Java中,将ResultSet映射为对象和队列及其他辅助函数

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;
    }