JDBC（一）（3）-阿里云开发者社区

JDBC（一）（2）+https://developer.aliyun.com/article/1556652

3.5 实操

代码结构：

util/JDBCUtils.java

package com.atguigu3.util;
/**
 * 
 * @Description 操作数据库的工具类
 * @author shkstart Email:shkstart@126.com
 * @version
 * @date 上午9:10:02
 *
 */
public class JDBCUtils {
  
  /**
   * 
   * @Description 获取数据库的连接
   * @author shkstart
   * @date 上午9:11:23
   * @return
   * @throws Exception
   */
  public static Connection getConnection() throws Exception {
    // 1.读取配置文件中的4个基本信息
    InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("jdbc.properties");
    Properties pros = new Properties();
    pros.load(is);
    String user = pros.getProperty("user");
    String password = pros.getProperty("password");
    String url = pros.getProperty("url");
    String driverClass = pros.getProperty("driverClass");
    // 2.加载驱动
    Class.forName(driverClass);
    // 3.获取连接
    Connection conn = DriverManager.getConnection(url, user, password);
    return conn;
  }
  /**
   * 
   * @Description 关闭连接和Statement的操作
   * @author shkstart
   * @date 上午9:12:40
   * @param conn
   * @param ps
   */
  public static void closeResource(Connection conn,Statement ps){
    try {
      if(ps != null)
        ps.close();
    } catch (SQLException e) {
      e.printStackTrace();
    }
    try {
      if(conn != null)
        conn.close();
    } catch (SQLException e) {
      e.printStackTrace();
    }
  }
  /**
   * 
   * @Description 关闭资源操作
   * @author shkstart
   * @date 上午10:21:15
   * @param conn
   * @param ps
   * @param rs
   */
  public static void closeResource(Connection conn,Statement ps,ResultSet rs){
    try {
      if(ps != null)
        ps.close();
    } catch (SQLException e) {
      e.printStackTrace();
    }
    try {
      if(conn != null)
        conn.close();
    } catch (SQLException e) {
      e.printStackTrace();
    }
    try {
      if(rs != null)
        rs.close();
    } catch (SQLException e) {
      e.printStackTrace();
    }
  }
}

bean/Customer.java

package com.atguigu3.bean;
import java.sql.Date;
/*
 * ORM编程思想  （object relational mapping）
 * 一个数据表对应一个java类
 * 表中的一条记录对应java类的一个对象
 * 表中的一个字段对应java类的一个属性
 * 
 */
public class Customer {
  
  private int id;
  private String name;
  private String email;
  private Date birth;
    //这里有参构造、无参构造、get、set、toString方法省略了。。。
}

bean/Order.java

package com.atguigu3.bean;
import java.sql.Date;
public class Order {
  private int orderId;
  private String orderName;
  private Date orderDate;
    //这里有参构造、无参构造、get、set、toString方法省略了。。。  
}

CustomerForQuery.java

package com.atguigu3.preparedstatement.crud;
import com.atguigu3.bean.Customer;
import com.atguigu3.util.JDBCUtils;
/**
 * 
 * @Description 针对于Customers表的查询操作
 * @author shkstart  Email:shkstart@126.com
 * @version 
 * @date 上午10:04:55
 *
 */
public class CustomerForQuery {
  
  @Test
  public void testQueryForCustomers(){
    String sql = "select id,name,birth,email from customers where id = ?";
    Customer customer = queryForCustomers(sql, 13);
    System.out.println(customer);
    
    sql = "select name,email from customers where name = ?";
    Customer customer1 = queryForCustomers(sql,"周杰伦");
    System.out.println(customer1);
  }
  
  /**
   * 
   * @Description 针对于customers表的通用的查询操作
   * @author shkstart
   * @throws Exception 
   * @date 上午10:23:40
   */
  public Customer queryForCustomers(String sql,Object...args){
    Connection conn = null;
    PreparedStatement ps = null;
    ResultSet rs = null;
    try {
      conn = JDBCUtils.getConnection();
      
      ps = conn.prepareStatement(sql);
      for(int i = 0;i < args.length;i++){
        ps.setObject(i + 1, args[i]);
      }
      
      rs = ps.executeQuery();
      //获取结果集的元数据 :ResultSetMetaData
      ResultSetMetaData rsmd = rs.getMetaData();
      //通过ResultSetMetaData获取结果集中的列数
      int columnCount = rsmd.getColumnCount();
      
      if(rs.next()){
        Customer cust = new Customer();
        //处理结果集一行数据中的每一个列
        for(int i = 0;i <columnCount;i++){
          //获取列值
          Object columValue = rs.getObject(i + 1);
          
