JAXB和构造函数

斯坦·库里林（Stan Kurilin）：

我开始学习JAXB，所以我的问题可能很愚蠢。现在我有了类，想要生成XML Schema。在执行此指令后，我得到了异常

IllegalAnnotationExceptions ...没有无参数的默认构造函数。

是的我的课程没有默认的无参数构造函数。太简单了我有类与包可见的构造函数/ final方法和偏离路线的参数。我该怎么做-创建一些特定的momemto / builder类或将我的构造函数指定为JAXB（以什么方式？）？谢谢。

bdoughan：

JAXB可以使用XML适配器来支持这种情况。考虑您具有以下对象，没有零参数构造函数：

package blog.immutable;

public class Customer {

    private final String name;
    private final Address address;

    public Customer(String name, Address address) {
        this.name = name;
        this.address = address;
    }

    public String getName() {
        return name;
    }

    public Address getAddress() {
        return address;
    }

}

您只需要创建此类的可映射版本：

package blog.immutable.adpater;

import javax.xml.bind.annotation.XmlAttribute;
import blog.immutable.Address;

public class AdaptedCustomer {

    private String name;
    private Address address;

    @XmlAttribute
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Address getAddress() {
        return address;
    }

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

}

还有一个在它们之间转换的XML适配器：

package blog.immutable.adpater;

import javax.xml.bind.annotation.adapters.XmlAdapter;
import blog.immutable.Customer;

public class CustomerAdapter extends XmlAdapter<AdaptedCustomer, Customer> {

    @Override
    public Customer unmarshal(AdaptedCustomer adaptedCustomer) throws Exception {
        return new Customer(adaptedCustomer.getName(), adaptedCustomer.getAddress());
    }

    @Override
    public AdaptedCustomer marshal(Customer customer) throws Exception {
        AdaptedCustomer adaptedCustomer = new AdaptedCustomer();
        adaptedCustomer.setName(customer.getName());
        adaptedCustomer.setAddress(customer.getAddress());
        return adaptedCustomer;
    }

}

然后，对于引用Customer类的属性，只需使用@XmlJavaTypeAdapter批注：

package blog.immutable;

import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
import blog.immutable.adpater.CustomerAdapter;

@XmlRootElement(name="purchase-order")
public class PurchaseOrder {

    private Customer customer;

    @XmlJavaTypeAdapter(CustomerAdapter.class)
    public Customer getCustomer() {
        return customer;
    }

    public void setCustomer(Customer customer) {
        this.customer = customer;
    }

}

有关更详细的示例，请参见：