scala - 反射

有时候我们想定义一个字符串的方法，然后通过scala的动态创建class，然后反射调用方法，在很多情景下是在学有用的，比较动态自定义spark的mapParations，当然了，每个人的需求都不一样，但是底层原理是一样的。

scala 动态反射创建方法

画饼

运行

object CreateTest{
  def main(args: Array[String]): Unit = {
    val cim = ClassCreateUtils("def toUps(str:String):String = str.toUpperCase")
    val value = cim.methods("toUps").invoke(cim.instance, "hello")
    println(value) // method1
    println(cim.invoke("World")) // method2
  }
}

输出

HELLO
WORLD

工具类实现

依赖

compile group: 'org.scala-lang', name: 'scala-library', version: '2.12.8'
compile group: 'org.scala-lang', name: 'scala-reflect', version: '2.12.8'
compile group: 'org.scala-lang', name: 'scala-compiler', version: '2.12.8'

compile group: 'org.apache.spark', name: 'spark-sql_2.12', version: '2.4.0'
compile group: 'org.apache.spark', name: 'spark-core_2.12', version: '2.4.0'
compile group: 'org.apache.spark', name: 'spark-repl_2.12', version: '2.4.0'

源码

import java.lang.reflect.Method
import java.util
import java.util.UUID
import scala.reflect.runtime.universe
import scala.tools.reflect.ToolBox

case class ClassInfo(clazz: Class[_], instance: Any, defaultMethod: Method, methods: Map[String, Method]) {
  def invoke[T](args: Object*): T = {
    defaultMethod.invoke(instance, args: _*).asInstanceOf[T]
  }
}

object ClassCreateUtils {
  private val clazzs = new util.HashMap[String, ClassInfo]()
  private val classLoader = scala.reflect.runtime.universe.getClass.getClassLoader
  private val toolBox = universe.runtimeMirror(classLoader).mkToolBox()


  def apply(func: String): ClassInfo = this.synchronized {
    var clazz = clazzs.get(func)
    if (clazz == null) {
      val (className, classBody) = wrapClass(func)
      val zz = compile(prepareScala(className, classBody))
      val defaultMethod = zz.getDeclaredMethods.head
      val methods = zz.getDeclaredMethods
      clazz = ClassInfo(
        zz,
        zz.newInstance(),
        defaultMethod,
        methods = methods.map { m => (m.getName, m) }.toMap
      )
      clazzs.put(func, clazz)
    }
    clazz
  }

  def compile(src: String): Class[_] = {
    val tree = toolBox.parse(src)
    toolBox.compile(tree).apply().asInstanceOf[Class[_]]
  }

  def prepareScala(className: String, classBody: String): String = {
    classBody + "\n" + s"scala.reflect.classTag[$className].runtimeClass"
  }

  def wrapClass(function: String): (String, String) = {
    val className = s"dynamic_class_${UUID.randomUUID().toString.replaceAll("-", "")}"
    val classBody =
      s"""
         |class $className extends Serializable{
         |  $function
         |}
            """.stripMargin
    (className, classBody)
  }

}