如何将嵌套XML元素内容映射为Map的字符串值？

使用的依赖 #

<dependency>
    <groupId>com.fasterxml.jackson.dataformat</groupId>
    <artifactId>jackson-dataformat-xml</artifactId>
    <version>2.8.7</version>
</dependency>

需求说明 #

需要处理如下XML，将其中名称随机的元素（例如<RandomName>，其内部内容也不固定）的元素名作为Map的key，把该元素下的所有XML内容作为字符串值存入Map，实现类似 RandomName -> <metadaten> ... </metadaten> 的映射。

示例XML #

<slices>
    <slice>
        <boundedBy>
            <Envelope>
                <axisLabels>Lat Long</axisLabels>
                <srsDimension>2</srsDimension>
                <lowerCorner>-44.975 111.975</lowerCorner>
                <upperCorner>-8.975 130.975</upperCorner>
            </Envelope>
        </boundedBy>
        <local_metadata_key>test123</local_metadata_key>
        <RandomName>
            <metadaten>
                <Kompression>0</Kompression>
                <Komprimierung>0</Komprimierung>
                <Belaubungszustand>3</Belaubungszustand>
                <Bemerkungen>keine</Bemerkungen>
            </metadaten>
        </RandomName>
        <fileReferenceHistory>testfile</fileReferenceHistory>   
    </slice>
</slices>

当前问题 #

编写了LocalMetadataChild类用于反序列化，但addKeyValue()方法中，只能拿到key为RandomName，而value始终是空字符串。需要让value等于该元素下的完整子XML内容（即<metadaten> ... </metadaten>部分）。

当前代码：

public class LocalMetadataChild {
    
    public static final String LOCAL_METADATA_TAG = "slice";

    private Map<String, String> localMetadataAttributesMap;
    
    private BoundedBy boundedBy;

    @JsonAnySetter
    // NOTE: To map an unknown list of properties, must use this annotation
    public void addKeyValue(String key, String value) {
        this.localMetadataAttributesMap.put(key, value);
    }

    public LocalMetadataChild() {
        this.localMetadataAttributesMap = new LinkedHashMap<>();
        this.boundedBy = new BoundedBy();
    }

    @JsonAnyGetter
    // NOTE: to unwrap the "map" from { "map": { "key": "value" } }, only keep { "key": "value" }
    public Map<String, String> getLocalMetadataAttributesMap() {
        return localMetadataAttributesMap;
    }
    
    public BoundedBy getBoundedBy() {
        return this.boundedBy;
    }

    public void setBoundedBy(BoundedBy boundedBy) {
        this.boundedBy = boundedBy;
    }

    public LocalMetadataChild(Map<String, String> localMetadataAttributesMap, BoundedBy boundedBy) {
        this.localMetadataAttributesMap = localMetadataAttributesMap;
        this.boundedBy = boundedBy;
    }
}

解决方案 #

问题出在@JsonAnySetter的参数类型：当元素包含子XML结构时，Jackson无法直接将其序列化为String，会默认解析为内部对象，导致传入空字符串。需要修改参数类型为JsonNode，再将其序列化为XML字符串存入Map。

修改后的代码 #

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.dataformat.xml.XmlMapper;

public class LocalMetadataChild {
    
    public static final String LOCAL_METADATA_TAG = "slice";

    private Map<String, String> localMetadataAttributesMap;
    
    private BoundedBy boundedBy;
    private final XmlMapper xmlMapper;

    @JsonAnySetter
    public void addKeyValue(String key, JsonNode value) throws Exception {
        // 将JsonNode序列化为XML字符串
        String xmlContent = xmlMapper.writeValueAsString(value);
        this.localMetadataAttributesMap.put(key, xmlContent);
    }

    public LocalMetadataChild() {
        this.localMetadataAttributesMap = new LinkedHashMap<>();
        this.boundedBy = new BoundedBy();
        this.xmlMapper = new XmlMapper();
    }

    public LocalMetadataChild(Map<String, String> localMetadataAttributesMap, BoundedBy boundedBy) {
        this.localMetadataAttributesMap = localMetadataAttributesMap;
        this.boundedBy = boundedBy;
        this.xmlMapper = new XmlMapper();
    }

    @JsonAnyGetter
    public Map<String, String> getLocalMetadataAttributesMap() {
        return localMetadataAttributesMap;
    }
    
    public BoundedBy getBoundedBy() {
        return this.boundedBy;
    }

    public void setBoundedBy(BoundedBy boundedBy) {
        this.boundedBy = boundedBy;
    }
}

关键说明 #

• 将@JsonAnySetter的第二个参数从String改为JsonNode，保留子元素的完整结构信息。
• 通过XmlMapper将JsonNode重新序列化为XML字符串，存入Map即可得到目标子XML内容。
• 若不需要外层包裹节点（仅需<metadaten>部分），可提取JsonNode的子节点后再序列化。

内容的提问来源于stack exchange，提问作者Bằng Rikimaru