cachedemo

探究 Redis + Cacheable 的使用
不同微服务共享缓存问题
探究由于微服务架构划分错误，两个微服务使用了相同的domain时，配置相同的key，redis读取缓存时存在缓存冲突的问题

场景

两个微服务，对象结构一致，但是包路径不同

两个User对象，结构完全一致，包路径不同

com.edwin.cache.account.User

package com.edwin.cache.account;

import lombok.*;

import java.io.Serializable;

@Setter
@Getter
@AllArgsConstructor
@NoArgsConstructor
@Builder
@ToString
public class User implements Serializable {
  private Long id;
  private String username;
  private String password;
}

com.edwin.cache.user.User

package com.edwin.cache.user;

import lombok.*;

import javax.persistence.*;
import java.io.Serializable;

@Setter
@Getter
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Builder
@Table(name = "user")
@ToString
public class User implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String username;
    private String password;
}

缓存方案

com.edwin.cache.account.User

@CacheConfig(cacheNames = "user")
@Repository
@RequiredArgsConstructor
public class AccountRepository {
private final AccountJpaRepository accountJpaRepository;

    public static final String USER_PEX = "USER_";

    @Cacheable(cacheNames = USER_PEX, key = "'user.id:'+#id")
    public User findUserById(Long id) {
        Optional<Account> optionalAccount = accountJpaRepository.findById(id);
        if (optionalAccount.isEmpty()) {
            return new User();
        }
        Account account = optionalAccount.get();
        return User.builder()
                .id(account.getId())
                .username(account.getUsername())
                .password(account.getPassword())
                .build();
    }
}

com.edwin.cache.user.UserRepository

@CacheConfig(cacheNames = "user")
@Repository
@RequiredArgsConstructor
public class UserRepository {
private final UserJpaRepository userJpaRepository;

    public static final String USER_PEX = "USER_";

    @Cacheable(cacheNames = USER_PEX, key = "'user.id:'+#id")
    public User findUserById(Long id) {
        return userJpaRepository.findById(id).orElse(new User());
    }
}

希望存到Redis后可以做缓存共享

方案1

配置一个 Map<String, String> 关系

Map<String, String> map = new HashMap<>();
map.put("com.edwin.cache.user.User","com.edwin.cache.account.User")
map.put("com.edwin.cache.account.User","com.edwin.cache.user.User")

当反序列化时，在读取二进制（Json）数据时，进行转换
问题：
- 如果redis存入的对象为 com.edwin.cache.user.User，当反序列化为 com.edwin.cache.account.User时，由于反序列化时需要把数据放进实例化对象中，这时候涉及到类加载，在account上下文中并没有com.edwin.cache.user.User的对象，因此会挂掉。
- 转换时并不知道是哪个对象在获取缓存

方案2

如同方案1也配置一个map关系
对redis存储的数据反序列化时，尝试类加载，如果不能加载该类，那么通过加载 map.get(key)的值，尝试类加载，如果失败，走原来的，如果成功，替换原来的序列化类加载路径

RedisSerializer 默认使用 JdkSerializationRedisSerializer

JdkSerializationRedisSerializer 默认会使用 org.springframework.core.serializer.support.SerializingConverter 和 org.springframework.core.serializer.support.DeserializingConverter, 我们只需要关注反序列化器
DeserializingConverter 中会使用 org.springframework.core.ConfigurableObjectInputStream
ConfigurableObjectInputStream 中有一个 resolveClass方法，我们只需要继承这个类并且把整个方法重写, 就可以按照需求加载对应的类

public class DemoObjectInputStream extends ConfigurableObjectInputStream {
    @Override
    protected Class<?> resolveClass(ObjectStreamClass classDesc) throws IOException, ClassNotFoundException {

        String name = classDesc.getName();
        System.out.println(name);

        Map<String, String> map = new HashMap<>();
        map.put("com.edwin.cache.account.User", "com.edwin.cache.user.User");
        map.put("com.edwin.cache.user.User", "com.edwin.cache.account.User");

        if (!ClassUtils.isPresent(name, classLoader)) {
            String className = map.get(name);
            if (!ObjectUtils.isEmpty(className) && ClassUtils.isPresent(className, classLoader)) {
                return ClassUtils.forName(className, this.classLoader);
            }
        }

        return super.resolveClass(classDesc);
    }
}

测试

分别启动服务 cache-service 和 cache-account

通过测试可以拿到相同的结果
访问 http://localhost:8080/user

curl http://localhost:8080/user | python -m json.too

[
    {
        "id": 1,
        "password": "111111",
        "username": "\u5f20\u4e09"
    },
    {
        "id": 2,
        "password": "222222",
        "username": "\u674e\u56db"
    },
    {
        "id": 3,
        "password": "333333",
        "username": "\u738b\u4e94"
    },
    {
        "id": 4,
        "password": "444444",
        "username": "\u7530\u516d"
    }
]

访问 http://localhost:8090/account

curl http://localhost:8090/account | python -m json.tool

[
    {
        "id": 1,
        "password": "111111",
        "username": "\u5f20\u4e09"
    },
    {
        "id": 2,
        "password": "222222",
        "username": "\u674e\u56db"
    },
    {
        "id": 3,
        "password": "333333",
        "username": "\u738b\u4e94"
    },
    {
        "id": 4,
        "password": "444444",
        "username": "\u7530\u516d"
    }
]

LiangLliu/cache-sharing

cachedemo

场景

方案1

方案2

测试