oralce中隔离机制TRANSACTION_SERIALIZABLE,该如何解决

public class UserDao {    public void get(String username){        Connection conn=null;        try {            conn=OracleConnectionUtil.getConnection();            conn.setAutoCommit(false);            conn.setTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);            PreparedStatement pstat = conn.prepareStatement("select * from user2 where username=?");            pstat.setString(1,username);            ResultSet rs = pstat.executeQuery();            if(rs.next()){                System.out.println(rs.getString(2));            }            rs.close();            pstat.close();            update(username,"2dddddddd");//更新上面查询的字段            conn.commit();        } catch (SQLException e) {            e.printStackTrace();        }finally{            if(conn!=null){                try {                    conn.close();                } catch (SQLException e) {                    e.printStackTrace();                }            }        }    }    public void insert(String username, String password){        Connection conn=null;        try {            conn=OracleConnectionUtil.getConnection();            conn.setAutoCommit(false);            PreparedStatement pstat = conn.prepareStatement("insert into user2 values(?,?)");            pstat.setString(1, username);            pstat.setString(2, password);            pstat.execute();            pstat.close();            conn.commit();        } catch (SQLException e) {                        e.printStackTrace();        }finally{            if(conn!=null){                try {                    conn.close();                } catch (SQLException e) {                    e.printStackTrace();                }            }        }    }    public void update(String username, String password){        Connection conn=null;        try {            conn=OracleConnectionUtil.getConnection();            conn.setAutoCommit(false);            PreparedStatement pstat = conn.prepareStatement("update user2 set password=? where username=?");            pstat.setString(2, username);            pstat.setString(1, password);            pstat.execute();            pstat.close();            conn.commit();        } catch (SQLException e) {                        e.printStackTrace();        }finally{            if(conn!=null){                try {                    conn.close();                } catch (SQLException e) {                    e.printStackTrace();                }            }        }    }    public static void main(String[] args) {        UserDao dao = new UserDao();        dao.get("u1");    }}