【JAVA高级】——初识JDBC中DAO数据访问对象

✅作者简介：热爱国学的Java后端开发者，修心和技术同步精进。

本文目录

​​💖 创建表teacher​​

​​💖 封装实体类Teacher​​

​​💖 编写TeacherDaoImpl类​​

​​💖 测试​​

​​✨ 测试增加数据​​

​​✨ 测试删除数据​​

​​✨ 测试修改数据​​

​​✨ 测试查询单个​​

​​✨ 测试查询所有​​

​​💖投票传送门（欢迎小伙伴们投票） ​​

（1）DAO(Data Access Object) ,数据访问对象，是一个数据访问接口，数据访问：顾名思义就是与数据库打交道。夹在业务逻辑与数据库资源中间。其作用就是为了实现功能的模块化，更有利于代码的维护和升级。

（2）之前代码中，业务逻辑代码和对数据库的访问操作代码全部写在一个类中，比较混乱，使用DAO实现业务逻辑与数据库访问相分离。

• 对同一张表的所有操作（增删改查，定义成方法）封装在XxxDaoImpl类中。Xxx表示实体类名
• 根据增删改查的不同功能实现具体的方法（insert、update、delete、select、selectAll）。

💖 创建表teacher

1、创建一张教师表teacher，表的字段如下：

         tid，教师编号，主键、自动增长。

         name，教师姓名，字符串类型、非空。

         age，年龄，int类型、非空。

         bornDate，Date类型

         email，邮箱，字符串类型，非空

         address，住址，字符串类型，非空

CREATE TABLE IF NOT EXISTS `teacher`(
  `tid` INT PRIMARY KEY AUTO_INCREMENT,
  `name` VARCHAR(10) NOT NULL,
  `age` INT NOT NULL,
  `bornDate` DATE,
  `email` VARCHAR(30) NOT NULL,
  `address` VARCHAR(30) NOT NULL
);

2、向teacher表中插入两条数据：

INSERT INTO `teacher` VALUES(1001,'zhangsan',29,'1993-11-26','1319866976@qq.com','安徽合肥蜀山区长江西路132号');
INSERT INTO `teacher` VALUES(1002,'lisi',31,'1991-9-16','147589641@qq.com','安徽合肥新站区环城西路12号');

💖 封装实体类Teacher

创建entity实体类Teacher类，封装属性，添加无参构造方法和有参构造方法，添加getXxx()/setXxx()方法

package com.cxyzxc.examples02;

import java.util.Date;

/**
 * entity实体类Teacher
 * 
 * @author 乐趣国学
 * 
 */
public class Teacher {
  /** 教师编号 */
  private int tid;
  /** 姓名 */
  private String name;
  /** 年龄 */
  private int age;
  /** 出生日期 */
  private Date bornDate;
  /** 邮箱 */
  private String email;
  /** 住址 */
  private String address;

  // 无参构造方法
  public Teacher() {
    super();
  }

  // 有参构造方法
  public Teacher(String name, int age, Date bornDate, String email,
      String address) {
    super();
    this.name = name;
    this.age = age;
    this.bornDate = bornDate;
    this.email = email;
    this.address = address;
  }

  public Teacher(int tid, String name, int age, Date bornDate, String email,
      String address) {
    super();
    this.tid = tid;
    this.name = name;
    this.age = age;
    this.bornDate = bornDate;
    this.email = email;
    this.address = address;
  }

  // getXxx()/setXxx()方法
  public int getTid() {
    return tid;
  }

  public void setTid(int tid) {
    this.tid = tid;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public int getAge() {
    return age;
  }

  public void setAge(int age) {
    this.age = age;
  }

  public Date getBornDate() {
    return bornDate;
  }

  public void setBornDate(Date bornDate) {
    this.bornDate = bornDate;
  }

  public String getEmail() {
    return email;
  }

  public void setEmail(String email) {
    this.email = email;
  }

  public String getAddress() {
    return address;
  }

  public void setAddress(String address) {
    this.address = address;
  }

  // 重写Object类中的toString()方法
  @Override
  public String toString() {
    return "tid=" + tid + ", name=" + name + ", age=" + age + ", bornDate="
        + bornDate + ", email=" + email + ", address=" + address;
  }
}

💖 编写TeacherDaoImpl类

编写TeacherDaoImpl类，提供增删改查方法，使用JDBC完成开发功能。

     （1）该类中提供对teacher表进行增、删、改、查单个、查所有5个方法。
     
     （2）该类中的代码只做数据库访问操作，不做任何业务逻辑操作。
     
     （3）该类只对数据库一张表进行操作，从而实现复用

包的结构如下：

package com.cxyzxc.examples04;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

