springboot项目自定义类，controller层直接返回这个类报如下错误，也实现了Serializable接口

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class org.springframework.context.expression.StandardBeanExpressionResolver and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: java.util.HashMap["user"]->com.wenbei.member.bean.User$$EnhancerBySpringCGLIB$$2c16abfb["targetSource"]->org.springframework.aop.target.SimpleBeanTargetSource["beanFactory"]->org.springframework.beans.factory.support.DefaultListableBeanFactory["parentBeanFactory"]->org.springframework.beans.factory.support.DefaultListableBeanFactory["beanExpressionResolver"])
	at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:77) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.SerializerProvider.reportBadDefinition(SerializerProvider.java:1191) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.DatabindContext.reportBadDefinition(DatabindContext.java:404) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.failForEmpty(UnknownSerializer.java:71) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.serialize(UnknownSerializer.java:33) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:722) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:166) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:722) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:166) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:722) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:166) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727) ~[jackson-databind-2.10.2.jar:2.10.2]
	at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:722) ~[jackson-databind-2.10.2.jar:2.10.2]
...

具体错误为

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: 
No serializer found for class org.springframework.context.expression.StandardBeanExpressionResolver 
and no properties discovered to create BeanSerializer (to avoid exception, 
disable SerializationFeature.FAIL_ON_EMPTY_BEANS) 
(through reference chain: java.util.HashMap["user"]-
>com.wenbei.member.bean.User$$EnhancerBySpringCGLIB$$2c16abfb["targetSource"]-
>org.springframework.aop.target.SimpleBeanTargetSource["beanFactory"]-
>org.springframework.beans.factory.support.DefaultListableBeanFactory["parentBeanFactory"]-
>org.springframework.beans.factory.support.DefaultListableBeanFactory["beanExpressionResolver"])

找不到xx类的序列化程序并且没有发现创建BeanSerializer的属性（为了避免异常，禁用SerializationFeature.FAIL_ON_EMPTY_BEANS）

哦我们看SerializationFeature.FAIL_ON_EMPTY_BEANS的注释了解到，不可序列化的类会抛该错，具有@JsonSerialize注解的空bean不会抛错。所以这个错是检查空bean的，并且改功能默认开启

解决该问题我们可以在被序列化的类上使用@JsonIgnoreProperties、@JsonIgnore、@JsonFormat注解
具体用法见Spring Boot程序中@JsonIgnoreProperties与@JsonIgnore基本使用