What is the use of servlets?
Servlets are Java classes which can be used on a web container or web server, and its main purpose is to handle user requests sent from a client such as a web browser and generate dynamic content in response. Servlets belong under the family of Java EE (Enterprise Edition) which provides a set of specifications and various other APIs to create web based applications.The goal that is set for servlets is that they should be highly customizable, reusable and also highly efficient . This is accomplished by the servlets first accepting requests sent by clients, then the servers carry out the required operations to generate a response, which is then sent back to the same client. Overall, the basic tasks of servlets are mostly centered around HTTP requests and responses, hence why they are essential in Java web applications.
The Role of Servlets in Web Applications
Probably the most important aspect of servlet technology is its deployment in web application architecture as it implements business logic as a middleware layer between client and web server. They enable the developers to interact with the user of an application in a dynamic, flexible and an efficient way. Here’s how they function in a typical web application:- Client Request: The client submits a request to the web application through a browser. These may include information such as form request submissions, URL parameters and cookies.
- Servlet Processing: The web server forwards this request to a Servlet, which is configured such a way so as to derive or create some meaningful information by collecting other relevant data, frequently from a database.
- Response Generation: The Servlet processes the request and creates a response. This is in HTML format, XML format or JSON format depending on the expectation of the client.
- Client Response: The response generated is sent back to the client and the content is displayed in a way useful to the user.
In this way, Servlets are critical components for logic creation of dynamic web pages including form submission, user authentication and other event-driven activities which show current values.
Understanding How Servlets Function
In order to comprehend the functioning of Servlets, touching upon their aforementioned relationship with the web container is of utmost importance. The web container is accountable for the initialization of servlets and also manages the interaction between the client and the servlets.1. Servlet Initialization:
In case a client makes a request for the first time to the server, this means that the servlet has to be configured by the web container. During this phase, the container places the servlet in the disk and transfers it into the memory by activating the init method. This method is usually intended for initialization purposes such as replacing idle threads, loading resources, and initializing variables.2. Request Handling:
Following the initialization of the servlet, the web container sends a message to the servlet with the client’s request by activating the service method. The service method is the center of the servlet processing. This method handles GET and POST methods, along with other methods supported by the member such as PUT and DELETE. It receives information from clients and responds to them appropriately as well.3. Generating Response:
When the service() method completes its processing, it creates the response. More often than not, this response happens to be some HTML code which is rendered back to the client. However, in more sophisticated web applications, the response could entail JSON, XML, or any other format for that matter.4. Servlet Destruction:
When the Servlet is considered to be no longer useful, it gets destroyed by the web container through the invocation of the destroy() method. This method also performs some other important functions like cleaning up activities including releasing resources or closing a connection to the database. This destruction procedure ensures the server is efficient and that it does not waste resources.In the course of the Servlet lifecycle, from installation and up to the destruction of the servlet, the application incorporated is dynamic, effective and highly scalable.
HTTP Servlets
Such types of Servlets as there are many, most focusing on handling HTTPRequest are regular HTTP Servlets. They are descendants of the HttpServlet which is a child of a general Servlet and contain the methods for requesting various forms of HTTP services from the client side.Some of the two main HTTP methods that a Servlet performs work with are:
1. GET: This method applies when a client is trying to get some information off a server. For instance, this occurs when a client is requesting a webpage or an image file.2. POST: This approach is followed while the client transmits data with the server, for example, submitting a form.
Every such method has a corresponding method implemented in the
HttpServlet class, specifically doGet and doPost . What this means is that the Servlet’s logic can be made more intricate depending on the particular request received.Key Concepts in Servlet Development
When it comes to Java Servlet Development there are a few things that you need to start with:- Servlet Container/Server : The servlet container (for example Apache Tomcat or Jetty), multiplexes, requests and servlets for one another and manages the flow of information between a client and the server. It is installed on the top of a web server and is a platform or environment for servlets to operate.
- Request and Response Objects: The request and response objects are vital for Servlet programming. The request object (
HttpServletRequest) is used for various purposes, the most typical example being requests from a client that contain information such as form or cookie data. The response object (HttpServletResponse) serves the opposite purpose, its members are used as data to be sent back to clients, usually content of type HTML or other objects of content type. - Session Management: A lot of web applications have the requirement of keeping a record of a user through several uses of the application. Session management is used to preserve the context over more than one transmission of data from the same client. This can be done by means of cookies, URL rewriting, or the HttpSession object provided by the Servlet API.
- Configuration of Servlets: Java servlets are configured in the file
web.xmlwhich is part of the deployment descriptor in a java web application. This file provides a mapping of HTTP requests to specific Servlets and also other settings such as members of initialization parameter mappings and session-timeout values executive. - Filters: In some cases it is necessary to carry out operations on request before they get to Servlet or on responses before they are sent back to the client. This is done with the use of filters, which enable one to extend the logging, authentication, and request validation, among others, functions in the request-response process.
