Mark, On 6/14/13 12:21 PM, Mark Thomas wrote: > On 14/06/2013 16:57, Christopher Schultz wrote: >> Mark, >> >> On 6/14/13 3:16 AM, Mark Thomas wrote: >>> On 14/06/2013 03:31, Christopher Schultz wrote: >>> >>>> It might be nice if this were not a one-of-many decision, but if a >>>> client could choose more than one type. A bit-mask or a list of >>>> scan-types would be nice. I could see the same type of scanner being >>>> used for multiple different purposes. >>> >>> That is what ServletContainerIniiializers are for. >> >> Well, crap. I had never seen those before. >> >> I'm curious, though. Thinking about this the other day with a colleague >> who was complaining about some kind of Spring configuration that >> evidently loaded every class available on the classpath and kept them in >> memory (thus leading to heap and PermGen issues), I concluded that the >> only sane way to do this kind of probing would be to probe everything in >> a ClassLoader that was intended to be discarded after the probing as to >> avoid loading classes unnecessarily. >> >> If an SCI retains a reference to any of the Class objects in the >> Set<Class> parameter, that hypothetical throw-away ClassLoader is no >> longer thrown-away. > > The early Tomcat 7 implementations did it like this - loaded every class > and then examined the class object. More recent implementations use BCEL > to look at the byte code. It is faster and uses less memory. We also use > caching to ensure each class is only processed once.
Cool. What Classloader gets used to actually load the Class objects,
though? In the pathological case of @HandlesType('java.lang.Object')
that means everything gets loaded into .. the WebappClassLoader?
One could imagine a case where an SCI wants to look at everything, but
then only ends up caring about 2% of what's been loaded. Is that just
the price you have to pay for inspecting everything -- that you
seriously waste PermGen? (at least for current Oracle JVMs)
-chris
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