Servlet

Servlet Terminology

There are some key points that must be known by the servlet programmer like server, container, get request, post request etc. Let’s first discuss these points before starting the servlet technology.

The basic terminology used in servlet are given below:

  1. HTTP
  2. HTTP Request Types
  3. Difference between Get and Post method
  4. Container
  5. Server and Difference between web server and application server
  6. Content Type
  7. Introduction of XML
  8. Deployment

HTTP (Hyper Text Transfer Protocol)

  1. Http is the protocol that allows web servers and browsers to exchange data over the web.
  2. It is a request response protocol.
  3. Http uses reliable TCP connections bydefault on TCP port 80.
  4. It is stateless means each request is considered as the new request. In other words, server doesn’t recognize the user bydefault.

http protocol used in servlet

Http Request Methods

Every request has a header that tells the status of the client. There are many request methods. Get and Post requests are mostly used.

The http request methods are:

  • GET
  • POST
  • HEAD
  • PUT
  • DELETE
  • OPTIONS
  • TRACE
HTTP Request Description
GET Asks to get the resource at the requested URL.
POST Asks the server to accept the body info attached. It is like GET request with extra info sent with the request.
HEAD Asks for only the header part of whatever a GET would return. Just like GET but with no body.
TRACE Asks for the loopback of the request message, for testing or troubleshooting.
PUT Says to put the enclosed info (the body) at the requested URL.
DELETE Says to delete the resource at the requested URL.
OPTIONS Asks for a list of the HTTP methods to which the thing at the request URL can respond

 

Anatomy of Get Request

As we know that data is sent in request header in case of get request. It is the default request type. Let’s see what informations are sent to the server.

anatomy of Get Request

Anatomy of Post Request

As we know, in case of post request original data is sent in message body. Let’s see how informations are passed to the server in case of post request.

anatomy of Post Request

Container

It provides runtime environment for JavaEE (j2ee) applications.

It performs many operations that are given below:

  1. Life Cycle Management
  2. Multithreaded support
  3. Object Pooling
  4. Security etc.

Server

It is a running program or software that provides services.

There are two types of servers:

  1. Web Server
  2. Application Server

Web Server

Web server contains only web or servlet container. It can be used for servlet, jsp, struts, jsf etc. It can’t be used for EJB.

Example of Web Servers are: Apache Tomcat and Resin.


Application Server

Application server contains Web and EJB containers. It can be used for servlet, jsp, struts, jsf, ejb etc.

Example of Application Servers are:

  1. JBoss Open-source server from JBoss community.
  2. Glassfish provided by Sun Microsystem. Now acquired by Oracle.
  3. Weblogic provided by Oracle. It more secured.
  4. Websphere provided by IBM.

Content Type

Content Type is also known as MIME (Multipurpose internet Mail Extension) Type. It is a HTTP header that provides the description about what are you sending to the browser.

There are many content types:

  • text/html
  • text/plain
  • application/msword
  • application/vnd.ms-excel
  • application/jar
  • application/pdf
  • application/octet-stream
  • application/x-zip
  • images/jpeg
  • video/quicktime etc.

 

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