Set<Approval> approvals = ...;
Set<Approval> pendingApprovals = approvals.stream().filter(approval -> approval.state().equals(ApprovalState.PENDING));
Set<Approval> approvalsCompletedByJohnDoe = approvals.stream().filter(approval -> approval.state().equals(ApprovalState.COMPLETE))
                                                            .filter(approval -> approval.completedBy().equals("johndoe"));