6
Java 使用指定 classloader 创建 class
source link: https://blog.yuantops.com/tech/define_class_with_custom_classloader/
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.
Java 使用指定 classloader 创建 class
有时需要在程序运行时动态创建 Java 类（加载自定义文件，或者是加载 Javassist 之类字节码增强工具创建出来的字节码等）。要注意的是，不同类加载器加载的类，彼此是不可见的，也就不能直接实例化。
要突破这个限制，需要一点 hack: 利用反射机制，在根据字节码创建类时，指定 classloader。下面的代码从著名的 jodd 库摘录，请自行学习。
/**
* Defines a class from byte array into the specified class loader.
* Warning: this is a <b>hack</b>!
* @param className optional class name, may be <code>null</code>
* @param classData bytecode data
* @param classLoader classloader that will load class
*/
public static Class defineClass(final String className, final byte[] classData, ClassLoader classLoader) {
if (classLoader == null) {
classLoader = Thread.currentThread().getContextClassLoader();
}
try {
final Method defineClassMethod = ClassLoader.class.getDeclaredMethod("defineClass", String.class, byte[].class, int.class, int.class);
defineClassMethod.setAccessible(true);
return (Class) defineClassMethod.invoke(classLoader, className, classData, 0, classData.length);
} catch (Throwable th) {
throw new RuntimeException("Define class failed: " + className, th);
}
}
Recommend
About Joyk
Aggregate valuable and interesting links.
Joyk means Joy of geeK