groovy - Groovy 中 propertyMissing 方法的静态版本是什么？

Question

好的 - 尝试查看/阅读，但不确定我有答案。

我有一个实用程序类，它在内部包装了一个静态 ConcurrentLinkedQueue。

实用程序类本身添加了一些静态方法 - 我不希望调用 new 来创建实用程序的实例。

我想拦截 getProperty 调用实用程序类 - 并在类定义中内部实现这些

我可以通过在使用实用程序类元类之前添加以下内容来实现此目的

UnitOfMeasure.metaClass.static.propertyMissing = {name -> println "accessed prop called $name"}

println UnitOfMeasure.'Each'

但是我想要做的是在类定义本身中声明拦截。我在类定义中尝试过这个 - 但它似乎从未被调用

static def propertyMissing (receiver, String propName) {
    println "prop $propName, saught"
}

我也尝试过

static def getProperty (String prop) { println "accessed $prop"}

但这也没有被称为。

因此，除了在使用之前在代码/脚本中添加到元类之外，如何在实用程序类中声明想要捕获属性访问的

我目前的实际类(class)看起来像这样

class UnitOfMeasure {
    static ConcurrentLinkedQueue UoMList = new ConcurrentLinkedQueue(["Each", "Per Month", "Days", "Months", "Years", "Hours", "Minutes", "Seconds" ])

    String uom

    UnitOfMeasure () {
        if (!UoMList.contains(this) )
            UoMList << this
    }

    static list () {
        UoMList.toArray()
    }

    static getAt (index) {
        def value = null
        if (index in 0..(UoMList.size() -1))
            value = UoMList[index]
        else if (index instanceof String) {
            Closure matchClosure = {it.toUpperCase().contains(index.toUpperCase())}
            def position = UoMList.findIndexOf (matchClosure)
            if (position != -1)
                value = UoMList[position]
        }
        value
    }

     static def propertyMissing (receiver, String propName) {
        println "prop $propName, saught"
    }


    //expects either a String or your own closure, with String will do case insensitive find
    static find (match) {
        Closure matchClosure
        if (match instanceof Closure)
            matchClosure = match
        if (match instanceof String) {
            matchClosure = {it.toUpperCase().contains(match.toUpperCase())}
        }
        def inlist = UoMList.find (matchClosure)
    }

    static findWithIndex (match) {
        Closure matchClosure
        if (match instanceof Closure)
            matchClosure = match
        else if (match instanceof String) {
            matchClosure = {it.toUpperCase().contains(match.toUpperCase())}
        }
        def position = UoMList.findIndexOf (matchClosure)
        position != -1  ? [UoMList[position], position] : ["Not In List", -1]
    }
}

我很欣赏为静态实用程序类而不是实例级属性拦截执行此操作的 secret ，并在类声明中执行此操作 - 而不是在调用之前添加到元类。

这样您就可以看到实际的类和调用的脚本 - 我已将这些附加在下面

我调用该类的脚本如下所示

println UnitOfMeasure.list()

def (uom, position) = UnitOfMeasure.findWithIndex ("Day")
println "$uom at postition $position"

// works UnitOfMeasure.metaClass.static.propertyMissing = {name -> println "accessed prop called $name"}
println UnitOfMeasure[4]
println UnitOfMeasure.'Per' 

有哪些错误是这样的

[Each, Per Month, Days, Months, Years, Hours, Minutes, Seconds]
Days at postition 2
Years
Caught: groovy.lang.MissingPropertyException: No such property: Per for class: com.softwood.portfolio.UnitOfMeasure
Possible solutions: uom
groovy.lang.MissingPropertyException: No such property: Per for class: com.softwood.portfolio.UnitOfMeasure
Possible solutions: uom
    at com.softwood.scripts.UoMTest.run(UoMTest.groovy:12)

Answer 1

调用propertyMissing方法的静态版本$static_propertyMissing:

static def $static_propertyMissing(String name) {
    // do something
}

此方法由 MetaClassImpl at line 1002 调用:

protected static final String STATIC_METHOD_MISSING = "$static_methodMissing";
protected static final String STATIC_PROPERTY_MISSING = "$static_propertyMissing";

// ...

protected Object invokeStaticMissingProperty(Object instance, String propertyName, Object optionalValue, boolean isGetter) {
    MetaClass mc = instance instanceof Class ? registry.getMetaClass((Class) instance) : this;
    if (isGetter) {
        MetaMethod propertyMissing = mc.getMetaMethod(STATIC_PROPERTY_MISSING, GETTER_MISSING_ARGS);
        if (propertyMissing != null) {
            return propertyMissing.invoke(instance, new Object[]{propertyName});
        }
    } else {
        // .....
    }
    // ....
}

示例:

class Hello {
    static def $static_propertyMissing(String name) {
        println "Hello, $name!"
    }
}

Hello.World

输出:

Hello, World!