How to Create Readonly User (for specific Schema) in Oracle Database

1) create user bolinf_readonly identified by readonly;

2) select username from dba_users
    where username like '%BOLINF%';

3) grant create session to BOLINF_READONLY

4) grant select any table to BOLINF_READONLY

5) create or replace trigger log_on_after_bolinf
    after logon ON BOLINF_READONLY.SCHEMA
    BEGIN
    EXECUTE IMMEDIATE 'alter session set CURRENT_SCHEMA = BOLINF';
    END;

Enjoy. . . . .
:)