泛型BaseDAO

对于属性比较多的bean,如果不使用hibernate 或者ibatis等持久化解决方案，写查询函数时，单单将ResultSet 转换成Object就是一件很痛苦的事情，因此可以采用java反射机制做一个BaseDao，把ResultSet 映射到Object 的操作封装起来，简化了DAO的开发，
本文参照了[url]http://blog.csdn.net/cping1982/archive/2007/10/01/1808647.aspx
[/url]并且做了一点改进


public static String[][] proterty2Column =
    {{"member_id","memberId"},
{"name", "name"}};
/**
* change the first char to upper case
* @param s
* @return
*/
private static String upperFirstChar(String s){
char [] chars = s.toCharArray();
chars[0] = Character.toUpperCase(chars[0]);
return new String(chars);
}
/**
* ResultSet 映射成 Object
* @param clzz
* @param rs
* @param obj
* @param fieldName
* @param varibleName
* @throws NoSuchMethodException
* @throws IllegalAccessException
* @throws InvocationTargetException
* @throws SQLException
* @throws NoSuchFieldException
* @throws SecurityException
*/
    private void  mapResultSet2Object(ResultSet rs, Object obj, String propertyName,
String columName)
throws NoSuchMethodException, IllegalAccessException,
InvocationTargetException, SQLException,
SecurityException, NoSuchFieldException {
    Class < ? extends Object >clazz = obj.getClass();
         Class < ? extends Object >propertyType = clazz.getDeclaredField(propertyName).
getType();
       Method method = clazz.getDeclaredMethod("set"+
     upperFirstChar( propertyName ), new Class[] { propertyType });
       if (propertyType == String.class)
           method.invoke(obj, (Object [])new String[]
{rs.getString( columName ) });
       else if (propertyType == int.class)
           method.invoke(obj, (Object [])new Integer[]
{new Integer( rs.getInt( columName )) });
       else if (propertyType == float.class)
           method.invoke(obj, (Object [])new Float[]
{new Float( rs.getFloat( columName )) });
       else if (propertyType == long.class)
           method.invoke(obj, (Object [])new Long[]
{new Long( rs.getLong( columName )) });
       else if (propertyType == double.class)
           method.invoke(obj, (Object [])new Double[]
{new Double( rs.getDouble( columName )) });
       else if(propertyType == Date.class){
       method.invoke(obj, (Object [])new Date[]
{rs.getDate(columName)});
       }
   }
    /**
     * 单行查询
     * @param
     * @param conn
     * @param sql
     * @param clazz
     * @param params
     * @return
     * @throws Exception
     */
    public  <T> T getItem(Connection conn, String sql, Class<T> clazz,
  String params[])throws Exception{
    PreparedStatement pstmt = null;
    ResultSet rset = null;
    T t  = null;
    try {
    pstmt = conn.prepareStatement(sql);
    //set parameter
               for(int i=0; i<params.length; i++){
    pstmt.setString(i+1, (String)params[i]);
    }
              rset = pstmt.executeQuery();
            if (rset.next()) {
                t =  clazz.newInstance();
    for(int i=0; i< proterty2Column.length; i++) {
                String propertyName = proterty2Column[i][1].trim();
                    String ColumnName = proterty2Column[i][0].trim();
                    mapResultSet2Object(rset, t, propertyName, ColumnName);
                }
            }
        } catch (Exception e) {
        e.printStackTrace();
    } finally {
        DBUtil.closeAll(conn, pstmt, rset);
    }
     return t;
    }

   /**
     * 多行查询
     * @param
     * @param conn
     * @param sql
     * @param proterty2Column
     * @param clazz
     * @return
     * @throws Exception
     */
    public   <T> List <T> getItems(Connection conn, String sql, Class<T> clazz, 
String[] params) throws Exception{
    if (proterty2Column.length == 0)
            return null;
    PreparedStatement pstmt = null;
    ResultSet rset = null;
    List<T> list = new ArrayList<T>();
    try {
    pstmt = conn.prepareStatement(sql);
               for(int i=0; i<params.length; i++){
    pstmt.setString(i+1, (String)params[i]);
    }
    rset = pstmt.executeQuery();
            while (rset.next()) {
    for(int i=0; i< proterty2Column.length; i++) {
                String propertyName = proterty2Column[i][1].trim();
                    String ColumnName = proterty2Column[i][0].trim();
                    fetchResult2Object(rset, obj, propertyName, ColumnName);
                }
                if( null == obj ) continue;
                list.add(obj);
            }
        } catch (Exception e) {
        e.printStackTrace();
    } finally {
        DBUtil.closeAll(conn, pstmt, rset);
    }
     return list;
    }