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  • java按某个字段对数据分组

    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    
    
    import com.alibaba.fastjson.JSONArray;
    import com.alibaba.fastjson.JSONObject;
    
    public class JsonTest {
        
        public static void main(String[] args) {
            String msg = "[{"serviceCode":"MCY000003","serviceName":"床位费","discount_rate":"80%","minoutdays":"0","maxoutdays":"5"},{"serviceCode":"MCY000002","serviceName":"床位费","discount_rate":"80%","minoutdays":"0","maxoutdays":"5"},{"serviceCode":"MCY000001","serviceName":"床位费","discount_rate":"80%","minoutdays":"0","maxoutdays":"5"},{"serviceCode":"MCY000001","serviceName":"床位费","discount_rate":"80%","minoutdays":"0","maxoutdays":"5"},{"serviceCode":"MCY000003","serviceName":"床位费","discount_rate":"80%","minoutdays":"0","maxoutdays":"5"},{"serviceCode":"MCY000005","serviceName":"床位费","discount_rate":"80%","minoutdays":"0","maxoutdays":"5"}]";
            groupByCode(msg);
        }
    
        private static Map<String, List<?>> groupByCode(String msg) {
            JSONArray data = JSONArray.parseArray(msg);
            Map<String, List<?>> dataMap = new HashMap<String, List<?>>();
            //数据分组算法
            for (int i = 0; i < data.size(); i++) {
                JSONObject json = (JSONObject)data.get(i);
                List<Object> tempList = (List<Object>) dataMap.get(json.get("serviceCode"));
                if(tempList == null) { //说明是第一次,则创建list
                    tempList = new ArrayList<>();
                    tempList.add(json);
                    dataMap.put(json.get("serviceCode").toString(), tempList);//放入map中
                }else {
                    tempList.add(json);
                }
            }
            //遍历
            for (String serviceCode : dataMap.keySet()) {
                System.out.println(serviceCode+":"+dataMap.get(serviceCode));
            }
            return dataMap;
        }
    
    }
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  • 原文地址:https://www.cnblogs.com/iyyy/p/9335941.html
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