将 JSON 转换为 Java 对象，如何使用 Jackson 解析 BadgerFish 约定

Question

使用 API 我收到这样的 JSON（现在保存到文件中）：

[{
    "LEI": {
        "$": "549300Q82NZ9NYNMZT63"
    },
    "Entity": {
        "LegalName": {
            "$": "United Nerds in Collaboration of Random Nerdiness AB"
        },
        "LegalAddress": {
            "Line1": {
                "$": "BOX 155"
            },
            "City": {
                "$": "Alingsas"
            },
            "Region": {
                "$": "SE-O"
            },
            "Country": {
                "$": "SE"
            },
            "PostalCode": {
                "$": "44123"
            }
        },
        "HeadquartersAddress": {
            "Line1": {
                "$": "BOX 155"
            },
            "City": {
                "$": "Alingsas"
            },
            "Region": {
                "$": "SE-O"
            },
            "Country": {
                "$": "SE"
            },
            "PostalCode": {
                "$": "44123"
            }
        },
        "BusinessRegisterEntityID": {
            "@register": "SE001",
            "$": "5568557184"
        },
        "LegalJurisdiction": {
            "$": "SE"
        },
        "LegalForm": {
            "$": "PRIVATA AKTIEBOLAG"
        },
        "EntityStatus": {
            "$": "ACTIVE"
        }
    },
    "Registration": {
        "InitialRegistrationDate": {
            "$": "2016-06-23T01:48:45.025Z"
        },
        "LastUpdateDate": {
            "$": "2016-06-23T01:48:44.945Z"
        },
        "RegistrationStatus": {
            "$": "ISSUED"
        },
        "NextRenewalDate": {
            "$": "2017-06-21T06:32:03.821Z"
        },
        "ManagingLOU": {
            "$": "EVK05KS7XY1DEII3R011"
        },
        "ValidationSources": {
            "$": "PARTIALLY_CORROBORATED"
        }
    }
}]

我想从中获取 Java 对象。我已经从提供的 xsd 文件中创建了 Java 对象。我正在运行的代码是：

public static void toJava() {
    ObjectMapper mapper = new ObjectMapper();
    try {
        File json = new File("C:\\temp\\JSON.json");
        LEIRecordType[] type = mapper.readValue(json, LEIRecordType[].class);
    } catch (JsonEOFException ex) {
        ex.printStackTrace();
    } catch (JsonMappingException ex) {
        ex.printStackTrace();
    } catch (IOException ex) {
        ex.printStackTrace();
    }
}

这会产生这些异常：

com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "LEI" (class   org.leiroc.data.schema.leidata._2014.LEIRecordType), not marked as ignorable (5 known properties: "lei", "registration", "entity", "nextVersion", "extension"])
 at [Source: (File); line: 3, column: 14] (through reference chain: java.lang.Object[][0]->org.leiroc.data.schema.leidata._2014.LEIRecordType["LEI"])
at com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:60)
at com.fasterxml.jackson.databind.DeserializationContext.handleUnknownProperty(DeserializationContext.java:822)
at com.fasterxml.jackson.databind.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:1152)
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownProperty(BeanDeserializerBase.java:1567)
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownVanilla(BeanDeserializerBase.java:1545)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:293)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:151)
at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:195)
at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:21)
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4001)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2890)
at Test.JSONParser.toJava(JSONParser.java:38)
at Test.JSONParser.main(JSONParser.java:29)

LEIRecordType 如下所示：

package org.leiroc.data.schema.leidata._2014;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlType;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "LEIRecordType", propOrder = {"lei", "entity", "registration", "nextVersion", "extension"})
public class LEIRecordType {

    @XmlElement(name = "LEI", required = true)
    protected String lei;

    @XmlElement(name = "Entity", required = true)
    protected EntityType entity;

    @XmlElement(name = "Registration", required = true)
    protected RegistrationType registration;

    @XmlElement(name = "NextVersion")
    protected LEIRecordNextVersionType nextVersion;

    @XmlElement(name = "Extension")
    protected ExtensionType extension;

    public String getLEI() {
        return this.lei;
    }

    public void setLEI(String paramString) {
        this.lei = paramString;
    }

    public EntityType getEntity() {
        return this.entity;
    }

    public void setEntity(EntityType paramEntityType) {
        this.entity = paramEntityType;
    }

    public RegistrationType getRegistration() {
        return this.registration;
    }

    public void setRegistration(RegistrationType paramRegistrationType) {
        this.registration = paramRegistrationType;
    }

    public LEIRecordNextVersionType getNextVersion() {
        return this.nextVersion;
    }

    public void setNextVersion(LEIRecordNextVersionType paramLEIRecordNextVersionType) {
        this.nextVersion = paramLEIRecordNextVersionType;
    }

    public ExtensionType getExtension() {
        return this.extension;
    }

    public void setExtension(ExtensionType paramExtensionType) {
        this.extension = paramExtensionType;
    }
}

我知道问题在于杰克逊正在锁定一个名为 LEI 的 Java 对象，并带有一个名为“$”的变量。但是没有。组织帮助服务说：

““$”对象总是复制相应 XML 元素的简单内容（即不是属性、子节点等）。 在适用的情况下，“$”对象应始终输入为 JSON 字符串。”

但据我了解，这不是 JSON 标准。

我的问题是：有没有办法让杰克逊将其解析为 LEI = "549300Q82NZ9NYNMZT63" 等，而不是使用变量“$”来反对 LEI？ 一天的大部分时间都被困在这个问题上。

