All SOAP messages are sent and received over a connection. With the SAAJ API, the connection is represented by a SOAPConnection object, which goes from the sender directly to its destination. This kind of connection is called a point-to-point connection because it goes from one endpoint to another endpoint. Messages sent using the SAAJ API are called request-response messages. They are sent over a SOAPConnection object with the call method, which sends a message (a request) and then blocks until it receives the reply (a response).
The following code fragment creates the SOAPConnection object connection and then, after creating and populating the message, uses connection to send the message. As stated previously, all messages sent over a SOAPConnection object are sent with the call method, which both sends the message and blocks until it receives the response. Thus, the return value for the call method is the SOAPMessage object that is the response to the message that was sent. The request parameter is the message being sent; endpoint represents where it is being sent.
SOAPConnectionFactory factory = SOAPConnectionFactory.newInstance(); SOAPConnection connection = factory.createConnection(); . . .// create a request message and give it content java.net.URL endpoint = new URL("http://fabulous.com/gizmo/order"); SOAPMessage response = connection.call(request, endpoint);
Note that the second argument to the call method, which identifies where the message is being sent, can be a String object or a URL object. Thus, the last two lines of code from the preceding example could also have been the following:
String endpoint = "http://fabulous.com/gizmo/order"; SOAPMessage response = connection.call(request, endpoint);
A web service implemented for request-response messaging must return a response to any message it receives. The response is a SOAPMessage object, just as the request is a SOAPMessage object. When the request message is an update, the response is an acknowledgment that the update was received. Such an acknowledgment implies that the update was successful. Some messages may not require any response at all. The service that gets such a message is still required to send back a response because one is needed to unblock the call method. In this case, the response is not related to the content of the message; it is simply a message to unblock the call method.
Now that you have some background on SOAP messages and SOAP connections, in the next section you will see how to use the SAAJ API.