我需要在jaxb中显示空值为空的元素.我正在使用moxy实现jaxb.
我发现这个选项
我发现这个选项
@XmlNullPolicy(emptyNodeRepresentsNull = true,nullRepresentationForXml = XmlMarshalNullRepresentation.EMPTY_NODE)
是否有任何类似的扩展可以应用于Class级别(对于其中定义的所有元素)
解决方法
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
使用标准的API,您可以通过@XmlElement注释来控制是否将空值表示为缺少节点或xsi：nil =“true”(请参阅：http://blog.bdoughan.com/2012/04/binding-to-json-xml-handling-null.html).
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.
<?xml version="1.0" encoding="UTF-8"?> <address> <city xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/> </address>
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
<?xml version="1.0" encoding="UTF-8"?> <address> <street/> <city/> </address>
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<String,Object> properties = new HashMap<String,Object>(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);
}
}
产量
<?xml version="1.0" encoding="UTF-8"?> <address> <street/> <city/> </address>
