServlet to create HTTP servlets for a website |
| HttpServletRequestWrapper | It implements HttpServletRequest and provide a convenient implementation to adapt the request to a servlet |
| HttpServletResponseWrapper | It implements HttpServletResponse and provide a convenient implementation to adapt the response from a servlet |
| HttpFilter | Provides an abstract class to create HTTP based filter for a web site |
| HttpSessionEvent | This is the class representing event notifications for changes to sessions within a Web application |
3. Conclusion
In this tutorial, we have discussed about the main interfaces and classes in Java Servlet API.
