Java Servlet Programming

The Request

We’ve seen how the servlet finds out about the server and about the client. Now it’s time to move on to the really important stuff: how a servlet finds out what the client wants.

Request Parameters

Each access to a servlet can have any number of request parameters associated with it. These parameters are typically name/value pairs that tell the servlet any extra information it needs to handle the request. Please don’t confuse these request parameters with init parameters, which are associated with the servlet itself.

An HTTP servlet gets its request parameters as part of its query string (for GET requests) or as encoded post data (for POST requests). A servlet used as a server-side include has its parameters supplied by PARAM tags. Other types of servlets can receive their parameters in other ways.

Fortunately, even though a servlet can receive parameters in a number of different ways, every servlet retrieves its parameters the same way, using getParameter() and getParameterValues() :

public String ServletRequest.getParameter(String name)
public String[] ServletRequest.getParameterValues(String name)

getParameter() returns the value of the named parameter as a String or null if the parameter was not specified.^[22] The value is guaranteed to be in its normal, decoded form. If the parameter has multiple values, the value returned is server-dependent. If there’s any chance a parameter could have more than one value, you should use the getParameterValues() method instead. ...