jpa 2 rudimentary tables

i have 2 tables:

a
s_id(key) name cli type

b
sa_id(key) s_id user pwd

so jpa
i have:

@entity
class a...{
   @onetomany(fetch=fetchtype.eager)
    @jointable( name="a_b", 
    joincolumns={@joincolumn(name="a_id", table="a",unique=false)}, 
    inversejoincolumns={@joincolumn(name="b_id", table="b", unique=true)} )
   collection<b> getb(){...}
}

class b only simple entity category anxiety a.

hopefully clear. doubt is: i unequivocally need join list such rudimentary join? can't finished rudimentary joincolumn something?