Executor 执行器类型

package com.fly.entity;

public class Student {
    private Integer id;
    private String name;
    private Integer age;
    private String major;
    private Double score;
    
    public Student() {}
    
    public Student(String name, Integer age, String major, Double score) {
        this.name = name;
        this.age = age;
        this.major = major;
        this.score = score;
    }
    
    // Getter 与Setter 省略
}

package com.fly.demo;

import com.fly.entity.Student;
import com.fly.mapper.StudentMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.ExecutorType;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.InputStream;
import java.util.Arrays;
import java.util.List;

public class ExecutorCompareDemo {
    
    private static SqlSessionFactory sqlSessionFactory;
    
    public static void main(String[] args) throws Exception {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        
        List<Student> students = Arrays.asList(
            new Student("大翔", 22, "计算机科学", 95.5),
            new Student("白歌", 21, "软件工程", 88.0),
            new Student("小崔", 20, "计算机科学", 92.0),
            new Student("黄俪", 21, "信息安全", 90.5),
            new Student("李眉", 22, "软件工程", 87.0)
        );
        
        testSimple(students);
        testReuse(students);
        testBatch(students);
    }
    
    // ========== SIMPLE 执行器 ==========
    static void testSimple(List<Student> students) {
        System.out.println("\n========== SIMPLE 执行器 ==========");
        try (SqlSession session = sqlSessionFactory.openSession(ExecutorType.SIMPLE)) {
            StudentMapper mapper = session.getMapper(StudentMapper.class);
            long start = System.currentTimeMillis();
            
            for (Student s : students) {
                int result = mapper.insertStudent(s);
                System.out.println("插入 " + s.getName() + "，返回：" + result);
            }
            
            session.commit();
            long cost = System.currentTimeMillis() - start;
            System.out.println("SIMPLE 总耗时：" + cost + " ms");
        }
    }
    
    // ========== REUSE 执行器 ==========
    static void testReuse(List<Student> students) {
        System.out.println("\n========== REUSE 执行器 ==========");
        try (SqlSession session = sqlSessionFactory.openSession(ExecutorType.REUSE)) {
            StudentMapper mapper = session.getMapper(StudentMapper.class);
            long start = System.currentTimeMillis();
            
            for (Student s : students) {
                int result = mapper.insertStudent(s);
                System.out.println("插入 " + s.getName() + "，返回：" + result);
            }
            
            session.commit();
            long cost = System.currentTimeMillis() - start;
            System.out.println("REUSE 总耗时：" + cost + " ms");
        }
    }
    
    // ========== BATCH 执行器 ==========
    static void testBatch(List<Student> students) {
        System.out.println("\n========== BATCH 执行器 ==========");
        SqlSession session = sqlSessionFactory.openSession(ExecutorType.BATCH);
        try {
            StudentMapper mapper = session.getMapper(StudentMapper.class);
            long start = System.currentTimeMillis();
            
            for (Student s : students) {
                int result = mapper.insertStudent(s);
                System.out.println("插入 " + s.getName() + "，返回：" + result + "（注意：BATCH 模式返回特殊值）");
            }
            
            System.out.println("--- 调用flushStatements 前，SQL 尚未发送到数据库 ---");
            
            // 手动flush，获取实际执行结果
            List<org.apache.ibatis.executor.BatchResult> batchResults = session.flushStatements();
            System.out.println("--- flushStatements 后 ---");
            for (org.apache.ibatis.executor.BatchResult br : batchResults) {
                System.out.println("Statement: " + br.getMappedStatement().getId());
                System.out.println("Update counts: " + java.util.Arrays.toString(br.getUpdateCounts()));
            }
            
            session.commit();
            long cost = System.currentTimeMillis() - start;
            System.out.println("BATCH 总耗时：" + cost + " ms");
        } finally {
            session.close();
        }
    }
}

// 反例：BATCH 模式下立即获取自增ID
SqlSession session = sqlSessionFactory.openSession(ExecutorType.BATCH);
StudentMapper mapper = session.getMapper(StudentMapper.class);

Student s = new Student("大翔", 22, "计算机科学", 95.5);
mapper.insertStudent(s);
// 错误！此时s.getId()为null，因为SQL 还没发送到数据库
System.out.println(s.getId());  // 输出 null

session.flushStatements();  // 必须flush 后才能获取ID
System.out.println(s.getId());  // 此时才有值
session.commit();
session.close();