我不明白EclipseLink MOXy属性或xml- XmlProperty的含义，有人能提供更多信息吗？

Question

我可以在谷歌上找到的只有3条信息，最详细的是设计文件，如下网址

http://wiki.eclipse.org/EclipseLink/DesignDocs/317962/Phase2.1#.40XmlProperty

它确实提到了“xml-property元数据标记将用于配置属性”。并给出了两个没有编组结果的例子如下：

Example: type-level property
The following example will demonstrate how a type-level property can be applied.

Setting xml-property on a type via EclipseLink XML metadata can be accomplished as follows:

<java-type name="org.example.Employee">
    <xml-properties>
        <xml-property name="identifier" value="101" value-type="java.lang.Integer" />
        <xml-property name="isTrue" value="false" value-type="java.lang.Boolean" />
    </xml-properties>
</java-type>
Setting @XmlProperty on a type via annotations can be accomplished as follows:

org.example.Employee.java
@XmlProperties({@XmlProperty(name="identifier", value="101", valueType=Integer.class), 
                @XmlProperty(name="isTrue", value="false", valueType=Boolean.class)})
public class Employee {
   ...
}
Example: property-level property
The following example will demonstrate how a property-level property can be applied.

Setting xml-property on a property via EclipseLink XML metadata can be accomplished as follows:

<java-type name="org.example.Employee">
    <java-attributes>
        <xml-element java-attribute="myelement">
            <xml-properties>
                <xml-property name="isAttribute" value="false" value-type="java.lang.Boolean" />
                <xml-property name="comment" value="this is an element" />
            </xml-properties>
        </xml-element>
    </java-attributes>
</java-type>
Setting @XmlProperty on a property via annotations can be accomplished as follows:

org.example.Employee.java
public class Employee {

  @XmlProperties({@XmlProperty(name="isAttribute", value="false", valueType=Boolean.class),
                  @XmlProperty(name="comment", value="this is an element")}
  public String myelement;
}

我也尝试了我的示例，但我无法区分使用和不使用xml属性的内容之间的任何区别。

谁能给我解释一下XmlProperty是做什么的？它会产生什么样的效果？或者什么时候使用XmlProperty？有没有包含封送处理结果的示例代码？

<?xml version="1.0"?>
<xml-bindings xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.eclipse.org/eclipselink/xsds/persistence/oxm http://www.eclipse.org/eclipselink/xsds/eclipselink_oxm_2_4.xsd"
    version="2.1">
    <xml-schema element-form-default="QUALIFIED">
        <xml-ns prefix="ns1" namespace-uri="http://www.example.org/customer" />
        <xml-ns prefix="ns2" namespace-uri="http://www.example.org/phone" />
        <xml-ns prefix="ns3" namespace-uri="http://www.example.org/addr" />
    </xml-schema>
    <java-types>
        <java-type name="example.gettingstarted.demo1.Customer">
            <xml-root-element />
            <xml-type namespace="http://www.example.org/customer"
                prop-order="name address phoneNumbers" />
            <xml-properties>
                <xml-property name="hello" value="false" value-type="java.lang.String" />
                <xml-property name="world" value="this is an element"
                    value-type="java.lang.String" />
            </xml-properties>
            <java-attributes>
                <xml-attribute java-attribute="name" xml-path="@name" />
                <xml-element java-attribute="address">
                </xml-element>
                <xml-element java-attribute="phoneNumbers" xml-path="contact-info/phone-number" />
            </java-attributes>
        </java-type>
        <java-type name="example.gettingstarted.demo1.PhoneNumber">
            <xml-root-element />
            <xml-type namespace="http://www.example.org/phone"></xml-type>
            <java-attributes>
                <xml-attribute java-attribute="type" />
                <xml-value java-attribute="value" />
            </java-attributes>
        </java-type>
        <java-type name="example.gettingstarted.demo1.Address">
        </java-type>
    </java-types>
</xml-bindings>

Java文件：

package example.gettingstarted.demo5;

import java.util.HashMap;
import java.util.Map;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.transform.Source;
import javax.xml.transform.stream.StreamSource;

import org.eclipse.persistence.jaxb.JAXBContextFactory;

import example.gettingstarted.demo1.Address;
import example.gettingstarted.demo1.Customer;
import example.gettingstarted.demo1.PhoneNumber;

/**
 * @author barry
 * make Customer.Address.street as Customer.@street
 */
public class Demo {

    @SuppressWarnings({ "rawtypes", "deprecation" })
    public static void main(String[] args) throws JAXBException {
        // Step 1 - Create the Domain Model
        Customer customer = new Customer();
        customer.setName("Jane Doe");
        Address address = new Address();
        address.setStreet("123 Any Street");
        address.setCity("My Town");
        customer.setAddress(address);
        PhoneNumber workPhoneNumber = new PhoneNumber();
        workPhoneNumber.setType("work");
        workPhoneNumber.setValue("613-555-1111");
        customer.getPhoneNumbers().add(workPhoneNumber);
        PhoneNumber cellPhoneNumber = new PhoneNumber();
        cellPhoneNumber.setType("cell");
        cellPhoneNumber.setValue("613-555-2222");
        customer.getPhoneNumbers().add(cellPhoneNumber);

