I have set up a simple dummy class as follows, and used a static initialiser to update the metaClass:
class DynamicExtendableClass {
static String declaredStaticString = "declared static string"
static String getDeclaredMethodStaticString () {
"static method returning string"
}
static {
println "static initialiser - adding dynamic properties and methods to metaClass"
DynamicExtendableClass.metaClass.addedProperty = "added property to class metaClass"
DynamicExtendableClass.metaClass.getAddedMethod = { -> "added closure as method" }
DynamicExtendableClass.metaClass.static.getStaticAddedMethod = { -> "added closure as static method" }
}
}
I have a simple test case like this:
#Test
void testExtendedMetaClassStuff () {
DynamicExtendableClass testInstance = new DynamicExtendableClass()
assertEquals ("added property to class metaClass", testInstance.addedProperty)
assertEquals ("added closure as static method", testInstance.getStaticAddedMethod()) //calls getStaticAddedMethod - groovy trick
assertEquals ("added closure as method", testInstance.addedMethod) //works. calls getAddedMethod - groovy trick for getXxx as property
assertEquals ("added closure as static method", DynamicExtendableClass.staticAddedMethod ) //works class static class Closure
}
Which works only once you create a first instance of the class which forces a switch to ExpandoMetaClass for you.
If you don't do this first the default HandleMetaClassImpl doesn't work for this.
However to get this to work for static you have to create closure like getXxxx = {-> ...}, which if you call 'DynamicExtendableClass.staticAddedMethod' will sneakily invoke the closure for you.
However, there's not really a means to add a property capability here for '.static' as there is on the standard metaClass itself. All you can do is set a closure onto .static. Why is this?
The other problem is having to create an instance of the class first to force the switch to ExpandoMetaClass, is there not a simple way to force the metaClass change when declaring the class in the first class, before creating any instances ?
I want to add some static properties (later some methods maybe ) dynamically to a class, but all you can add is static closures, which is a little limiting on the scenario I had in mind.
PostScript
I managed to force a change of metaClass on class without having to create an instance, but it's a bit hard work:
#Test
void testMetaClassStatic () {
println DynamicExtendableClass.metaClass
MetaClassRegistry registry = GroovySystem.getMetaClassRegistry()
MetaClass origMC = registry.getMetaClass(DynamicExtendableClass)
assert origMC.getClass() == HandleMetaClass //default implementation
ExpandoMetaClass emc = new ExpandoMetaClass (DynamicExtendableClass, true, true)
emc.static.getStaticAddedMethod = {-> "static hello from my emc"}
emc.initialize()
registry.removeMetaClass(DynamicExtendableClass)
registry.setMetaClass(DynamicExtendableClass, emc)
assert DynamicExtendableClass.metaClass.getClass() == ExpandoMetaClass
assert DynamicExtendableClass.staticAddedMethod == "static hello from my emc"
registry.removeMetaClass(DynamicExtendableClass)
registry.setMetaClass(DynamicExtendableClass, origMC)
}
But doing this breaks my previously working tests (not sure why) with:
Could not initialize class extensible.DynamicExtendableClass
java.lang.NoClassDefFoundError: Could not initialize class extensible.DynamicExtendableClass
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
at org.codehaus.groovy.reflection.CachedConstructor.invoke(CachedConstructor.java:73)
at org.codehaus.groovy.runtime.callsite.ConstructorSite$ConstructorSiteNoUnwrapNoCoerce.callConstructor(ConstructorSite.java:108)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallConstructor(CallSiteArray.java:59)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callConstructor(AbstractCallSite.java:263)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callConstructor(AbstractCallSite.java:268)
at extensible.DynamicExtendableClassTest.testExtendedMetaClassStuff(DynamicExtendableClassTest.groovy:22)
at ...
Another postscript
I did a little exploration with a debugger. 1st the metaClass.static returns a class of type ExpandoMetaClass.ExpandoMetaProperty which of itself isn't terribly useful. You can do a direct .#this$0 field access however which just points the same metaClass instance as the target class you start with.
Therefore ignoring this you can do a direct field grab on <yourClass>.metaClass.#expandoProperties (I tried to get this via reflection using:
PropertyValue expandoProperties = clazz.metaClass.getMetaPropertyValues().find{it.name == 'expandoProperties'}
List<MetaBeanProperty> MBprops2= properties.getValue()
Map m2 = MBprops.findAll{Modifier.isPublic(it.modifiers)}.collectEntries{[(it.name), it.getProperty(clazz)] }
but it doesn't get the same content as the direct field access does.
