利用Groovy与生俱来的动态特性，创建DSL(Domain Specific Language)是一件十分容易的事情。
下面通过一个例子，向大家展示一下用Groovy创建DSL的优雅之处：
利用下面这种语法
person {
name {
firstname 'Daniel'
lastname 'Sun'
}
}
或
person {
name {
firstname = '山风'
lastname = '小子'
}
}
创建一个Person对象。
def createMetaClass(Class clazz, Closure closure) {
/*
为传入的Class对象创建一个ExpandoMetaClass实例，但不将该ExpandoMetaClass实例注册到MetaClassRegistry对象中
*/
def emc = new ExpandoMetaClass(clazz, false)
/*
该closure用来初始化ExpandoMetaClass对象，这种写法的思想与Template Method Pattern有异曲同工之妙
*/
closure(emc)
emc.initialize() // 完成初始化过程
return emc
}
def executeScript(dslScriptCode, rootName, closure) {
Script dslScript = new GroovyShell().parse(dslScriptCode) // 读取并解析DSL代码，返回一个Script对象
dslScript.metaClass = createMetaClass(dslScript.class) { emc ->
/*
动态新增一个名为"$rootName"的方法，注意"$rootName"的值决定于运行时，比如本例中的值为person
*/
emc."$rootName" = closure
}
return dslScript.run() // 执行DSL代码
}
class Name {
String firstname
String lastname
String toString() {
"$firstname.$lastname"
}
}
class Person {
Name name
Person(name) {
this.name = name
}
String toString() {
"My name is $name"
}
}
/*
PersonDelegate对象是下面作为参数传入‘person方法’的closure的delegate，形象点说，closure就是那对大括号{}以及大括号中的内容
如果您对closure的delegate不太熟悉，可以参考在下的另一篇文章《Groovy解惑——closure中的delegate》(http://www.blogjava.net/BlueSUN/archive/2007/12/22/169580.html)
person {
}
*/
class PersonDelegate {
def person
PersonDelegate(person) {
this.person = person
}
/*
关于methodMissing这一特殊方法，请参考在下的另一篇文章《Groovy高效编程——动态改变对象的能力》(http://www.blogjava.net/BlueSUN/archive/2007/07/15/130318.html)
*/
def methodMissing(String name, Object args) {
if ('name' == name && args[0] instanceof Closure) {
def nameClosure = args[0]
/*
给nameClosure的delegate赋值，nameClosure就是name旁边的那个closure即一对大括号{}以及大括号中的内容
*/
nameClosure.delegate = new NameDelegate(person)
nameClosure.resolveStrategy = Closure.DELEGATE_FIRST // 指明closure中变量和方法的解析策略，本例选择DELEGATE_FIRST
nameClosure()
}
}
/*
关于propertyMissing这一特殊方法，请参考在下的另一篇文章《Groovy高效编程——动态改变对象的能力》(http://www.blogjava.net/BlueSUN/archive/2007/07/15/130318.html)
*/
def propertyMissing(String name) {}
}
/*
类似于PersonDelegate，
NameDelegate对象是下面作为参数传入‘name方法’的closure的delegate
name {
}
*/
class NameDelegate {
def person
NameDelegate(person) {
this.person = person
}
/*
下面这些getter和setter是为了实现下面这种赋值而写的： firstname = '山风'和lastname = '小子'
person {
name {
firstname = '山风'
lastname = '小子'
}
}
*/
def getFirstname() {
return person.name.firstname
}
def setFirstname(String firstname) {
person.name.firstname = firstname
}
def getLastname() {
return person.name.lastname
}
def setLastname(String lastname) {
person.name.lastname = lastname
}
def methodMissing(String name, Object args) {
if ('firstname' == name) {
person.name.firstname = args[0]
} else if ('lastname' == name) {
person.name.lastname = args[0]
}
}
def propertyMissing(String name) {}
}
/*
在这篇文章中，演示了两种赋值方式，各位可以根据自己的喜好选择一种，我个人偏好第一种 :)
*/
// 本例DSL的第一种写法
def dslScriptCode = '''
person {
name {
firstname 'Daniel'
lastname 'Sun'
}
}
'''
def scriptClosure = { Closure personClosure ->
def person = new Person(new Name())
personClosure.delegate = new PersonDelegate(person)
personClosure.resolveStrategy = Closure.DELEGATE_FIRST
personClosure()
return person
}
def person = executeScript(dslScriptCode, 'person', scriptClosure)
println person
// 本例DSL的第二种写法
def dslScriptCode2 = '''
person {
name {
firstname = '山风'
lastname = '小子'
}
}
'''
def scriptClosure2 = { Closure personClosure ->
def person2 = new Person(new Name())
personClosure.delegate = new PersonDelegate(person2)
personClosure.resolveStrategy = Closure.DELEGATE_FIRST
personClosure()
return person2
}
def person2 = executeScript(dslScriptCode2, 'person', scriptClosure2)
println person2
运行结果：
My name is Daniel.Sun
My name is 山风.小子
附：
朝花夕拾——Groovy & Grails
posted on 2008-05-17 00:38
山风小子 阅读(5692)
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