private static ClassLoader findBootstrapClassLoader() {
        Field bootstrapClassLoader;
        try {
            bootstrapClassLoader = ClassLoader.class.getDeclaredField("bootstrapClassLoader");
        } catch (NoSuchFieldException e) {
            try {
                bootstrapClassLoader = ClassLoader.class.getDeclaredField("systemClassLoader");
            } catch (NoSuchFieldException e2) {
                throw new IllegalStateException("bootstrapClassLoader not found Caused by:" + e.getMessage() + ", and " + e2.getMessage(), e2);
            }
        }
        try {
            bootstrapClassLoader.setAccessible(true);
            return (ClassLoader) bootstrapClassLoader.get(ClassLoader.class);
        } catch (IllegalAccessException e) {
            throw new IllegalStateException("bootstrapClassLoader access fail Caused by:" + e.getMessage(), e);
        }
    }
for ibm j9 jvm

@author Woonduk Kang(emeroad)
agent-module/bootstraps/bootstrap-core/src/main/java/com/navercorp/pinpoint/bootstrap/classloader/J9BootLoader.java