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 : 2
alarm1 : 1
alarm3 : 3

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

来源：https://www.cnblogs.com/miracle-luna/p/12508281.html