无法通过Retrofit将XML响应解析为Kotlin数据类

问题场景 #

调用返回XML格式的REST API，使用Retrofit搭配SimpleXML Converter Factory解析为Kotlin数据类时，出现以下错误：

org.simpleframework.xml.core.ElementException: Element 'result[1]/author[1]' does not have a match in class BookList

API返回的XML响应：

<category>
    <api-version>1.0</api-version>
    <books>
        <list>
            <result>
                <author>Hello1</author>
                <brief>Hii</brief>
            </result>
            <result>
                <author>Hello2</author>
                <brief>Hii2</brief>
            </result>
        </list>
    </books>
</category>

原Kotlin数据类定义：

data class CategoryResponseModel(
        @field:Element(name = "api-version", required = false)
        @param:Element(name = "api-version", required = false)
        val apiVersion: String? = null,

        @field:Element(name = "books", required = false)
        @param:Element(name = "books", required = false)
        val books: Books? = null
)

data class Books(
        @field:Element(name = "list", required = false)
        @param:Element(name = "list", required = false)
        val list: BookList? = null
)

@Root(name = "list")
data class BookList(
        @field:Element(name = "result", required = false)
        @param:Element(name = "result", required = false)
        val result: List<BookSearchResult>? = null,
)

data class BookSearchResult(
        @field:Element(name = "author", required = false)
        @param:Element(name = "author", required = false)
        val author: String? = null,

        @field:Element(name = "brief", required = false)
        @param:Element(name = "brief", required = false)
        val briefSynopsis: String? = null,
)

错误原因 #

SimpleXML解析列表类型时，必须使用@ElementList注解标记，而非普通的@Element。原代码中BookList类用@Element标记List<BookSearchResult>，导致解析器无法识别多个<result>元素是列表项，进而抛出匹配错误。

修正方案 #

修改BookList类的注解为@ElementList，并添加inline = true参数（因为<result>元素直接嵌套在<list>下，没有额外的列表包裹元素）。同时简化Kotlin数据类的注解写法，无需同时标注@field:和@param:。

修正后的完整数据类：

data class CategoryResponseModel(
    @field:Element(name = "api-version", required = false)
    val apiVersion: String? = null,

    @field:Element(name = "books", required = false)
    val books: Books? = null
)

data class Books(
    @field:Element(name = "list", required = false)
    val list: BookList? = null
)

@Root(name = "list")
data class BookList(
    @field:ElementList(name = "result", inline = true, required = false)
    val result: List<BookSearchResult>? = null
)

data class BookSearchResult(
    @field:Element(name = "author", required = false)
    val author: String? = null,

    @field:Element(name = "brief", required = false)
    val briefSynopsis: String? = null
)

关键说明 #

• @ElementList：专门用于标记XML中的重复元素列表
• inline = true：当列表元素直接作为父元素的子节点（而非被单独的列表容器包裹）时必须添加该参数
• Kotlin中只需标注@field:注解即可，无需重复标注@param:，简化代码结构

内容的提问来源于stack exchange，提问作者Purvesh Dodiya