HTML Forms

Handling The Client Request — Form Data

Concepts

• Reading individual request parameters
• Handling missing and malformed data

The Role of Form Data

Getting data from users.

1. The HTML form tag.

   <form method="GET" action="/trivial" />
   

2. The HTML input tags.

   <input type="text" name="firstName" value="Fred" />
   
   <input type="radio" name="options" value="type1" />
   <input type="radio" name="options" value="type2" />
   

3. The Submit button.

   <input type="submit" value="Enter" />
   

Reading Form Data from Servlets

Reading Single Values

• The HttpServletRequest class has methods for getting data from HTML forms
• getParameter(“parameter”): This method gets one parameter. The name is case sensitive. The argument must match the “name” attribute on the form.
• getParameterNames(): This method returns all the names of all form input tags as an Enumeration.
• getParameterValues(“parameter”): This method returns all the values for inputs tags with the same name. An example is a select tag with the multiple attribute set.

Example

• Sample HTML Form
• RequestParameterSample.java

Missing and Malformed Data

• If getParameter is called and the parameter is missing then the method will return null.
• If getParameter is called and the user has not entered anything in the field then the method will return an empty String (i.e., "").