public class DAO {

    // INSERT, UPDATE, DELETE 操作都可以包含在其中

    public void update(String sql, Object... args) {

        Connection conn = null;

        PreparedStatement ps = null;

        try {

            conn = JDBCTools.getConnection();

            ps = conn.prepareStatement(sql);

            for (int i = 0; i < args.length; i++) {

                ps.setObject(i + 1, args[i]);

            }

            ps.executeUpdate();

        } catch (Exception e) {

            e.printStackTrace();

        } finally {

            JDBCTools.close(null, ps, conn);

        }

    }

    // 查询一条记录, 返回对应的对象

    public <T> T get(Class<T> clazz, String sql, Object... args) {

        T entity = null;

        // 1获取Connection

        Connection conn = null;

        // 2 获取PreparedStatement

        PreparedStatement ps = null;

        // 3填充占位符

        ResultSet rs = null;

        try {

            conn = JDBCTools.getConnection();

            ps = conn.prepareStatement(sql);

            for (int i = 0; i < args.length; i++) {

                ps.setObject(i + 1, args[i]);

            }

            // 4 进行查询得到rs

            rs = ps.executeQuery();

            // 5若 ResultSet中有记录，

            // 准备一个MAP 键：存放列的别名，值：存放列的值

            Map<String, Object> values = new HashMap<String, Object>();

            // 6得到ResultSetMetaData对象

            ResultSetMetaData rmsd = rs.getMetaData();

            // 7处理ResultSet，把指针向下移动一个单位

            if (rs.next()) {

                // 8 由ResultSetMetaData 对象得到结果集中有多少列

                for (int i = 0; i < rmsd.getColumnCount(); i++) {

                    // 9由ResultSetMetaData得到每一列的别名，由rs得到每一列的值

                    String columnLabel = rmsd.getColumnLabel(i + 1);

                    Object columnValue = rs.getObject(i + 1);

                    // 10 填充Map

                    values.put(columnLabel, columnValue);

                }

            }

            if (values.size() > 0) {

                // 11 用反射创建Class对应的对象

                entity = clazz.newInstance();

                // 12 遍历Map对象，用反射填充对象的属性值：

                // 属性名为Map中的key 属性值为Map中的value

                for (Map.Entry<String, Object> map : values.entrySet()) {

                    String fieldName = map.getKey();

                    Object fieldValue = map.getValue();

                    BeanUtils.setProperty(entity, fieldName, fieldValue);

                }

            }

        } catch (Exception e) {

            e.printStackTrace();

        } finally {

            JDBCTools.close(rs, ps, conn);

        }

        return entity;

    }

}

public class DAOTest {

    DAO dao = new DAO();

    @Test

    public void testUpdate() {

        String sql = "INSERT INTO customers(name,email,birth)VALUES(?,?,?)";

        dao.update(sql, "XiaoWang", "XiaoWang@guigu.com", new Date(

                new java.util.Date().getTime()));

    }

    @Test

    public void testGet() {

        String sql="SELECT flow_id flowId, type, id_card iDCard, "

                + "exam_card examCard, student_name studentName, "

                + "location, grade " + "FROM examstudent WHERE flow_id = ?";

        Student stu=dao.get(Student.class, sql, 9);

        System.out.println(stu);

    }

}