5.1 Reading Request Headers

Reading headers is straightforward; just call the getHeader method of HttpServletRequest with the name of the header. This call returns a String if the specified header was supplied in the current request, null otherwise . In HTTP 1.0, all request headers are optional; in HTTP 1.1, only Host is required. So, always check for null before using a request header.

Core Approach


Always check that the result of request.getHeader is non- null before using it.

Header names are not case sensitive. So, for example, request.getHeader("Connection") is interchangeable with request.getHeader("connection") .

Although getHeader is the general-purpose way to read incoming headers, a few headers are so commonly used that they have special access methods in HttpServletRequest . Following is a summary.

  • getCookies

    The getCookies method returns the contents of the Cookie header, parsed and stored in an array of Cookie objects. This method is discussed in more detail in Chapter 8 (Handling Cookies).

  • getAuthType and getRemoteUser

    The getAuthType and getRemoteUser methods break the Authorization header into its component pieces.

  • getContentLength

    The getContentLength method returns the value of the Content-Length header (as an int ).

  • getContentType

    The getContentType method returns the value of the Content-Type header (as a String ).

  • getDateHeader and getIntHeader

    The getDateHeader and getIntHeader methods read the specified headers and then convert them to Date and int values, respectively.

  • getHeaderNames

    Rather than looking up one particular header, you can use the getHeaderNames method to get an Enumeration of all header names received on this particular request. This capability is illustrated in Section 5.2 (Making a Table of All Request Headers).

  • getHeaders

    In most cases, each header name appears only once in the request. Occasionally, however, a header can appear multiple times, with each occurrence listing a separate value. Accept-Language is one such example. You can use getHeaders to obtain an Enumeration of the values of all occurrences of the header.

Finally, in addition to looking up the request headers, you can get information on the main request line itself (i.e., the first line in the example request just shown), also by means of methods in HttpServletRequest . Here is a summary of the four main methods.

  • getMethod

    The getMethod method returns the main request method (normally, GET or POST , but methods like HEAD , PUT , and DELETE are possible).

  • getRequestURI

    The getRequestURI method returns the part of the URL that comes after the host and port but before the form data. For example, for a URL of http://randomhost.com/servlet/search.BookSearch?subject=jsp , getRequestURI would return "/servlet/search.BookSearch" .

  • getQueryString

    The getQueryString method returns the form data. For example, with http://randomhost.com/servlet/search.BookSearch?subject=jsp , getQueryString would return "subject=jsp" .

  • getProtocol

    The getProtocol method returns the third part of the request line, which is generally HTTP/1.0 or HTTP/1.1 . Servlets should usually check getProtocol before specifying response headers (Chapter 7) that are specific to HTTP 1.1.

Core Servlets and JavaServer Pages (Vol. 1.Core Technologies)
Core Servlets and Javaserver Pages: Core Technologies, Vol. 1 (2nd Edition)
ISBN: 0130092290
EAN: 2147483647
Year: 2002
Pages: 194

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