MetaProgramming

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title: MetaProgramming permalink: GroovyNotes/MetaProgramming category: GroovyNotes parent: GroovyNotes layout: default has_children: false share: true shortRepo:

• groovynotes
• default

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Table of contents

{: .text-delta } 1. TOC {:toc}

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Objects

properties to map

intCmd.class
        .declaredFields
        .findAll { !it.synthetic }
        .collectEntries { [it.name, intCmd."$it.name"] }

can also use slurper

class BaseObject {
    Map asMap() {
        def jsonSlurper = new groovy.json.JsonSlurperClassic()
        Map map = jsonSlurper.parseText(this.asJson())
        return map
    }

    String asJson() {
        def jsonOutput = new groovy.json.JsonOutput()
        String json = jsonOutput.toJson(this)
        return json
    }
}

Object Extensions

if you don’t know the  name of method at runtime

   peter.invokeMethod(“walk”, 10)

MetaProgramming

Create Class Prop Dynamically

code example from class constructor

dynamicProperties.eachWithIndex { String newProp, Integer index ->
    if (index < 4) {
        String propName = newProp.substring(1).replaceAll("\\s", "")
        String propNameCamelCased = Character.toString(newProp.charAt(0)).toUpperCase() + noWhite
        this.metaClass["get${propNameCamelCased}"] = raw.get(newProp)
    }
}

to invoke a property dynamically

obj[usrRequestedProperty], obj.”$usrRequestedProperty”

iterate over an objects properties

obj.properties.each {}

check if property exists

object.hasProperty(methodName)

iterate through objects methods

   object.methods.each{}

iterate through methods

test.metaClass.methods.each{ method -> if (method.name == ‘thismethod’) method.invoke(arg)}

check if method exists

object.respondsTo(methodName)    

Class object -- reflection

dynamically create class

Class<?> clazz=Class.forName("java.util.Date");
        Object date=clazz.newInstance();

Class<?> clazz=Class.forName("com.foo.MyClass");
        Constructor<?> constructor=clazz.getConstructor(String.class,Integer.class);
        Object instance=constructor.newInstance("stringparam",42);

def p3 = Class.forName("Person").newInstance()
assert p3

using groovy classLoader

def instance = this.class.classLoader.loadClass('Item', true, false)?.newInstance()

Code Example

Class clazz = configMap.get(name)
Object typeConfigProps = wSConfigCommand.getProperty(name)
Object newInstance = clazz.newInstance([*: newClientOrderConfig.properties, *: typeConfigProps.properties] as Object)
newInstance.wSConfigType = type
newInstance.clientSetup = newClientSetup
def err = validatingClosure(newInstance)
if (err) {
    returnObj.errors = [(err.name): err]
} else {
    returnObj = [(type.getKey()): newInstance.save(flush: true).id]
}

possible errors

1. the JVM can't find or can't load your class
2. the class you're trying to instantiate doesn't have the right sort of constructors
3. the constructor itself threw an exception
4. the constructor you're trying to invoke isn't public
5. a security manager has been installed and is preventing reflection from occurring