JDBC 元数据信息

java.sql.Connection conn = JdbcUtils.getConnection();
		DatabaseMetaData dbmd = conn.getMetaData();
		System.out.println("db name: " + dbmd.getDatabaseProductName());
		System.out.println("tx: " + dbmd.supportsTransactions());
		conn.close();

通过conn.getMetaData()方法可以获取数据库的信息,如产品名称,是否支持事务等等

public class ParameterMetaTest {

	/**
	 * @param args
	 * @throws SQLException
	 */
	public static void main(String[] args) throws SQLException {
		Object[] params = new Object[] { "lisi", 100f };
		read("select * from user where name=? and  money > ?", params);
	}

	static void read(String sql, Object[] params) throws SQLException {
		Connection conn = null;
		PreparedStatement ps = null;
		ResultSet rs = null;
		try {
			conn = JdbcUtils.getConnection();
			ps = conn.prepareStatement(sql);
 			ParameterMetaData pmd = ps.getParameterMetaData();
 			int count = pmd.getParameterCount();
			for (int i = 1; i <= count; i++) {
				// System.out.print(pmd.getParameterClassName(i) + "\t");
				// System.out.print(pmd.getParameterType(i) + "\t");
				// System.out.println(pmd.getParameterTypeName(i));
				ps.setObject(i, params[i - 1]);
			}

			rs = ps.executeQuery();

			while (rs.next()) {
				System.out.println(rs.getInt("id") + "\t"
						+ rs.getString("name") + "\t" + rs.getDate("birthday")
						+ "\t" + rs.getFloat("money"));
			}

		} finally {
			JdbcUtils.free(rs, ps, conn);
		}
	}

}

参数的元数据信息,可以利用

ParameterMetaData pmd = ps.getParameterMetaData();
 			int count = pmd.getParameterCount();

获取sql的参数个数,以及各个参数的详细信息,然后使用一个Object[]数组传递参数,使得查询更加灵活,只需要传入sql语句和参数数组

public class ResultSetMetaDataTest {

	/**
	 * @param args
	 * @throws SQLException
	 */
	public static void main(String[] args) throws SQLException {
		List<Map<String, Object>> datas = read("select id, name as n from user where id < 5");
		System.out.println(datas);
	}

	static List<Map<String, Object>> read(String sql) throws SQLException {
		Connection conn = null;
		PreparedStatement ps = null;
		ResultSet rs = null;
		try {
			conn = JdbcUtils.getConnection();
			ps = conn.prepareStatement(sql);
			rs = ps.executeQuery();
			ResultSetMetaData rsmd = rs.getMetaData();
			int count = rsmd.getColumnCount();
			String[] colNames = new String[count];
			for (int i = 1; i <= count; i++) {
				// System.out.print(rsmd.getColumnClassName(i) + "\t");
				// System.out.print(rsmd.getColumnName(i) + "\t");
				// System.out.println(rsmd.getColumnLabel(i));
				colNames[i - 1] = rsmd.getColumnLabel(i);//rsmd.getColumnLabel的index从1开始
			}
			List<Map<String, Object>> datas = new ArrayList<Map<String, Object>>();

			while (rs.next()) {
				Map<String, Object> data = new HashMap<String, Object>();
				for (int i = 0; i < colNames.length; i++) {
					data.put(colNames[i], rs.getObject(colNames[i]));
				}
				datas.add(data);
			}
			return datas;
		} finally {
			JdbcUtils.free(rs, ps, conn);
		}
	}

}

利用结果集元数据将查询结果封装为map,再使用一个List将Map封装,即可实现结果集的查询