由于没有原生支持，肯定要写UDF

直接上代码

import com.alibaba.fastjson.JSON;
import org.apache.spark.sql.api.java.UDF2;
import scala.collection.Seq;

import java.util.HashMap;
import java.util.Map;

public class ToJsonUdf implements UDF2<Seq<String>, Seq<String>, String> {


    @Override
    public String call(Seq<String> keys, Seq<String> values) {

        Map<String, String> map = new HashMap<>();

        for (int i = 0; i < keys.size(); i++) {
            String key = keys.apply(i);
            String val = "";
            if (values.size() > i) {
                val = values.apply(i);
            }
            map.put(key, val);
        }

        return JSON.toJSONString(map);
    }
}

针对写好的UDF的使用

Select

toJson(map_keys(myMapField),map_values(myMapField) ) as jsonStr

From myTable