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Monday, October 5, 2009

J2EE Class -2

WEB BROWSER AND WEB SERVER:

* A web browser lets a user to request a resource.

* The web server gets the request, finds the resource, and returns something back to the user. The returned resource can be a HTML page, a picture, a sound file or even a PDF document. The client asks for the resource and the server sends it back.

In short, A web server takes a client request and gives something back to the client.

REASONS A WEB SERVER DOESN'T SEND A RESOURCE:

* A server doesn't send a resource if its not there, or even if it’s not where the server is expecting it to be. "404 Not Found" is the error response you get when the server can’t find what we asked for.

WEB CLIENT:

* Clients mean both (or either) the human user and the browser application.

* The browser is the piece of software (like Netscape or Mozilla) that knows how to communicate with the server. The browser’s other big job is interpreting the HTML code and rendering the web page for the user.

* The client is the browser application doing what the user asked it to do.

FUNCTIONALITY OF A WEB CLIENT:

A web client lets the user request something on the server, and shows the user the result of the request.

* CLIENTS AND SERVERS COMMUNICATE USING HTML and HTTP.

HTML(HyperText Markup Language):

When a server answers a request,the server usually sends some type of content to the browser so that the browser can display it. Servers often send the browser a set of instructions written in HTML. The HTML tells the browser how to present the content to the user. All web browsers know what to do with HTML, although sometimes an older browser might not understand parts of a page that was written using newer versions of HTML.

HTTP(HyperText Transfer Protocol):

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. The client sends an HTTP request, and the server answers with an HTTP response.

HTML and HTTP IN SHORT:

if you’re a web server, you speak HTTP.
When a web server sends an HTML page to the client, it sends it using HTTP.