Jackson collection deserializer to accept empty xml tags

To make Jackson's collection deserializer accept empty XML tags as empty collections, you can use a custom deserializer and annotate your collection property with @JsonDeserialize to specify the custom deserializer.

Here's an example of how you can achieve this:

1. Create a Custom Collection Deserializer: First, create a custom deserializer for the collection you want to handle empty tags. In this example, we'll use a List as the collection type:

javaCopy code
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class EmptyListDeserializer extends StdDeserializer<List<?>> {

    public EmptyListDeserializer() {
        super(List.class);
    }

    @Override
    public List<?> deserialize(JsonParser parser, DeserializationContext context) throws IOException {
        JsonNode node = parser.getCodec().readTree(parser);

        if (node.isArray()) {
            List<Object> list = new ArrayList<>();
            for (JsonNode itemNode : node) {
                // Deserialize each item in the list
                list.add(context.readValue(itemNode.traverse(parser.getCodec()), Object.class));
            }
            return list;
        }

        // If the node is not an array, return an empty list
        return new ArrayList<>();
    }
}

2. Use the Custom Deserializer in Your Model Class: Next, apply the custom deserializer to the collection property in your model class using the @JsonDeserialize annotation:

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import com.fasterxml.jackson.databind.annotation.JsonDeserialize;

public class MyModel {
    // Other properties

    @JsonDeserialize(using = EmptyListDeserializer.class)
    private List<String> myCollection;

    // Getters and setters
}

Now, when Jackson encounters an empty XML tag for the myCollection property, it will deserialize it as an empty list, rather than throwing an error or leaving it as null.

Remember to configure Jackson to use your custom deserializer when deserializing XML. The exact configuration will depend on the framework or environment you are using (e.g., Spring Boot, JAX-RS, etc.).

By using this approach, you can handle empty XML tags as empty collections in Jackson's deserialization process.