我强烈建议使用不存在节点或xsi：nil =“true”属性来表示null.这最适用于模式验证(即< age />或< age>< / age>不是xsd：int类型的有效元素.但是,如果您不能在这里完成您的用例：

标准JAXB行为

import javax.xml.bind.annotation.*;

@XmlRootElement

@XmlAccessorType(XmlAccessType.FIELD)

public class Address {

private String street;

@XmlElement(nillable=true)

private String city;

}

以下是两个字段的值为空的XML输出.

MOXY – 覆盖此类行为

MOXy不提供注释来为类中的所有属性指定空策略.但是,您可以通过@XmlCustomizer注释来使用DescriptorCustomizer,并调整本机MOXy映射元数据来完成相同的操作.

DescriptorCustomizer(AddressCustomizer)

import org.eclipse.persistence.config.DescriptorCustomizer;

import org.eclipse.persistence.descriptors.ClassDescriptor;

import org.eclipse.persistence.mappings.DatabaseMapping;

import org.eclipse.persistence.oxm.mappings.XMLDirectMapping;

import org.eclipse.persistence.oxm.mappings.nullpolicy.XMLNullRepresentationType;

public class AddressCustomizer implements DescriptorCustomizer {

@Override

public void customize(ClassDescriptor descriptor) throws Exception {

for(DatabaseMapping mapping : descriptor.getMappings()) {

if(mapping.isAbstractDirectMapping()) {

XMLDirectMapping xmlDirectMapping = (XMLDirectMapping) mapping;

xmlDirectMapping.getNullPolicy().setMarshalNullRepresentation(XMLNullRepresentationType.EMPTY_NODE);

xmlDirectMapping.getNullPolicy().setNullRepresentedByEmptyNode(true);

}

}

}

}

DomainModel(地址)

import javax.xml.bind.annotation.*;

import org.eclipse.persistence.oxm.annotations.XmlCustomizer;

@XmlRootElement

@XmlAccessorType(XmlAccessType.FIELD)

@XmlCustomizer(AddressCustomizer.class)

public class Address {

private String street;

@XmlElement(nillable=true)

private String city;

}

产量

MOXY – 覆盖所有类别的行为

如果你想覆盖所有映射类的空处理,我建议改用SessionEventListener.如果您愿意,也可以使用此方法来更新单个类的元数据.

SessionEventListener(NullPolicySessionEventListener)

import org.eclipse.persistence.descriptors.ClassDescriptor;

import org.eclipse.persistence.mappings.DatabaseMapping;

import org.eclipse.persistence.oxm.mappings.XMLDirectMapping;

import org.eclipse.persistence.oxm.mappings.nullpolicy.XMLNullRepresentationType;

import org.eclipse.persistence.sessions.*;

public class NullPolicySessionEventListener extends SessionEventAdapter {

@Override

public void preLogin(SessionEvent event) {

Project project = event.getSession().getProject();

for(ClassDescriptor descriptor : project.getOrderedDescriptors()) {

for(DatabaseMapping mapping : descriptor.getMappings()) {

if(mapping.isAbstractDirectMapping()) {

XMLDirectMapping xmlDirectMapping = (XMLDirectMapping) mapping;

xmlDirectMapping.getNullPolicy().setMarshalNullRepresentation(XMLNullRepresentationType.EMPTY_NODE);

xmlDirectMapping.getNullPolicy().setNullRepresentedByEmptyNode(true);

}

}

}

}

}

演示代码

import java.util.*;

import javax.xml.bind.*;

import org.eclipse.persistence.jaxb.JAXBContextProperties;

import org.eclipse.persistence.sessions.SessionEventListener;

public class Demo {

public static void main(String[] args) throws Exception {

Map properties = new HashMap(1);

SessionEventListener sessionEventListener = new NullPolicySessionEventListener();

properties.put(JAXBContextProperties.SESSION_EVENT_LISTENER,sessionEventListener);

JAXBContext jc = JAXBContext.newInstance(new Class[] {Address.class},properties);

Address address = new Address();

Marshaller marshaller = jc.createMarshaller();

marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT,true);

marshaller.marshal(address,System.out);

}

}

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