@Override public Data process(Data data) { Data item = DataFactory.create(); item.put("time", LocalDateTime.now().toString()); String[] evKeys = {"@stream"}; for (String key : evKeys) { if (data.containsKey(key)) { item.put(key, data.get(key)); } } // add objects by specified keys to data item for (String key : keys) { item.put(key, data.get(key)); } try { if (writeBlock && !firstLine) { bw.write(","); } bw.write(gson.toJson(item)); bw.newLine(); bw.flush(); firstLine = false; } catch (IOException ioex) { ioex.printStackTrace(); } return data; }