The direct field access returns a Map where the key is the string value of any added closures or properties added dynamically to the metaClass, and the value is a MetaBeanProperty reference.
On that MetaBeanProperty you can invoke the getProperty (object) using with the class metaClass or per instance metaClass - and it returns the value of that property (whether it's just a closure or a real property) for you. You can also test whether its static or not:
Map m4 = thisMc.#expandoProperties
MetaBeanProperty asm = m4['addedStaticMethod']
def val2 = asm.getProperty(clazz)
boolean isstatic = Modifier.isStatic(asm.modifiers)
Kind of brutal but it sort of works if you want to dynamically query the dynamic editions to the metaclass.
The problem of forcing the switch from default metaClass to the ExpandoMetaClass remains a problem. The best way seems to create a throw away class instance as this does the one time switch for you.
I tried to force this myself using the metaClass registry which you can do, but then the future create new instance for your class seems to stop working ie. doing somethings like this and putting the original back afterwords seems to break any future new <MyClass>() calls.
MetaClassRegistry registry = GroovySystem.getMetaClassRegistry()
MetaClass origMC = registry.getMetaClass(DynamicExtendableClass)
assert origMC.getClass() == MetaClassImpl //default implementation
def constructors = MetaClassImpl.getConstructors()
ExpandoMetaClass emc = new ExpandoMetaClass (DynamicExtendableClass, true, true)
emc.static.getStaticAddedMethod = {-> "static hello from my emc"}
emc.constructor = { new DynamicExtendableClass() }
emc.initialize()
registry.removeMetaClass(DynamicExtendableClass)
registry.setMetaClass(DynamicExtendableClass, emc)
assert DynamicExtendableClass.metaClass.getClass() == ExpandoMetaClass
assert DynamicExtendableClass.staticAddedMethod == "static hello from my emc"
registry.removeMetaClass(DynamicExtendableClass)
registry.setMetaClass(DynamicExtendableClass, origMC)
Related
It seems that setting a default value for a class property, is not honored by #Builder.
#Test
void test() {
assert Foo.builder().build().getProp() != null // fail
}
#Builder
class Foo {
Map prop = [:]
}
I'll probably fix this by overriding the build method but how?
Not really sure about the implementation of builder() method of #Builder.
I believe you need to initialize the properties / members of the class, then do .build() to create the instance of the class.
Here is the example:
import groovy.transform.builder.Builder
#Builder
class Foo {
Map prop
}
def map = [a:1, b:2]
def f = Foo.builder().prop(map).build()
assert map == f.prop // or you can use f.getProp()
You can quickly try it online Demo
If you notice, the demo example shows how you can initialize multiple properties while building the object.
I have two immutable groovy classes that have a few shared values that I'm trying to abstract to a parent class. However when I create the following, the second test case always fails. Although everything compiles correctly and no error is thrown at runtime, when I assign the parent property int he constructor, it is never set, resulting in a null value. I havent found any documentation that forbids this, but I'm wondering is this even possible? I've tried a number of configuration of Annotations and class-types (e.g. removing abstract from the parent) but nothing seems to work short of just removing the #Immutable tag altogether.
abstract class TestParent {
String parentProperty1
}
#ToString(includeNames = true)
#Immutable
class TestChild extends TestParent {
String childProperty1
String childProperty2
}
class TestCase {
#Test
void TestOne() {
TestChild testChild = new TestChild(
childProperty1: "childOne",
childProperty2: "childTwo",
parentProperty1: "parentOne"
)
assert testChild
assert testChild.parentProperty1
}
}
Based on the code for the ImmutableASTTransformation, the Map-arg constructor added by the createConstructorMapCommon method does not include a call to super(args) in the method body.
which means that immutable classes are self contained by default
Now if you want to do it you need to use composition instead of inheritance and this is an example of how you can do it :
import groovy.transform.*
#TupleConstructor
class A {
String a
}
#Immutable(knownImmutableClasses=[A])
class B {
#Delegate A base
String b
}
def b = new B(base: new A("a"), b: "b")
assert b.a
i hope this will help :)
I've been trying to create a TEMPORARY override on new objects, and then to remove the override on the objects themselves. I'm not sure if this can be done, but here is what I've tried so far.
