jdk8 stream高级使用方法
作者：互联网
@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;
}
标签：BigDecimal,stream,高级,System,jdk8,println,new,out 来源： https://www.cnblogs.com/song27/p/16392152.html