I want to override a method definition in Grails. I am trying to use Groovy metaprogramming as the class which I want to override belongs to a framework.
Below is the original class.
class SpringSocialSimpleSignInAdapter implements SignInAdapter {
private RequestCache requestCache
SpringSocialSimpleSignInAdapter(RequestCache requestCache) {
this.requestCache = requestCache;
}
String signIn(String localUserId, Connection<?> connection, NativeWebRequest request) {
SignInUtils.signin localUserId
extractOriginalUrl request
}
}
I am trying to override like below
SpringSocialSimpleSignInAdapter.metaClass.signIn = {java.lang.String str, org.springframework.social.connect.Connection conn, org.springframework.web.context.request.NativeWebRequest webreq ->
println 'coming here....' // my implementation here
return 'something'
}
But for some reason overriding is not hapening. I am not able to figure it out. Any help would be greatly appretiated.
Thanks
Yeah, seems like that bug. I don't know your whole scenario, but anyway, here's a small workaround i made:
In your class definition, you don't implement the interface
You create your object and do your metamagic
Use groovy coercion to make it act as the interface and then you can pass it around
Here is a small script i made using JIRA bug to prove it:
interface I {
def doIt()
}
class T /*implements I*/ {
def doIt() { true }
}
def t = new T()
assert t.doIt()
t.metaClass.doIt = { -> false }
// here the coercion happens and the assertion works fine
def i = t as I
assert !i.doIt()
assert !t.doIt()
// here the polymorphism happens fine
def iOnlyAcceptInterface(I i) { assert !i.doIt() }
iOnlyAcceptInterface(i)
Related
It appears the convention for converting objects in Groovy is to use the as operator and override asType(). For example:
class Id {
def value
#Override
public Object asType(Class type) {
if (type == FormattedId) {
return new FormattedId(value: value.toUpperCase())
}
}
}
def formattedId = new Id(value: "test") as FormattedId
However, Grails over-writes the implementation of asType() for all objects at runtime so that it can support idioms like render as JSON.
An alternative is to re-write the asType() in the Grails Bootstrap class as follows:
def init = { servletContext ->
Id.metaClass.asType = { Class type ->
if (type == FormattedId) {
return new FormattedId(value: value.toUpperCase())
}
}
}
However, this leads to code duplication (DRY) as you now need to repeat the above in both the Bootstrap and the Id class otherwise the as FormattedId will not work outside the Grails container.
What alternatives exist to writing conversion code in Groovy/Grails that do not break good code/OO design principals like the Single Responsibility Principal or DRY? Are Mixins are good use here?
You can use the Grails support for Codecs to automatically add encodeAs* functions to your Grails archetypes:
class FormattedIdCodec {
static encode = { target ->
new FormattedId((target as String).toUpperCase()
}
}
Then you can use the following in your code:
def formattedId = new Id(value: "test").encodeAsFormattedId
My un-elegant solution is to rename the original asType(), and make a new asType() that calls it, and to also make your BootStrap overwrite astType with a call to that method:
so, your class:
class Id {
def value
#Override
public Object asType(Class type) {
return oldAsType(type);
}
public Object oldAsType(Class type) {
if (type == FormattedId) {
return new FormattedId(value: value.toUpperCase())
}
}
}
In my app, I had asType defined in a number of classes, so I ended up using a common closure in BootStrap.groovy:
def useOldAsType = {Class clazz ->
delegate.oldAsType(clazz)
}
Id.metaClass.asType = useOldAsType;
Value.metaClass.asType = useOldAsType;
OtherClass.metaClass.asType = useOldAsType;
SubclassOfValue.metaClass.asType = useOldAsType;
Note that if you have a subclass that does not override asType, but you want it to use the superclass's, you must also set it in BootStrap.
I have piece of code as follows
def revisedSections=sections.collect{sectionObj->
sectionObj.questionCategories=sectionObj.questionCategories.collect{qCat->
def flag=false
this.questionSet.questions = this.questionSet.questions.collect{qObj->
if(qCat.category == qObj.questionCategory.category){
qCat.questions.add(qObj)
//this.questionSet.questions.remove(qObj)
flag=true
}
qObj
}
if(flag){
qCat
}
}
sectionObj
}
log.debug('revisedSections'+revisedSections)
this.metaClass.getSectionsData={-> revisedSections }
log.debug 'this.sectionsData '+this.sectionsData
I want to add sectionsData property to the instance and then convert the instance to json
but i am not able to access the dynamically added property with this code, is there something i am missing ?
You can use mixins to accomplish what you're looking for. Something like the following is native and acceptable Groovy:
class RevisedSection {
String sectionData
}
class Section {
String name
}
Section.mixin RevisedSection
def section = new Section(sectionData: "Data", name: "Section Name")
assert section.sectionData == "Data"
Hope this helps!
If I understand what you are trying to achieve correctly, it is easily feasible with meta programming, and it should work.
Without information about the context of your code I can only guess at the base class of your object etc, so here's some code run in the groovy console, which works perfectly
class D {
int someValue
def init() {
this.metaClass.getSomeString={->someValue as String}
}
}
def d=new D()
d.init()
d.someValue=76
println d.someString
The result is of course the string '76' being printed to the console.
