JAXB 和构造函数 [英] JAXB and constructors

问题描述

我开始学习 JAXB，所以我的问题可能很愚蠢.现在我有课程并想生成 XML 模式.按照 this 指令我得到异常

I'm starting learning JAXB, so my question can be very silly. Now I have classes and want generate XML Schema. Going after this instruction I get exception

IllegalAnnotationExceptions ... 没有无参数默认值构造函数.

IllegalAnnotationExceptions ... does not have a no-arg default constructor.

是的.我的课程没有默认的无参数构造函数.这太容易了.我有带有包可见构造函数/最终方法的类，当然还有带参数的类.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.

Yeah. My classes haven't default no-arg constructors. It's too easy. I have classes with package visible constructors / final methods and off course with arguments. What shall I do - create some specific momemto/builder classes or specify my constructors to JAXB (in what way?) ? Thanks.

推荐答案

JAXB 可以使用 XML 适配器支持这种情况.考虑您有以下没有零参数构造函数的对象:

JAXB can support this case using an XML Adapter. Consider you have the following object with no zero-arg constructor:

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:

You simply need to create a mappable version of this class:

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;
    }

}

还有一个用于在它们之间进行转换的 XML 适配器:

And an XML Adapter to convert between them:

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 注释:

Then for properties that refer to the Customer class, simply use the @XmlJavaTypeAdapter annotation:

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，请参阅:

• http://bdoughan.blogspot.com/2010/12/jaxb-and-immutable-objects.html

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