jdk8 stream高级使用方法

@Data
public class Order {

    private String account;
    private String orderNo;
    private Long quantity;
    private BigDecimal amount;
    private Status status;
}
public enum Status {

    start,process,finish;

}

 

 

public class OrderStreamExample {


    public static void main(String[] args) {
        OrderStreamExample example = new OrderStreamExample();
        example.baseOperation();
        example.stream();
    }

    public void baseOperation(){
        IntConsumer action = v-> System.out.print(v+"\t");
        //int startInclusive, int endExclusive
        IntStream.range(1,7).forEachOrdered(action);

        System.out.println();
        List<Integer> intList = Arrays.asList(40, 32, 53, 22, 11, 89, 76);
        int max = intList.stream()
                .max(Comparator.comparing(Integer::intValue)).get();
        int min = Arrays.asList(BigDecimal.valueOf(20),BigDecimal.valueOf(30),BigDecimal.valueOf(25)).stream()
                .min(Comparator.comparing(BigDecimal::intValue)).get().intValue();
        System.out.println("max="+max+",\tmin="+min);
        int sum1 = intList.stream().collect(Collectors.summingInt(o->o));
        int sum2 = intList.stream().reduce(0,Integer::sum);
        int sum3 = intList.stream().reduce(0,(a,b)->a+b);
        System.out.println("求和sum:\t"+sum1+"\t,"+sum2+"\t,"+sum3);

        IntSummaryStatistics statistics = intList.parallelStream().collect(Collectors.summarizingInt(o->o));
        System.out.println("sum="+statistics.getSum()+",\t平均:"+statistics.getAverage()+",\t个数："+statistics.getCount()+",\t最大数："+statistics.getMax());


        List<String> propList = Arrays.asList("profile=native", "debug=true", "logging=warn", "interval=500", "interval=1000");
        Map<String,String> propMap = new ConcurrentHashMap<>();
        propList.stream().forEach(o->{
            String[] kv = o.split("\\=",2);
            propMap.put(kv[0],kv[1]);
        });
        System.out.println("properties转换："+new Gson().toJson(propMap));

        System.out.println("=======================");
    }

    public void stream(){
        List<Order> orderList = buildOrderList();
        //默认升序，排序只能使用stream
        List<Order> sortedList = orderList.stream().sorted(Comparator.comparing(Order::getAmount)).collect(toList());
        System.out.println("默认升序");
        System.out.println(new Gson().toJson(sortedList));
        //降序
        List<Order> sortedReversedList = orderList.stream().sorted(Comparator.comparing(Order::getAmount).reversed()).collect(toList());
        System.out.println("降序");
        System.out.println(new Gson().toJson(sortedReversedList));

        //按account分组
        Map<String, List<Order>> accountGroupList = orderList.stream().collect(Collectors.groupingBy(o->o.getAccount()));
        //按account分组最大的金额
        Map<String,BigDecimal> accountMaxAmountMap = orderList.stream().collect(
                Collectors.groupingBy(o->o.getAccount(),
                        Collectors.collectingAndThen(
                                Collectors.maxBy(Comparator.comparing(Order::getAmount))
                                ,f->f.map(o->o.getAmount()).get())));
        System.out.println("按account分组最大的金额");
        System.out.println(new Gson().toJson(accountMaxAmountMap));
        //按account分组金额最大的对象
        Map<String,Order> accountMaxOrderMap = orderList.stream().collect(
                Collectors.groupingBy(o->o.getAccount(),
                        Collectors.collectingAndThen(
                                Collectors.maxBy(Comparator.comparing(Order::getAmount))
                                ,Optional::get))); //f->f
        System.out.println("按account分组金额最大的对象");
        System.out.println(new Gson().toJsonTree(accountMaxOrderMap));
        //按status分组统计纪录数
        Map<Status,Long> statusCountMap = orderList.stream().collect(Collectors.groupingBy(o->o.getStatus(),Collectors.counting()));
        System.out.println("按status分组统计纪录数");
        System.out.println(new Gson().toJsonTree(statusCountMap));
        //按account分组统计总金额
        Map<String,BigDecimal> accountSumAmountMap = orderList.stream().collect(
                Collectors.groupingBy(o->o.getAccount()
                        ,Collectors.mapping(o->o.getAmount(),reducing(BigDecimal.ZERO,BigDecimal::add)))
        );
        System.out.println("按account分组统计总金额");
        System.out.println(new Gson().toJsonTree(accountSumAmountMap));

        //按account分组，把quantity组装字符串
        Map<String,String> accountQuantityMap = orderList.stream().collect(
                Collectors.groupingBy(o->o.getAccount()
                        , Collectors.mapping(o->String.valueOf(o.getQuantity()),joining(",","[","]")))
        );
        System.out.println("按account分组，把quantity组装字符串");
        System.out.println(new Gson().toJson(accountQuantityMap));

        //按account分组，封装成新对象
        Map<String,OrderVO> accountOrderVOMap = orderList.stream().collect(
                Collectors.groupingBy(o->o.getAccount()
                        ,Collectors.collectingAndThen(toList(),list->{
                            OrderVO vo = new OrderVO();
                            vo.setAccount(list.stream().findAny().get().getAccount());
                            vo.setQuantity(list.stream().map(o->o.getQuantity()).reduce(0L,Long::sum));
                            vo.setAmount(list.stream().map(o->o.getAmount()).reduce(BigDecimal.ZERO,BigDecimal::add));
                            return vo;
                        })
                )
        );
        System.out.println("按account分组，封装成新对象");
        System.out.println(new Gson().toJson(accountOrderVOMap));


    }


    private List<Order> buildOrderList(){
        List<Order> list = new ArrayList<>();
        list.add(buildOrder("tom","D1001",100L,new BigDecimal("100"),Status.start));
        list.add(buildOrder("jerry","J1001",140L,new BigDecimal("200"),Status.process));
        list.add(buildOrder("tom","D1002",200L,new BigDecimal("220"),Status.finish));
        list.add(buildOrder("jerry","J1002",500L,new BigDecimal("500"),Status.start));
        list.add(buildOrder("tom","D1003",300L,new BigDecimal("300"),Status.finish));
        list.add(buildOrder("tom","D1004",400L,new BigDecimal("400"),Status.process));
        list.add(buildOrder("jerry","J1003",300L,new BigDecimal("300"),Status.start));
        list.add(buildOrder("tom","D1005",550L,new BigDecimal("550"),Status.process));
        list.add(buildOrder("tom","D1006",50L,new BigDecimal("50"),Status.process));
        list.add(buildOrder("jerry","J1004",150L,new BigDecimal("150"),Status.finish));
        return list;
    }

    private Order buildOrder(String account, String orderNo, Long quantity, BigDecimal amount, Status status){
        Order order = new Order();
        order.setAccount(account);
        order.setOrderNo(orderNo);
        order.setQuantity(quantity);
        order.setAmount(amount);
        order.setStatus(status);
        return order;
    }
}
@Data
class OrderVO{
    private String account;
    private Long quantity;
    private BigDecimal amount;
}