Generating Classes at Runtime and Invoking Their Methods With and Without the Use of Reflection in Java 8 and Later

package org.burningwave.core.examples.classfactory;

import static org.burningwave.core.assembler.StaticComponentContainer.Constructors;

import java.lang.reflect.Modifier;

import java.time.LocalDateTime;

import java.time.ZoneId;

import java.util.Date;

import org.burningwave.core.Virtual;

import org.burningwave.core.assembler.ComponentContainer;

import org.burningwave.core.assembler.ComponentSupplier;

import org.burningwave.core.classes.AnnotationSourceGenerator;

import org.burningwave.core.classes.ClassFactory;

import org.burningwave.core.classes.ClassSourceGenerator;

import org.burningwave.core.classes.FunctionSourceGenerator;

import org.burningwave.core.classes.GenericSourceGenerator;

import org.burningwave.core.classes.TypeDeclarationSourceGenerator;

import org.burningwave.core.classes.UnitSourceGenerator;

import org.burningwave.core.classes.VariableSourceGenerator;

public class RuntimeClassExtender {

    @SuppressWarnings("resource")

    public static void execute() throws Throwable {

        UnitSourceGenerator unitSG = UnitSourceGenerator.create("packagename").addClass(

            ClassSourceGenerator.create(

                TypeDeclarationSourceGenerator.create("MyExtendedClass")

            ).addModifier(

                Modifier.PUBLIC

            //generating new method that override MyInterface.convert(LocalDateTime)

            ).addMethod(

                FunctionSourceGenerator.create("convert").setReturnType(

                    TypeDeclarationSourceGenerator.create(

                        Comparable.class

                    ).addGeneric(

                        GenericSourceGenerator.create(Date.class)

                    )

                )

                .addParameter(VariableSourceGenerator.create(LocalDateTime.class, "localDateTime"))

                .addModifier(Modifier.PUBLIC)

                .addAnnotation(AnnotationSourceGenerator.create(Override.class))

                .addBodyCodeRow(

                    "return Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant());"

                ).useType(ZoneId.class)

            ).addConcretizedType(

                MyInterface.class

            ).expands(ToBeExtended.class)

        );

        System.out.println("\nGenerated code:\n" + unitSG.make());

        //With this we store the generated source to a path

        unitSG.storeToClassPath(System.getProperty("user.home") + "/Desktop/bw-tests");

        ComponentSupplier componentSupplier = ComponentContainer.getInstance();

        ClassFactory classFactory = componentSupplier.getClassFactory();

        //this method compile all compilation units and upload the generated classes to default

        //class loader declared with property "class-factory.default-class-loader" in 

        //burningwave.properties file (see "Overview and configuration").

        //If you need to upload the class to another class loader use

        //loadOrBuildAndDefine(LoadOrBuildAndDefineConfig) method

        Class<?> generatedClass = classFactory.loadOrBuildAndDefine(

            unitSG

        ).get(

            "packagename.MyExtendedClass"

        );

        ToBeExtended generatedClassObject =

            Constructors.newInstanceOf(generatedClass);

        generatedClassObject.printSomeThing();

        System.out.println(

            ((MyInterface)generatedClassObject).convert(LocalDateTime.now()).toString()

        );

        //You can also invoke methods by casting to Virtual (an interface offered by the

        //library for faciliate use of runtime generated classes)

        Virtual virtualObject = (Virtual)generatedClassObject;

        //Invoke by using reflection

        virtualObject.invoke("printSomeThing");

        //Invoke by using MethodHandle

        virtualObject.invokeDirect("printSomeThing");

        System.out.println(

            ((Date)virtualObject.invokeDirect("convert", LocalDateTime.now())).toString()

        );

    }   

    public static class ToBeExtended {

        public void printSomeThing() {

            System.out.println("Called method printSomeThing");

        }

    }

    public static interface MyInterface {

        public Comparable<Date> convert(LocalDateTime localDateTime);

    }

    public static void main(String[] args) throws Throwable {

        execute();

    }

}