Java中List转Map

1转成⼀对⼀的，⼀个字段对应⼀个对象

`Map maps = deviceRepairTypes.stream().collect(Collectors.toMap(DeviceSpareType::getId, Function.identity(), (key1, key2) -> key2));`  

后⾯的key1，key2 是指定⼀种覆盖规则，防⽌key冲突

2.⼀个字段对应⼀个对象属性

Map maps = deviceRepairTypes.stream().collect(Collectors.toMap(DeviceSpareType::getId, DeviceSpareType::getAge, (key1, key2) -> key2));

3.⼀个字段对应多个对象

Map> groupBy = deviceRepairTypes.stream().collect(Collectors.groupingBy(DeviceSpareType::getId));