一、分析

实际应用场景，list中的元素的某个属性是重复的，因此可以按照此元素对list进行分组，最终放到Map集合，此元素为key值，分组后的list为value值

二、实现代码

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public static Map<String,List<User>> splitGroup(List<User> list){
    //初始化一个map
    Map<String,List<User>> map = new HashMap<>();
    for(User user : list){
        String key = user.getId();
        if(map.containsKey(key)){
            //如果map中存在以此id作为的key,将数据元素存放当前key的list集合中
            map.get(key).add(user);
        }else{
            //map中不存在以此id作为的key，新建key用来存放数据
            List<User> userList = new ArrayList<>();
            userList.add(user);
            map.put(key,userList);
        }
    }
    return map;

三、测试代码及测试结果

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public static void main(String[] args) {
    List<User> list = new ArrayList<>();
    //当前测试以id来分组，User实体类中成员变量有id及name，全参构造方法，toString方法
    list.add(new User("1", "1"));
    list.add(new User("1", "2"));
    list.add(new User("2", "2"));
    list.add(new User("2", "3"));
    list.add(new User("2", "4"));
    list.add(new User("3", "3"));
    
    //测试普通方法
    //Map<String, List<User>> stringListMap = splitGroup(list);
    
    //测试stream流
    Map<String,List<User>> stringListMap = list.stream().collect(Collectors.groupingBy(User::getId));        

    //将map集合转为set集合遍历
    Set<Map.Entry<String, List<User>>> entries = stringListMap.entrySet();
    for(Map.Entry m : entries){
        System.out.println(m);
    }
}

测试的结果如下

imagebf042a82007d3da8.png

四、实战

原数据结构

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public class ThresholdVo {

    @ApiModelProperty(value = "站点ID")
    private Integer siteId;

    @ApiModelProperty(value = "站点名称")
    private String siteName;

    @ApiModelProperty(value = "站点状态")
    private Integer state;

    @ApiModelProperty(value = "所属项目ID")
    private Integer projId;

    @ApiModelProperty(value = "所属项目名称")
    private String projName;

    @ApiModelProperty(value = "设备ID")
    private String deviceId;

    @ApiModelProperty(value = "设备名称")
    private String deviceName;

    @ApiModelProperty(value = "设备编号")
    private String dNo;

    @ApiModelProperty(value = "检测能力code")
    private String mCode;

    @ApiModelProperty(value = "低阈值")
    private BigDecimal lowThreshold;

    @ApiModelProperty(value = "实际值")
    private Float av;

    @ApiModelProperty(value = "高阈值")
    private BigDecimal highThreshold;

    @ApiModelProperty(value = "基础高层")
    private BigDecimal basicHigh;

    @ApiModelProperty(value = "时间")
    @JsonFormat(timezone = "GMT+8", pattern = "yyyy-MM-dd HH:mm:ss")
    private Date updateTime;

    @ApiModelProperty(value = "是否异常")
    private Integer isError;
}

目标数据结构

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public class RealTimeDataVo {

    @ApiModelProperty(value = "站点ID")
    private Integer siteId;

    @ApiModelProperty(value = "站点名称")
    private String siteName;

    @ApiModelProperty(value = "站点状态")
    private Integer state;

    @ApiModelProperty(value = "所属项目ID")
    private Integer projId;

    @ApiModelProperty(value = "所属项目名称")
    private String projName;

    @ApiModelProperty(value = "设备ID")
    private String deviceId;

    @ApiModelProperty(value = "设备名称")
    private String deviceName;

    @ApiModelProperty(value = "设备编号DeviceNo")
    private String waterId;

    @ApiModelProperty(value = "时间")
    @JsonFormat(timezone = "GMT+8", pattern = "yyyy-MM-dd HH:mm:ss")
    private Date date;

    @ApiModelProperty(value = "监测能力")
    private List<MoniVo> moniVoList;
}
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public class MoniVo {

    @ApiModelProperty(value = "检测能力code")
    private String moniCode;

    @ApiModelProperty(value = "实际值")
    private Float av;

    @ApiModelProperty(value = "低阈值")
    private BigDecimal lowThreshold;

    @ApiModelProperty(value = "高阈值")
    private BigDecimal highThreshold;

    @ApiModelProperty(value = "基础高层")
    private BigDecimal basicHigh;

    @ApiModelProperty(value = "是否异常")
    private Integer isError;
}

结构变化

image92b803f7aae32e4e.png

代码实现

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List<RealTimeDataVo> realTimeDataVoList = new ArrayList<>();
//用map来进行去重
HashMap<RealTimeDataVo, List<MoniVo>> map = new HashMap<>();
for (ThresholdVo thresholdVo : thresholdVos){
    RealTimeDataVo realTimeDataVo = new RealTimeDataVo(thresholdVo);
    MoniVo moniVo = new MoniVo(thresholdVo);
    if(map.containsKey(realTimeDataVo)){
        //如果map中存在以此realTimeDataVo作为的key,将moniVo存放当前key的list集合中
        map.get(realTimeDataVo).add(moniVo);
    }else{
        //map中不存在以此realTimeDataVo作为的key，新建key用来存放List<MoniVo>
        List<MoniVo> moniVoList = new ArrayList<>();
        moniVoList.add(moniVo);
        map.put(realTimeDataVo,moniVoList);
    }
}
for (RealTimeDataVo realTimeDataVo : map.keySet()) {
    realTimeDataVo.setMoniVoList(map.get(realTimeDataVo));
    realTimeDataVoList.add(realTimeDataVo);
}

参考博客

https://blog.csdn.net/shang_0122/article/details/108753580