关于java:JavaStream用法

1. 将list转为map

   Map<Long, ItemTO> itemMap =    items.stream().collect(Collectors.toMap(ItemTO::getEventId, Function.identity(), (v1, v2)->v1));

2. List中对象的某个属性值拿进去作为一个list

// 去重List<Long> ids = items.stream().map(ItemTO::getId).distinct().collect(Collectors.toList());// 不去重List<Long> ids = items.stream().map(ItemTO::getId).collect(Collectors.toList());

3. 将list转为Map<Long, List>

Map<Long, List<ItemTO>> itemListMap = itemList.stream().collect(Collectors.groupingBy(item -> item.getId()));Map<Long, ItemTO> itemMap =        items.stream().collect(Collectors.toMap(ItemTO::getEventId, Function.identity(), (v1, v2)->v1));

4. 将list中的string转为long

List<Long> idList = groupList.stream().map(group->Long.parseLong(group.getGroupLeaderId())).collect(Collectors.toList());

5. 过滤操作

groupIdList.stream().filter(x -> x!=null).collect(Collectors.toList());List<Long> allPlatformIids = allStoreItemIndexResultTOS.stream().filter(t -> StoreItemTypeEnum.PLATFORM.getType()      .equals(t.getType())).map(StoreItemIndexResultTO::getIid).collect(Collectors.toList());//过滤洽购数量为0的skuList<ObmSkuInfoTO> skuCollectList = skuInfoTOList.stream().        filter(e -> e.getNum() > 0).collect(Collectors.toList());/** * 在订单列表中过滤指定的oid * @param effectiveLists * @param oid * @return */private List<ItemTO> filterOrder(List<ItemTO> itmeList, long oid) {    return itmeList.stream().filter(p -> {        if (p.getOid().equals(oid)) {            return false;        }        return true;    }).collect(Collectors.toList());}

6. 将list中对象的两个属性值别离作为map的key和value

itemList.stream().filter(t -> t.getId() != null)        .collect(Collectors.toMap(ItemTO::getId, ItemTO::getName, (k1, k2)->k2));

7. 对list做操作

// 交加List<String> intersection = list1.stream().filter(item -> list2.contains(item)).collect(toList());// 差集 (list1 - list2)List<String> reduce1 = list1.stream().filter(item -> !list2.contains(item)).collect(toList());// 差集 (list2 - list1)List<String> reduce2 = list2.stream().filter(item -> !list1.contains(item)).collect(toList());// 并集List<String> listAll = list1.parallelStream().collect(toList());List<String> listAll2 = list2.parallelStream().collect(toList());listAll.addAll(listAll2);// 去重并集List<String> listAllDistinct = listAll.stream().distinct().collect(toList());System.out.println("---失去去重并集 listAllDistinct---“);// 循环输入listAllDistinct.parallelStream().forEachOrdered(System.out :: println);

8. map的操作，移除

// 通过value移除map.values().removeIf(value -> !value.contains("1"));// 通过key移除map.keySet().removeIf(key -> key != 1);// key或者value移除map.entrySet().removeIf(entry -> entry.getKey() != 1);

9. 排序操作

// 升序itemList = itemList.stream().sorted(Comparator.comparingInt(ItemTO::getPtPrice)).collect(Collectors.toList());// 降叙itemList = itemList.stream().sorted(Comparator.comparingInt(ItemTO::getPtPrice).reversed()).collect(Collectors.toList());

10. groupBy操作

//aMap<Long,List<Long>> exhibitionPitemMap = list.stream().collect(Collectors.groupingBy(TestDTO1::getLevle1CategoryId, Collectors.mapping(TestDTO1::getPitemId, Collectors.toList())));//bMap<Long, List<TestDTO2>> categoryPitemMap = list.stream().collect(Collectors.groupingBy(TestDTO2::getLevle1CategoryId));

11. map转list用法

Map<String, String> map = new HashMap<>(); // Convert all Map keys to a ListList<String> result = new ArrayList(map.keySet()); // Convert all Map values to a ListList<String> result2 = new ArrayList(map.values()); // Java 8, Convert all Map keys to a ListList<String> result3 = map.keySet().stream() .collect(Collectors.toList());// Java 8, Convert all Map values to a ListList<String> result4 = map.values().stream() .collect(Collectors.toList());// Java 8, seem a bit long, but you can enjoy the Stream features like filter and etc.List<String> result5 = map.values().stream() .filter(x -> !"apple".equalsIgnoreCase(x)) .collect(Collectors.toList());