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Getting Started

1. use mvn install to build project or you can directly download the source as zip and import as project in eclipse.
2. I used maven for sorting dependencies.
3. mvn install will also run all the test cases.

Defining Work

public interface Work extends Callable<WorkReport> {

    String getName();

    WorkReport call();
}

Defining Workflow

public interface WorkFlow extends Work {

}

I have created 3 implementations of workflow :

1. Sequential
2. Conditional
3. Parallel

To create a parallel flow we can use parallel flow builder

ParallelFlow parallelFlow = ParallelFlow .Builder.aNewParallelFlow()
        .named("execute 'work1', 'work2' and 'work3' in parallel")
        .execute(work1, work2, work3)
        .build();

The parallel flow builder can be combined with sequential flow so that we achieve a hierarchy of workflows.

SequentialFlow sequentialFlow = SequentialFlow .Builder.aNewSequentialFlow()
        ..named("execute 'work1', 'work2' and 'work3' in sequence")
        .execute(work1)
        .then(work2)
        .then(work3)
        .build();

Conditional Flow will help us with some sort of condition based / rule based workflow execution.

ConditionalFlow conditionFlow = ConditionalFlow.Builder.aNewConditionalFlow()
        .named("my conditional flow")
        .execute(work1)
        .when(WorkReportPredicate.COMPLETED)
        .then(work2)
        .otherwise(work3)
        .build();

Hedge fund example

Below example shows us how to chain different flows together using sequential, parallel and conditional.

@Test
    public void defineWorkFlowHedgeFundAndExecuteIt() throws Exception {

		HedgeFundWork work1 = new HedgeFundWork("Trader Raise Fund Request");
		HedgeFundWork work2 = new HedgeFundWork("Research Analyst Approval");
		HedgeFundWork work3 = new HedgeFundWork("Fund Manager Approval");
		HedgeFundWork work4 = new HedgeFundWork("Division Head Approval");
		HedgeFundWork work5 = new HedgeFundWork("Operations Approval");

        WorkFlow workflow = aNewSequentialFlow()
                .execute(aNewRepeatFlow()   // Start workflow with the request
                            .named(work1.getName())  
                            .build())
                .then(aNewConditionalFlow()
                        .execute(aNewParallelFlow()  // Execute approvals parallely
                                    .named(work2.getName()+" and "+work3.getName())
                                    .execute(work2, work3)
                                    .build())
                        .when(COMPLETED)  // when above completes execute next in hierarchy
                        .then(work4)
                        .when(COMPLETED) // when above completes execute next in hierarchy
                        .then(work5)
                        .build())
                .build();

        WorkFlowEngine workFlowEngine = aNewWorkFlowEngine().build();
        WorkReport workReport = workFlowEngine.run(workflow);
        System.out.println("workflow report = " + workReport);
    }

Custom Flows

Custom flows can be implemented using the WorkFlow interface. The WorkFlowEngine works against interfaces, so your implementation should be work without any issues

Reporting

I am using future task in executor framework to write a very basic reporting code.

public interface WorkReport {
    WorkStatus getStatus();

    Throwable getError();
}