java - 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事情，但是 java 代理(用 -javaagent 指定)是否在单独的线程中运行？我读过 a Java agent is a pluggable library that runs embedded in a JVM and intercepts the classloading process ，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；没有单独的线程)？

再一次，我觉得我应该能够弄清楚，但是对我好一点，我工作太努力了，我的大脑有点炸了:P

谢谢!

Answer 1

ClassFileTransformer 被 ClassLoader 调用。对您链接的文章中的变压器进行一点修改，看起来像这样:

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)