在使用Java XStream進行對象映射時，可以通過定義不同的別名和映射規則來處理復雜對象的映射。以下是一個示例，演示了如何映射一個包含多個屬性和對象的復雜對象：

import com.thoughtworks.xstream.XStream;

public class Main {

    public static void main(String[] args) {
        XStream xstream = new XStream();
        
        // 定義別名
        xstream.alias("person", Person.class);
        xstream.alias("address", Address.class);
        
        // 添加字段映射
        xstream.aliasField("firstName", Person.class, "firstName");
        xstream.aliasField("lastName", Person.class, "lastName");
        xstream.aliasField("street", Address.class, "street");
        xstream.aliasField("city", Address.class, "city");
        xstream.aliasField("zipCode", Address.class, "zipCode");
        
        // 創建一個復雜對象
        Person person = new Person("John", "Doe");
        Address address = new Address("123 Main St", "Anytown", "12345");
        person.setAddress(address);
        
        // 將復雜對象序列化為XML
        String xml = xstream.toXML(person);
        System.out.println(xml);
        
        // 將XML反序列化為復雜對象
        Person person2 = (Person) xstream.fromXML(xml);
        System.out.println(person2);
    }
}

class Person {
    private String firstName;
    private String lastName;
    private Address address;

    public Person(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "Person{" +
                "firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                ", address=" + address +
                '}';
    }
}

class Address {
    private String street;
    private String city;
    private String zipCode;

    public Address(String street, String city, String zipCode) {
        this.street = street;
        this.city = city;
        this.zipCode = zipCode;
    }

    @Override
    public String toString() {
        return "Address{" +
                "street='" + street + '\'' +
                ", city='" + city + '\'' +
                ", zipCode='" + zipCode + '\'' +
                '}';
    }
}

在這個示例中，我們定義了兩個類Person和Address，并使用XStream進行對象映射。通過定義別名和字段映射，我們可以將復雜對象序列化為XML，并將XML反序列化為復雜對象。