如何强制JAXB为无maxOccurs的元素生成List类型字段？

我在WSDL中定义了两个复杂类型，二者仅在maxOccurs="unbounded"配置上存在差异：

<xs:complexType name="TypeGetPaymentDetailsAdditionRequest">
    <xs:sequence>
        <xs:element name="PaymentDetails"
                    type="tns:TypeGetPaymentDetailAdditionRequest"/>
    </xs:sequence>
</xs:complexType>
<xs:complexType name="TypeGetPaymentDetailsRequest">
    <xs:sequence>
        <xs:element name="PaymentDetails"
                    type="tns:TypeGetPaymentDetailRequest"
                    maxOccurs="unbounded"/>
    </xs:sequence>
</xs:complexType>

但通过JAXB（版本com.sun.xml.bind:jaxb-xjc:2.1.7）生成的Java类结构不符合预期：

• 带maxOccurs="unbounded"的TypeGetPaymentDetailsRequest生成了List<>类型字段：

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(
    name = "TypeGetPaymentDetailsRequest",
    propOrder = {"paymentDetails"}
)
public class TypeGetPaymentDetailsRequest {
    @XmlElement(
        name = "PaymentDetails",
        required = true
    )
    protected List<TypeGetPaymentDetailRequest> paymentDetails;

    public TypeGetPaymentDetailsRequest() {
    }

    public List<TypeGetPaymentDetailRequest> getPaymentDetails() {
        if (this.paymentDetails == null) {
            this.paymentDetails = new ArrayList();
        }

        return this.paymentDetails;
    }
}

• 不带maxOccurs="unbounded"的TypeGetPaymentDetailsAdditionRequest生成了单个对象字段：

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(
    name = "TypeGetPaymentDetailsAdditionRequest",
    propOrder = {"paymentDetails"}
)
public class TypeGetPaymentDetailsAdditionRequest {
    @XmlElement(
        name = "PaymentDetails",
        required = true
    )
    protected TypeGetPaymentDetailAdditionRequest paymentDetails;

    public TypeGetPaymentDetailsAdditionRequest() {
    }

    public TypeGetPaymentDetailAdditionRequest getPaymentDetails() {
        return this.paymentDetails;
    }

    public void setPaymentDetails(TypeGetPaymentDetailAdditionRequest value) {
        this.paymentDetails = value;
    }
}

我需要强制让TypeGetPaymentDetailsAdditionRequest类中的paymentDetails字段也生成为List<>类型，该怎么做？

针对JAXB 2.1.7版本，有两种可行方案：

方案一：修改WSDL/XSD定义 #

直接在目标元素上显式添加maxOccurs="unbounded"，若需要确保至少有一个元素，可同时保留minOccurs="1"：

<xs:complexType name="TypeGetPaymentDetailsAdditionRequest">
    <xs:sequence>
        <xs:element name="PaymentDetails"
                    type="tns:TypeGetPaymentDetailAdditionRequest"
                    maxOccurs="unbounded"
                    minOccurs="1"/>
    </xs:sequence>
</xs:complexType>

这是最直接的方式，符合XML Schema语义，JAXB会自动生成List<>类型字段。

方案二：使用JAXB绑定自定义文件 #

如果无法修改原始WSDL/XSD，可创建绑定文件（如jaxb-bindings.xml），通过自定义规则强制生成集合类型：

<jaxb:bindings xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
               xmlns:xs="http://www.w3.org/2001/XMLSchema"
               jaxb:version="2.1">
    <jaxb:bindings schemaLocation="your-service.wsdl" node="/xs:schema">
        <jaxb:bindings node="//xs:complexType[@name='TypeGetPaymentDetailsAdditionRequest']//xs:element[@name='PaymentDetails']">
            <jaxb:property>
                <jaxb:baseType name="java.util.List"/>
            </jaxb:property>
        </jaxb:bindings>
    </jaxb:bindings>
</jaxb:bindings>

调用xjc工具时指定该绑定文件：

xjc -b jaxb-bindings.xml your-service.wsdl

或在Maven等构建工具中配置绑定文件路径，确保生成代码时应用规则。注意需保证节点路径与目标元素完全匹配。

内容的提问来源于stack exchange，提问作者Eljah