Scala URLClassLoader没有重新加载类文件

Question

I am running a scala project where I need to execute some rules. The rules will be dynamically added or removed from scala class file at runtime.

So, I want whenever the rules class modify, it should reload to get the changes without stopping the execution process.

I used runtime.getruntime.exec() to compile it

and am URL Class loader to get the modified code from classes

The exec() run fines. and in target folder classes gets modifies also, even when I am using URL Class Loader, not getting any error.

But it is giving me same result which i have on starting of the project. It's not giving me modification code.

Below is the code which I am using.

package RuleEngine

import akka.actor._
import akka.http.scaladsl.Http
import akka.http.scaladsl.server.Directives._
import akka.stream.ActorMaterializer
import akka.util.Timeout

import scala.io.StdIn
import Executor.Compute
import scala.concurrent.{Await, ExecutionContextExecutor}
import scala.concurrent.duration._


object StatsEngine {

def main(args: Array[String]) {

implicit val system: ActorSystem = ActorSystem("StatsEngine")
implicit val materializer: ActorMaterializer = ActorMaterializer()
implicit val executionContext: ExecutionContextExecutor = system.dispatcher

implicit val timeout = Timeout(10 seconds)
val computeDataActor = system.actorOf(Props[Compute],"ComputeData")


val route = {
  post {
    path("computedata"/) {
        computeDataActor ! "Execute"
        complete("done")
      }
    }
  }


val bindingFuture = Http().bindAndHandle(route , "localhost", 9000)

println(s"Server online at http://localhost:9000/\nPress RETURN to stop...")
 }
}

This is the main object file where I have created Akka HTTP to make API's

It will call computeDataActor whose code is below.

package Executor

import java.io.File
import java.net.URLClassLoader

import CompiledRules.RulesList
import akka.actor.Actor

class Compute extends Actor{

  def exceuteRule(): Unit ={
    val rlObj = new RulesList
    rlObj.getClass.getDeclaredMethods.map(name=>name).foreach(println)

    val prcs = Runtime.getRuntime().exec("scalac /home/hduser/MStatsEngine/Test/RuleListCollection/src/main/scala/CompiledRules/RuleList.scala -d  /home/hduser/MStatsEngine/Test/RuleListCollection/target/scala-2.11/classes/")
    prcs.waitFor()

    val fk = new File("/home/hduser/MStatsEngine/Test/RuleListCollection/target/scala-2.11/classes/").toURI.toURL

    val classLoaderUrls = Array(fk)

    val urlClassLoader = new URLClassLoader(classLoaderUrls)

    val beanClass = urlClassLoader.loadClass("CompiledRules.RulesList")

    val constructor = beanClass.getConstructor()

    val beanObj = constructor.newInstance()

    beanClass.getDeclaredMethods.map(x=>x.getName).foreach(println)

  }
  override def receive: Receive ={
    case key:String => {
      exceuteRule()
    }
  }
}

Rules are imported which is mentioned below.

package CompiledRules

class RulesList{

  def R1 : Any = {
    return "executing R1"
  }

  def R2 : Any = {return "executing R2"}
//  def R3 : Any = {return "executing R3"}
  //def R4 : Any = {return "executing R4"}
  def R5 : Any = {return "executing R5"}
}//Replace

So, whene i execute code, and on calling API, I will get ouput as

R1
R2
R5

Now, without stopping the project, I will uncomment R3 and R4. And I will call API again, As I am executing code again, using

runtime.getruntime.exec()

it will compile the file and update classes in target

So, i used URLClassLoader to get new object of modification code.

But Unfortunately I am getting same result always which i have on starting of the project

R1
R2
R5

Below is link for complete project Source Code

Answer 1

val beanClass = urlClassLoader.loadClass("CompiledRules.RulesList")
    val constructor = beanClass.getConstructor()
    val beanObj = constructor.newInstance()

Is just creating the newInstance of Already loaded class.

Java's builtin Class loaders always checks if a class is already loaded before loading it. loadClass

protected Class<?> loadClass(String name,
             boolean resolve)
                  throws ClassNotFoundException

Loads the class with the specified binary name. The default implementation of this method searches for classes in the following order: Invoke findLoadedClass(String) to check if the class has already been loaded.

Invoke the loadClass method on the parent class loader. If the parent is null the class loader built-in to the virtual machine is used, instead.

Invoke the findClass(String) method to find the class.

To reload a class you will have to implement your own ClassLoader subclass as in this link