Java8 stream 求和，最大，最小，平均

double notionalSum = list.stream().mapToDouble((e->Double.valueOf(e.get("notional")!=null?e.get("notional").toString():"0"))).sum();

double notionalSum = list.stream().mapToDouble((e->Double.valueOf(e.get("notional")!=null?e.get("notional").toString():"0"))).max();

double notionalSum = list.stream().mapToDouble((e->Double.valueOf(e.get("notional")!=null?e.get("notional").toString():"0"))).min();

double notionalSum = list.stream().mapToDouble((e->Double.valueOf(e.get("notional")!=null?e.get("notional").toString():"0"))).average();