/**
 * 
 * @author 乐趣国学
 * 
 */
public class TeacherDaoImpl {

  // 新增：向teacher表中插入一条数据（一条数据对应一个Teacher对象）,插入成功，返回一个受影响行数值（int类型）
  public int insert(Teacher teacher) {

    Connection connection = null;
    PreparedStatement preparedStatement = null;
    String sql = "insert into `teacher`(name,age,bornDate,email,address) values(?,?,?,?,?);";

    connection = DBUtils.getConnection();

    try {
      preparedStatement = connection.prepareStatement(sql);
      // 绑定参数，赋值
      preparedStatement.setString(1, teacher.getName());
      preparedStatement.setInt(2, teacher.getAge());
      //将java.util.Date类型日期时间转换为java.sql.Date类型，然后插入到数据库中
      preparedStatement.setDate(3, DateUtils.utilDateToSqlDate(teacher.getBornDate()));
      preparedStatement.setString(4, teacher.getEmail());
      preparedStatement.setString(5, teacher.getAddress());
      // 执行SQL语句，返回受影响的行数值
      int result = preparedStatement.executeUpdate();
      // 将结果返回给调用者
      return result;
    } catch (SQLException e) {
      e.printStackTrace();
    } finally {
      DBUtils.closeAll(connection, preparedStatement, null);
    }
    return 0;
  }

  // 删除：根据教师tid删除一条数据,删除成功，返回一个受影响行数值（int类型）
  public int delete(int tid) {

    Connection connection = null;
    PreparedStatement preparedStatement = null;
    String sql = "delete from teacher where tid = ?;";

    connection = DBUtils.getConnection();

    try {
      preparedStatement = connection.prepareStatement(sql);
      // 绑定参数，赋值
      preparedStatement.setInt(1, tid);
      // 执行SQL语句，返回受影响的行数值
      int result = preparedStatement.executeUpdate();
      // 将结果返回给调用者
      return result;
    } catch (SQLException e) {
      e.printStackTrace();
    } finally {
      DBUtils.closeAll(connection, preparedStatement, null);
    }
    return 0;
  }

  // 修改：修改teacher表中的数据，可能对任意的一个字段进行修改，所以方法中直接传递一个对象进行修改,修改成功，返回一个受影响行数值（int类型）
  public int update(Teacher teacher) {

    Connection connection = null;
    PreparedStatement preparedStatement = null;
    String sql = "update teacher set name = ?,age = ?,bornDate = ?,email = ?,address = ? where tid = ?;";

    connection = DBUtils.getConnection();

    try {
      preparedStatement = connection.prepareStatement(sql);
      // 绑定参数，赋值
      preparedStatement.setString(1, teacher.getName());
      preparedStatement.setInt(2, teacher.getAge());
      //将java.util.Date类型日期时间转换为java.sql.Date类型，然后插入到数据库中
      preparedStatement.setDate(3, DateUtils.utilDateToSqlDate(teacher.getBornDate()));
      preparedStatement.setString(4, teacher.getEmail());
      preparedStatement.setString(5, teacher.getAddress());
      preparedStatement.setInt(6, teacher.getTid());
      // 执行SQL语句，返回受影响的行数值
      int result = preparedStatement.executeUpdate();
      // 将结果返回给调用者
      return result;
    } catch (SQLException e) {
      e.printStackTrace();
    } finally {
      DBUtils.closeAll(connection, preparedStatement, null);
    }
    return 0;
  }

  // 查询单个：根据教师tid查询一条数据，查询成功返回一个结果集（ResultSet类型）,从结果集中取出元素，封装成一个Teacher对象，将该对象返回
  public Teacher select(int tid) {

    Connection connection = null;
    PreparedStatement preparedStatement = null;
    ResultSet resultSet = null;
    Teacher teacher = null;
    String sql = "select * from teacher where tid = ?;";

    connection = DBUtils.getConnection();

    try {
      preparedStatement = connection.prepareStatement(sql);
      // 绑定参数，赋值
      preparedStatement.setInt(1, tid);
      resultSet = preparedStatement.executeQuery();
      // 处理结果集，因为是查询单个数据，所以不需要循环遍历获取数据，集合中有数据就取出来
      if (resultSet.next()) {
        teacher = new Teacher();
        int teacherid = resultSet.getInt("tid");
        String name = resultSet.getString("name");
        int age = resultSet.getInt("age");
        Date bornDate = resultSet.getDate("bornDate");
        String email = resultSet.getString("email");
        String address = resultSet.getString("address");
        // 将获取的赋值给teacher对象
        teacher.setTid(teacherid);
        teacher.setName(name);
        teacher.setAge(age);
        teacher.setBornDate(bornDate);
        teacher.setEmail(email);
        teacher.setAddress(address);
      }
      return teacher;
    } catch (SQLException e) {
      e.printStackTrace();
    } finally {
      DBUtils.closeAll(connection, preparedStatement, null);
    }
    return null;
  }

