我正在尝试将 Java 库中的 Java 对象转换为 XML 文件。但是，我遇到了这个问题:

A a = new A();

// initializing for a

JAXBContext jc = JAXBContext.newInstance("libraryA.A");

Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(a, System.out);

然后我得到了这个异常:

javax.xml.bind.JAXBException: "libraryA.a" doesnt contain ObjectFactory.class or jaxb.index
    at com.sun.xml.internal.bind.v2.ContextFactory.createContext(ContextFactory.java:186)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:128)
    at javax.xml.bind.ContextFinder.find(ContextFinder.java:290)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:372)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:337)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:244)

如果我改变:JAXBContext jc = JAXBContext.newInstance("libraryA.a");

到:

JAXBContext jc = JAXBContext.newInstance(libraryA.A.class);

然后我有另一个异常(exception):

com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 2 counts of IllegalAnnotationExceptions

library.A is an interface, and JAXB can't handle interfaces.
    this problem is related to the following location:
        at library.A

library.A does not have a no-arg default constructor.
    this problem is related 

to the following location:
    at library.A

最佳答案

背景信息(来自 Related Question)

根据您对我对上一个问题的回答所做的评论，领域模型已经与 JAXB 一起使用。让您的客户端和服务器通过 XML 进行通信的最简单方法是在两端利用已注释的模型。

I just have checked the source code of my client. In the process, we need to convert back a xml file which is generated from java objects to xml file using: javax.xml.bind.JAXBContext & javax.xml.bind.Marshaller. so my question is it possible to read back the xml file to the same java objects? then we can use the java objects for a further step. Thanks in advance!

更新

您的问题似乎是由于域模型是通过具有支持实现类的接口(interface)定义的。下面我将演示如何使用 JAXB 实现(Metro、MOXy、JaxMe 等)处理此问题。

演示代码

import java.io.File;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(CustomerImpl.class);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        File xml = new File("input.xml");
        Customer customer = (Customer) unmarshaller.unmarshal(xml);

        Address address = customer.getAddress();
        System.out.println(address.getStreet());

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(customer, System.out);
    }

}

接口(interface)模型

以下接口(interface)代表我们的领域模型。这些接口(interface)在未被利用时用于引导 JAXBContext。

客户

public interface Customer {

    public Address getAddress();

    public void setAddress(Address address);

}

地址

public interface Address {

    public String getStreet();

    public void setStreet(String street);

}

实现类

实现类是将使用 JAXB 映射到 XML 的内容。

CustomerImpl

请注意，在 CustomerImpl 类中，我们使用 address 属性上的 @XmlElement 注释来指定类型为 AddressImpl.

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement(name="customer")
public class CustomerImpl implements Customer {

    private Address address;

    @XmlElement(type=AddressImpl.class)
    public Address getAddress() {
        return address;
    }

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

}

AddressImpl

public class AddressImpl implements Address {

    private String street;

    public String getStreet() {
        return street;
    }

    public void setStreet(String street) {
        this.street = street;
    }

}

输入.xml

<?xml version="1.0" encoding="UTF-8"?>
<customer>
    <address>
        <street>1 Any Street</street>
    </address>
</customer>

关于java - 将 Java 对象转换为 XML，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/5964996/