code: public static String getProperty(Object bean, String fieldName, WriteConvertible writeConvertible)
              throws Excel4JException {
  
          if (bean == null || fieldName == null)
              throw new IllegalArgumentException("Operating bean or filed class must not be null");
          Method method;
          Object object;
          try {
              method = getterOrSetter(bean.getClass(), fieldName, FieldAccessType.GETTER);
              object = method.invoke(bean);
          } catch (IntrospectionException | IllegalAccessException | InvocationTargetException e) {
              throw new Excel4JException(e);
          }
          if (null != writeConvertible && writeConvertible.getClass() != DefaultConvertible.class) {
              // 写入转换器
              object = writeConvertible.execWrite(object);
          }
          return object == null ? "" : object.toString();
      }
docs: 根据属性名与属性类型获取字段内容
  
  @param bean             对象
  @param fieldName        字段名
  @param writeConvertible 写入转换器
  @return 对象指定字段内容
  @throws Excel4JException 异常