saaj

SAAJ, or the SOAP with Attachments API for Java, is a standard Java API that provides a programmatic model for creating, parsing, and manipulating SOAP messages, including attachments. It offers a transport-neutral way to work with SOAP envelopes, headers, bodies, and binary or textual attachments, enabling robust interaction with SOAP-based web services.

The API is defined by a set of interfaces and classes in the javax.xml.soap package (and, in newer environments, jakarta.xml.soap). Key types include SOAPMessage, SOAPPart, SOAPEnvelope, SOAPHeader, SOAPBody, and AttachmentPart. Supporting factories such as SOAPConnectionFactory, MessageFactory, and methods on SOAPMessage facilitate the creation, sending, and processing of messages. Attachments are represented by AttachmentPart objects, which can carry data via MIME content types and data handlers. A typical workflow involves creating a SOAPMessage, constructing the envelope structure, optionally adding attachments, and sending the message through a SOAPConnection.

SAAJ relies on MIME multipart/related messaging to carry attachments alongside the SOAP envelope, supporting both SOAP with Attachments (SwA) and modern transmission optimization techniques such as MTOM (Message Transmission Optimization Mechanism). This enables efficient transfer of binary data within SOAP messages while preserving a standard API surface.

In practice, SAAJ provides low-level, programmatic access to SOAP messages and is often used in scenarios where fine-grained control over the SOAP structure or attachments is required. It complements higher-level web service stacks, such as JAX-WS, by offering direct message construction and inspection capabilities. The API originated within the Java API for XML Messaging (JAXM) and was part of the Java EE platform; in Jakarta EE, the package name has migrated to jakarta.xml.soap.