A SOAP message constructed according to the SOAP 1.1 specification can only contain data encoded as XML. The SOAP with attachments specification defines an extension of the SOAP that allows additional data items — which may or may not be XML — to be transferred along with a SOAP message. SAAJ supports SOAP with attachments and provides a simple API that allows the transfer of arbitrary data. However, as we’ll see, at the detailed level this interface is not quite as easy to use as it could be.
As a demonstration of the use of attachments, the book image web service uses the SAAJ API to return the cover images for one or more of the books that it knows about. To see how this works, start the client using the following command:
When the list of book titles appears, select one or more of them by clicking on them with the mouse (hold down the Control key to select more than one), then press the “Fetch” button. The selected images will appear in the user interface, as shown in Figure 3-7, and the message used to deliver them will be written to the command window. Since the message contains the binary data for the images, you’ll see some strange characters in the output window. Leaving out the image data itself, a typical message used to transfer three cover images is shown in Figure 3-8.
Figure 3-7. Using ...