// Say I have a class like:
class Validator {
boolean validate() { println "code here to return actual true/false"; false }
}
// I have two integration points one of them is Here before construction:
// First integration point:
// Save actual validate function
def realValidate = Validator.&validate
// Make new instances of Validator have the validate function hardwired to true
Validator.metaClass.validate { -> println "hardwired true"; true }
// Code I'd rather not modify
// Now some code executes which news up an instance and calls validate
def validator = new Validator()
validator.validate() // This correctly calls our override
// Second integration point.
// Without newing up a new Validator object, I'd like to remove the override.
Validator.metaClass = null
validator.metaClass.validate = Validator.&validate
// This throws "java.lang.IllegalArgumentException: object is not an instance of declaring class"
//validator.validate()
// So maybe I have to explicitly say:
realValidate.resolveStrategy = Closure.DELEGATE_FIRST
// But this still throws the same exception
//validator.validate()
// Perhaps if I tell my objects metaclass to forget about validate, it will bubble up and look for the method on its declaring class?
validator.metaClass.validate = { -> throw new MissingMethodException("validate", Validator.class, (Object[])[], false) }
// This throws MissingMethodException: No signature of method: Validator.validate() is applicable for argument types: () values: []
// Possible solutions: validate(), wait()
//validator.validate()
Apologies for not having a super specific question, since I don't know what all is possible in this particular area. I'd love both the reason why my code doesn't work, as well as alternatives to make it work.
This could be a per instance meta class problem... Validator.metaClass = null will set the global meta class for the Validator class to default. but your validator instance here is a Groovy class and thus stores a separate reference to the meta class in the instance itself. Calls with that instance will not go through a lookup of the global meta class and instead use the per instance meta class (the reference stored in the instance itself). Thus validator.metaClass = null is the only way to reset this
A small modification to your strategy would be fruitful. Use metaClass on the object instead of the Class.
// Say I have a class like:
class Validator {
boolean validate() { println "code here to return actual true/false"; false }
}
def validator = new Validator()
// mark that the pointer is on object instead of class
def realValidate = validator.&validate
validator.metaClass.validate { -> println "hardwired true"; true }
validator.validate() // This correctly calls our override
// Second integration point.
// DO NOT NEED THIS
// validator.metaClass = null
// Assign the method pointer to validate to call original validate
validator.metaClass.validate = realValidate
validator.validate()
Your approach did not work because you had validate() overridden on the metaClass of Class reference instead of the object itself.
I am running into a problem while trying to use property access in Groovy. Take the following class:
class Foo {
Map m = [:]
String bar
void getProperty(String name) {
m.get name
}
def setProperty(String name, value) {
m.set name, value
}
String getBarString() {
return bar // local access, does not go through getProperty()
}
}
It overrides the getter and setter to simply place the values into a Map rather than into the object's normal property space. In the abstract this is a bit silly, but imagine that instead of placing the data into a map we were persisting it to a DB or something else useful.
Unfortunately, the following code now won't work:
foo = new Foo()
foo.bar = "blerg" // using foo.bar invokes the setProperty interceptor
assert foo.bar == "blerg" // this will work fine as foo.bar here uses the getProperty interceptor
assert foo.getBarString() == "blerg" // explosion and fire! getBarString accesses bar locally without going through the getProperty interceptor so null will actually be returned.
Certainly there are workarounds for this, setProperty could set both the MetaProperty and the Map value, etc. However, all of the strategies I've thought of require a lot of extra caution from the programmer to make sure they are accessing class properties in the exact way that they mean to.
Furthermore, some of the built in awesome stuff in Groovy (like #Delegate for example) uses direct MetaProperty access rather than going through getProperty so the following would never work:
class Meep {
String getMyMeep() {
return "MEEP!!!"
}
}
class Foo {
Map m = [:]
String bar
#Delegate Meep meep
void getProperty(String name) {
m.get name
}
def setProperty(String name, value) {
m.set name, value
}
String getBarString() {
return bar
}
}
foo = new Foo()
foo.meep = new Meep() // uses setProperty and so does not place the Meep in the Map m
foo.getMyMeep()
A null pointer exception is thrown on the last line as #Delegate uses MetaProperty direct access (effectively this.meep.getMyMeep() rather than the getProperty interceptor. Unfortunately 'meep' is null, though getProperty('meep') would not be.
In short what I'm looking for is a strategy to solve the following criteria:
intercept property read/write to enable automatic alternative data storage
transparent or near-transparent interface for other developers (I don't want to make other folks' lives significantly harder)
allow for local access of variables using the MetaProperty/this/etc. access methods
Thanks in advance!
