第一个MyBatis程序

package com.fly.entity;

import java.math.BigDecimal;

/**
 * 学生实体类：与 student 表一一对应
 */
public class Student {
    private Integer id;
    private String name;
    private Integer age;
    private String major;
    private BigDecimal score;

    // 构造方法
    public Student() {}

    public Student(String name, Integer age, String major, BigDecimal score) {
        this.name = name;
        this.age = age;
        this.major = major;
        this.score = score;
    }

    // Getter / Setter
    public Integer getId() { return id; }
    public void setId(Integer id) { this.id = id; }
    
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    
    public Integer getAge() { return age; }
    public void setAge(Integer age) { this.age = age; }
    
    public String getMajor() { return major; }
    public void setMajor(String major) { this.major = major; }
    
    public BigDecimal getScore() { return score; }
    public void setScore(BigDecimal score) { this.score = score; }

    @Override
    public String toString() {
        return "Student{id=" + id + ", name='" + name + "', age=" + age 
            + ", major='" + major + "', score=" + score + "}";
    }
}

package com.fly.mapper;

import com.fly.entity.Student;
import java.util.List;

/**
 * 学生数据访问接口
 * 方法名与 StudentMapper.xml 中的 id 严格一致
 */
public interface StudentMapper {
    
    /** 根据 ID 查询学生 */
    Student findById(Integer id);
    
    /** 查询所有学生 */
    List<Student> findAll();
    
    /** 新增学生 */
    int insert(Student student);
    
    /** 更新学生信息 */
    int update(Student student);
    
    /** 根据 ID 删除学生 */
    int deleteById(Integer id);
}

package com.fly;

import com.fly.entity.Student;
import com.fly.mapper.StudentMapper;
import com.fly.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;

import java.math.BigDecimal;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        // 1. 查询单条
        System.out.println("========== 1. 查询 ID=1 的学生 ==========");
        try (SqlSession session = MyBatisUtil.getSqlSessionFactory().openSession()) {
            StudentMapper mapper = session.getMapper(StudentMapper.class);
            Student student = mapper.findById(1);
            System.out.println("结果: " + student);
        }

        // 2. 查询全部
        System.out.println("\n========== 2. 查询所有学生 ==========");
        try (SqlSession session = MyBatisUtil.getSqlSessionFactory().openSession()) {
            StudentMapper mapper = session.getMapper(StudentMapper.class);
            List<Student> list = mapper.findAll();
            list.forEach(s -> System.out.println("结果: " + s));
        }

        // 3. 插入
        System.out.println("\n========== 3. 插入新学生 ==========");
        try (SqlSession session = MyBatisUtil.getSqlSessionFactory().openSession()) {
            StudentMapper mapper = session.getMapper(StudentMapper.class);
            Student newbie = new Student("赵六", 23, "人工智能", new BigDecimal("91.00"));
            int rows = mapper.insert(newbie);
            session.commit(); // 必须手动提交！
            System.out.println("影响行数: " + rows + ", 生成主键: " + newbie.getId());
        }

        // 4. 更新
        System.out.println("\n========== 4. 更新学生 ==========");
        try (SqlSession session = MyBatisUtil.getSqlSessionFactory().openSession()) {
            StudentMapper mapper = session.getMapper(StudentMapper.class);
            Student update = new Student("大翔", 23, "计算机科学", new BigDecimal("96.00"));
            update.setId(1);
            int rows = mapper.update(update);
            session.commit();
            System.out.println("影响行数: " + rows);
        }

        // 5. 删除
        System.out.println("\n========== 5. 删除学生 ==========");
        try (SqlSession session = MyBatisUtil.getSqlSessionFactory().openSession()) {
            StudentMapper mapper = session.getMapper(StudentMapper.class);
            int rows = mapper.deleteById(6); // 删除刚插入的赵六
            session.commit();
            System.out.println("影响行数: " + rows);
        }

        // 6. 验证最终状态
        System.out.println("\n========== 6. 验证最终数据 ==========");
        try (SqlSession session = MyBatisUtil.getSqlSessionFactory().openSession()) {
            StudentMapper mapper = session.getMapper(StudentMapper.class);
            List<Student> list = mapper.findAll();
            list.forEach(s -> System.out.println("结果: " + s));
        }
    }
}

package com.fly.util;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;

public class MyBatisUtil {
    private static final SqlSessionFactory sqlSessionFactory;

    static {
        try (InputStream is = Resources.getResourceAsStream("mybatis-config.xml")) {
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
        } catch (IOException e) {
            throw new ExceptionInInitializerError(e);
        }
    }

    public static SqlSessionFactory getSqlSessionFactory() {
        return sqlSessionFactory;
    }
}