getCharacterEncoding obtains information about the encoding format used for the request in Java

Create QR Code JIS X 0510 in Java getCharacterEncoding obtains information about the encoding format used for the request
getCharacterEncoding obtains information about the encoding format used for the request
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isSecure finds out if the request was made over a secure channel getParameterNames obtains a list of all parameter names in the request getRemoteAddr determines the IP address of the client that sent the request getParameter is used to retrieve the first parameter value associated with a named parameter type
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getParameterValues is used to retrieve multiple parameter values associated with a named parameter type
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Several other methods are provided for querying different aspects of the request object See javaxservletServletRequest[1] for more information A specialized version,
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HttpServletRequest, for HTTP based servlet requests is also available See javaxservlethttpHttpServletRequest for more information
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If you are new to Java or unsure about this reference, see the "Conventions" section in the
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Preface of this book shows a simple usage scenario involving a request object
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Figure 10- 3
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Figure 10-3 Using the request object
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HttpSession session = requestgetSession(true); : : // obtain the values for UserID and password String loginID = rquestgetParameter ("USERID"); String loginPassword = requestgetParameter ("PASSWORD"); :
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Response Generation
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A request generally warrants a response, and servlets are no exception in this regard
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Servlets make use of ServletResponse to simplify this common task The ServletResponse object, commonly referred to as the response object, is in fact provided to a servlet alongside the request object as a parameter to the service method
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Output can be written in either binary or character format by obtaining a handle to either a ServletOutputStream object or a PrintWriter object, respectively Some of the other methods provided by the ServletResponse interface are contained in the following list:
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getOutputStream obtains the handle to a ServletOutputStream object for binary data
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getWriter obtains the handle to a PrintWriter object for characte r data setBufferSize can be used to establish the buffer size for the response to enable better performance tuning
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flushBuffer flushes the current contents of the buffer
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For more information, see javaxservletResponseObject and javaxservlet ServletOutputStream
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An HTTP specific response object is also available and provides additional capabilities related to HTTP response header formulation See javaxservlet httpHttpServletResponse for more information
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Figure 10- 4
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shows a simple usage scenario involving a response object
Figure 10-4 Generating the response
PrintWriter out; : // set content type responsesetContentType("text/html"); : out = responsegetWriter(); outprintln("<HTML><HEAD><TITLE>"); : outprintln("Login Unsuccessful"); : outflush(); outclose();
Alternatives for Response Generation
If you take a good look at Figure 10-4 , you will see several HTML tags involved in the generation of output from the servlet This represents only one approach for generation of dynamic output
Another similar but more structured approach is to use libraries of HTML files to generate common headers and footers for the necessary response Web pages, with the dynamic portion of the page still generated much like what was shown in Figure
10- 4
A third and cleaner approach is to use the power of JSP and JavaBeans whenever possible In this approach, the servlet simply needs to forward to a JSP page that contains all of the necessary presentation information and use JSP technology and JavaBeans to fill in the dynamic content portions of the page Other than the forward, the servlet has little else to do with presentation except perhaps coordinating the necessary items for the JSP page to successfully do its work
We discuss this approach further in
HTTP Request Handlers
The HttpServlet class extends the GenericServlet class and therefore inherits all of the standard servlet capabilities In addition to the basic servlet life cycle methods and convenience method, the more complex HttpServlet class adds methods to aid in the processing of HTTP requests These commonly used handler methods are
doGet: Handles HTTP GET requests doPost: Handles HTTP POST requests
In the case of doGet, there is an additional method used for conditional HTTP GET support (the d ifferent HTTP request types are explained later in this section) The getLastModified method is like HTTP GET, but only returns content if it has changed since a specified time This method can only be used if doGet has also been overridden and is intended to be used in cases where you are dealing with content that does not change much from request to request
Advanced Handler Methods
There are several advanced handler methods that are defined as well:
doPut: Handles HTTP PUT requests doDelete: Handles HTTP DELETE requests doOptions: Handles HTTP OPTIONS requests doTrace: Handles HTTP TRACE requests
Unlike the GenericServlet class, servlets based on HttpServlet have almost no valid reason to override the service method Instead, you typically override these request handlers, which the base service method implementation calls when appropriate The doOptions and doTrace methods also have virtually no valid reason to be overridden and are present only for full HTTP support An HttpServlet must override at least one method, which usually means one of the remaining life cycle methods or request handlers