Gradle作为一个构建工具自然不会自己去创造一门语言来支撑自己，那么它用的是哪门子语言呢？什么语言能写成这样：

task hello {doLast {println 'Hello world!'}
}

如此风骚的语法自然要归Groovy莫属了。

什么是Groovy

官方介绍如下：

Apache Groovy is a powerful, optionally typed and dynamic language, with static-typing and static compilation capabilities, for the Java platform aimed at improving developer productivity thanks to a concise, familiar and easy to learn syntax. It integrates smoothly with any Java program, and immediately delivers to your application powerful features, including scripting capabilities, Domain-Specific Language authoring, runtime and compile-time meta-programming and functional programming.

大概意思是Groovy是一门运行在java平台上的强大的、可选类型的、动态语言。使用Groovy可以使你的应用具备脚本，DSL定义，运行时和编译时元编程，函数式编程等功能。

接下来将分几个小节简单介绍Groovy的语法规范。

Groovy语法

注释

Groovy使用的注释有一下几种：

1.单行注释

// a standalone single line commentprintln "hello" // a comment till the end of the line

2.多行注释

/* a standalone multiline commentspanning two lines */println "hello" /* a multiline comment startingat the end of a statement */println 1 /* one */ + 2 /* two */

3.文档注释

/*** A Class description*/class Person {/** the name of the person */String name    /*** Creates a greeting method for a certain person.** @param otherPerson the person to greet* @return a greeting message*/String greet(String otherPerson) {       "Hello ${otherPerson}"}
}

4.组织行

#!/usr/bin/env groovyprintln "Hello from the shebang line"

这类脚本注释主要用于表明脚本的路径。

字符串

单引号字符串

单引号字符串对应java中的String，不支持插入。

'a single quoted string'

字符串连接

assert 'ab' == 'a' + 'b'

三引号字符串

'''a triple single quoted string'''

三引号字符串同样对应java中的String，不支持动态插入。三引号字符串支持多行：

def aMultilineString = '''line one
line two
line three'''

转义

Groovy中使用\来进行转义

'an escaped single quote: \' needs a backslash'

双引号字符串

"a double quoted string"

如果双引号字符串中没有插入表达式的话对应的是java中的String对象，如果有则对应Groovy中的GString对象。

Groovy中使用${}来表示插入表达式，$来表示引用表达：

def name = 'Guillaume' // a plain stringdef greeting = "Hello ${name}"assert greeting.toString() == 'Hello Guillaume'

def person = [name: 'Guillaume', age: 36]assert "$person.name is $person.age years old" == 'Guillaume is 36 years old'

shouldFail(MissingPropertyException) {println "$number.toString()"}

插入闭包表达式

def sParameterLessClosure = "1 + 2 == ${-> 3}" assert sParameterLessClosure == '1 + 2 == 3'def sOneParamClosure = "1 + 2 == ${ w -> w << 3}" assert sOneParamClosure == '1 + 2 == 3'

def number = 1 def eagerGString = "value == ${number}"def lazyGString = "value == ${ -> number }"assert eagerGString == "value == 1" assert lazyGString ==  "value == 1" number = 2 assert eagerGString == "value == 1" assert lazyGString ==  "value == 2"

关于闭包，暂时先看看就行，等后面具体学习完闭包以后再回来看这几个表达式就简单了。

三双引号字符串

def name = 'Groovy'def template = """Dear Mr ${name},You're the winner of the lottery!Yours sincerly,Dave
"""assert template.toString().contains('Groovy')

斜杠字符串

Groovy也可以使用/来定义字符串，主要用于正则表达式

def fooPattern = /.*foo.*/assert fooPattern == '.*foo.*'

def escapeSlash = /The character \/ is a forward slash/assert escapeSlash == 'The character / is a forward slash'

def multilineSlashy = /onetwothree/assert multilineSlashy.contains('\n')

def color = 'blue'def interpolatedSlashy = /a ${color} car/assert interpolatedSlashy == 'a blue car'

/和//和/字符串

def name = "Guillaume"def date = "April, 1st"def dollarSlashy = $/Hello $name,today we're ${date}.$ dollar sign$$ escaped dollar sign\ backslash/ forward slash$/ escaped forward slash$/$ escaped dollar slashy string delimiter
/$assert [    'Guillaume',    'April, 1st',    '$ dollar sign',    '$ escaped dollar sign',    '\\ backslash',    '/ forward slash',        '$/ escaped forward slash',        '/$ escaped dollar slashy string delimiter'].each { dollarSlashy.contains(it) }

字符

单引号字符串如果只有一个字符会被转化成char类型。

列表

Groovy中列表使用[]表示，其中可以包含任意类型的元素：

def heterogeneous = [1, "a", true]

使用下标进行取值和赋值

def letters = ['a', 'b', 'c', 'd']assert letters[0] == 'a'     assert letters[1] == 'b'assert letters[-1] == 'd'    assert letters[-2] == 'c'letters[2] = 'C'             assert letters[2] == 'C'letters << 'e'               assert letters[ 4] == 'e'assert letters[-1] == 'e'assert letters[1, 3] == ['b', 'd']
assert letters[2..4] == ['C', 'd', 'e']

数组

Groovy中复用List来充当数组，但如果要明确定义真正的数组需要使用类似java的定义方法

String[] arrStr = ['Ananas', 'Banana', 'Kiwi']  assert arrStr instanceof String[]
assert !(arrStr instanceof List)def numArr = [1, 2, 3] as int[]      assert numArr instanceof int[]
assert numArr.size() == 3

键值数组

Groovy中键值数组使用如下

def colors = [red: '#FF0000', green: '#00FF00', blue: '#0000FF']   assert colors['red'] == '#FF0000'    assert colors.green  == '#00FF00'    colors['pink'] = '#FF00FF'           colors.yellow  = '#FFFF00'           assert colors.pink == '#FF00FF'assert colors['yellow'] == '#FFFF00'assert colors instanceof java.util.LinkedHashMap