How a web site recognize the web browser? - web

Question

Some sites are arrange the layout by itself when accessed through a smartphone or a pc. I wonder how is it done (Javascript? getting the browser data?). I would really appreciate some help, I am learning JAVA, thanks.

Answer 1

Each request of web browser have agent-string, which contain necessary information. Look at this page for description of agent string. http://en.wikipedia.org/wiki/User_agent

Answer 2

The browser sends a header with each GET request with a variety of information about itself. See here for an example, but the particular information your are talking about (browser type) is sent in the User-Agent field. With some http client libraries, you are able to control some of the fields sent in order to assume the identity of other types of client.

Answer 3

This is done by reading the user agent, usually using javascript (on websites).
Javascript example here.

Answer 4

The Website recognizes the Browser via the user agent string. This is a unique identifier that tells the site the browser type and version.
This can be detected in javascript via navigator.userAgent
It is also sent to the server in the Get Request as a header field
Example:
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.5 (KHTML, like Gecko) Chrome/19.0.1084.56 Safari/536.5
The Java Servlet code to get this would be (More Info Here):
public final void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
String agent = req.getHeader("user-agent");
if (agent != null && agent.indexOf("MSIE") > -1) {
// Internet Explorer mode
} else {
// Non-Internet Explorer mode
}
}
Obligatory Wikipedia Reference:
http://en.wikipedia.org/wiki/User_agent
The User-Agent string format is currently specified by Section 14.43
of RFC 2616 (HTTP/1.1) The format of the User-Agent string in HTTP is
a list of product tokens (keywords) with optional comments. For
example if your product were called WikiBrowser, your user agent
string might be WikiBrowser/1.0 Gecko/1.0. The "most important"
product component is listed first. The parts of this string are as
follows:
Product name and version (WikiBrowser/1.0) Layout engine and
version(Gecko/1.0). In this case, this indicates the Layout engine and
version. Unfortunately, during the browser wars, many web servers were
configured to only send web pages that required advanced features to
clients that were identified as some version of Mozilla.
For this reason, most Web browsers use a User-Agent value as follows:
Mozilla/[version] ([system and browser information]) [platform]
([platform details]) [extensions]. For example, Safari on the iPad has
used the following:
Mozilla/5.0 (iPad; U; CPU OS 3_2_1 like Mac OS X; en-us)
AppleWebKit/531.21.10 (KHTML, like Gecko) Mobile/7B405 The components
of this string are as follows:
Mozilla/5.0: Previously used to indicate compatibility with the
Mozilla rendering engine (iPad; U; CPU OS 3_2_1 like Mac OS X; en-us):
Details of the system in which the browser is running
AppleWebKit/531.21.10: The platform the browser uses (KHTML, like
Gecko): Browser platform details Mobile/7B405: This is used by the
browser to indicate specific enhancements that are available directly
in the browser or through third parties. An example of this is
Microsoft Live Meeting which registers an extension so that the Live
Meeting service knows if the software is already installed, which
means it can provide a streamlined experience to joining meetings.