android - 如何在杰克逊 json 反序列化中跳过包装对象

Question

我正在尝试使用杰克逊反序列化以下字符串。

{
  "roomName": "u8ec29p0j7q2m9f",
  "broadcastPresenceRoles": {
    "broadcastPresenceRole": [
      "moderator",
      "participant",
      "visitor"
    ]
  },
  "owners": {
    "owner": "anewuser@shahanshah"
  },
  "admins": {
    "admin": "sanjeet@shahanshah"
  },
  "members": null,
  "outcasts": {
    "outcast": [
      "sawan@shahanshah",
      "sus@shahanshah"
    ]
  },
  "ownerGroups": {
    "ownerGroup": "Friends"
  }
}

这是来自 openfire rest api 的响应。我对包装数组的包装器对象有问题。这里

"broadcastPresenceRoles": {
    "broadcastPresenceRole": [
      "moderator",
      "participant",
      "visitor"
    ]
  },

我试过这个来打开容器，但没有成功。我不认为编写包装类是个好主意（因为我将不得不编写几个包装类）。此外，我需要通用解决方案，因此我可以将它与其他响应一起使用，因为 api 具有类似包装对象格式的其他响应. 提前致谢。

Answer 1

@JsonDeserialize您可以使用inside 创建一个自定义注释并创建一个JsonDeserializer实现ContextualDeserializer. 这个想法的灵感来自您提到的解决方案，但在 json 对象中展开任何一个属性更为通用。

以下是使用@JacksonAnnotationsInside注释容器包含的自定义注释@JsonDeserialize：

@Retention(RetentionPolicy.RUNTIME)
@JacksonAnnotationsInside
@JsonDeserialize(using = JsonUnwrapPropertyDeserializer.class)
public @interface JsonUnwrapProperty {
}

JsonDeserializer以及实现的习惯ContextualDeserializer：

public class JsonUnwrapPropertyDeserializer extends JsonDeserializer<Object> implements ContextualDeserializer {

    private JavaType unwrappedJavaType;
    private String unwrappedProperty;

    @Override
    public JsonDeserializer<?> createContextual(final DeserializationContext deserializationContext, final BeanProperty beanProperty) throws JsonMappingException {
        unwrappedProperty = beanProperty.getMember().getName();
        unwrappedJavaType = beanProperty.getType();
        return this;
    }

    @Override
    public Object deserialize(final JsonParser jsonParser, final DeserializationContext deserializationContext) throws IOException {
        final TreeNode targetObjectNode = jsonParser.readValueAsTree().get(unwrappedProperty);
        return jsonParser.getCodec().readValue(targetObjectNode.traverse(), unwrappedJavaType);
    }
}

和使用示例：

public class MyBean {

    @JsonProperty("broadcastPresenceRoles")
    @JsonUnwrapProperty
    private List<String> broadcastPresenceRole;

    @JsonProperty("admins")
    @JsonUnwrapProperty
    private String admin;

    // constructor, getter and setter
}

@JsonProperty是定位包装器对象，@JsonUnwrappProperty是反序列化json对象并将一个属性提取到带注释的字段中。

编辑：

以下是一个例子ObjectMapper：

String json = "{\n" +
        "  \"broadcastPresenceRoles\": {\n" +
        "    \"broadcastPresenceRole\": [\n" +
        "      \"moderator\",\n" +
        "      \"participant\",\n" +
        "      \"visitor\"\n" +
        "    ]\n" +
        "  },\n" +
        "  \"admins\": {\n" +
        "    \"admin\": \"sanjeet@shahanshah\"\n" +
        "  }\n" +
        "}";

final ObjectMapper mapper = new ObjectMapper();
final MyBean myBean = mapper.readValue(json, MyBean.class);

System.out.println(myBean.getBroadcastPresenceRole());
System.out.println(myBean.getAdmin());

输出：

[主持人、参与者、访客]

sanjeet@shahanshah

Answer 2

我创建了一个基于@wilson 响应解决 NPE 的变体

import java.io.IOException;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

import com.fasterxml.jackson.annotation.JacksonAnnotationsInside;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.BeanProperty;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.deser.ContextualDeserializer;

@Retention(RetentionPolicy.RUNTIME)
@JacksonAnnotationsInside
@JsonDeserialize(using = JsonUnwrapProperty.JsonUnwrapPropertyDeserializer.class)
public @interface JsonUnwrapProperty {

  public static class JsonUnwrapPropertyDeserializer extends JsonDeserializer<Object>
      implements ContextualDeserializer {

    private JavaType unwrappedJavaType;
    private String unwrappedProperty;

    @Override
    public JsonDeserializer<?> createContextual(final DeserializationContext deserializationContext,
        final BeanProperty beanProperty) throws JsonMappingException {
      unwrappedProperty = beanProperty.getMember().getName();
      unwrappedJavaType = beanProperty.getType();
      return this;
    }

    @Override
    public Object deserialize(final JsonParser jsonParser, final DeserializationContext deserializationContext)
        throws IOException {
      System.out.println(String.format("Ignoring %s in %s/%s", unwrappedProperty,
        jsonParser.currentName(), jsonParser.nextFieldName()));
      JsonToken token = jsonParser.nextValue();
      return jsonParser.getCodec().readValue(jsonParser, unwrappedJavaType);
    }
  }
}