JSP IN ACTION in Java

Draw Denso QR Bar Code in Java JSP IN ACTION

The FORM element is the basic structure behind HTML forms and has three main purposes: I To group input elements together syntactically I To identify a server-side program that handles the form processing I To specify what data values are to be sent and in what form A FORM element is described in HTML with the <FORM> tag The syntax of this element is shown here: <FORM action= uri method= method enctype= content type accept-charset= charsets

accept= content types name= form name > </FORM> The attributes and their values are described in the following section

Of the six attributes listed, the only required one is action In practice, attributes other than action and method are rarely used Here are the definitions of each attribute

When a form is completed and the user clicks the Submit button, the Web browser creates an HTTP request that packages all the form data and sends it to a program on some Web server This program is specified in the action attribute The value of the action attribute must be an HTTP Uniform Resource Identifier (URI) (See http://wwwietforg/rfc/rfc2396txt for the formal definition of a URI) This means it has the form [http://<servername>][/]<path> To submit the form, the Web browser opens a socket connection to the specified server (which defaults to the server from which the HTML page was downloaded) and makes an HTTP request using the specified path The path typically points to a servlet, JSP page, or CGI program This program receives the HTTP request and the form data, either in the URI itself or in an input stream, depending on the HTTP method used (see the following method) Specifying a query string on the URI is possible In this case, the parameter(s) encoded in the query string is merged with those specified in the body of the form This is usually unnecessary because a hidden field can accomplish the same purpose

The HTTP protocol provides a number of request types used for file transfer, download, delete, and diagnostic operations Of these, only GET and POST are valid for use in HTML forms The method attribute is where this is specified An HTTP GET or POST request is ordinarily interpreted by the Web server as a request to retrieve the document named in the URI When the Web server has been configured to handle servlets, CGI programs, or other server-side scripting environments, it interprets requests for those resources as requests to invoke them as programs The output produced by such a program (typically an HTML document) is sent back to the requester, the same as if it were a static document requested by name The difference between the GET and POST methods when used in an HTML form is in how they supply input data to the server process:

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I GET Form values are appended to the URI as a query string I POST Form values are supplied in the input stream

Although either method can be used, and the servlet API makes the choice fairly transparent, several characteristics should be taken into account Because GET requests cause input values to be appended to the request URI, they are visible as name/value pairs on the browser address line and in Web server logs This makes GET undesirable for sending sensitive data like passwords Moreover, some servers and browsers may have restrictions on the length of URL s they can handle In addition, GET requests are described in the HTTP specification as idempotent, which means they can safely be repeated without undesirable side effects Under certain circumstances, this means a server can tell a client to reuse its existing copy of a resource rather than sending it a new copy This is usually not what you want as a response from form input For these reasons, POST is usually a better choice for the request method The method attribute is optional If not specified, GET is used by default The value of the attribute can be specified in either uppercase or lowercase