SpringBoot+redis 使用jackson2JsonR

错误提示

org.springframework.data.redis.serializer.SerializationException: Could not read JSON: Cannot construct instance of `com.example.learn_1.entity.LearnUser` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (byte[])"["com.example.learn_1.entity.LearnUser",{"userId":null,"userName":"唢呐","userAge":988,"remark":null}]"; line: 1, column: 42]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `com.example.learn_1.entity.LearnUser` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)

代码

RedisConfig

    @Bean("userRedistemplate")
    public RedisTemplate<String, Object> redisTemplate(RedisConnectionFactory redisConnectionFactory) {
        RedisTemplate<String, Object> template = new RedisTemplate<String, Object>();
        // 将刚才的redis连接工厂设置到模板类中
        template.setConnectionFactory(redisConnectionFactory);
        // 设置key的序列化器
        template.setKeySerializer(new StringRedisSerializer());
        // 设置value的序列化器
        //使用Jackson 2，将对象序列化为JSON
        Jackson2JsonRedisSerializer jackson2JsonRedisSerializer = new Jackson2JsonRedisSerializer(Object.class);
        //json转对象类，不设置默认的会将json转成hashmap
        ObjectMapper om = new ObjectMapper();
        om.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);
        om.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);
        jackson2JsonRedisSerializer.setObjectMapper(om);
        template.setValueSerializer(jackson2JsonRedisSerializer);

        return template;
    }

entity

@Data
@Builder
@Accessors(chain = true)
public class LearnUser //extends BaseEntity
{
    private static final long serialVersionUID = 1L;

    @TableId(value = "user_id", type = IdType.AUTO)
    private Integer userId;

    private String userName;

    private Integer userAge;

    private String remark;


}

test

    @Test
    public void testRedisTemplate(){
        // 以注解的形式把 bean 注入Spring 并获取 Spring 的上下文环境
        AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(RedisConfig.class);
        // 获取自己配置的 bean 实例
        RedisTemplate template = ctx.getBean(RedisTemplate.class);
        LearnUser user =  LearnUser.builder().userAge(988).userName("唢呐").build();
        template.opsForValue().set("key1", user);
        System.out.println(template.opsForValue().get("key1"));
    }

解决

1. 在entity中添加注解@AllArgsConstructor(access = AccessLevel.PRIVATE)

2. 新建一个无参构造方法

    LearnUser(){

    }

• 根据错误提示(no Creators, like default construct, exist)分析得无法创建实例
• 报错行

System.out.println(template.opsForValue().get("key1"));

• 即在使用jackson2JsonRedisSerializer反序列化创建LearnUser对象时,发现LearnUser类中没有合适的构造方法,确定问题在LearnUser类中
• 贴上链接https://www.jianshu.com/p/0d8fc3df3647?from=timeline&isappinstalled=0
• 原因在于使用lombok插件,添加@Builder后,为LearnUser创建了一个全参的构造方法,而jackson2JsonRedisSerializer无法调用这个构造方法.
• 添加注解后,@Builder为我们创建的构造方法会被修饰为Private,防止了@Builder注解对其他类的影响

总结

1. 关于@Builder为什么使用建造者模式,建议阅读Effective Java一书
2. 只是一个小问题,虽然报错信息交杂,只要认真阅读,即可找到出路
3. 学会利用idea的反编译工具
4. 当没有定义构造方法时,java会自动创建一个无参的构造方法,当手动书写构造方法时,会使用手动书写的构造方法