Reading Form Data from Servlets

Reading Form Data from Servlets

• The browser uses two methods to pass this information to web server. 
• These methods are GET Method and POST Method.

• GET:
• The GET method sends the encoded user information appended to the page request. 
• The page and the encoded information are separated by the ? (question mark) symbol as follows −
• Example: https://profcdpatel.blogspot.com/search?q=java
• The GET method is the default method to pass information from browser to web server
• Never use the GET method if you have a password or other sensitive information to pass to the server. 
• The GET method has size limitation: only 1024 characters can be used in a request string.
• Servlet handles this type of requests using doGet() method.

• POST:
• A generally more reliable method of passing information to a backend program is the POST method. 
• This packages the information in exactly the same way as the GET method, but instead of sending it as a text string after a ? (question mark) in the URL it sends it as a separate message. 
• This message comes to the backend program in the form of the standard input which you can parse and use for your processing. 
• Servlet handles this type of requests using doPost() method.

Reading Form Data using Servlet

• Servlets handles form data parsing automatically using the following methods depending on the situation.
  

• getParameter():You call req.getParameter() method to get the value of a form parameter.
• A method of HttpServletRequest.
• Case-sensitive parameter name as an argument.
• URL-decoding is done automatically.
• An empty string is returned if the parameter exists but has no value.
• null is returned if there was no such parameter.
• Parameter names are case sensitive. 
• Syntax: public String getParameter(String name)
• Description: is used to obtain the value of a parameter by name.
• Example:
  

• getParameterValues(): Call this method if the parameter appears more than once and returns multiple values, for example checkbox.
• If the same parameter name might appear in the form data more than once, you should call getParameterValues.
• It returns an array of strings.
• The return value of getParameterValues is null for nonexistent parameter names.
• It is a one-element array when the parameter has only a single value.

• Syntax: public String[] getParameterValues(String name)
• Description: returns an array of String containing all values of given parameter name. It is mainly used to obtain values of a Multi select list box.
• Example (in HTML):
  

• Example (in JAVA):
  

• getParameterNames() − Call this method if you want a complete list of all parameters in the current request.

• Syntax: java.util.Enumeration getParameterNames()
• Description : returns an enumeration of all of the request parameter names.
• Example(in HTML)
  

• Example (in JAVA)