On the server, response handlers are invoked on outgoing responses immediately before the transport handlers are invoked; on the client, they are invoked immediately after the transport handlers have been invoked. See Figure 8.

On the server, the SOAP message handler generated by HydraExpress is always invoked on the outgoing message as the last response handler before the transport handlers. This is true even though it does not appear in the <response-handlers> element of the handlers configuration file, <servicecontextname>_handlers.xml (used to configure server-side handlers and discussed in Chaining Handlers on the Server).

A single SOAP message handler can function either as a request message handler, a response message handler, or both. The rwsf::CallInfo interface provides methods for determining whether the message is a request or response.

The rwsf::CallInfo::isRequest() method returns true for a request message, causing the SOAP message handler to parse the message as an incoming request. This method returns false for a response message, causing the SOAP message handler to construct the SOAP response message. You, too, can use this method to create a handler that serves as both a request and a response handler, but note that such custom handlers must be configured in both the <request-handlers> and <response-handlers> elements of <servicecontextname>_handlers.xml, discussed in Chaining Handlers on the Server.

In fact, rwsf::CallInfo also has an isClient() method that returns true on the client side and false on the server side. With this method, a single handler could be used for both request and response handling on both the client and the server.