Java_jdbc 基础笔记之十三 数据库连接（DAO）

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", "[e-mail]", 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);    }}