SOAP with Attachments API for Java

SOAP with Attachments API for Java (SAAJ) is used for SOAP
messaging that works behind the scenes in the Java API for XML-based RPC (JAX-RPC) implementation.

Web services uses SOAP messages to represent remote procedure calls between the client and the server. In normal JAX-RPC flows, the SOAP message is deserialized into a series of Java value type business objects that represent the parameters and return values. In addition, JAX-RPC provides APIs that support applications and handlers to manipulate the SOAP message directly. The SOAP message is manipulated using the SAAJ data model. The primary interface in the SAAJ model is javax.xml.soap.SOAPElement.

WebSphere Application Server uses SAAJ Version 1.2. The main benefit of SAAJ Version 1.2 is that the model extends the Document Object Model (DOM) model. The DOM model is used by applications that manipulate XML. Using this model applications are able to process an SAAJ model that uses pre-existing DOM code. It is also easier to convert pre-existing DOM objects to SAAJ objects.

Messages created using SAAJ follow SOAP standards. A SOAP message is represented in the SAAJ model as a javax.xml.soap.SOAPMessage object. The XML content of the message is represented by a javax.xml.soap.SOAPPart object. Each SOAP part has a SOAP envelope. This envelope is represented by the SAAJ javax.xml.SOAPEnvelope object. The SOAP specification defines various elements that reside in the SOAP envelope; SAAJ defines objects for the various elements in the SOAP envelope.

The SOAP message can also contain non-XML data that is called attachments. These attachments are represented by SAAJ AttachmentPart objects that are accessible from the SOAPMessage object. A number of reasons exist as to why handlers and applications use the generic SOAPElement API instead of a tightly bound mapping:

• The Web service might be a conduit to another Web service. In this case, the SOAP message is only forwarded.

• The Web service might manipulate the message using a different data model, for example a Service Data Object (SDO). It is easier to convert the message from a SAAJ Document Object Model (DOM) to a different data model.

• A handler, for example, a digital signature validation handler, might want to manipulate the message generically.

To review the entire SAAJ API, see Web services: Resources for learning.