Servlet & jsp

Web server and web browser

 It’s a take and give policy in between client
and server through HTTP(Hyper Text Transport
Protocol)
 Server takes a request from client and return
something back to client.
 Take and give routine is done through browser.
 Web browser provides the platform to access
server content on client machine.

 The client’s request contains the name and
address (the URL), of the thing the client is
looking for.
 Usually the server has a lot of “contents” that
has to be sent to client. That contents
WebPages, images and other resource.
 The server’s response contains the actual
document that the client requested (or an error
code if the request could not be processed).

What does a web client does?

 A web client lets the user request something on the
server, and shows the user the result of the request.
 The browser is the piece of software that knows how
to communicate with the server. So from now
on, when we use the term client, we usually won’t
care whether we’re talking about the human user
or the browser app. In other words, the client is the
browser app doing what the user asked it to do.

Communication between Server and
browser

Clients and servers know HTML and HTTP

 When a server answers a request, the server
usually sends some type of content to the
browser so that the browser can display it.
 Server sends instruction/data to browser in
html(hyper text mark up language)
 Most of the conversations held on the web
between clients and servers are held using the
HTTP protocol, which allows for simple request
and response conversations.

What the hell browser creates ?

 The browser is a application software reads
through the HTML code which information sent
by the server to the client according to the
client request, creates the web page, and
renders it to the user’s display.

What exactly is the HTTP Protocol ?

 HTTP - It means Hyper Text Transport Protocol.
 HTTP runs on top of TCP/IP. Then ,what is TCT/IP.
 TCP is responsible for making sure that a file sent
from one network node to another ends up as a
complete file at the destination, even though
the file is split into chunks when it’s sent.
 IP is the underlying protocol that moves/routes
the chunks (packets) from one host to another
on their way to the destination.

Continued……

 HTTP, then, is another network protocol that has
Web-specific features, but it depends on TCP/IP to
get the complete request and response from one
place to another. The structure of an HTTP
conversation is a simple Request/ Response
sequence; a browser requests, and a server
responds.
 Key elements of
 Request
 Responds

Continued……

 Key elements of Request
 HTTP method (The action to be performed)

 The page to access (A URL)

 Form parameters (Like arguments to methods)

 Key elements of Respond
 A status code(To check whether the request was
successful or not )
 The content -type(Text, pictures, movies, HTML and etc)

 The content(The actual HTML, images and etc)

HTML is part of the HTTP response
 An HTTP response can
contain HTML. HTTP adds
header information to
the top of whatever
content is in the
response (in other HTTP Header
words, the thing coming
back from the server).
An HTML browser uses
HTTP Body
that header info to help
process the HTML page.

If that’s the response, what’s in the request?
The first ?

 One of the important features is an HTTP
method name. These aren’t Java methods, but
the idea is similar.
 The method name speaks the server the kind of
request that’s being made, and how the rest of
the message will be formatted. The HTTP
protocol has several methods.
 GET
 POST

Magic Get & Post

 GET is the simplest HTTP method, and its main job in
life is to ask the server to get a resource and send it
back.
 The point of GET is to get something back from the
server.
 POST is a more powerful request. It’s like a GET plus
plus. With POST, you can request something and at
the same time send form data to the server (later in
this chapter we’ll see what the server might do with
that data).

Some other Http methods besides get & post

 Those are the two big ones that everybody uses.
But there are a few rarely used methods (and
Servlets can handle them) including
HEAD, TRACE, PUT, DELETE, OPTIONS, and
CONNECT.

Get or Post which one is better

 The total amount of characters in a GET is really
limited , hence it is not useful for bigger data.
 The data you send with the GET is appended to
the URL up in the browser bar. So, whatever you
send is exposed. So there is less security in Get
method.
 The user can’t bookmark a form submission if
you use POST instead of GET.

URL explanations

 URL - Uniform Resource Locators

Protocol , Server & Url
 Protocol set of rules which tells the server how
communications will be held.
 Server is the unique name of the physical server you’re
looking for. This name maps to a unique IP address. IP
addresses are numeric and take the form “xxx.yyy.zzz.aaa”.
You can specify an IP address here instead of a server
name, but a server name is a lot easier to remember.
 URL is optional. A single server supports many ports. A server
application is identified by a port. If you don’t specify a port in
your URL, then port 80 is the default, and as luck would have
it, that’s the default port for web servers.

Path & Resources

 Path: The path to the location, on the server, of the
resource being requested. Because most of the
early servers on the web ran Unix, Unix syntax is still
used to describe the directory hierarchies on the
web server.
 Resource: The name of the content being
requested. This could be an HTML page, a
servlet, an image, PDF, music, video, or anything
else the server feels like serving. If this optional part
of the URL is left out, most web servers will look for
index.html by default.

Reserved Ports

Be care full , never fix your port to these reserved ports.

As web Server Loves to love to serve Static
web pages

 As a static page sits there in a directory. The
server finds and hands it back to client as it is .
Each and every client sees same thing .
 The page goes client exactly same as it was
placed in the server .

Servlet

 There are many advantages to using Java over
Perl for the things you want to do with CGI.
Performance, for one thing.
 With Perl, the server has to launch a heavy-
weight process for each and every request for
that resource!
 Servlets stay loaded and client requests for a
Servlet resource are handled as separate
threads of a single running Servlet.

Tier Architecture
 Tier architecture is three
types -
 Single tier architecture
 Two tier architecture
 Three tier architecture
 Single tier architecture
combines all
Presentation ,logic and
data and keep at one
place. There is no
separation of data, logic
and presentation.
Single tier Architecture

Servlet Demystified (write, deploy, run) in
Tomcat apache server

 However we are here working on Tomcat
apache server.
 So to work on tomcat we have to create a
directory tree as like below under the webapps.

Continued….

 Well to deploy your Servlet program you have to
create a folder according your choice inside of the
webapps folder.
example - holiday
 Then create one more folders in between the folder
you just created inside(i.e. holiday) of webapps.
 WEN-INF
 Now in WEB-INF folder we create another folder
which name most be Classes keep all XML file
which will help us to connect the java file(i.e
x.class) which are inside of Classes folder

Continued….

 In Classes folder all java compiled Servlet files
will be stored. We can create our own package
inside of Classes folder.

Full tree structure of deployment directory

Classes

Some packages

WEB-INF

Lib

WebAppDirectory
tlds

META-INF MANIFEST.MF

Servlet & jsp

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