What is the static version of propertyMissing method in Groovy? - groovy

Question

ok - tried looking /reading and not sure i have an answer to this.
I have a Utility class which wraps a static ConcurrentLinkedQueue internally.
The utility class itself adds some static methods - i dont expect to call new to create an instance of the Utility.
I want to intercept the getProperty calls the utility class - and implement these internally in the class definition
I can achieve this by adding the following to the utility classes metaclass, before i use it
UnitOfMeasure.metaClass.static.propertyMissing = {name -> println "accessed prop called $name"}
println UnitOfMeasure.'Each'
however what i want to do is declare the interception in the class definition itself. i tried this in the class definition - but it never seems to get called
static def propertyMissing (receiver, String propName) {
println "prop $propName, saught"
}
i also tried
static def getProperty (String prop) { println "accessed $prop"}
but this isnt called either.
So other than adding to metaClass in my code/script before i use, how can declare the in the utility class that want to capture property accesses
the actual class i have looks like this at present
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 $propName, saught"
}
//expects either a String or your own closure, with String will do case insensitive find
static find (match) {
Closure matchClosure
if (match instanceof Closure)
matchClosure = match
if (match instanceof String) {
matchClosure = {it.toUpperCase().contains(match.toUpperCase())}
}
def inlist = UoMList.find (matchClosure)
}
static findWithIndex (match) {
Closure matchClosure
if (match instanceof Closure)
matchClosure = match
else if (match instanceof String) {
matchClosure = {it.toUpperCase().contains(match.toUpperCase())}
}
def position = UoMList.findIndexOf (matchClosure)
position != -1 ? [UoMList[position], position] : ["Not In List", -1]
}
}
i'd appreciate the secret of doing this for a static utility class rather than instance level property interception, and doing it in class declaration - not by adding to metaClass before i make the calls.
just so you can see the actual class, and script that calls - i've attached these below
my script thats calling the class looks like this
println UnitOfMeasure.list()
def (uom, position) = UnitOfMeasure.findWithIndex ("Day")
println "$uom at postition $position"
// works UnitOfMeasure.metaClass.static.propertyMissing = {name -> println "accessed prop called $name"}
println UnitOfMeasure[4]
println UnitOfMeasure.'Per'
which errors like this
[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

Static version of propertyMissing method is called $static_propertyMissing:
static def $static_propertyMissing(String name) {
// do something
}
This method gets invoked by MetaClassImpl at line 1002:
protected static final String STATIC_METHOD_MISSING = "$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 {
// .....
}
// ....
}
Example:
class Hello {
static def $static_propertyMissing(String name) {
println "Hello, $name!"
}
}
Hello.World
Output:
Hello, World!