java 8對List的處理

1.for循環
list.forEach(item -> {
            list中的每個item元素做指定的操作
            //item.setState(0);
            //item.setRemark("");
        });
2.去重
List<String> list = Arrays.asList("AA", "BB", "CC", "BB", "CC", "AA", "AA");
long l = list.stream().distinct().count();// 3
List<String> newList = list.stream().distinct().collect(Collectors.toList());
3.過濾
caseBillList是一個不為空的List<CaseBill>
返回List<CaseBill>，item ->  后面為過濾的條件（滿足指定條件的會被篩選出來返回）
caseBillList.stream()
            .filter(item -> StringUtils.isEmpty(item.getHospitalCode()) || "0".equals(item.getHospitalCode()))
            .collect(Collectors.toList());
4.搜集實體類的指定屬性值，返回List<指定屬性的類型>
map(CaseBill::getReceiptNo)-map(實體類::指定屬性)
List<String> receiptNoList= caseBillList.stream()
                        .map(CaseBill::getReceiptNo)
                        .distinct()//去重
                        .collect(Collectors.toList());
String receiptNos = String.join(",",receiptNoList);
5.分組
List<CheckGoodsMx> checkGoodsList 不為空的數據List
返回Map<依據實體類中某個屬性分組的類型, List<實體類>>
// groupingBy(CheckGoodsMx::getDrcode)-groupingBy(實體類::getDrcode)
Map<String, List<CheckGoodsMx>> drcodeMap =checkGoodsList.stream().collect(
                Collectors.groupingBy(CheckGoodsMx::getDrcode));

具體可以參考以下這篇博文，有具體的測試代碼

https://blog.csdn.net/qq_33142257/article/details/62891612