server/protocols/jmap-draft/src/main/java/org/apache/james/jmap/draft/json/MultipleClassesDeserializer.java

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package org.apache.james.jmap.draft.json;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import com.google.common.base.Preconditions;

public class MultipleClassesDeserializer extends StdDeserializer<Object> {

    private final Map<String, Class<?>> registry = new HashMap<>();

    MultipleClassesDeserializer() {
        super(Object.class);
    }

    @Override
    public Object deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        ObjectMapper mapper = (ObjectMapper) p.getCodec();
        final JsonNode root = mapper.readTree(p);

        return registry.entrySet().stream()
                .filter(req -> ! (root.at(req.getKey()).isMissingNode()))
                .map(x -> readValue(mapper, root, x.getValue()))
                .findFirst()
                .orElseThrow(() -> JsonMappingException.from(ctxt, "Can't map request to a known registered class"));
    }

    private Object readValue(ObjectMapper mapper, JsonNode root, Class<?> clazz) {
        try {
            return mapper.treeToValue(root, clazz);
        } catch (JsonProcessingException e) {
            throw new RuntimeException(e);
        }
    }

    public void registerClass(String uniqueJsonPath, Class<?> clazz) {
        Preconditions.checkArgument(! registry.containsKey(uniqueJsonPath), "Path %s has already been registered", uniqueJsonPath);
        registry.put(uniqueJsonPath, clazz);
    }
}