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使用JavaAssist修改现有类时出错

java-assist bytecode-manipulation java

1

Amir Afghani · 技术社区 · 6 年前

我正在进行以下代码战挑战:

https://www.codewars.com/kata/hack-22/train/java

public static Yossarian loophole() throws Throwable {
    ClassPool pool = ClassPool.getDefault();
    //Loader cl = new Loader(pool);
    CtClass yossarianClass = pool.get("Yossarian");
    int modifiers = yossarianClass.getDeclaredMethod("isCrazy").getModifiers();
    if(Modifier.isFinal(modifiers)) {
        System.out.println("Removing Final");
        int notFinalModifier = Modifier.clear(modifiers, Modifier.FINAL);
        yossarianClass.getDeclaredMethod("isCrazy").setModifiers(notFinalModifier);
        yossarianClass.rebuildClassFile();
    }
    final CtClass saneYossarianClass = ClassPool.getDefault().makeClass("SaneYossarian");
    saneYossarianClass.setSuperclass(yossarianClass);
    final CtMethod overrideMethod = CtNewMethod.make("public boolean isCrazy() { return true; }", saneYossarianClass);
    saneYossarianClass.addMethod(overrideMethod);
    final Class<?> aClass = saneYossarianClass.toClass(Yossarian.class.getClassLoader(), Yossarian.class.getProtectionDomain());
    return (Yossarian) aClass.newInstance();
}

我得到了以下错误:

线程“main”javassist中出现异常。CannotCompileException:由java编写。ClassFormatError:类SaneYossarian覆盖最终方法isCrazy。()Z

使现代化

1 回复 | 直到 6 年前

1

Antoniossss 6 年前

final Class<?> aClass = saneYossarianClass.toClass(Yossarian.class.getClassLoader(), Yossarian.class.getProtectionDomain());

使用

 final Class<?> aClass = saneYossarianClass.toClass();

出于某些原因,这对我很有用:

public final class SomeClassHavingFinals {

    public final void sayHelloBoy() {
        System.out.println("I am saying hello original");
    }
}

以及:

public static void main(String[] args)
            throws NotFoundException, CannotCompileException, InstantiationException, IllegalAccessException,
            NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException, IOException {
        ClassPool pool = ClassPool.getDefault();
        CtClass clazz = pool.get("testapp.SomeClassHavingFinals");
        clazz.defrost();
        clazz.setModifiers(Modifier.PUBLIC);
        clazz.getDeclaredMethod("sayHelloBoy").setModifiers(Modifier.PUBLIC);
        clazz.toClass();

        CtClass extension = pool.makeClass("SomeExtension");
        extension.setSuperclass(clazz);
        final CtMethod overrideMethod = CtNewMethod.make("public void sayHelloBoy() { System.out.println(\"Im overriden\"); }",
                extension);
        extension.addMethod(overrideMethod);
        Object ei = extension.toClass().newInstance();
        ei.getClass().getDeclaredMethod("sayHelloBoy").invoke(ei);
    }

输出

所以它看起来是有效的。IDK内部,但toClass()似乎会导致重新生成文件定义。