          //获取每个列的列名
//          String columnName = rsmd.getColumnName(i + 1);
          String columnLabel = rsmd.getColumnLabel(i + 1);
          
          //给cust对象指定的columnName属性，赋值为columValue：通过反射
          Field field = Customer.class.getDeclaredField(columnLabel);
          field.setAccessible(true);
          field.set(cust, columValue);
        }
        return cust;
      }
    } catch (Exception e) {
      e.printStackTrace();
    }finally{
      JDBCUtils.closeResource(conn, ps, rs);
      
    }
    
    return null;
  }
  
  
  @Test
  public void testQuery1() {
    Connection conn = null;
    PreparedStatement ps = null;
    ResultSet resultSet = null;
    try {
      conn = JDBCUtils.getConnection();
      String sql = "select id,name,email,birth from customers where id = ?";
      ps = conn.prepareStatement(sql);
      ps.setObject(1, 1);
      
      //执行,并返回结果集
      resultSet = ps.executeQuery();
      //处理结果集
      if(resultSet.next()){//next():判断结果集的下一条是否有数据，如果有数据返回true,并指针下移；如果返回false,指针不会下移。
        
        //获取当前这条数据的各个字段值
        int id = resultSet.getInt(1);
        String name = resultSet.getString(2);
        String email = resultSet.getString(3);
        Date birth = resultSet.getDate(4);
        
      //方式一：
//      System.out.println("id = " + id + ",name = " + name + ",email = " + email + ",birth = " + birth);
        
      //方式二：
//      Object[] data = new Object[]{id,name,email,birth};
        //方式三：将数据封装为一个对象（推荐）
        Customer customer = new Customer(id, name, email, birth);
        System.out.println(customer);
        
      }
    } catch (Exception e) {
      e.printStackTrace();
    }finally{
      //关闭资源
      JDBCUtils.closeResource(conn, ps, resultSet);
      
    }
  }
  
}

OrderForQuery.java

package com.atguigu3.preparedstatement.crud;
import com.atguigu3.bean.Order;
import com.atguigu3.util.JDBCUtils;
/**
 * 
 * @Description 针对于Order表的通用的查询操作
 * @author shkstart  Email:shkstart@126.com
 * @version 
 * @date 上午10:43:58
 *
 */
public class OrderForQuery {
  /*
   * 针对于表的字段名与类的属性名不相同的情况：
   * 1. 必须声明sql时，使用类的属性名来命名字段的别名
   * 2. 使用ResultSetMetaData时，需要使用getColumnLabel()来替换getColumnName(),
   *    获取列的别名。
   *  说明：如果sql中没有给字段其别名，getColumnLabel()获取的就是列名
   * 
   * 
   */
  @Test
  public void testOrderForQuery(){
    String sql = "select order_id orderId,order_name orderName,order_date orderDate from `order` where order_id = ?";
    Order order = orderForQuery(sql,1);
    System.out.println(order);
  }
  
  /**
   * 
   * @Description 通用的针对于order表的查询操作
   * @author shkstart
   * @date 上午10:51:12
   * @return
   * @throws Exception 
   */
  public Order orderForQuery(String sql,Object...args){
    
    Connection conn = null;
    PreparedStatement ps = null;
    ResultSet rs = null;
    try {
      conn = JDBCUtils.getConnection();
      ps = conn.prepareStatement(sql);
      for(int i = 0;i < args.length;i++){
        ps.setObject(i + 1, args[i]);
      }
      
      //执行，获取结果集
      rs = ps.executeQuery();
      //获取结果集的元数据
      ResultSetMetaData rsmd = rs.getMetaData();
      //获取列数
      int columnCount = rsmd.getColumnCount();
      if(rs.next()){
        Order order = new Order();
        for(int i = 0;i < columnCount;i++){
          //获取每个列的列值:通过ResultSet
          Object columnValue = rs.getObject(i + 1);
          //通过ResultSetMetaData
          //获取列的列名：getColumnName() --不推荐使用
          //获取列的别名：getColumnLabel()
//          String columnName = rsmd.getColumnName(i + 1);
          String columnLabel = rsmd.getColumnLabel(i + 1);
          
