Jackson 的 NPE 试图序列化一个不存在的字段？

Question

这是我的简单 bean

@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class Foo {

    private String firstName;
    private String lastName;

    public String getFullName(){
     return firstName + lastName;
    }

}

当此对象在 Spring-boot controller 中与 Jackson 序列化时，我收到以下错误

j.l.NullPointerException: null
   com.example.foobar.foo.getFullName(Foo.java:28)
  s.r.NativeMethodAccessorImpl.invoke0(NativeMethodAccessorImpl.java)
  s.r.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  s.r.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  j.l.reflect.Method.invoke(Method.java:498)
  c.f.j.d.s.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:653)
  c.f.j.d.s.s.BeanSerializerBase.serializeFields(BeanSerializerBase.java:690)..
  28 common frames omitted\nWrapped by: c.f.j.d.JsonMappingException: (was java.lang.NullPointerException) 
  (through reference chain: com.example.foobar.foo[\"fullName\"])
   c.f.j.d.JsonMappingException.wrapWithPath(JsonMappingException.java:379)
  c.f.j.d.JsonMappingException.wrapWithPath(JsonMappingException.java:339)
  c.f.j.d.s.s.StdSerializer.wrapAndThrow(StdSerializer.java:343)
  c.f.j.d.s.s.BeanSerializerBase.serializeFields(BeanSerializerBase.java:698)
  c.f.j.d.s.BeanSerializer.serialize(BeanSerializer.java:155)
  c.f.j.d.s.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:292)
  c.f.j.d.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1419)
  c.f.j.d.ObjectWriter.writeValue(ObjectWriter.java:940)
  o.s.h.c.j.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:267)...
  23 common frames omitted\nWrapped by: o.s.h.c.HttpMessageNotWritableException: Could not write content: (was java.lang.NullPointerException) (through reference chain: com.example.foobar.foo[\"fullName\"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: com.example.foobar.foo[\"fullName\"])
                                                                                                                                                o.s.h.c.j.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:274 ..."

这是我发送的requestBody

{"firstName": "foo",
"lastName: null
}

Jackson 是否在尝试序列化 fullName 属性？但我没有声明这样的字段。这是预期的行为吗？我找不到支持此行为的文档。

谢谢

Answer 1

您的猜测是正确的，Jackson 正试图通过其 getter 方法查找字段名称，但它找不到。因此 NPE。

不同的解决方案

对 getFullName 方法使用 @JsonIgnore。
您可以通过在 spring 引导 application.properties 文件
中设置此属性来禁用此功能
spring.jackson.mapper.use-getters-as-setters=false

如果你想用 java 代码来做（如果不使用 spring 引导），你可以用这样的 bean 声明来做

@Bean
public Jackson2ObjectMapperBuilder objectMapperBuilder() {
  Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
  builder.featuresToDisable(MapperFeature.USE_GETTERS_AS_SETTERS);
  return builder;
}

Jackson 的 NPE 试图序列化一个不存在的字段？

NPE from Jackson trying to serializing a field that does not exists?

spring-boot

jackson2

jackson-databind