如何在从JSON反序列化期间忽略具有空值的属性

I'm trying to deserialize a JSON string into a ConcurrentHashMap object and I'm getting errors because my JSON contains properties with null values, but ConcurrentHashMap does not accept null values. Here is the fragment of code:

我正在尝试将JSON字符串反序列化为ConcurrentHashMap对象，并且我收到错误，因为我的JSON包含具有空值的属性，但ConcurrentHashMap不接受空值。这是代码片段：

ObjectMapper mapper = new ObjectMapper();
return mapper.readValue(jsonString, ConcurrentHashMap.class);

Is there a way to ignore properties with null values during deserialization? I know that we can ignore these properties during serialization:

有没有办法在反序列化期间忽略具有空值的属性？我知道在序列化过程中我们可以忽略这些属性：

mapper.setSerializationInclusion(JsonInclude.NON_NULL);

But what about deserialization process?

但是反序列化过程呢？

2 个解决方案

#1

The following trick has worked for me:

以下技巧对我有用：

ObjectMapper mapper = new ObjectMapper();

String jsonString = "{\"key1\": 1, \"key2\": null, \"key3\": 3}";

ConcurrentHashMap<String, Object> map = mapper.readValue(jsonString, new ConcurrentHashMap<String, Object>() {
    @Override
    public Object put(String key, Object value) {
        return value != null ? super.put(key, value) : null;
    }
}.getClass());

System.out.println(map); // {key1=1, key3=3}

The idea is to simply override ConcurrentHashMap.put() method so that it ignores null values that are to be added to the map.

我们的想法是简单地覆盖ConcurrentHashMap.put（）方法，以便忽略要添加到地图的空值。

Instead of an anonymous inner class, you could create your own class that extends from ConcurrentHashMap:

您可以创建自己的从ConcurrentHashMap扩展的类，而不是匿名内部类：

public class NullValuesIgnorerConcurrentHashMap<K, V>
    extends ConcurrentHashMap<K, V> {

    @Override
    public V put(K key, V value) {
        return value != null ? super.put(key, value) : null;
    }
}

Then you would use this class to deserialize to a ConcurrentHashMap:

然后，您将使用此类反序列化为ConcurrentHashMap：

ConcurrentHashMap<String, Object> map = 
    mapper.readValue(jsonString, NullValuesIgnorerConcurrentHashMap.class);

System.out.println(map); // {key1=1, key3=3}

With this approach, the returned map would never throw NullPointerException on put() when given a null value.

使用这种方法，返回的映射在给定空值时永远不会在put（）上抛出NullPointerException。

#2

There may be a better way but a workaround would be:

可能有更好的方法，但解决方法是：

Map<String, Object> map = mapper.readValue(jsonString, HashMap.class);
map.values().removeIf(o -> o == null);
return new ConcurrentHashMap<> (map);

#1