自定义类加载器

1.自定义类加载器， 实现findClass方法。loadClass在找不到类时会调用此方法

public class MyClassLoader extends ClassLoader {

        @Override
        protected Class<?> findClass(String name) throws ClassNotFoundException {
            try{
                String filePath = "/Users/zhanjun/Desktop/" + name.replace('.', File.separatorChar) + ".class";
                //指定读取磁盘上的某个文件夹下的.class文件：
                File file = new File(filePath);
                FileInputStream fis = new FileInputStream(file);
                byte[] bytes = new byte[fis.available()];
                fis.read(bytes);
                //调用defineClass方法，将字节数组转换成Class对象
                Class<?> clazz = this.defineClass(name, bytes, 0, bytes.length);
                fis.close();
                return clazz;
            }catch (FileNotFoundException e){
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {

            }
            return super.findClass(name);
        }
    }

2. 调用

public static void main(String[] args) throws Exception {
    Class clazz0 = new MyClassLoader().loadClass("com.sankuai.discover.memory.OOM");
}