Java Lambda List转Map代码实例

在有些开发场景，需要对 List 对象列表进行过滤处理，并将有用的数据存放到Map中。

例如：告警对象，包含告警uuid（alarmUuid） 和 设备uuid（objUuid），需要对 objUuid = -1的告警进行过滤，并将过滤后告警数据的alarmUuid和 objUuid以键值对的形式保存到Map中。

1、告警对象定义如下：

/** * Created by Miracle Luna on 2020/3/16 */public class AlarmInfoResponse { private String alarmUuid; private String objUuid; public AlarmInfoResponse(String alarmUuid, String objUuid) { this.alarmUuid = alarmUuid; this.objUuid = objUuid; } public String getAlarmUuid() { return alarmUuid; } public void setAlarmUuid(String alarmUuid) { this.alarmUuid = alarmUuid; } public String getObjUuid() { return objUuid; } public void setObjUuid(String objUuid) { this.objUuid = objUuid; } @Override public String toString() { return 'AlarmInfoResponse{' +'alarmUuid=’' + alarmUuid + ’’’ +', objUuid=’' + objUuid + ’’’ +’}’; }}

2、过滤代码如下：

/** * Created by Miracle Luna on 2020/3/16 */public class LambdaFilterListToMap { public static void main(String[] args) { List<AlarmInfoResponse> alarmInfoResponseList = new ArrayList<>(); AlarmInfoResponse response0 = new AlarmInfoResponse('alarm0', '-1'); AlarmInfoResponse response1 = new AlarmInfoResponse('alarm1', '1'); AlarmInfoResponse response2 = new AlarmInfoResponse('alarm2', '2'); AlarmInfoResponse response3 = new AlarmInfoResponse('alarm3', '3'); alarmInfoResponseList.add(response0); alarmInfoResponseList.add(response1); alarmInfoResponseList.add(response2); alarmInfoResponseList.add(response3); // 方式1：先使用foreach遍历（遍历过程中条件判断） Map<String, String> alarmObjUuidMap1 = new HashMap<>(); alarmInfoResponseList.forEach(alarmInfoResponse -> { if(!'-1'.equals(alarmInfoResponse.getObjUuid())) {alarmObjUuidMap1.put(alarmInfoResponse.getAlarmUuid(), alarmInfoResponse.getObjUuid()); } }); System.out.println('============= 方式1 ===================='); alarmObjUuidMap1.forEach((alarmUuid, objUuid) -> System.out.println(alarmUuid + ' : ' + objUuid)); // 方式2：使用流过滤，再使用foreach遍历 Map<String, String> alarmObjUuidMap2 = new HashMap<>(); alarmInfoResponseList.stream(). filter(alarmInfoResponse -> !'-1'.equals(alarmInfoResponse.getObjUuid())). forEach(alarmInfoResponse -> alarmObjUuidMap2.put(alarmInfoResponse.getAlarmUuid(), alarmInfoResponse.getObjUuid())); System.out.println('n============= 方式2 ===================='); alarmObjUuidMap2.forEach((alarmUuid, objUuid) -> System.out.println(alarmUuid + ' : ' + objUuid)); }}

3、运行结果如下：

============= 方式1 ====================alarm2 : 2alarm1 : 1alarm3 : 3

============= 方式2 ====================alarm2 : 2alarm1 : 1alarm3 : 3

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