by Dinesh Thakur Category: introduction to Servlet

• Once web server is started one daemon process will be started to listen to clients continuously and to trap and take the client generated Http request.

• The process that runs continuously is called as daemon process.

 
by Dinesh Thakur Category: introduction to Servlet

• Listens to client request continuously (HTTP Request).

• Traps and takes client generated HTTP Request.

• Passes the HTTP request to an appropriate web resource program of web application (deployed web application).

 
by Dinesh Thakur Category: introduction to Servlet

Both are send input values to target web resource program like servlet program along with the request. The difference are



 
by Dinesh Thakur Category: introduction to Servlet

• The text that allows non-sequential access through hyper link is called as “hyper text”.

• Protocol http defines set of rules that are required to pass hyper text between browser to server and server to browser.

 
by Dinesh Thakur Category: introduction to Servlet

When four requests are given to a Servlet program.

a) The Servlet container creates one object of that Servlet class.

b) Servlet container starts 4 threads on that object representing 4 requests on per request basis.

 
by Dinesh Thakur Category: introduction to Servlet

In Java, Servlet container (also known as aWeb container) generates dynamic web pages. So servlet container is the essential part of the web server that interacts with the java servlets. Servlet Container communicates between client Browsers and the servlets.



 
by Dinesh Thakur Category: introduction to Servlet

Java Servlet life cycle consists of a series of events that begins when the Servlet container loads Servlet, and ends when the container is closed down Servlet. A servlet container is the part of a web server or an application server that controls a Servlet by managing its life cycle. Basically there are three phases of the life cycle.



 
by Dinesh Thakur Category: introduction to Servlet

There is a possibility of developing ‘n’ types of servlets, like httpservlet, ftpservlet, smtpservlet etc. for all these protocol specific servlet classes GenericServlet is the common super class containing common properties and logics. So, GenericServlet is not a separate type of servlet.



 
by Dinesh Thakur Category: introduction to Servlet

Server side web technology is used to develop dynamic web resource programs that having the capability to generate dynamic web pages. Server side web technologies are two types.

 
by Dinesh Thakur Category: introduction to Servlet

Client side programs can be written using different client side technologies. These are given to develop client side web resources such as html (Web), JavaScript (Netscape), VBScript (Microsoft), AJAX (asynchronous JavaScript and xml) programming languages.

 
by Dinesh Thakur Category: introduction to Servlet

Before creating the first servlet, you need to understand the Servlet API and Tomcat Servlet container. The Servlet API provides interfaces and classes that are required to built servlets. These interfaces and classes are group into the following two packages :



 
by Dinesh Thakur Category: introduction to Servlet

The Common Gateway Interface (CGI) is the first technology used to generate dynamic contents. It allows a web client to pass data to the application running on the web server so that a dynamic web page can be returned to the client according to the input data. For example, when you use a search engine, buy a book at an online store; get a stock quote etc., your browser uses CGI to communicate with a server side application.



 
by Dinesh Thakur Category: introduction to Servlet

Java servlets provide web developers with a simple consistent mechanism for extending the functionality of a web server and provide dynamic behaviour for web applications. Servlets are Java classes that function like CGI programs. They accept a request from a client (usually a web browser), process that request and return a response to the client. All servlets are loaded and executed by a servlet container that can run by itself or as a component of a web server. The servlet container is also referred to as a servlet engine in the early days of servlet technology.



 
by Dinesh Thakur Category: introduction to Servlet

• The logic and data of stand alone, desktop applications are specific to that computer where these applications are running.

• The logics and data of client-server applications, two-tier applications like JDBC applications are specific to one network where they are running. In the above said two-tier, client-server applications the server allows only known clients (recognized clients).



 
by Dinesh Thakur Category: Basic Servlet Examples

Like doGet () method, the do Post () method is invoked by server through service () method to handle HTTP POST request. The doPost () method is used when large amount of data is required to be passed to the server which is not possible with the help of doGet () method.

 
by Dinesh Thakur Category: Basic Servlet Examples

The doGet () method is invoked by server through service () method to handle a HTTP GET request. This method also handles HTTP HEAD request automatically as HEAD request is nothing but a GET request having no body in the code for response and only includes request header fields. To understand the working of doGet () method, let us consider a sample program to define a servlet for handling the HTTP GET request.



 
by Dinesh Thakur Category: Basic Servlet Examples

The GenericServlet class implements the Servlet and ServletConfig interfaces. Since service () method is declared as an abstract method in GenericServlet class, it is an abstract class. The class extending this class must implement the service () method. It is used to create servlets which are protocol independent.



 
by Dinesh Thakur Category: Basic Servlet Examples

The process of selecting file from the client machine file system and sending that file to the server machine system is known as file uploading. File uploading and downloading using servlet-api is a complex process, that is why industry uses JavaZoom 3rd party API.

 
by Dinesh Thakur Category: Basic Servlet Examples

HttpServletResponse is a predefined interface present in javax.servlet.http package. It can be said that it is a mirror image of request object. The response object is where the servlet can write information about the data it will send back. Whereas the majority of the methods in the request object start with GET, indicating that they get a value, many of the important methods in the response object start with SET, indicating that they change some property. Note that these interfaces adhere to the usual naming conventions for beans.



 
by Dinesh Thakur Category: Basic Servlet Examples

HttpServletRequest is an interface and extends the ServletRequest interface. By extending the ServletRequest this interface is able to allow request information for HTTP Servlets. Object of the HttpServletRequest is created by the Servlet container and, then, it is passed to the service method (doGet(), doPost(), etc.) of the Servlet.



 

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About Dinesh Thakur

Dinesh ThakurDinesh Thakur holds an B.C.A, MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to Contact us.