All validators are injected into WorkflowExecutionValidator. private List<Validator> validators WorkflowExecutionValidator will pick up an appropriate validator from a list and check if transition is allowed. Validators are implemented for each workflow execution status Validators are applied in production code

public class WorkflowExecutionValidator {
  private List<Validator> validators;
  public boolean isAllowed(WorkflowExecution workflowExecution, WorkflowExecution wf, WorkflowExecutionState state) {
    ...
    //if (state == WorkflowExecutionState.FAILED) {
    //  validators.get(WorkflowExecutionState.FAILED.ordinal()).isAllowed(workflowExecution, state)
    //}
    //if (state == WorkflowExecutionState.SUCCEEDED) {
    //  validators.get(WorkflowExecutionState.SUCCEEDED.ordinal()).isAllowed(workflowExecution, state)
    //}
    //if (state == WorkflowExecutionState.RUNNING) {
    //  validators.get(WorkflowExecutionState.RUNNING.ordinal()).isAllowed(workflowExecution, state)
    //}
    //if (state == WorkflowExecutionState.WAITING) {
    //  validators.