用jdbc向数据库插入数据后获取生成的主键值

public Integer addClass(ClassEntity classEntity) {
Connection conn=null;
PreparedStatement preparedStatement=null;
ResultSet resultSet=null;
Integer id=null;
try {
conn=DBUtils.getConn();
//在preparedstatement里加入statement.RETURN_GENERATED_KEYS参数，代表需要获取自增主键值
preparedStatement=conn.prepareStatement("insert into class (name,sid)values(?,?)",**Statement.RETURN_GENERATED_KEYS**);
preparedStatement.setString(1, classEntity.getName());
preparedStatement.setInt(2, 1);
//在这里必须先提交修改，然后再获取主键，否则会报空指针异常
preparedStatement.executeUpdate();
resultSet=preparedStatement.getGeneratedKeys();
if(resultSet.next()){
id=resultSet.getInt(1);
}
return id;
} catch (SQLException e) {
e.printStackTrace();
throw new DaoException(e.getMessage(),e);
}finally{
DBUtils.closeConnection(conn);
}
}