查询和删除

查询代码：

/**     * MVC: Model View Controller     *      * 把 View 视图(看得见的, 需要进行输入的)、 Model 模型(实际的逻辑代码: Dao 在这一部分)、 Controller     * 控制器(连接视图和模型的代码: 测试方法) 分开     */    @Test    public void testGetStudent() throws SQLException, Exception {        // 1. 获取输入的信息: 可能是一个身份证号也可能是一个准考证号.        String cardId = getCardIdFromConsole();        if (cardId == null) {            return;        }        // 2. 执行查询        Student student = null;        StudentDao studentDao = new StudentDao();        // 准考证号        if (cardId.length() == 15) {            student = studentDao.getByExamCard(cardId);        }        // 身份证号        else {            student = studentDao.getByIdCard(cardId);        }        // 3. 打印学员信息        printStudent(student);    }    private void printStudent(Student student) {        System.out.println("==========查询结果==========");        System.out.println("流水号:" + student.getId());        System.out.println("四级\\六级:" + student.getType());        System.out.println("身份证号:" + student.getIdCard());        System.out.println("准考证号:" + student.getExamCard());        System.out.println("学生姓名:" + student.getStudentName());        System.out.println("区域:" + student.getLocation());        System.out.println("成绩:" + student.getGrade());    }    private String getCardIdFromConsole() {        System.out.println("选择您要输入的类型.");        System.out.println("a:准考证号");        System.out.println("b:身份证号");        Scanner scanner = new Scanner(System.in);        String type = scanner.next();        if (!("a".equals(type) || "b".equals(type))) {            System.out.println("您的输入有误, 请重新进入程序");            return null;        }        if ("a".equals(type)) {            System.out.println("请输入准考证号:");        } else {            System.out.println("请输入身份证号:");        }        return scanner.next();    }

StudentDao.java

public Student getByExamCard(String cardId) throws SQLException, Exception {    //QueryRunner 是线程安全的!    private QueryRunner queryRunner = new QueryRunner();        String sql = "SELECT flow_id id, type, id_card idCard, exam_card examCard, "                + "student_name studentName, location, grade "                + "FROM examstudent "                + "WHERE exam_card = ?";        return queryRunner.query(JdbcUtils.getConnection(), sql, new BeanHandler(Student.class), cardId);    }    public Student getByIdCard(String cardId) throws SQLException, Exception {        //QueryRunner 是线程安全的!    private QueryRunner queryRunner = new QueryRunner();        String sql = "SELECT flow_id id, type, id_card idCard, exam_card examCard, "                + "student_name studentName, location, grade "                + "FROM examstudent "                + "WHERE id_card = ?";        return queryRunner.query(JdbcUtils.getConnection(), sql, new BeanHandler(Student.class), cardId);    }

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删除代码：

@Test    public void testDeleteByExamCard() throws SQLException, Exception {        String examCardId = getExamCardIdFromConsole();        StudentDao2 studentDao = new StudentDao2();        Connection connection = null;        try {            connection = JdbcUtils.getConnection();            // 开启事务            connection.setAutoCommit(false);            int rowNumber = studentDao.deleteByExamCard(connection, examCardId);            if (rowNumber == 1) {                System.out.println("删除成功!");            } else if (rowNumber == 0) {                System.out.println("查无此人, 请重新输入.");            }            // 提交事务            DbUtils.commitAndCloseQuietly(connection);        } catch (Exception e) {            e.printStackTrace();            // 回滚事务            DbUtils.rollbackAndClose(connection);        }    }

StudentDao.java

public int deleteByExamCard(String examCardId) throws SQLException, Exception {        String sql = "DELETE FROM examstudent WHERE exam_card = ?";        //对于 update 而言, 返回值实际上是该条 SQL 语句作用的行数.         //以删除为例, 若删除了 n 行, 则返回值为 n        return queryRunner.update(JdbcUtils.getConnection(), sql, examCardId);    }

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疑问：

    // 问题1: 数据库事务: 如何关闭数据库连接呢 ? 在后面说完数据库事务后来重构代码 ?    // 问题2: 批量处理: 可以同时录入多条记录吗 ? 若录入多条记录, 和录入一条记录有区别吗 ?    // 问题3: 更加通用的 DAO: 适用于更多实体类的 DAO. 需要用到反射技术. 同时使用 DBUtils    // 问题4: 如何向数据表中插入一张图片 ? 以及如何把图片从数据表中获取出来    // 问题5: 数据库连接池