java classloader jar_java urlclassloader 动态加载jar包时出现ClassNotFound

我想给程序做一个加载外部jar的功能,在查阅相关资料后我了解到可以重写URLClassLoader做到

所以我仿照网上的教程编写了下方的代码

public class ModuleClassLoader extends URLClassLoader {

private static ModuleClassLoader instance;

private static URLClassLoader classLoader = (URLClassLoader) ClassLoader.getSystemClassLoader();

private static final Method ADD_URL = initAddMethod();

static {

ClassLoader.registerAsParallelCapable();

}

private ModuleClassLoader(URL[] urls) {

super(urls);

}

public static ModuleClassLoader getInstance() {

if (instance == null) {

instance = new ModuleClassLoader(new URL[]{});

}

return instance;

}

private static Method initAddMethod() {

try {

Method addUrl = URLClassLoader.class.getDeclaredMethod("addURL", URL.class);