Groovy将字符串类型转换为自定义类型的方法

将一个字符串转换为自定义类型：

例如Quantity是自定义的一个class，现在想这么调用
Quantity quantity = "100个" as Quantity
或
def quantity = "100个".asType(Quantity)

需要重载String的asType方法（String.metaClass.asType）。具体实现如下（注意static方法块）：

package com.cninsure.datatype

/**
* 数量单位
*/
class Quantity extends InsDataType {
??? Number amount
??? String unit

??? Quantity() {
??? }

??? static {
??????? String.metaClass.asType {? Class c ->
??????????? if (Quantity == c) {
??????????????? Quantity.from(delegate)
??????????? } else {
??????????????? delegate.asType(c)
??????????? }
??????? }
??? }

??? @Override
??? void build(val) {
??????? if (val instanceof Quantity) {
??????????? this.amount = val.amount
??????????? this.unit = val.unit
??????????? return
??????? }
??????? def regular = /^(/d+(/./d+)?)/s?(/S+)?/
??????? if (!(val ==~ regular)) {
??????????? throw new IllegalArgumentException("模式不匹配")
??????? }
??????? def result = (val =~ regular)?????????? //拆分
??????? Number value = result[0][1]
??????? String qu = result[0][3]

??????? this.amount = value
??????? this.unit = qu
??????? return
??? }

??? static Quantity from(val) {
??????? if (val instanceof Quantity) return val
??????? Quantity quantity = new Quantity()
??????? quantity.build(val)
??????? return quantity
??? }

??? @Override
??? boolean identity(Object val) {
??????? if (!(val instanceof Quantity)) {
??????????? val = from(val)
??????? }
??????? if (amount == val.amount && unit == val.unit) return true
??????? return false
??? }

??? @Override
??? String display() {
??????? return amount.toString() + unit.toString()
??? }

??? public String toString() { ??????? return "Quantity{" + ??????????????? "amount=" + amount + ??????????????? ",unit='" + unit + '/'' + ??????????????? '}'; ??? } }