如何检测java系统类？

问题描述

我正在尝试向系统类添加自定义行为（FileInputStream / FileOutputStream）。我使用以下转换方法编写了自定义ClassFileTransformer：

I'm trying to add custom behaviour to system classes (FileInputStream/FileOutputStream). I wrote custom ClassFileTransformer with the following transform method:

public byte[] transform(ClassLoader arg0, String arg1, Class arg2, ProtectionDomain arg3, byte[] arg4) throws IllegalClassFormatException {
    System.out.println("class name: " + arg1);
    return arg4;
}

当我运行示例程序时：

public static void main(String[] args) throws Exception {
    new FileOutputStream("file");
}

我看到没有系统类没有传递给转换。

I see that no system classes are not passed to transform.

有没有办法修改系统类？在此先感谢！

Is there any way to modify system classes? Thanks in advance!

推荐答案

在调用pre-main方法和ClassFileTransformer之前，已经加载了一些（并非所有）系统类被添加。如果你想要转换这些类，你可以在添加ClassFileTransformer之后调用Instrumentation #reversformClasses（Instrumentation＃getAllLoadedClasses（））之类的东西。注意，您必须使用Instrumentation＃addTransformer（ClassFileTransformer，true）来指示您的变换器支持重新转换类。

Some (not all) system classes are already loaded before the pre-main method is invoked and your ClassFileTransformer is added. If you want to transform these classes as well, you can invoke something like Instrumentation#retransformClasses(Instrumentation#getAllLoadedClasses()) after adding your ClassFileTransformer. Note, you have to use Instrumentation#addTransformer(ClassFileTransformer, true) to indicate that your transformer supports retransformation of classes.

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