        // Step 2 - Convert the Domain Model to XML
        final Map<String, Source> metadataSourceMap = new HashMap<String, Source>();
        metadataSourceMap.put("example.gettingstarted.demo1", new StreamSource("./example/gettingstarted/demo5/eclipselink-oxm.xml"));

        final Map<String, Object> properties = new HashMap<String, Object>();
        properties.put(JAXBContextFactory.ECLIPSELINK_OXM_XML_KEY, metadataSourceMap);

        final Class[] classes = new Class[1];
        classes[0] = Customer.class;

        JAXBContext jaxbContext = (JAXBContext) JAXBContext.newInstance(classes, properties);
        Marshaller marshaller = jaxbContext.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(customer, System.out);
    }
}

不管是否应用了xml-property，我的输出如下所示。

                My Town           123 Any Street                           613-555-1111           613-555-2222

Answer 1

的@XmlProperty扩展是一种将自定义数据放入MOXy原生映射元数据的方法。它用于一些非常独特的用例。我将在下面演示如何使用它。

JAVA模型

在这个示例中，我将使用以下模型。

package forum15651379;

public class Foo {

    private String bar;

    public String getBar() {
        return bar;
    }

    public void setBar(String bar) {
        this.bar = bar;
    }

}

演示代码

在下面的演示代码中，JAXBContext将被引导到MOXy的外部映射文档(参见：http://blog.bdoughan.com/2010/12/extending-jaxb-representing-annotations.html)。

package forum15651379;

import java.util.*;
import javax.xml.bind.*;
import org.eclipse.persistence.jaxb.JAXBContextProperties;

public class Demo {

    public static void main(String[] args) throws Exception {
        Map<String, Object> properties = new HashMap<String, Object>(1);
        properties.put(JAXBContextProperties.OXM_METADATA_SOURCE, "forum15651379/oxm.xml");
        JAXBContext jc = JAXBContext.newInstance(new Class[] {Foo.class}, properties);

        Foo foo = new Foo();
        foo.setBar("Hello World");

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

}

常见用例

下面是典型的用例。映射使用java-attributes元素定义。

oxm.xml

<?xml version="1.0" encoding="UTF-8"?>
<xml-bindings
    xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    package-name="forum15651379">
    <java-types>
        <java-type name="Foo">
           <xml-root-element name="FOO"/>
            <java-attributes>
                <xml-element java-attribute="bar" name="BAR">
                </xml-element>
            </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

输出

<?xml version="1.0" encoding="UTF-8"?>
<FOO>
   <BAR>Hello World</BAR>
</FOO>

高级用例

oxm.xml

我扩展了oxm.xml以包含属性，并指定了一个描述符定制器。

<?xml version="1.0" encoding="UTF-8"?>
<xml-bindings
    xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm"
    package-name="forum15651379">
    <java-types>
        <java-type name="Foo" xml-customizer="forum15651379.FooCustomizer">
            <xml-properties>
                <xml-property name="key1" value="value1"/>
                <xml-property name="key2" value="value2"/>
            </xml-properties>
           <xml-root-element name="FOO"/>
            <java-attributes>
                <xml-element java-attribute="bar" name="BAR">
                    <xml-properties>
                        <xml-property name="key3" value="value3"/>
                        <xml-property name="key4" value="value4"/>
                    </xml-properties>
                </xml-element>
            </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

描述符定制器(FooCustomizer)

描述符定制器允许您访问MOXy的原生映射元数据。下面是一个简单的示例，展示了如何处理oxm.xml文件中指定的属性。

package forum15651379;

import org.eclipse.persistence.config.DescriptorCustomizer;
import org.eclipse.persistence.descriptors.ClassDescriptor;
import org.eclipse.persistence.oxm.XMLDescriptor;
import org.eclipse.persistence.oxm.mappings.XMLDirectMapping;

public class FooCustomizer implements DescriptorCustomizer{

    @Override
    public void customize(ClassDescriptor descriptor) throws Exception {
        XMLDescriptor xmlDescriptor = (XMLDescriptor) descriptor;
        String key1Value = (String) xmlDescriptor.getProperty("key1");
        xmlDescriptor.setDefaultRootElement(key1Value);

        XMLDirectMapping barMapping = (XMLDirectMapping) xmlDescriptor.getMappingForAttributeName("bar");
        String key3Value = (String) barMapping.getProperty("key3");
        barMapping.setXPath(key3Value + "/text()");
    }

}

输出

下面我们将看到我们在FooCustomizer中所做的事情对生成的XML的影响。

<?xml version="1.0" encoding="UTF-8"?>
<value1>
   <value3>Hello World</value3>
</value1>