I have more than once in the past tried to find an open source SWIFT message parser. There are some defunct/ idle projects (one MT94X parser, jSWIFT, SWIFT Message Parser in Java) and some import/ export components that are part of larger projects (e.g. gnucash). I have now stumbled upon a proper stand alone and open source (LGPL) SWIFT message parser called WIFE.
WIFE is written in Java and sports parsing all message categories and service messages into a message model (message, blocks, tags). This model can be written to a SWIFT message. WIFE also supports converting to and from a (albeit non-standard) XML format and persisting messages using Hibernate. Interesting find! Might come in handy for some projects.