Question

HttpServletRequest.getParameterValues() returns a String[] containing all values of a given HTTP request parameter. Does anyone know if the order of the values in this array is guaranteed by specification to by the same as the order which those values were passed through in the request?

For example, if I have the GET query string x=1&x=2&x=3, am I guaranteed to receive the String[] {"1", "2", "3"} when I call getParameterValues()? It seems to work in practice, but I can’t find anything which specifies that this must be the case, so I’m reluctant to rely on it.

Answer 1

The javadoc for ServletRequest (v2.5 javadoc) does not mention anything about the ordering of values for that method. As such, I wouldn’t rely on the order being preserved.

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Update: also checked the spec document for 2.5, contains the following information relating to getParameterValues(). It does not mention anything about ordering with respect to the query string, so I think the behaviour you are seeing is implementation detail, not defined as part of the interface.

The parameters are stored as a set of
name-value pairs. Multiple parameter
values can exist for any given
parameter name. The following methods
of the ServletRequest interface are
available to access parameters:

• getParameter
• getParameterNames
• getParameterValues
• getParameterMap

The
getParameterValues method returns an
array of String objects containing all
the parameter values associated with a
parameter name. The value returned
from the getParameter method must be
the first value in the array of String
objects returned by
getParameterValues. The
getParameterMap method returns a
java.util.Map of the parameter of the
request, which contains names as keys
and parameter values as map values.

For future reference, the Java Servlet specs can be downloaded from Sun, I mean Oracle’s website. You can double check the specific servlet version you’re interested in there.