  // 查询所有：将teacher表中的所有数据全部查询出来，查询成功返回一个结果集（ResultSet类型）,从结果集中取出元素，封装成多个Teacher对象，将多个对象存储在集合中，返回这个集合
  public List<Teacher> selectAll() {

    Connection connection = null;
    PreparedStatement preparedStatement = null;
    ResultSet resultSet = null;
    Teacher teacher = null;
    List<Teacher> teacherList = new ArrayList<Teacher>();
    String sql = "select * from teacher;";

    connection = DBUtils.getConnection();

    try {
      preparedStatement = connection.prepareStatement(sql);
      resultSet = preparedStatement.executeQuery();
      // 查询出来多个结果，存在resultSet结果集中，遍历该结果集
      while (resultSet.next()) {
        int teacherid = resultSet.getInt("tid");
        String name = resultSet.getString("name");
        int age = resultSet.getInt("age");
        Date bornDate = resultSet.getDate("bornDate");
        String email = resultSet.getString("email");
        String address = resultSet.getString("address");
        teacher = new Teacher(teacherid, name, age, bornDate, email,
            address);
        teacherList.add(teacher);
      }
      return teacherList;
    } catch (SQLException e) {
      e.printStackTrace();
    } finally {
      DBUtils.closeAll(connection, preparedStatement, null);
    }
    return null;
  }
}

💖 测试

✨ 测试增加数据

package com.cxyzxc.examples04;

public class TestTeacherInsert {

  public static void main(String[] args) {
    // 创建TteacherDaoImpl类对象
    TeacherDaoImpl teacherDaoImpl = new TeacherDaoImpl();
    //创建字符串类型的日期
    String strDate = "1992-03-22";
    
    // 创建Teacher类对象
    //DateUtils.strDateToUtilDate(strDate)：将字符串类型的日期时间转换为java.util.Date类型
    Teacher teacher = new Teacher("王五", 32, DateUtils.strDateToUtilDate(strDate), "1319866123@qq.com","安徽合肥蜀山区淠河路200号");
    // 将teacher对象插入到数据库teacher表中
    int result = teacherDaoImpl.insert(teacher);
    if (result == 1) {
      System.out.println("数据插入成功");
    } else {
      System.out.println("数据插入失败");
    }
  }
}

✨ 测试删除数据

package com.cxyzxc.examples04;

public class TestTeacherDelete {

  public static void main(String[] args) {
    // 创建TteacherDaoImpl类对象
    TeacherDaoImpl teacherDaoImpl = new TeacherDaoImpl();

    int result = teacherDaoImpl.delete(1003);
    if (result == 1) {
      System.out.println("数据删除成功");
    } else {
      System.out.println("数据删除失败");
    }
  }
}

✨ 测试修改数据

package com.cxyzxc.examples04;

public class TestTeacherUpdate {

  public static void main(String[] args) {
    // 创建TteacherDaoImpl类对象
    TeacherDaoImpl teacherDaoImpl = new TeacherDaoImpl();
    //创建字符串类型日期时间
    String strDate = "2000-03-22";
    
    // 创建Teacher类对象
    //DateUtils.strDateToUtilDate(strDate)：将字符串类型的日期时间转换为java.util.Date类型
    Teacher teacher = new Teacher(1002,"李四", 22, DateUtils.strDateToUtilDate(strDate), "1319869999@qq.com","安徽合肥蜀山区淠河路19号");
    // 将teacher对象插入到数据库teacher表中
    int result = teacherDaoImpl.update(teacher);
    if (result == 1) {
      System.out.println("数据修改成功");
    } else {
      System.out.println("数据修改败");
    }
  }
}

✨ 测试查询单个

package com.cxyzxc.examples04;

public class TeacherSelectOne {

  public static void main(String[] args) {
    // 创建TteacherDaoImpl类对象
    TeacherDaoImpl teacherDaoImpl = new TeacherDaoImpl();

    Teacher teacher = teacherDaoImpl.select(1002);
    if (teacher != null) {
      System.out.println(teacher);
    } else {
      System.out.println("没有这个老师");
    }
  }
}

✨ 测试查询所有

package com.cxyzxc.examples04;

import java.util.List;

public class TeacherSelectAll {

  public static void main(String[] args) {
    // 创建TteacherDaoImpl类对象
    TeacherDaoImpl teacherDaoImpl = new TeacherDaoImpl();

    List<Teacher> teacherList = teacherDaoImpl.selectAll();
    // 遍历teacherList集合
    for (Teacher teacher : teacherList) {
      System.out.println(teacher);
    }
  }
}