code: public String formatPOJO2JSON(Object pojo) {
  		StringWriter stringWriter = new StringWriter();
  		String json = "";
  		try {
  			JsonGenerator gen = new JsonFactory()
  					.createJsonGenerator(stringWriter);
  			MAPPER.writeValue(gen, pojo);
  			gen.close();
  			json = stringWriter.toString();
  		} catch (Exception e) {
  			LOGGER.error(pojo.getClass().getName() + "转json出错", e);
  		}
  		return json;
  	}
docs: POJO对象转换为JSON
  @param pojo
  @return