关于对象关系映射(ORM)在数据库访问中用到的最多,在Java中,很多库都试图将一个ResultSet映射为一个自定义的Java Bean对象或队列,下面是我的实现

1 从ResultSet中读取数据

首先是,如何能正确的从ResultSet中读取到自己想要的数据,包括已知列序号和已知列名的情况.

已知列序号,读取ResultSet中的数据值:

public static <T> T ReadValue(Class<T> t, ResultSet set, int columnIndex) throws SQLException;

已知列名,读取 ResultSet中的数据值:

public static <T> T ReadValue(Class<T> t, ResultSet set, Map<String, Integer> columns, String field)

columns中存储这列索引与列名的对应关系,如果该参数为空,则自己创建这样一个队列.

下面是实现

	/**
	 * 取得ResultSet中的值
	 * @param t
	 * @param set
	 * @param columnIndex
	 * @return
	 * @throws SQLException
	 */
	@SuppressWarnings("unchecked")
	public static <T> T ReadValue(Class<T> t, ResultSet set, int columnIndex) throws SQLException {
		if (t == null || set == null) {
			return null;
		}

		if (t == Object.class) {
			return (T)set.getObject(columnIndex);
		}
		if (t == Integer.class) {
			Object val = set.getInt(columnIndex);
			return (T)val;
		}
		if (t == short.class) {
			Object val = set.getShort(columnIndex);
			return (T)val;
		}
		if (t == Boolean.class) {
			Object val = set.getBoolean(columnIndex);
			return (T)val;
		}
		if (t == long.class) {
			Object val = set.getLong(columnIndex);
			return (T)val;
		}
		if (t == float.class) {
			Object val = set.getFloat(columnIndex);
			return (T)val;
		}
		if (t == double.class) {
			Object val = set.getDouble(columnIndex);
			return (T)val;
		}
		if (t == String.class) {
			Object val = set.getString(columnIndex);
			return (T)val;
		}
		if (t == java.sql.Date.class) {
			Object val = set.getDate(columnIndex);
			return (T)val;
		}
		if (t == java.sql.Time.class) {
			Object val = set.getTime(columnIndex);
			return (T)val;
		}
		if (t == java.sql.Timestamp.class) {
			Object val = set.getTimestamp(columnIndex);
			return (T)val;
		}
		if (t == Byte.class) {
			Object val = set.getByte(columnIndex);
			return (T)val;
		}
		return (T)set.getObject(columnIndex);
	}

/**
	 * 取得ResultSet中的值
	 * @param t
	 * @param set
	 * @param columns
	 * @param field
	 * @return
	 * @throws SQLException
	 */
	public static <T> T ReadValue(Class<T> t, ResultSet set, Map<String, Integer> columns, String field) throws SQLException {
		if (columns == null) {
			columns = GetFieldIndex(set);
		}
		if (columns == null) {
			return null;
		}
		if (!columns.containsKey(field)) {
			return null;
		}

		int index = columns.get(field);
		return ReadValue(t, set, index);
	}

	/**
	 * 取得列名对应的列索引
	 * @param set
	 * @return
	 * @throws SQLException
	 */
	public static Map<String, Integer> GetFieldIndex(ResultSet set) throws SQLException {
		if (set == null) {
			return null;
		}
		ResultSetMetaData meta = set.getMetaData();
		if (meta == null) {
			return null;
		}
		Map<String, Integer> map = new HashMap<String, Integer>();
		int count = meta.getColumnCount();
		for (int i = 0; i < count; i++) {
			map.put(meta.getColumnName(i), i);
		}
		return map;
	}

　　其实GetFieldIndex还是可以扩展的,例如包含数据的类型,暂时不需要,也没有进行扩展.

2 数据到对象的映射

下面是数据到对象的映射

接口:

/**
	 * 根据ResultSet装载对象
	 * @param cls
	 * @param t
	 * @param set
	 * @param columns
	 * @return
	 * @throws SQLException
	 */
	public static <T> boolean FillObject(Class<T> cls, T t, ResultSet set, Map<String, Integer> columns) throws SQLException

　实现:

	/**
	 * 根据ResultSet装载对象
	 * @param cls
	 * @param t
	 * @param set
	 * @param columns
	 * @return
	 * @throws SQLException
	 */
	public static <T> boolean FillObject(Class<T> cls, T t, ResultSet set, Map<String, Integer> columns) throws SQLException {
		if (cls == null || t == null || set == null) {
			return false;
		}

		if (columns == null) {
			columns = GetFieldIndex(set);
		}

		final Map<String, Integer> cols = columns;
		return HiCBO.FillObjectEx(t, cls, new IEventRet8Param<Object, String>(){
			@Override
			public final Object OnEvent(String v) {
				try {
				return ReadValue(Object.class, set, cols, v);
				} catch (Exception ex) {
					ex.printStackTrace();
					return null;
				}
			}
		});
	}

/**
	 * 创建并装载对象数据
	 * @param cls
	 * @param set
	 * @return
	 */
	public static <T> T CreateObject(Class<T> cls, ResultSet set, Map<String, Integer> columns) {
		try
		{
			T t = cls.newInstance();
			FillObject(cls, t, set, columns);
			return t;
		} catch (Exception ex) {
			ex.printStackTrace();
			return null;
		}
	}

　　注: CreateObject中,如果T没有默认构造函数,则会存在问题,编译时期不会进行错误提示,这一点需要注意.

取得队列:

/**
	 * 取得Set的列表
	 * @param cls
	 * @param set
	 * @return
	 * @throws SQLException
	 */
	public static <T> List<T> GetResultsList(Class<T> cls, ResultSet set) throws SQLException {
		if (cls == null || set == null) {
			return null;
		}		

		Map<String, Integer> columns = GetFieldIndex(set);
		if (columns == null) {
			return null;
		}
		if (!set.first()) {
			return null;
		}

		List<T> list = new ArrayList<T>();
		T t = GetFirst(cls, set, columns);
		if (t != null) {
			list.add(t);
		}
		while (set.next()) {
			T it = CreateObject(cls, set);
			if (it != null) {
				list.add(it);
			}
		}
		return list;
	}