自定义缓存

package com.fly.cache;

import org.apache.ibatis.cache.Cache;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * 自定义缓存：带操作日志的内存缓存
 * 用于教学演示，观察MyBatis何时put、何时get、何时clear
 */
public class LoggingCache implements Cache {
    
    private final String id;
    private final Map<Object, Object> cache = new HashMap<>();
    private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
    
    public LoggingCache(String id) {
        this.id = id;
        System.out.println("[自定义缓存] 创建缓存实例，ID=" + id);
    }
    
    @Override
    public String getId() {
        return id;
    }
    
    @Override
    public void putObject(Object key, Object value) {
        System.out.println("[自定义缓存] PUT  key=" + key.hashCode() + ", value类型=" + value.getClass().getSimpleName());
        cache.put(key, value);
    }
    
    @Override
    public Object getObject(Object key) {
        Object value = cache.get(key);
        if (value != null) {
            System.out.println("[自定义缓存] HIT  key=" + key.hashCode());
        } else {
            System.out.println("[自定义缓存] MISS key=" + key.hashCode());
        }
        return value;
    }
    
    @Override
    public Object removeObject(Object key) {
        System.out.println("[自定义缓存] REMOVE key=" + key.hashCode());
        return cache.remove(key);
    }
    
    @Override
    public void clear() {
        System.out.println("[自定义缓存] CLEAR 清空全部缓存，当前size=" + cache.size());
        cache.clear();
    }
    
    @Override
    public int getSize() {
        return cache.size();
    }
    
    @Override
    public ReadWriteLock getReadWriteLock() {
        return readWriteLock;
    }
}

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.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.InputStream;

public class CustomCacheDemo {
    public static void main(String[] args) throws Exception {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        
        System.out.println("========== 第一次SqlSession 查询 ==========");
        SqlSession session1 = sqlSessionFactory.openSession();
        StudentMapper mapper1 = session1.getMapper(StudentMapper.class);
        Student s1 = mapper1.selectById(4);  // 查询黄俪
        System.out.println("查询结果：" + s1.getName() + "，专业：" + s1.getMajor());
        session1.commit();
        session1.close();
        
        System.out.println("\n========== 第二次SqlSession 查询（应命中缓存）==========");
        SqlSession session2 = sqlSessionFactory.openSession();
        StudentMapper mapper2 = session2.getMapper(StudentMapper.class);
        Student s2 = mapper2.selectById(4);  // 应命中二级缓存
        System.out.println("查询结果：" + s2.getName() + "，专业：" + s2.getMajor());
        session2.close();
        
        System.out.println("\n========== 第三次SqlSession 更新（应清空缓存）==========");
        SqlSession session3 = sqlSessionFactory.openSession();
        StudentMapper mapper3 = session3.getMapper(StudentMapper.class);
        mapper3.updateScoreById(4, 95.0);  // 更新黄俪分数
        session3.commit();  // commit触发缓存清空
        session3.close();
        
        System.out.println("\n========== 第四次SqlSession 再次查询 ==========");
        SqlSession session4 = sqlSessionFactory.openSession();
        StudentMapper mapper4 = session4.getMapper(StudentMapper.class);
        Student s4 = mapper4.selectById(4);  // 缓存已清空，重新查库
        System.out.println("查询结果：" + s4.getName() + "，分数：" + s4.getScore());
        session4.close();
    }
}

package com.fly.cache;

import org.apache.ibatis.cache.Cache;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;

import java.io.*;

/**
 * Redis缓存实现思路（教学版，未完整实现连接池管理）
 */
public class RedisCache implements Cache {
    
    private final String id;
    private static JedisPool jedisPool;
    
    static {
        JedisPoolConfig config = new JedisPoolConfig();
        config.setMaxTotal(100);
        jedisPool = new JedisPool(config, "localhost", 6379, 2000, "password");
    }
    
    public RedisCache(String id) {
        this.id = id;
    }
    
    @Override
    public String getId() {
        return id;
    }
    
    @Override
    public void putObject(Object key, Object value) {
        try (Jedis jedis = jedisPool.getResource()) {
            // 使用序列化存储
            byte[] keyBytes = serialize(key);
            byte[] valueBytes = serialize(value);
            // 设置过期时间600秒
            jedis.setex(keyBytes, 600, valueBytes);
        } catch (Exception e) {
            throw new RuntimeException("Redis缓存写入失败", e);
        }
    }
    
    @Override
    public Object getObject(Object key) {
        try (Jedis jedis = jedisPool.getResource()) {
            byte[] valueBytes = jedis.get(serialize(key));
            return valueBytes != null ? deserialize(valueBytes) : null;
        } catch (Exception e) {
            throw new RuntimeException("Redis缓存读取失败", e);
        }
    }
    
    @Override
    public Object removeObject(Object key) {
        try (Jedis jedis = jedisPool.getResource()) {
            byte[] keyBytes = serialize(key);
            Object value = getObject(key);
            jedis.del(keyBytes);
            return value;
        } catch (Exception e) {
            throw new RuntimeException("Redis缓存删除失败", e);
        }
    }
    
    @Override
    public void clear() {
        try (Jedis jedis = jedisPool.getResource()) {
            // 按前缀删除该命名空间的所有缓存
            // 实际生产应使用Redis Scan或Hash结构
            jedis.del((id + ":*").getBytes());
        } catch (Exception e) {
            throw new RuntimeException("Redis缓存清空失败", e);
        }
    }
    
    @Override
    public int getSize() {
        // Redis中统计该命名空间key数量
        return 0;  // 简化示意
    }
    
    private byte[] serialize(Object object) throws IOException {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baos);
        oos.writeObject(object);
        oos.close();
        return baos.toByteArray();
    }
    
    private Object deserialize(byte[] bytes) throws IOException, ClassNotFoundException {
        ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
        ObjectInputStream ois = new ObjectInputStream(bais);
        Object obj = ois.readObject();
        ois.close();
        return obj;
    }
}

// 反例：不实现getReadWriteLock，返回null
public class BadCache implements Cache {
    // ... 其他方法省略 ...
    
    @Override
    public ReadWriteLock getReadWriteLock() {
        return null;  // 错误！MyBatis外层SynchronizedCache依赖此锁
    }
}