看懂Gradle脚本（7）- ext {}函数是如何实现的

本质上是重写了get() 和 set()方法，结合闭包代理，实现拦截任意属性定义(set)与获取(get)，具体实现代码如下：

```
class DataObject {
    HashMap<String, Object> props = new HashMap<String, Object>()

Object get(String name) {
        return props.get(name)
    }

void set(String name, @Nullable Object value) {
        props.put(name, value)
    }
}

def myExtInstance = new DataObject()

def myExt = { Closure closure ->
    def data = myExtInstance
    closure.delegate = data;
    // need this resolve strategy for properties or they just get
    // created in the closure instead of being delegated to the object
    // to be configured. For methods you don't need this as the default
    // strategy is usually fine.
    closure.resolveStrategy = Closure.DELEGATE_FIRST
    closure() // execute the configuration closure
    println data.springVersion
}

myExt {
    springVersion = "3.1.0.RELEASE"
    emailNotification = "build@master.org"
}

println "myExtInstance.springVersion" + myExtInstance.springVersion
```
详情阅读官网文档[ExtraPropertiesExtension](https://docs.gradle.org/current/dsl/org.gradle.api.plugins.ExtraPropertiesExtension.html)