我強烈建議使用不存在節點或xsi：nil =“true”屬性來表示null.這最適用于模式驗證(即< age />或< age>< / age>不是xsd：int類型的有效元素.但是,如果您不能在這里完成您的用例：

標準JAXB行為

import javax.xml.bind.annotation.*;

@XmlRootElement

@XmlAccessorType(XmlAccessType.FIELD)

public class Address {

private String street;

@XmlElement(nillable=true)

private String city;

}

以下是兩個字段的值為空的XML輸出.

MOXY – 覆蓋此類行為

MOXy不提供注釋來為類中的所有屬性指定空策略.但是,您可以通過@XmlCustomizer注釋來使用DescriptorCustomizer,并調整本機MOXy映射元數據來完成相同的操作.

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;

}

產量

MOXY – 覆蓋所有類別的行為

如果你想覆蓋所有映射類的空處理,我建議改用SessionEventListener.如果您愿意,也可以使用此方法來更新單個類的元數據.

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);

}

}

}

}

}

演示代碼

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);

}

}

產量

總結

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