question: public Long putClassLoader ( ClassLoader classLoader ) { if ( classLoader == null ) throw new IllegalArgumentException ( "Argument cannot be null - 'classLoader'." ) ; Long previousId = _classLoaderToIdMap . get ( classLoader ) ; if ( previousId != null ) return previousId ; synchronized ( _lock ) { previousId = _classLoaderToIdMap . get ( classLoader ) ; if ( previousId != null ) return previousId ; removeMarkers ( ) ; long id = generateClassLoaderKey ( ) ; if ( _logger . isLoggable ( Level . FINE ) ) _logger . fine ( "introducing new class loader to cache [" + ClassLoaderHelper . getClassLoaderLogName ( classLoader ) + "] to the class provider, class loader designated id is " + id ) ; _classLoaders . put ( id , new ClassLoaderContext ( classLoader , Represent . REGULAR ) ) ; _classLoaderToIdMap . put ( classLoader , id ) ; return id ; } }
target:  Add new class loader to the cache, if the class loader is already present, the existing key will be returned