BPMN Support
brainslug is able to export flow definitions to BPMN 2.0 as rendered image or XML definitions file.
The following examples use this flow:
FlowBuilder simpleFlow = new FlowBuilder() {
@Override
public void define() {
flowId(id("simpleFlow"));
start(event(id("start")))
.execute(task(id("task")).display("A Task"))
.execute(task(id("task2")).display("Another Task"))
.end(event(id("end")));
}
};
BPMN Renderer
Format format = Format.JPG;
JGraphBpmnRenderer renderer = new JGraphBpmnRenderer(new DefaultSkin());
String fileName = simpleFlow.getName() + "." + format.name();
FileOutputStream outputFile = new FileOutputStream(fileName);
renderer.render(simpleFlow, outputFile, format);

also see: JGraphBpmnRendererTest.
BPMN XML Export
BpmnModelTransformer bpmnModelTransformer = new BpmnModelTransformer();
String bpmnXml = bpmnModelTransformer.toBpmnXml(simpleFlow);
will produce
<?xml version="1.0" encoding="UTF-8"?>
<definitions xmlns="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:activiti="http://activiti.org/bpmn" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:omgdc="http://www.omg.org/spec/DD/20100524/DC" xmlns:omgdi="http://www.omg.org/spec/DD/20100524/DI" typeLanguage="http://www.w3.org/2001/XMLSchema" expressionLanguage="http://www.w3.org/1999/XPath" targetNamespace="http://www.activiti.org/test">
<process id="471ff134-4050-497b-bf80-d1fa5164f311" name="471ff134-4050-497b-bf80-d1fa5164f311" isExecutable="true">
<startEvent id="start" name="start"></startEvent>
<serviceTask id="task" name="A Task"></serviceTask>
<serviceTask id="task2" name="Another Task"></serviceTask>
<endEvent id="end" name="end"></endEvent>
<sequenceFlow sourceRef="start" targetRef="task"></sequenceFlow>
<sequenceFlow sourceRef="task" targetRef="task2"></sequenceFlow>
<sequenceFlow sourceRef="task2" targetRef="end"></sequenceFlow>
</process>
<bpmndi:BPMNDiagram id="BPMNDiagram_471ff134-4050-497b-bf80-d1fa5164f311">
<bpmndi:BPMNPlane bpmnElement="471ff134-4050-497b-bf80-d1fa5164f311" id="BPMNPlane_471ff134-4050-497b-bf80-d1fa5164f311"></bpmndi:BPMNPlane>
</bpmndi:BPMNDiagram>
</definitions>
also see: BpmnModelTransformerTest