自定义类加载器

public class MyClassLoader extends ClassLoader{ //继承ClassLoader父类
    /**
     * name就是类名称
     */
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        String path="/tmp/myclasspath/"+name+".class";
        System.out.println("path:"+path);
        ByteArrayOutputStream os=new ByteArrayOutputStream();
        try {
            Files.copy(Paths.get(path),os);
            byte[] bytes=os.toByteArray();

            //byte[] -> *.class
            return  defineClass(name,bytes,0,bytes.length);//父类中的defineClass加载，如果找不到会调用本类的defineClass进行加载
        } catch (IOException e) {
            e.printStackTrace();
            throw new ClassNotFoundException("类文件未找到",e);
        }
    }
}

 public static void main(String[] args) throws ClassNotFoundException, IllegalAccessException, InstantiationException {
        MyClassLoader classLoader=new MyClassLoader();
        Class<?> c1=classLoader.loadClass("HelloWorld");
        Class<?> c2=classLoader.loadClass("HelloWorld");
        System.out.println(c1==c2);
        c1.newInstance();
        //System.out.println(c1.newInstance());
    }

true