对象映射器在将对象转换为字符串Java时删除空值和null值

Question

为了响应api调用，我将发送Json class Object作为响应。

我需要这样的响应，而不会删除空对象。

{
"links": {
"products": [],
"packages": []
},
"embedded":{
"products": [],
"packages": []
}
}

但最终的反应看起来像这个

{
"links": {},
"embedded": {}
}

Answer 1

需要注意的两件事：

1. null和empty是不同的东西
2. AFAIK-Jackson配置为默认情况下使用null值序列化属性

请确保正确初始化对象中的属性。例如：

class Dto {
private Link link;
private Embedded embedded;
//constructor, getters and setters...
}
class Link {
//by default these will be empty instead of null
private List<Product> products = new ArrayList<>();
private List<Package> packages = new ArrayList<>();
//constructor, getters and setters...
}

请确保您的类没有使用此注释@JsonInclude(JsonInclude.Include.NON_NULL)扩展另一个类。示例：

//It tells Jackson to exclude any property with null values from being serialized
@JsonInclude(JsonInclude.Include.NON_NULL)
class BaseClass {
}
//Any property with null value will follow the rules stated in BaseClass
class Dto extends BaseClass {
private Link link;
private Embedded embedded;
//constructor, getters and setters...
}
class Link extends BaseClass {
/* rest of the design */
}

如果你有后者，并且你不能编辑BaseClass，那么你可以在特定的类中定义不同的规则：

class Link extends BaseClass{
//no matter what rules are defined elsewhere, this field will be serialized
@JsonInclude(JsonInclude.Include.ALWAYS)
private List<Product> products;
//same here
@JsonInclude(JsonInclude.Include.ALWAYS)
private List<Package> packages;
//constructor, getters and setters...
}