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Requests and Responses

Methods in the HttpServlet class that handle client requests take two arguments:

1. An HttpServletRequest object, which encapsulates the data from the client
    
2. An HttpServletResponse object, which encapsulates the response to the client
    

HttpServletRequest Objects

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:
 

• The 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.)
   
• For HTTP GET requests, the getQueryString method returns a String of raw data from the client. You must parse this data yourself to obtain the parameters and values.
   
• For HTTP POST, PUT, and DELETE requests,
   
  • If you expect text data, the getReader method returns a BufferedReader for you to use to read the raw data.
     
  • If you expect binary data, the getInputStream method returns a ServletInputStream for you to use to read the raw data
     

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Note: Use either a getParameter[Values] method or one of the methods that allow you to parse the data yourself. They can not be used together in a single request.

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HttpServletResponse Objects

An HttpServletResponse object provides two ways of returning data to the user:
 

• The getWriter method returns a Writer
   
• The 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.
 

HTTP Header Data

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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