code: @SuppressWarnings("unchecked")
      @Override
      public String convertToDocument(StreamMessage message)
      {
          if (this.mapper == null)
          {
              this.mapper = new ObjectMapper();
          }
  
          String jsonStr = message.getField(this.field).toString();
          Map<String, Object> jsonMap = null;
  
          try
          {
              jsonMap = this.mapper.readValue(jsonStr, HashMap.class);
          }
          catch (IOException ex)
          {
              throw new RuntimeException(ex);
          }
  
          // Kibana用のタイムスタンプフィールドを追加
          jsonMap.put("@timestamp", jsonMap.get("time"));
          // 数値データをNumeric型の変数として投入するよう変換
          convertToNumeric(jsonMap);
          String result = null;
  
          try
          {
              result = this.mapper.writeValueAsString(jsonMap);
          }
          catch (JsonProcessingException ex)
          {
              throw new RuntimeException(ex);
          }
  
          return result;
      }
docs: {@inheritDoc}