使用 Jackson 映射时将默认值设置为空字段

问题描述

我正在尝试使用 Jackson 将一些 JSON 对象映射到 Java 对象.JSON 对象中的某些字段是必需的(我可以用 @NotNull 标记)，而有些是可选的.

I am trying to map some JSON objects to Java objects with Jackson. Some of the fields in the JSON object are mandatory(which I can mark with @NotNull) and some are optional.

与Jackson 映射后，所有未在JSON 对象中设置的字段在Java 中都会有一个空值.是否有与 @NotNull 类似的注释可以告诉 Jackson 为 Java 类成员设置默认值，以防它为空?

After the mapping with Jackson, all the fields that are not set in the JSON object will have a null value in Java. Is there a similar annotation to @NotNull that can tell Jackson to set a default value to a Java class member, in case it is null?

为了使问题更清楚，这里有一些代码示例.

To make the question more clear here is some code example.

Java 对象:

class JavaObject {
    @NotNull
    public String notNullMember;

    @DefaultValue("Value")
    public String optionalMember;
}

JSON 对象可以是:

The JSON object can be either:

{
    "notNullMember" : "notNull"
}

或:

{
    "notNullMember" : "notNull",
    "optionalMember" : "optional"
}

@DefaultValue 注释只是为了显示我的要求.这不是真正的注释.如果 JSON 对象类似于第一个示例，我希望 optionalMember 的值是 "Value" 而不是 null.有没有做这种事情的注解?

The @DefaultValue annotations is just to show what I am asking. It's not a real annotation. If the JSON object is like in the first example I want the value of the optionalMember to be "Value" and not null. Is there an annotation that does such a thing?

推荐答案

没有设置默认值的注解.
您只能在 java 类级别设置默认值:

There is no annotation to set default value.
You can set default value only on java class level:

public class JavaObject
{
    public String notNullMember;

    public String optionalMember = "Value";
}

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