JPA(Hibernate)代理类的hibernateLazyInitializer属性系列化异常

　　今天在Spring Boot项目中使用JPA(Hibernate)进行数据库访问时，

spring:
  jpa:
    generate-ddl: false
    show-sql: true
    hibernate:
      ddl-auto: none
    open-in-view: true

　　查询一个实体对象时出现异常：

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: com.xgclassroom.model.User$HibernateProxy$PpGM4JxY["hibernateLazyInitializer"])

　　仔细看了下报错信息，发现直接原因是：jackson在对hibernate的持久化实体类的代理对象进行序列化时，代理类中的"hibernateLazyInitializer"属性为空，触发了系列化规划SerializationFeature.FAIL_ON_EMPTY_BEANS，即“出现空Bean时触发序列化失败”！

　　"hibernateLazyInitializer"属性为空之所以为空是因为我们禁用了延迟加载（open-in-view: true），设为false又会引发no Session错误。

　　报错信息中告诉我们可以通过禁用jackson的SerializationFeature.FAIL_ON_EMPTY_BEANS这条系列化规则来避免该异常(异常信息中的红色字所示)，我们可以通过以下方式使用禁用了SerializationFeature.FAIL_ON_EMPTY_BEANS规则的新ObjectMapper替换默认的ObjectMapper的方法来达到目的：

@SpringBootApplication
@Configuration
public class ProviderUserApplication {
    public static void main(String[] args) {
        SpringApplication.run(ProviderUserApplication.class, args);
    }

    @Bean
    public ObjectMapper objectMapper() {
        return new ObjectMapper().disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);
    }
}

　　

　　当然，也可以直接在相应的要实体类上通过@JsonIgnoreProperties忽略掉为空的属性的系列化：

@Getter
@Setter
@Entity
@JsonIgnoreProperties(value = {"hibernateLazyInitializer"})
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column
    private String username;

    @Column
    private String name;

    @Column
    private Integer age;

    @Column
    private BigDecimal balance;
}

　　下面来看一下两种方法重到的系列化结果样例：

{"id":1,"username":"account1","name":"张三","age":20,"balance":100.00,"hibernateLazyInitializer":{}}

{"id":1,"username":"account1","name":"张三","age":20,"balance":100.00}