Another suggestion, with a statically compiled getter:
class D {
private Closure computation
int someValue
def init() {
this.computation={someValue}
}
String getSomeString(){
computation() as String
}
}
Take the following controller:
package test
class TestController {
static defaultAction = "test"
def test() {
render "test"
}
}
Why is test defined with def test() { instead of something like void test() {? Isn't the def keyword only used for closures or functions in a script (i.e. not in a Groovy class)?
render is void so in this case the test action could be void, but in the case where you return a model map the action has to be non-void:
def create() {
[personInstance: new Person(params)]
}
Since some actions can return a value and some don't, the general syntax has to return def to support all variants.
Burt's answer is correct but the real problem I was having is that I misunderstood what def is. Rather than being like var in JavaScript, you can think of it like Object in Java.
I thought that using def was like doing (JavaScript)
var test = function() {
alert("test");
}
while in reality it's just like (Java)
public Object test() {
return someObject;
}
It's not a different kind of function/closure, it's like a return type—def can be applied to any object (Groovy has no data primitives, so any value is also an object, unlike in Java).
It helps my Java brain to think of
def bar = "foo";
as
Object bar = "foo";
Normally for a Grails domain or command class, you declare your constraints and the framework adds a validate() method that checks whether each of these constraints is valid for the current instance e.g.
class Adult {
String name
Integer age
void preValidate() {
// Implementation omitted
}
static constraints = {
name(blank: false)
age(min: 18)
}
}
def p = new Person(name: 'bob', age: 21)
p.validate()
In my case I want to make sure that preValidate is always executed before the class is validated. I could achieve this by adding a method
def customValidate() {
preValidate()
validate()
}
But then everyone who uses this class needs to remember to call customValidate instead of validate. I can't do this either
def validate() {
preValidate()
super.validate()
}
Because validate is not a method of the parent class (it's added by metaprogramming). Is there another way to achieve my goal?
You should be able to accomplish this by using your own version of validate on the metaclass, when your domain/command class has a preValidate() method. Something similar to the below code in your BootStrap.groovy could work for you:
class BootStrap {
def grailsApplication // Set via dependency injection
def init = { servletContext ->
for (artefactClass in grailsApplication.allArtefacts) {
def origValidate = artefactClass.metaClass.getMetaMethod('validate', [] as Class[])
if (!origValidate) {
continue
}
def preValidateMethod = artefactClass.metaClass.getMetaMethod('preValidate', [] as Class[])
if (!preValidateMethod) {
continue
}
artefactClass.metaClass.validate = {
preValidateMethod.invoke(delegate)
origValidate.invoke(delegate)
}
}
}
def destroy = {
}
}
You may be able to accomplish your goal using the beforeValidate() event. It's described in the 1.3.6 Release Notes.
I don't know how to use binding with closures in Groovy. I wrote a test code and while running it, it said, missing method setBinding on the closure passed as parameter.
void testMeasurement() {
prepareData(someClosure)
}
def someClosure = {
assertEquals("apple", a)
}
void prepareData(testCase) {
def binding = new Binding()
binding.setVariable("a", "apple")
testCase.setBinding(binding)
testCase.call()
}
This works for me with Groovy 1.7.3:
someClosure = {
assert "apple" == a
}
void testMeasurement() {
prepareData(someClosure)
}
void prepareData(testCase) {
def binding = new Binding()
binding.setVariable("a", "apple")
testCase.setBinding(binding)
testCase.call()
}
testMeasurement()
In this script example, the setBinding call is setting a in the scripts binding (as you can see from the Closure documentation, there is no setBinding call). So after the setBinding call, you can call
println a
and it will print out "apple"
So to do this in the class, you can set the delegate for the closure (the closure will revert back to this delegate when a property cannot be found locally) like so:
class TestClass {
void testMeasurement() {
prepareData(someClosure)
}
def someClosure = { ->
assert "apple" == a
}
void prepareData( testCase ) {
def binding = new Binding()
binding.setVariable("a", "apple")
testCase.delegate = binding
testCase.call()
}
}
And it should grab the value fro a from the delegate class (in this case, a binding)
This page here goes through the usage of delegate and the scope of variables in Closures
Indeed, instead of using a Binding object, you should be able to use a simple Map like so:
void prepareData( testCase ) {
testCase.delegate = [ a:'apple' ]
testCase.call()
}
Hope it helps!
This is really strange behaviour: removing the "def" in front of someClosure declaration makes the script work in JDK1.6 Groovy:1.7.3
Update: This was posted in the answer above. My mistake to repeat it.
Update: Why it works? Without a def first line is taken as a property assignment which calls setProperty and makes the variable available in binding, which is resolved later.
a def should have worked as well as per (http://docs.codehaus.org/display/GROOVY/Groovy+Beans)
someClosure = {
assert "apple", a
print "Done"
}
void testMeasurement() {
prepareData(someClosure)
}
void prepareData(testCase) {
def binding = new Binding()
binding.setVariable("a", "apple")
testCase.setBinding(binding)
testCase.call()
}
testMeasurement()
I could reproduce the problem you mention by following code. But i am not sure if this is the correct way to use Binding. GroovyDocs says they are to be used with scripts. Could you point me to documentation which suggests such usage of Binding with Closures.
class TestBinding extends GroovyTestCase {
void testMeasurement() {
prepareData(someClosure)
}
def someClosure = {
assertEquals("apple", a)
}
void prepareData(testCase) {
def binding = new Binding()
binding.setVariable("a", "apple")
//this.setBinding(binding)
testCase.setBinding(binding)
testCase.call()
}
}
This was answered on groovy mailing list:
In a script, def foo will create a local variable, not a property
(private field + getter/setter).
Think of a script a bit like if it's the body of a run() or main() method.
That's where and how you can define local variables.