Re: DatabaseMetaData.getColumns() returns 0 fileds when create a synonym on?

Create synonym doesn't implicitly GRANT select to any user. I don't see any GRANT SELECT
You are also recommended to
a) make sure your synonym names are equal to your table names (or you will end up in a mess)
b) make sure you aren't barking to the wrong tree, by reproducing this behavior in sql*plus

-- 
Sybrand Bakker
Senior Oracle DBA