如何封装一个数据库查询,并把结果返回给调用者

/**
	 * 查询一个sql语句.结果返回一个list集合
	 * @param sql
	 * @return
	 * @throws SQLException
	 */
	public List query(String sql) throws SQLException {
		List list = new ArrayList();
		Connection conn = null;
		PreparedStatement ps = null;
		ResultSet rs = null;
		Map map = null;
		try {
			//得到数据库连接
			conn = JdbcUtils.getConnection();

			//创建查询语句
			ps = conn.prepareStatement(sql);

			//得到ResultSetMetaData对象,从而获得结果集的所有信息,包括每一列的label
			ResultSetMetaData rmd = ps.getMetaData();
			int count = rmd.getColumnCount();
			String label[] = new String[count];

			for (int i = 1; i <= count; i++) {
				label[i - 1] = rmd.getColumnLabel(i);
			}

			//执行sql语句
			rs = ps.executeQuery();

			//遍历每一行数据
			while (rs.next()) {
				map = new HashMap();
				//处理一行数据,把列名和数据作为key,value存到map集合中
				for (int i = 0; i < count; i++)
					map.put(label[i], rs.getObject(label[i]));

				//每一行数据作为一个对象添加到list集合中,返回给调用者
				list.add(map);
			}
			//list的size()代表结果返回多少行数据
			return list;
		} finally {
			//关闭资源
			JdbcUtils.close(conn, ps, rs);
		}
	}

封装数据库连接和关闭的工具类

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public final class JdbcUtils {
	private static final String url = 
			"jdbc:mysql://localhost:3306/struct?user=root&password=root";

	static {
		try {
			Class.forName("com.mysql.jdbc.Driver");
		} catch (ClassNotFoundException e) {

			throw new ExceptionInInitializerError(e);
		}
	}

	// 获得数据库连接
	public static Connection getConnection() throws SQLException {
		return DriverManager.getConnection(url);
	}

	// 关闭数据库连接
	public static void close(Connection conn, Statement stmt, ResultSet rs)
			throws SQLException {
		try {
			if (rs != null)
				rs.close();
		} finally {
			try {
				if (stmt != null)
					stmt.close();
			} finally {
				if (conn != null)
					conn.close();
			}

		}

	}
}