GetParameterValues

getParameterValues is a method in the Servlet API used to retrieve all values associated with a specific request parameter from an HTTP request. It is defined in the HttpServletRequest interface and returns a String array containing every value that the parameter has for the current request.

The method signature is String[] getParameterValues(String name). When a parameter with the given name is present in the request, the returned array contains all of its values in the order they were sent. If the parameter appears only once, the array contains a single element. If the parameter does not exist, the method returns null. This makes it particularly useful for handling multi-valued inputs such as multi-select fields, groups of checkboxes with the same name, or repeated query parameters.

Common usage involves checking for null and iterating over the values, for example: String[] values = request.getParameterValues("colors"); if (values != null) { for (String v : values) { /* process v */ } }. Unlike getParameter, which returns only the first value, getParameterValues provides access to all submitted values.

Notes for developers include ensuring proper decoding of request parameters by configuring the request character encoding early in the request handling process, commonly with request.setCharacterEncoding("UTF-8"), to avoid garbled input when values contain non-ASCII characters. The method is widely used in Java-based web applications and is compatible with both GET and POST requests, depending on how the client submits the parameters.