Jackson JSON：将属性的 Map<String,Object> 解编回其原始 class

Question

我正在使用第三方库（准确地说是 Elasticsearch 2.3.3），它已经为我将给定的 JSON 结构解析为 Map<String,Object> 实例，我想要创建对象的 class 实例，该对象最初编组为 JSON:

编组： MarshallableObject → marshalled_object.json
解组： marshalled_object.json → Map<String,Object> → MarshallableObject)

此外，这里是一些说明逻辑的示例代码：

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Arrays;
import java.util.Map;
import java.util.stream.Stream;

import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.client.transport.TransportClient;
import org.elasticsearch.common.transport.InetSocketTransportAddress;
import org.elasticsearch.index.query.QueryBuilders;

import com.fasterxml.jackson.databind.ObjectMapper;

public final class AttrMapUnmarshallingTest {

    /**
     * This class was directly used in the process for creating JSON documents indexed by Elasticsearch
     */
    public static final class MarshallableObject {

        public String bar;

        public String foo;

    }

    private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

    public static void main(final String[] args) throws UnknownHostException {
        try (final TransportClient client = TransportClient.builder().build().addTransportAddress(new InetSocketTransportAddress(InetAddress.getLoopbackAddress(), 9300))) {

            final SearchResponse response = client.prepareSearch("news").setTypes("article")
                .setQuery(QueryBuilders.matchQuery("text", "advertisement")).execute().actionGet();
        final Stream<Map<String, Object>> attrMaps = Arrays.stream(response.getHits().getHits())
                .map(hit -> hit.sourceAsMap());
        final Stream<MarshallableObject> objs = attrMaps.map(attrMap -> {
            // TODO: Find way of converting attr map into original class
            // which was marshalled into JSON
            // final MarshallableObject obj = OBJECT_MAPPER.read(attrMap);
            });
        }
    }

}

Answer 1

我在 SearchHit class 上做了一些阅读，这是我认为可能有效的方法：

Stream<MarshallableObject> objs = Arrays.stream(response.getHits().getHits())
    .filter(hit->hit.hasSource()) // For some reason source could be null.
    .map(hit->
         OBJECT_MAPPER.readValue(hit.sourceAsString(), 
                                 MarshallableObject.class));

注意：您需要声明 MarshallableObject class static 才能进行读取。显然，无法从 json 字符串中重建隐藏的 ParentClass$this 引用。

祝你好运。

Jackson JSON：将属性的 Map<String,Object> 解编回其原始 class

Jackson JSON: Unmarshalling a Map<String,Object> of attributes back into its original class

java

json

elasticsearch

jackson

unmarshalling