          //通过反射，将对象指定名columnName的属性赋值为指定的值columnValue
          Field field = Order.class.getDeclaredField(columnLabel);
          field.setAccessible(true);
          field.set(order, columnValue);
        }
        
        return order;
      }
    } catch (Exception e) {
      e.printStackTrace();
    }finally{
      
      JDBCUtils.closeResource(conn, ps, rs);
    }
    
    return null;  
  }
  
  
  @Test
  public void testQuery1(){
    
    Connection conn = null;
    PreparedStatement ps = null;
    ResultSet rs = null;
    try {
      conn = JDBCUtils.getConnection();
      String sql = "select order_id,order_name,order_date from `order` where order_id = ?";
      ps = conn.prepareStatement(sql);
      ps.setObject(1, 1);
      
      rs = ps.executeQuery();
      if(rs.next()){
        int id = (int) rs.getObject(1);
        String name = (String) rs.getObject(2);
        Date date = (Date) rs.getObject(3);
        
        Order order = new Order(id, name, date);
        System.out.println(order);
      }
    } catch (Exception e) {
      e.printStackTrace();
    }finally{
      
      JDBCUtils.closeResource(conn, ps, rs);
    }
    
  }
  
}

PreparedStatementQueryTest.java

package com.atguigu3.preparedstatement.crud;
import com.atguigu3.bean.Customer;
import com.atguigu3.bean.Order;
import com.atguigu3.util.JDBCUtils;
/**
 * 
 * @Description 使用PreparedStatement实现针对于不同表的通用的查询操作
 * @author shkstart Email:shkstart@126.com
 * @version
 * @date 上午11:32:55
 *
 */
public class PreparedStatementQueryTest {
  
  @Test
  public void testGetForList(){
    
    String sql = "select id,name,email from customers where id < ?";
    List<Customer> list = getForList(Customer.class,sql,12);
    list.forEach(System.out::println);
    
    String sql1 = "select order_id orderId,order_name orderName from `order`";
    List<Order> orderList = getForList(Order.class, sql1);
    orderList.forEach(System.out::println);
  }
  
  public <T> List<T> getForList(Class<T> clazz,String sql, Object... args){
    Connection conn = null;
    PreparedStatement ps = null;
    ResultSet rs = null;
    try {
      conn = JDBCUtils.getConnection();
      ps = conn.prepareStatement(sql);
      for (int i = 0; i < args.length; i++) {
        ps.setObject(i + 1, args[i]);
      }
      rs = ps.executeQuery();
      // 获取结果集的元数据 :ResultSetMetaData
      ResultSetMetaData rsmd = rs.getMetaData();
      // 通过ResultSetMetaData获取结果集中的列数
      int columnCount = rsmd.getColumnCount();
      //创建集合对象
      ArrayList<T> list = new ArrayList<T>();
      while (rs.next()) {
        T t = clazz.newInstance();
        // 处理结果集一行数据中的每一个列:给t对象指定的属性赋值
        for (int i = 0; i < columnCount; i++) {
          // 获取列值
          Object columValue = rs.getObject(i + 1);
          // 获取每个列的列名
          // String columnName = rsmd.getColumnName(i + 1);
          String columnLabel = rsmd.getColumnLabel(i + 1);
          // 给t对象指定的columnName属性，赋值为columValue：通过反射
          Field field = clazz.getDeclaredField(columnLabel);
          field.setAccessible(true);
          field.set(t, columValue);
        }
        list.add(t);
      }
      
      return list;
    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      JDBCUtils.closeResource(conn, ps, rs);
    }
    return null;
  }
  
  @Test
  public void testGetInstance(){
    String sql = "select id,name,email from customers where id = ?";
    Customer customer = getInstance(Customer.class,sql,12);
    System.out.println(customer);
    
