Jackson: what if there is a lack of property- Jackson: What happens if a property is missing?

problem ：

What happens if I annotate a constructor parameter using @JsonProperty but the Json doesn't specify that property. If I use @JsonProperty Annotation constructor parameters , but Json The property is not specified , What will happen .What value does the constructor get? What value does the constructor get ？

How do I differentiate between a property having a null value versus a property that is not present in the JSON? How to distinguish between attributes with null values and JSON Properties that do not exist in ？

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Solution ：

Reference resources ： https://stackoom.com/en/question/YufZ