模板模式----JDBC模板

Template Method模式的应用场景是:
1. 你想将相同的算法放在一个类中,将算法变化的部分放在子类中实现。
2. 子类公共的算法应该放在一个公共的类中,避免代码重复。

 

Template Method模式可以限制所留下的虚方法只对其继承类可见,外部使用者不一定能够直接使用这些虚方法。

 

下面是示例代码：

 

public abstract class BaseDao {
   
    /**
     * 增，删，改方法
     * @param sql
     * @param args sql参数
     * @return
     * @throws DaoException
     */ 
    public int update(String sql, Object[] args) throws DaoException { 
        Connection conn = null; 
        PreparedStatement ps = null; 
        ResultSet rs = null; 
        try { 
            conn = JdbcUtils.getConnection(); 
            ps = conn.prepareStatement(sql); 
            for (int i = 0; i < args.length; i++) 
                ps.setObject(i + 1, args[i]); 
            return ps.executeUpdate(); 
        } catch (SQLException e) { 
            throw new DaoException(e.getMessage(), e); 
        } finally { 
            JdbcUtils.free(rs, ps, conn); 
        } 
    } 
 
    /**
     * 返回一个对象
     * @param
     * @param sql
     * @param args
     * @return
     * @throws DaoException
     */ 
    public T find(String sql, Object[] args) throws DaoException { 
        Connection conn = null; 
        PreparedStatement ps = null; 
        ResultSet rs = null; 
        try { 
            conn = JdbcUtils.getConnection(); 
            ps = conn.prepareStatement(sql); 
            for (int i = 0; i < args.length; i++) 
                ps.setObject(i + 1, args[i]); 
            rs = ps.executeQuery(); 
            T t = null; 
            if (rs.next()) { 
                t = rowMapper(rs); 
            } 
            return t; 
        } catch (SQLException e) { 
            throw new DaoException(e.getMessage(), e); 
        } finally { 
            JdbcUtils.free(rs, ps, conn); 
        } 
    } 
 
    /**
     * 返回一个List
     * @param
     * @param sql
     * @param args
     * @return
     * @throws DaoException
     */ 
    public List list(String sql, Object[] args) throws DaoException { 
        Connection conn = null; 
        PreparedStatement ps = null; 
        ResultSet rs = null; 
        try { 
            conn = JdbcUtils.getConnection(); 
            ps = conn.prepareStatement(sql); 
            for (int i = 0; i < args.length; i++) 
                ps.setObject(i + 1, args[i]); 
            rs = ps.executeQuery(); 
            T t = null; 
            List list = new ArrayList(); 
            while (rs.next()) { 
                t = rowMapper(rs); 
                list.add(t); 
            } 
            return list; 
        } catch (SQLException e) { 
            throw new DaoException(e.getMessage(), e); 
        } finally { 
            JdbcUtils.free(rs, ps, conn); 
        } 
    } 
 
    /**
     * rowMapper
     * @param rs
     * @return
     * @throws DaoException
     */
    abstract protected T rowMapper(ResultSet rs) throws DaoException;
}

 

实现类的代码：

 

public class UserDaoImpl extends BaseDao implements UserDao {

    public User findUser(int id) throws DaoException {
        String sql = "select *from t_user where id=?";
        Object[] args = new Object[] { id };
        User user = super.find(sql, args);
        return user;
    }

    public List listUser(String username) throws DaoException {
        String sql = "select *from t_user where username=?";
        Object[] args = new Object[] { username };
        List list = super.list(sql, args);
        for (User u : list) {
            System.out.println(u.getUserId());
        }
        return list;
    }

    @SuppressWarnings("unchecked")
    protected User rowMapper(ResultSet rs) throws DaoException {
        User user = new User();
        try {
            user.setId(rs.getInt("id"));
            user.setUsername(rs.getString("username"));
            user.setBrithday(rs.getDate("brithday"));
        } catch (SQLException e) {
            throw new DaoException(e.getMessage(), e);
        }
        return user;
    }