▁or ▁E JB ▁be ans . ▁ ▁The ▁ ▁method ▁starts ▁a ▁global ▁transaction ▁and ▁associ ates ▁the ▁transaction ▁with ▁the ▁calling ▁thread . ▁The ▁transaction - to - thread ▁association ▁is ▁managed ▁trans par ently ▁by ▁the ▁Trans action ▁Manager . ▁ ▁Support ▁for ▁nested ▁transactions ▁is ▁not ▁required . ▁The ▁User Transaction . begin ▁method ▁throws ▁the ▁Not Support ed Exception ▁when ▁the ▁calling ▁thread ▁is ▁already ▁associated ▁with ▁a ▁transaction ▁and ▁the ▁transaction ▁manager ▁implementation ▁does ▁not ▁support ▁nested ▁transactions . ▁ ▁Trans action ▁context ▁propag ation ▁between ▁application ▁programs ▁is ▁provided ▁by ▁the ▁underlying ▁transaction ▁manager ▁implementations ▁on ▁the ▁client ▁and ▁server ▁machines . ▁The ▁transaction ▁context ▁format ▁used ▁for ▁propag ation ▁is ▁protocol ▁dependent ▁and ▁must ▁be ▁negoti ated ▁between ▁the ▁client ▁and ▁server ▁hosts . ▁For ▁example , ▁if ▁the ▁transaction ▁manager ▁is ▁an ▁implementation ▁of ▁the ▁J TS ▁specification , ▁it ▁will ▁use ▁the ▁transaction ▁context ▁propag ation ▁format ▁as ▁specified ▁in ▁the ▁C OR BA ▁O TS ▁ 1 . 1 ▁specification . ▁Trans action ▁propag ation ▁is ▁transparent ▁to ▁application ▁programs . ▁ ▁@ Transaction al ▁annotation ▁The ▁ ▁annotation ▁provides ▁the ▁application ▁the ▁ability ▁to ▁control ▁transaction ▁boundaries ▁declar atively . ▁This ▁annotation ▁can ▁be ▁applied ▁to ▁any ▁class ▁that ▁the ▁Java ▁E E ▁specification ▁defines ▁as ▁a ▁managed ▁bean ▁( which ▁includes ▁C DI ▁managed ▁be ans ). ▁ ▁The ▁code ▁sample ▁below ▁illustr ates ▁the ▁usage ▁of ▁@ Transaction al ▁in ▁a ▁request ▁scop ed ▁C DI ▁managed ▁bean : ▁