需求場(chǎng)景：通過(guò)URLClassLoader從jar文件中加載類并創(chuàng)建實(shí)例，可實(shí)現(xiàn)運(yùn)行時(shí)動(dòng)態(tài)加載

1、要加載的jar：

1）接口類IC

package cn.fjs;public interface IC {public void action(); }
2）實(shí)例類C

package cn.fjs;public class C implements IC{public void action(){System.out.println("Hi i am A class.");} }
export到j(luò)ar，放在指定目錄，如D:\\tmp\\C.jar

2、動(dòng)態(tài)加載：

1）接口類IC

package cn.fjs;public interface IC {public void action(); }
2）調(diào)度類Test

package cn.fjs;import java.io.File; import java.net.URL; import java.net.URLClassLoader; import java.util.Scanner;public class Test implements Runnable{public Test(){new Thread(this).start();}public void run(){System.out.print("Pls enter the jar directory:like D\\tmp\\C.jar \n");Scanner sc = new Scanner(System.in);String dir = sc.next();System.out.print("Pls enter the class name:like cn.fjs.C \n");String cname = sc.next();load(dir,cname);System.out.println("\n\n");}private void load(String dir,String cname){String jarName = "file:"+dir;System.out.println(jarName);try{File file = new File(jarName);URL url = file.toURL();URLClassLoader loader = new URLClassLoader(new URL[]{url});Class aClass = loader.loadClass(cname);//利用Java反射機(jī)制創(chuàng)建實(shí)例測(cè)試方法IC ic = (IC)aClass.newInstance();ic.action();}catch (Exception e){e.printStackTrace();}}public static void main(String[] args){new Test();} }

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