There are use cases which we need to generate a UUID( universally unique identifier ) from the WSO2 ESB server for the back end services. There are two commonly used UUID types, Version 1 UUID or Time UUID A Version 1 UUID use a scheme relying only on timestamp and the MAC address of the computer on which it is generated Version 4 UUID Version 4 UUIDs use a scheme relying only on random numbers Getting a version 4 UUID is really easy in ESB, since we already have one in the message flow. So we can extract it like follows, <property name="MessageID" expression="fn:substring-after(get-property('MessageID'), 'urn:uuid:')"/> But in case of version 1 UUID or Time UUID, we have to use script mediator or class mediator to generate a UUID . Script mediator is slower compared to the class mediator. A simple class mediator which can use for version 1 UUID generation can be found here . This class mediator uses this library to gene