getHeaderNames

getHeaderNames is a method in the Java Servlet API used to obtain the names of all HTTP headers present in an incoming request. It is defined on the HttpServletRequest interface and is implemented by servlet containers. The method returns an Enumeration<String> of header names, enabling callers to iterate over the available headers.

Headers can have multiple values for the same name, so you typically use getHeaders(String name) to retrieve all values for a header, or getHeader(String name) to fetch a single value (usually the first). To list all headers, you iterate over the enumeration returned by getHeaderNames and call getHeader or getHeaders for each header name.

Example:

Enumeration<String> headerNames = request.getHeaderNames();

while (headerNames.hasMoreElements()) {

String name = headerNames.nextElement();

String value = request.getHeader(name);

// process name and value

}

In modern code, you may convert the enumeration to a more convenient collection, for example by using Collections.list(request.getHeaderNames()) to obtain a List<String>, which can then be processed with streams.

See also: HttpServletRequest, getHeader, getHeaders. The method is available in both the Java EE (javax.servlet.http.HttpServletRequest) and the Jakarta EE (jakarta.servlet.http.HttpServletRequest) namespaces, reflecting the namespace transition in newer specifications.