code: public static String format(ConfigurablePropertyAccessor bw, Object obj,
  			String prop) {
  		String key = obj.getClass().getName() + "_" + prop;
  
  		if (!cache.containsKey(key))
  			canFormat(bw, obj, prop);
  
  		Object val = bw.getPropertyValue(prop);
  
  		if (val == null)
  			return null;
  		if (val.getClass().isArray())
  			return null;
  
  		if (!cache.get(key))
  			return val.toString();
  
  		TypeDescriptor td = bw.getPropertyTypeDescriptor(prop);
  		val = get().convert(val, td, TypeDescriptor.valueOf(String.class));
  
  		return val == null ? null : val.toString();
  	}
docs: 如果有格式可应用则应用
  
  @param bw
  @param obj
  @param prop
  @return