用于地图的Jackson自定义KeyDeserializer，不包括key为null的条目 [英] Jackson custom KeyDeserializer for Map, excluding entries where key is null

问题描述

我的POJO中的自定义密钥反序列化器如下:

The custom key deserializer in my POJO as follows:

@JsonDeserialize(keyUsing = MyCustomKeyDeserializer.class)
@JsonInclude
private Map<T, @Range(min = 0, max = 100) Integer> ratios;

但是，我遇到的情况是以前有效的密钥不再有效，并且希望提供向后兼容性.

However, I have a situation where a key that was previously valid, is no longer valid and would like to offer backward compatibility.

例如，如果用于接受键 AGE 和 HEIGHT 的代码并且想开始排除 HEIGHT ，则JSON对象 {"AGE":30，"HEIGHT":60} 将反序列化为地图中的 {"AGE":30}

For example, if the code used to accept the keys AGE and HEIGHT and would like to start excluding HEIGHT, the JSON object {"AGE": 30, "HEIGHT": 60} would be deserialized to just {"AGE": 30} in the map

我尝试解决此问题的方法是从 MyCustomKeyDeserializer 类返回一个 null 值.但是，该地图现在最终以包含 null 作为键之一的条目结尾.有没有办法从地图中排除空键?还是提供这种行为的另一种方法?

The way I tried to approach it was by returning a null value from the MyCustomKeyDeserializer class. However, the map is now ending up with an entry containing null as one of the keys. Is there a way to exclude null keys from the map? Or a different approach to providing such behavior?

序列化程序的代码如下:

The code for the serializer is along the lines as follows:

public class MyCustomKeyDeserializer extends KeyDeserializer {

    private Map<String, Object> registry;

    @Override
    public Object deserializeKey(final String key, final DeserializationContext ctxt) 
       throws IOException {
        return registry.get(key);
    }
}

推荐答案

如果知道键名是什么，则可以使用 com.fasterxml.jackson.annotation.JsonIgnoreProperties 批注:

If you know what is the key name is, you can just use com.fasterxml.jackson.annotation.JsonIgnoreProperties annotation:

@JsonIgnoreProperties(value = {"HEIGHT"})
@JsonDeserialize(keyUsing = MyCustomKeyDeserializer.class)
private Map<T, @Range(min = 0, max = 100) Integer> ratios;

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