You could use
foo.#meep = new Meep()
in order to directly access properties bypassing setProperty method.
That doesn't completely solves your problem though as the foo.meep still triggers set/getProperty.
Another way you could go about is by using getter and setter of the meet directly, i.e.
foo.setMeep(new Meep())
So, one unified way would be to define all of the variables as private and use get/set*PropertyName*
By using an AST Transformation I can do the following:
walk a class's structure and rename all local fields to something like x -> x.
add a getter/setter for each renamed field like this
def get_x_() {
x
}
...in order to access x as a field rather than as a Groovy property
- now apply the transformation on the following class
class Foo {
def x
def y
Map m = [:]
#Delegate Date date // for testing if non-local fields work
def getProperty(String name) {
if (this.respondsTo("get__${name}__")) // if this is one of our custom fields
return "get__${name}__"()
"get${Verifier.capitalize(name)}"() // pass to specific getter method
}
void setProperty {
if (this.respondsTo("set__${name}__")) {
"set__${name}__"(value)
m[name] = value
if (name == "x") y = x + 1
return
}
"set${Verifier.capitalize(name)}"(value)
}
}
now run a testing method like this:
public void testAST() {
def file = new File('./src/groovy/TestExample.groovy')
GroovyClassLoader invoker = new GroovyClassLoader()
def clazz = invoker.parseClass(file)
def out = clazz.newInstance()
out.x = 10
assert out.y == 11
out.y = 5
assert out.y == 5
out.x = 2
assert out.m.containsKey('x')
assert out.m.x == 2
assert out.m.y == 3
out.date = new Date()
assert out.time && out.time > 0
}
And everything should work out including m getting updated, date delegate method time getting accessed properly, etc.
-Glenn
Is there a way in Groovy that I can add code to a constructor when a class is instantiated? I have a Groovy class (but I can't modify the source of this particular one), but I was hoping there was a way to inject code (maybe via the metaclass) so my code gets run as part of the constructor (in this case there is only one, default constructor).
Thanks,
Jeff
You can override the constructor, but it's a little tricky, particularly if you're overriding the default constructor. You need to assign a closure to the class's metaClass.constructor, and the closure should return a new instance. The tricky part is that if you call the constructor you've overriden, you'll get into a recursive loop and generate a stack overflow. You need another way to get an instance of the class, such as a different constructor.
For testing, it's sometimes possible to get around this limitation. Usually, it's enough to first instantiate an object, then override the constructor to return the existing instance. Example:
class MyObject {
String something
MyObject() { something = "initialized" }
}
testInstance = new MyObject()
testInstance.something = "overriden"
MyObject.metaClass.constructor = { -> testInstance }
aNewObject = new MyObject()
assert aNewObject.is(testInstance)
assert aNewObject.something == "overriden"
It is possible to add new constructors or replace the old one. If you need the original constructor, you can use reflection for that:
MyObject.metaClass.constructor = { -> // for the no-arg ctor
// use reflection to get the original constructor
def constructor = MyObject.class.getConstructor()
// create the new instance
def instance = constructor.newInstance()
// ... do some further stuff with the instance ...
println "Created ${instance}"
instance
}
Note that you have to change this if you have parameters to your constructors, e.g:
// Note that the closure contains the signature of the constructor
MyObject.metaClass.constructor = { int year, String reason ->
def constructor = MyObject.class.getConstructor(Integer.TYPE, String.class)
def instance = constructor.newInstance(
2014, "Boy, am I really answering a question three years old?")
// ... do some further stuff with the instance ...
println "Created ${instance}"
instance
}
PS: Note that when you want to add constructors which are not yet existent, use the << operator instead: MyObject.metaClass.constructor << { /* as above */ }.
You can bypass the limitations in the solution proposed by storing the original constructor using standard Java reflection. For example, this is what I do initialize a class (basic injection) in a spock test:
def setupSpec() {
MockPlexusContainer mockPlexusContainer = new MockPlexusContainer()
def oldConstructor = MY_CLASS.constructors[0]
MY_CLASS.metaClass.constructor = { ->
def mojo = oldConstructor.newInstance()
mockPlexusContainer.initializeContext(mojo)
return mojo
}
}
This gets invoked only once, but eveytime someone calls a constructor I get a different instance avoiding cleaning values and ensuring thread safety.