Jackson Mapper序列化空对象而不是null [英] Jackson Mapper serialize empty object instead of null

问题描述

假设我有课程Foo

public class Foo {
    private Bar bar;
}

和Bar

public class Bar {
    private String fizz;
    private String bang;
}

编辑：为了澄清我不拥有 Foo 和 Bar 并且不能改变这些类。

EDIT: For clarification I do not own Foo and Bar and cannot alter these classes.

如果我想序列化一个Foo类型的空对象，它的成员是Bar类型，将返回null。

If I want to serialize an empty object of type Foo, it's member, which is of type Bar, will be returned as null.

String json = objectMapper.writeValueAsString(new Foo()); // "{"bar" : null}"

我有什么方法可以得到对象映射器序列化一个空的Bar对象，而不必实例化一个新的Bar实例，然后将其添加到一个新的Foo实例？

Is there any way I can get the object mapper to serialize an empty Bar object without having to instantiate a new instance of Bar and then adding it to a new instance of Foo?

String json = objectMapper.writeValueAsString(new Foo()) // "{bar": {"fizz" : null, "bang" : null } }"

推荐答案

您可以创建一个自定义序列化程序来序列化Foo对象。然后在您的自定义FooSerializer实现中，您可以检查空值和将其序列化为默认的Bar实例。请参阅 https：// spin。 atomicobject.com/2016/07/01/custom-serializer-jackson/ 或 http ：//www.baeldung.com/jackson-custom-serialization ，了解如何创建自定义序列的一些示例lizers。

You could create a custom serializer for serializing Foo objects. Then in your custom FooSerializer implementation, you could check for a null bar value and serialize it as a default Bar instance. See https://spin.atomicobject.com/2016/07/01/custom-serializer-jackson/ or http://www.baeldung.com/jackson-custom-serialization for some examples of how to create custom serializers.

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