@UPDATE 根据客户服务，这种 JSON 格式显然被称为“The BadgerFish 约定”。

Answer 1

由于 $ 对象始终是 String，您可以为处理 BadgerFish 包装器对象的字符串创建自定义反序列化器。

此反序列化程序检查 String 值周围是否存在 BadgerFish 包装器对象并将其解包。正常的String 值像往常一样反序列化。

public class BadgerFishDeserializer extends StdDeserializer<String> {

    private static final long serialVersionUID = 1L;

    private static final SerializedString BADGER_FISH_FIELD_NAME = new SerializedString("$");

    public BadgerFishDeserializer() {
        super(String.class);
    }

    @Override
    public String deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        // do we have a wrapper object?
        if (jp.isExpectedStartObjectToken()) {          
            // check if first field name is equal to '$'
            if (!jp.nextFieldName(BADGER_FISH_FIELD_NAME)) {
                ctxt.reportInputMismatch(String.class, "Expected BadgerFish field name '$', but got '%s'", jp.getCurrentName());
            }
            jp.nextValue();  // proceed to the actual value
            String value = jp.getValueAsString();  // read value as string
            jp.nextToken();  // consume END_OBJECT of wrapper object
            return value;
        }
        // else: just return string value
        return jp.getValueAsString();
    }

}

最后在您的 Jackson ObjectMapper 实例上注册模块：

SimpleModule module = new SimpleModule();
module.addDeserializer(String.class, new BadgerFishDeserializer());
mapper.registerModule(module);

注意：如果您只想解开某些属性，您可以创建一个自定义注解并使用BeanDeserializerModifier 来检查注解，然后提供一个处理包装对象的反序列化程序。

值得深思：

• 创建注释
• 修改反序列化器以始终期望包装对象（在纯字符串上失败）
• 创建DeserializerModifier
• 在ObjectMapper 上注册DeserializerModifier

困难的部分：

public class BadgerFishDeserializerModifier extends BeanDeserializerModifier {

    @Override
    public BeanDeserializerBuilder updateBuilder(DeserializationConfig config, BeanDescription beanDesc, BeanDeserializerBuilder builder) {
        Iterator<SettableBeanProperty> props = builder.getProperties();
        while (props.hasNext()) {
            SettableBeanProperty prop = props.next();
            if (prop.getAnnotation(MyAnnotation.class) != null) {   
                builder.addOrReplaceProperty(prop.withValueDeserializer(new BadgerFishDeserializer()), true);
            }
        }
        return builder;
    }

}

Answer 2

这很有帮助！我最终不得不为 String 和 XMLGregorianCalendar 做一个特殊的反序列化器。但问题并不止于此。 BadgerFish 从生成的类中获取@XMLAttributes 并将它们设置为@value 而不是“value”。比如：

"BusinessRegisterEntityID": {
        "@register": "SE001",
        "$": "5568557184"
    }

那么他们还有什么方法可以将字段名称自定义回原始名称？目前我现在得到这个异常：

Exception in thread "main" com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "@register" (class leigen.BusinessRegisterEntityIDType), not marked as ignorable (2 known properties: "value", "register"])
at [Source: (File); line: 44, column: 27] (through reference chain: java.lang.Object[][0]->leigen.LEIRecordType["Entity"]->leigen.EntityType["BusinessRegisterEntityID"]->leigen.BusinessRegisterEntityIDType["@register"])
at com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:60)
at com.fasterxml.jackson.databind.DeserializationContext.handleUnknownProperty(DeserializationContext.java:822)
at com.fasterxml.jackson.databind.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:1152)
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownProperty(BeanDeserializerBase.java:1567)
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownVanilla(BeanDeserializerBase.java:1545)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:293)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:151)
at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:136)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:287)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:151)
at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:136)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:287)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:151)
at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:195)
at com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:21)
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4001)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2890)
at Test.JSONParser.toJava(JSONParser.java:47)
at Test.JSONParser.main(JSONParser.java:28)

我可以通过在配置中添加“忽略”（DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES）来绕过这个问题，就像我现在的当前代码一样：

    public static LEIRecordType[] toJava(File json) throws JsonParseException, JsonMappingException, IOException {
    ObjectMapper mapper = new ObjectMapper();
    SimpleModule module = new SimpleModule();
    module.addDeserializer(String.class, new BadgerFishStringDeserializer());
    module.addDeserializer(XMLGregorianCalendar.class, new BadgerFishXMLGregorianCalendarDeserializer());
    module.addDeserializer(NameType.class, new BadgerFishNameTypeDeserializer());
    mapper.registerModule(module);
    mapper.registerModule(new JaxbAnnotationModule()); // To be able to read JAXB annotations.

    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    return mapper.readValue(json, LEIRecordType[].class);
}   

但这只会将以@开头的值设置为空。还有其他方法可以解决这个问题吗？否则，我将不得不为我生成的所有类编写一个自定义反序列化器，大约是 25 个（下一个版本中总会有更多）。我已经为 NameType 做了一个，但对于其他示例，还需要更多。

Answer 3

我认为明确的解决方案是使用@JsonProperty("$"):

ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
List<LEIModel> leiList = Arrays.asList(mapper.readValue(response.toString(), LEIModel[].class));

LEIModel 类：

public class LEIModel {
   @JsonProperty("Entity")
   private Entity entity;

   public Entity getEntity() {
       return entity;
   }

   public void setEntity(Entity entity) {
       this.entity = entity;
   }
}

实体类：

public class Entity {
   @JsonProperty("LegalName")
   private LegalName legalName;

   public LegalName getLegalName() {
       return legalName;
   }

   public void setLegalName(LegalName legalName) {
       this.legalName = legalName;
   }
}

LegalName 类：

public class LegalName {
   @JsonProperty("$")
   private String value;

   public String getValue() {
       return value;
   }

   public void setValue(String value) {
       this.value = value;
   }
}