    String sql1 = "select order_id orderId,order_name orderName from `order` where order_id = ?";
    Order order = getInstance(Order.class, sql1, 1);
    System.out.println(order);
  }
  /**
   * 
   * @Description 针对于不同的表的通用的查询操作，返回表中的一条记录
   * @author shkstart
   * @date 上午11:42:23
   * @param clazz
   * @param sql
   * @param args
   * @return
   */
  public <T> T getInstance(Class<T> clazz,String sql, Object... args) {
    Connection conn = null;
    PreparedStatement ps = null;
    ResultSet rs = null;
    try {
      conn = JDBCUtils.getConnection();
      ps = conn.prepareStatement(sql);
      for (int i = 0; i < args.length; i++) {
        ps.setObject(i + 1, args[i]);
      }
      rs = ps.executeQuery();
      // 获取结果集的元数据 :ResultSetMetaData
      ResultSetMetaData rsmd = rs.getMetaData();
      // 通过ResultSetMetaData获取结果集中的列数
      int columnCount = rsmd.getColumnCount();
      if (rs.next()) {
        T t = clazz.newInstance();
        // 处理结果集一行数据中的每一个列
        for (int i = 0; i < columnCount; i++) {
          // 获取列值
          Object columValue = rs.getObject(i + 1);
          // 获取每个列的列名
          // String columnName = rsmd.getColumnName(i + 1);
          String columnLabel = rsmd.getColumnLabel(i + 1);
          // 给t对象指定的columnName属性，赋值为columValue：通过反射
          Field field = clazz.getDeclaredField(columnLabel);
          field.setAccessible(true);
          field.set(t, columValue);
        }
        return t;
      }
    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      JDBCUtils.closeResource(conn, ps, rs);
    }
    return null;
  }
}

PreparedStatementUpdateTest.java

package com.atguigu3.preparedstatement.crud;
import com.atguigu1.connection.ConnectionTest;
import com.atguigu3.util.JDBCUtils;
/*
 * 使用PreparedStatement来替换Statement,实现对数据表的增删改操作
 * 
 * 增删改；查
 * 
 * 
 */
public class PreparedStatementUpdateTest {
  
  @Test
  public void testCommonUpdate(){
//    String sql = "delete from customers where id = ?";
//    update(sql,3);
    
    String sql = "update `order` set order_name = ? where order_id = ?";
    update(sql,"DD","2");
    
  }
  
  //通用的增删改操作
  public void update(String sql,Object ...args){//sql中占位符的个数与可变形参的长度相同！
    Connection conn = null;
    PreparedStatement ps = null;
    try {
      //1.获取数据库的连接
      conn = JDBCUtils.getConnection();
      //2.预编译sql语句，返回PreparedStatement的实例
      ps = conn.prepareStatement(sql);
      //3.填充占位符
      for(int i = 0;i < args.length;i++){
        ps.setObject(i + 1, args[i]);//小心参数声明错误！！
      }
      //4.执行
      ps.execute();
    } catch (Exception e) {
      e.printStackTrace();
    }finally{
      //5.资源的关闭
      JDBCUtils.closeResource(conn, ps);
      
    }
    
    
  }
  
  //修改customers表的一条记录
  @Test
  public void testUpdate(){
    Connection conn = null;
    PreparedStatement ps = null;
    try {
      //1.获取数据库的连接
      conn = JDBCUtils.getConnection();
      //2.预编译sql语句，返回PreparedStatement的实例
      String sql = "update customers set name = ? where id = ?";
      ps = conn.prepareStatement(sql);
      //3.填充占位符
      ps.setObject(1,"莫扎特");
      ps.setObject(2, 18);
      //4.执行
      ps.execute();
    } catch (Exception e) {
      e.printStackTrace();
    }finally{
      //5.资源的关闭
      JDBCUtils.closeResource(conn, ps);
      
    }
  }
  
  // 向customers表中添加一条记录
  @Test
  public void testInsert() {
    Connection conn = null;
    PreparedStatement ps = null;
    try {
      // 1.读取配置文件中的4个基本信息
      InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("jdbc.properties");
      Properties pros = new Properties();
      pros.load(is);
      String user = pros.getProperty("user");
      String password = pros.getProperty("password");
      String url = pros.getProperty("url");
      String driverClass = pros.getProperty("driverClass");
      // 2.加载驱动
      Class.forName(driverClass);
      // 3.获取连接
      conn = DriverManager.getConnection(url, user, password);
      
//    System.out.println(conn);
      
      //4.预编译sql语句，返回PreparedStatement的实例
      String sql = "insert into customers(name,email,birth)values(?,?,?)";//?:占位符
      ps = conn.prepareStatement(sql);
      //5.填充占位符
      ps.setString(1, "哪吒");
      ps.setString(2, "nezha@gmail.com");
      SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
      java.util.Date date = sdf.parse("1000-01-01");
      ps.setDate(3, new Date(date.getTime()));
      
      //6.执行操作
      ps.execute();
    } catch (Exception e) {
      e.printStackTrace();
    }finally{
      //7.资源的关闭
      try {
        if(ps != null)
          ps.close();
      } catch (SQLException e) {
        e.printStackTrace();
      }
      try {
        if(conn != null)
          conn.close();
      } catch (SQLException e) {
        e.printStackTrace();
      }
      
