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Methods in the
HttpServletclass that handle client requests take two arguments:
- An
HttpServletRequestobject, which encapsulates the data from the client
- An
HttpServletResponseobject, which encapsulates the response to the client
An HttpServletRequest object provides access to HTTP header
data, such as any cookies found in the request and the HTTP method with
which the request was made. The HttpServletRequest object
also allows you to obtain the arguments that the client sent as part of the
request.
To access client data:
getParameter method returns the value of a named
parameter. If your parameter could have more than one value, use
getParameterValues instead. The
getParameterValues method returns an array of values for the
named parameter. (The method getParameterNames provides the
names of the parameters.) getQueryString method returns a
String of raw data from the client. You must parse this data
yourself to obtain the parameters and values.getReader method returns a
BufferedReader for you to use to read the raw data. getInputStream method
returns a ServletInputStream for you to use to read the raw data
Note: Useeither agetParameter[Values]methodor one of the methods that allow you to parse the data yourself. They can not be used together in a single request.
An HttpServletResponse object provides two ways of returning
data to the user:
getWriter method returns a Writer
getOutputStream method returns a
ServletOutputStream Use the getWriter method to return text data to the user, and
the getOutputStream method for binary data.
Closing the Writer or ServletOutputStream after
you send the response allows the server to know when the response is complete.
You must set HTTP header data before you access the
Writer or OutputStream. The
HttpServletResponse class provides methods to access the header
data. For example, the setContentType method sets the content
type. (This header is often the only one manually set.)
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