Java callouts enable you to use external Java classes to manipulate messages flowing through the Mediator. Only one Java callout is supported per operation or event subscription. The callout class must implement the oracle.tip.mediator.common.api.IjavaCallout interface. Callouts are available for both static and dynamic routings. Figure 20-37 shows a sample Mediator with two operations, in which both the operations have one routing rule each and the first operation has a callout class.