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:
- HTTP
- HTTP Request Types
- Difference between Get and Post method
- Container
- Server and Difference between web server and application server
- Content Type
- Introduction of XML
- Deployment
HTTP (Hyper Text Transfer Protocol)
- Http is the protocol that allows web servers and browsers to exchange data over the web.
- It is a request response protocol.
- Http uses reliable TCP connections bydefault on TCP port 80.
- It is stateless means each request is considered as the new request. In other words, server doesn't recognize the user bydefault.
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 |
What is the difference between Get and Post?
There are many differences between the Get and Post request. Let's see these differences:
| GET | POST |
|---|---|
| 1) In case of Get request, only limited amount of data can be sent because data is sent in header. | In case of post request, large amount of data can be sent because data is sent in body. |
| 2) Get request is not secured because data is exposed in URL bar. | Post request is secured because data is not exposed in URL bar. |
| 3) Get request can be bookmarked | Post request cannot be bookmarked |
| 4) Get request is idempotent. It means second request will be ignored until response of first request is delivered. | Post request is non-idempotent |
| 5) Get request is more efficient and used more than Post | Post request is less efficient and used less than get. |
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 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. 
Container
It provides runtime environment for JavaEE (j2ee) applications.
It performs many operations that are given below:
- Life Cycle Management
- Multithreaded support
- Object Pooling
- Security etc.
Server
It is a running program or software that provides services.
There are two types of servers:
- Web Server
- 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:
- JBoss Open-source server from JBoss community.
- Glassfish provided by Sun Microsystem. Now acquired by Oracle.
- Weblogic provided by Oracle. It more secured.
- 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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