java代理是否在单独的线程中运行？

Question

我觉得这是我应该知道的,但是java代理(用-javaagent指定)是否在一个单独的线程中运行？我已经读过Java代理是一个可嵌入的库,它运行嵌入在JVM中并拦截了类加载过程,但我想确定:它是否真的拦截它们(这听起来像是在另一个线程中运行并监视类加载)或者它是否由JVM通知(JVM调用它来解析类加载;它没有单独的线程)？

再一次,我觉得我应该能够弄明白,但对我好,我工作太辛苦了,我的大脑有点油炸:P

谢谢!

Answer 1

ClassFoader调用ClassFileTransformer.从链接的文章对变换器进行一点修改,如下所示:

public byte[] transform(ClassLoader loader, String className,
        Class redefiningClass, ProtectionDomain domain, byte[] bytes)
        throws IllegalClassFormatException {
    new RuntimeException("Transformer to Transform Class: " + className)
            .printStackTrace(System.out);
    return bytes;
}

产生这个输出:

java.lang.RuntimeException: Transformer to Transform Class: MyMain
    at com.javalobby.tnt.instrument.SimpleTransformer.transform(SimpleTransformer.java:14)
    at sun.instrument.TransformerManager.transform(Unknown Source)
    at sun.instrument.InstrumentationImpl.transform(Unknown Source)
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClassCond(Unknown Source)
    at java.lang.ClassLoader.defineClass(Unknown Source)
    at java.security.SecureClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.access$000(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)