    }
    
  }
}

练习

练习题1：从控制台向数据库的表customers中插入一条数据，表结构如下：

代码结构如下：

Exer1Test.java

package com.atguigu4.exer;
import com.atguigu3.util.JDBCUtils;
//课后练习1
public class Exer1Test {
  
  @Test
  public void testInsert(){
    Scanner scanner = new Scanner(System.in);
    System.out.print("请输入用户名：");
    String name = scanner.next();
    System.out.print("请输入邮箱：");
    String email = scanner.next();
    System.out.print("请输入生日：");
    String birthday = scanner.next();//'1992-09-08'
    
    String sql = "insert into customers(name,email,birth)values(?,?,?)";
    int insertCount = update(sql,name,email,birthday);
    if(insertCount > 0){
      System.out.println("添加成功");
      
    }else{
      System.out.println("添加失败");
    }
    
  }
  
  
  // 通用的增删改操作
  public int update(String sql, Object... args) {// sql中占位符的个数与可变形参的长度相同！
    Connection conn = null;
    PreparedStatement ps = null;
    try {
      // 1.获取数据库的连接
      conn = JDBCUtils.getConnection();
      // 2.预编译sql语句，返回PreparedStatement的实例
      ps = conn.prepareStatement(sql);
      // 3.填充占位符
      for (int i = 0; i < args.length; i++) {
        ps.setObject(i + 1, args[i]);// 小心参数声明错误！！
      }
      // 4.执行
      /*
       * ps.execute():
       * 如果执行的是查询操作，有返回结果，则此方法返回true;
       * 如果执行的是增、删、改操作，没有返回结果，则此方法返回false.
       */
      //方式一：
//      return ps.execute();
      //方式二：
      return ps.executeUpdate();
    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      // 5.资源的关闭
      JDBCUtils.closeResource(conn, ps);
    }
    return 0;
  }
}

练习题2：创立数据库表 examstudent，表结构如下：

向数据表中添加如下数据：

代码实现1：插入一个新的student 信息

请输入考生的详细信息

Type:

IDCard:

ExamCard:

StudentName:

Location:

Grade:

信息录入成功!

Student.java

package com.atguigu4.exer;
/*
 * Type: 
IDCard:
ExamCard:
StudentName:
Location:
Grade:
 */
public class Student {
  private int flowID;//流水号
  private int type;//考试类型
  private String IDCard;//身份证号
  private String examCard;//准考证号
  private String name;//学生姓名
  private String location;//所在城市
  //这里有参构造、无参构造、get、set、toString方法省略了。。。
}

Exer2Test.java

package com.atguigu4.exer;
import com.atguigu3.util.JDBCUtils;
//课后练习2
public class Exer2Test {
  // 问题1：向examstudent表中添加一条记录
  /*
   *  Type: 
    IDCard:
    ExamCard:
    StudentName:
    Location:
    Grade:
   */
  @Test
  public void testInsert(){
    Scanner scanner = new Scanner(System.in);
    System.out.print("四级/六级：");
    int type = scanner.nextInt();
    System.out.print("身份证号：");
    String IDCard = scanner.next();
    System.out.print("准考证号：");
    String examCard = scanner.next();
    System.out.print("学生姓名：");
    String studentName = scanner.next();
    System.out.print("所在城市：");
    String location = scanner.next();
    System.out.print("考试成绩：");
    int grade = scanner.nextInt();
    
    String sql = "insert into examstudent(type,IDCard,examCard,studentName,location,grade)values(?,?,?,?,?,?)";
    int insertCount = update(sql,type,IDCard,examCard,studentName,location,grade);
    if(insertCount > 0){
      System.out.println("添加成功");
    }else{
      System.out.println("添加失败");
    }
    
    
    
  }
  // 通用的增删改操作
  public int update(String sql, Object... args) {// sql中占位符的个数与可变形参的长度相同！
    Connection conn = null;
    PreparedStatement ps = null;
    try {
      // 1.获取数据库的连接
      conn = JDBCUtils.getConnection();
      // 2.预编译sql语句，返回PreparedStatement的实例
      ps = conn.prepareStatement(sql);
      // 3.填充占位符
      for (int i = 0; i < args.length; i++) {
        ps.setObject(i + 1, args[i]);// 小心参数声明错误！！
      }
      // 4.执行
      /*
       * ps.execute(): 
       * 如果执行的是查询操作，有返回结果，则此方法返回true;
       * 如果执行的是增、删、改操作，没有返回结果，则此方法返回false.
       */
      // 方式一：
      // return ps.execute();
      // 方式二：
      return ps.executeUpdate();
    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      // 5.资源的关闭
      JDBCUtils.closeResource(conn, ps);
    }
    return 0;
  }
}

