Create a Groovy class dynamically

Question

Given a class name I would like to dynamically create a Groovy class add properties and methods to it. I create the new class using

instance = this.class.cla         


        

Answer 1

a nice variant would be to use the GroovyShell.

def c = """ 
package de.myCorp.test

class Test {
    def a
    def b
    def c    

    Test(String c){ this.c = c}

    public String greet(){
        return "hello "+a
    }

    public void count(){
        (1..4).each{
            println it
        }
    }

}

def class UsingTest {
    Test mytest = null

    UsingTest (Test test){  this.mytest = test }

    def using(){
        mytest.greet();
    }

}
"""


GroovyShell gs = new GroovyShell()
//I hope this is not a too bad hack ^^ 
def erg = gs.evaluate(c+";['test':Test, 'using':UsingTest];")

def testclass = erg["test"].newInstance("Charlotte on Ice")
    testclass.a = "hugo"
    testclass.b = "sepp"


testclass.count() 
assert testclass.greet() == "hello hugo"

assert testclass.c == "Charlotte on Ice"
assert testclass.class.name == "de.myCorp.test.Test"


def usingclass = erg['using'].newInstance(testclass)
usingclass.mytest.a = "Fritzl"
assert usingclass.using() == "hello Fritzl" 

...and especially notice the GroovyShell.evaluate(URI uri) types... GroovyShellDoc

Answer 2

I have more or less been able to get it working by using GroovyClassLoader and SimpleTemplateEngine. here is the code:

class ClassBuilder {

    GroovyClassLoader loader
    String name
    Class cls
    def imports
    def fields
    def methods

    def ClassBuilder(GroovyClassLoader loader) {
        this.loader = loader
        imports = []
        fields = [:]
        methods = [:]
    }

    def setName(String name) {
        this.name = name
    }

    def addImport(Class importClass) {
        imports << "${importClass.getPackage().getName()}" +
                ".${importClass.getSimpleName()}"
    }

    def addField(String name, Class type) {
        fields[name] = type.simpleName
    }

    def addMethod(String name, Closure closure) {
        methods[name] = closure
    }

    def getCreatedClass() {

        def templateText = '''
<%imports.each {%>import $it\n <% } %> 
class $name
{
<%fields.each {%>    $it.value $it.key \n<% } %>
}
'''
        def data = [name: name, imports: imports, fields: fields]

        def engine = new groovy.text.SimpleTemplateEngine()
        def template = engine.createTemplate(templateText)
        def result = template.make(data)
        cls = loader.parseClass(result.toString())
        methods.each {
            cls.metaClass."$it.key" = it.value
        }
        return cls
    }
}

and here is an example of how I use it to create a class dynamically:

import java.util.Calendar
def builder = new ClassBuilder(this.class.classLoader)
builder.setName("MyClass");

builder.addImport(Calendar)

builder.addField('field1', Integer)
builder.addField('field2', Integer)

builder.addMethod('sum') { field1 + field2 }

builder.addMethod('product') { field1 * field2 }

builder.addMethod('testCalendar') {
    println Calendar.getInstance().getTime()
}

Class myClass = builder.getCreatedClass()
def myInstance = myClass.newInstance()

myInstance.field1 = 1
myInstance.field2 = 2

println myInstance.sum()
println myInstance.product()

myInstance.setField2(1500)
println myInstance.getField2()

myInstance.testCalendar()