INTERACTIVE WEB SERVICES WITH JAVA

HTML Forms

Users send information to servers via forms:

The Poll Service

Who wins the World Cup 2006?
Please enter your email address:

HTML source:
<h3>The Poll Service</h3> <form action="http://freewig.brics.dk/users/laudrup/soccer.jsp" method="post"> Who wins the World Cup 2006? <select name="bet"> <option value="fr">France!</option> <option selected value="dk">Denmark!</option> <option value="other country">someone else?</option> </select><br> Please enter your email address: <input type="text" name="email"><br> <input type="submit" name="Submit" value="Go!"> </form>

<h3>The Poll Service</h3> <form action="http://freewig.brics.dk/users/laudrup/soccer.jsp" method="post"> Who wins the World Cup 2006? <select name="bet"> <option value="fr">France!</option> <option selected value="dk">Denmark!</option> <option value="other country">someone else?</option> </select><br> Please enter your email address: <input type="text" name="email"><br> <input type="submit" name="Submit" value="Go!"> </form>

The browser collects the reply in a query string:
bet=other+country&email=john.doe%40notmail.com&Submit=Go%21

bet=other+country&email=john.doe%40notmail.com&Submit=Go%21

Values are URL-encoded: space becomes +, non-alphanumeric chars become %hexcode - assuming enctype="application/x-www-form-urlencoded" (the default)

GET vs. POST?

GET with hardwired querystring can be used in links (<a href="...">...</a>) :-)
GET has server-specific limits on input lengths :-(
GET querystrings usually end in the server logs :-(
GET is (in principle) idempotent - results are cached unless explicitly "expired"
GET is the default for form :-(

Uploading files requires POST and a different encoding of form data:
<form method="post" enctype="multipart/form-data" ...> <input type="file" ...>

<form method="post" enctype="multipart/form-data" ...> <input type="file" ...>

The response then contains:

file name (or full path, depending on browser)
data MIME type
encoding type