代码实现2：在 eclipse中建立 java 程序：输入身份证号或准考证号可以查询到学生的基本信息。结果如下：

//问题2：根据身份证号或者准考证号查询学生成绩信息
  @Test
  public void queryWithIDCardOrExamCard(){
    System.out.println("请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 selection = scanner.next();
    if("a".equalsIgnoreCase(selection)){//if(selection.equalsIgnoreCase("a")){
      System.out.println("请输入准考证号：");
      String examCard = scanner.next();
      String sql = "select FlowID flowID,Type type,IDCard,ExamCard examCard,StudentName name,Location location,Grade grade from examstudent where examCard = ?";
      
      Student student = getInstance(Student.class,sql,examCard);
      if(student != null){
        System.out.println(student);
        
      }else{
        System.out.println("输入的准考证号有误！");
      }
      
    }else if("b".equalsIgnoreCase(selection)){
      System.out.println("请输入身份证号：");
      String IDCard = scanner.next();
      String sql = "select FlowID flowID,Type type,IDCard,ExamCard examCard,StudentName name,Location location,Grade grade from examstudent where IDCard = ?";
      
      Student student = getInstance(Student.class,sql,IDCard);
      if(student != null){
        System.out.println(student);
        
      }else{
        System.out.println("输入的身份证号有误！");
      }
    }else{
      System.out.println("您的输入有误，请重新进入程序。");
    }
    
  }
  
  public <T> T getInstance(Class<T> clazz,String sql, Object... args) {
    Connection conn = null;
    PreparedStatement ps = null;
    ResultSet rs = null;
    try {
      conn = JDBCUtils.getConnection();
      ps = conn.prepareStatement(sql);
      for (int i = 0; i < args.length; i++) {
        ps.setObject(i + 1, args[i]);
      }
      rs = ps.executeQuery();
      // 获取结果集的元数据 :ResultSetMetaData
      ResultSetMetaData rsmd = rs.getMetaData();
      // 通过ResultSetMetaData获取结果集中的列数
      int columnCount = rsmd.getColumnCount();
      if (rs.next()) {
        T t = clazz.newInstance();
        // 处理结果集一行数据中的每一个列
        for (int i = 0; i < columnCount; i++) {
          // 获取列值
          Object columValue = rs.getObject(i + 1);
          // 获取每个列的列名
          // String columnName = rsmd.getColumnName(i + 1);
          String columnLabel = rsmd.getColumnLabel(i + 1);
          // 给t对象指定的columnName属性，赋值为columValue：通过反射
          Field field = clazz.getDeclaredField(columnLabel);
          field.setAccessible(true);
          field.set(t, columValue);
        }
        return t;
      }
    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      JDBCUtils.closeResource(conn, ps, rs);
    }
    return null;
  }

代码实现3：完成学生信息的删除功能

//问题3：删除指定的学生信息
  @Test
  public void testDeleteByExamCard(){
    System.out.println("请输入学生的考号：");
    Scanner scanner = new Scanner(System.in);
    String examCard = scanner.next();
    //查询指定准考证号的学生
    String sql = "select FlowID flowID,Type type,IDCard,ExamCard examCard,StudentName name,Location location,Grade grade from examstudent where examCard = ?";
    Student student = getInstance(Student.class,sql,examCard);
    if(student == null){
      System.out.println("查无此人，请重新输入");
    }else{
      String sql1 = "delete from examstudent where examCard = ?";
      int deleteCount = update(sql1, examCard);
      if(deleteCount > 0){
        System.out.println("删除成功");
      }
    }
  }
  //优化以后的操作：
  @Test
  public void testDeleteByExamCard1(){
    System.out.println("请输入学生的考号：");
    Scanner scanner = new Scanner(System.in);
    String examCard = scanner.next();
    String sql = "delete from examstudent where examCard = ?";
    int deleteCount = update(sql, examCard);
    if(deleteCount > 0){
      System.out.println("删除成功");
    }else{
      System.out.println("查无此人，请重新输入");
    }
  }

JDBC（一）（3）

3.5 实操

练习

热门文章

最新文章

相关电子书