java8Stream操作集锦

将List中某个字段取出形成新的List,场景,角色授权

List<Integer> userRoleList = sysUserRoles.stream()
                .map(SysUserRole::getRoleId).collect(Collectors.toList());

将List中某几个字段取出形成新的List,场景,list中的数据是从多个表中查出结合而成,需要筛选出两个表中字段相同值不同的数据

for (OrderDeviceVO o :
                list) {
            List<OrderDeviceDependVO> child = orderDeviceMap.get(o.getId())
            .stream().map(
                    orderDeviceVO -> new OrderDeviceDependVO(orderDeviceVO.getDimName()
                            ,orderDeviceVO.getSourceId()
                            ,orderDeviceVO.getDeviceCode()
                            ,orderDeviceVO.getChannelCode())
            )
            .collect(Collectors.toList());  
}

根据List中某个字段分组

//获得excel数据
List<ExcelEntity> excelEntities = readExcel();
        
//根据设备编码进行分组
Map<String, List<ExcelEntity>> collect = excelEntities.stream().collect(Collectors.groupingBy(ExcelEntity::getDeviceCode));

根据List中某个字段分组形成Map,场景,List中某一列的值某一个字段值是重复的,需要统计此重复值的数量有多少

Map<String,List<OrderDeviceVO>> orderDeviceMap = list.stream()
                .collect(Collectors.groupingBy(OrderDeviceVO::getId));

过滤list中某些不想要的值,形成新的list,过滤条件就是写想要留下的表达式,要不为空的就判断不为空

List<AltgorithmExcelEntity> notnull = center.stream().filter(r-> StringUtils.isNotBlank(r.getTenantName())).collect(Collectors.toList());

对list中某几个字段同时分组,形成新的map

Function<AltgorithmExcelEntity,List<String>> compositeKey = altgorithmExcelEntity -> Arrays.asList(altgorithmExcelEntity.getAlgorithmCode(),altgorithmExcelEntity.getChannelCode(),altgorithmExcelEntity.getDeviceCode());

Map<List<String>,List<AltgorithmExcelEntity>> groupMap =
                    sublist.stream().collect(Collectors.groupingBy(compositeKey,Collectors.toList()));

将list中某个字段用逗号连接形成字符串并去重

String collect = list.stream().map(ZongExcelEntity::getProductName)
                    .collect(Collectors.joining(","));
            
String norepeat = Arrays.stream(collect.split(","))
          .distinct()
          .collect(Collectors.joining(","));