Question

我正在尝试使字符串为空时JAXB不会封送空标记。我可以通过创建XmlAdapter来创建它，其中将返回insted空字符串null。但就这样，我将不得不用这个适配器注释每个属性。

有没有办法让它更全球化？

Answer 1

EclipseLink JAXB（MOXy）允许您在包级别指定XmlAdapter java.lang.String（我是MOXy技术主管）：

<强>包信息

@XmlJavaTypeAdapter(value=StringAdapter.class, type=String.class)
package example;

import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

<强> StringAdapter

package example;

import javax.xml.bind.annotation.adapters.XmlAdapter;

public class StringAdapter extends XmlAdapter<String, String> {

    @Override
    public String unmarshal(String v) throws Exception {
        return v;
    }

    @Override
    public String marshal(String v) throws Exception {
        if("".equals(v)) {
            return null;
        }
        return v;
    }

}

<强>根

package example;

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Root {

    private String foo;
    private String bar;

    public String getFoo() {
        return foo;
    }

    public void setFoo(String foo) {
        this.foo = foo;
    }

    public String getBar() {
        return bar;
    }

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

}

<强> jaxb.properties

要将MOXy用作JAXB提供程序，您需要在与模型类相同的包中包含名为jaxb.properties的文件，并带有以下条目：

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

<强>演示

package example;

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

public class Demo {

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

        Root root = new Root();
        root.setFoo("");
        root.setBar("");

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

}

注意

由于我认为JAXB参考实现中存在错误，如果您使用Java SE 6中包含的JAXB版本，则会引发以下异常：

Exception in thread "main" java.lang.NullPointerException at com.sun.xml.bind.v2.runtime.output.Encoded.setEscape(Encoded.java:107) at com.sun.xml.bind.v2.runtime.output.UTF8XmlOutput.doText(UTF8XmlOutput.java:315) at com.sun.xml.bind.v2.runtime.output.UTF8XmlOutput.text(UTF8XmlOutput.java:299) at com.sun.xml.bind.v2.runtime.output.IndentingUTF8XmlOutput.text(IndentingUTF8XmlOutput.java:153) at com.sun.xml.bind.v2.runtime.XMLSerializer.leafElement(XMLSerializer.java:325) at com.sun.xml.bind.v2.model.impl.RuntimeBuiltinLeafInfoImpl$1.writeLeafElement(RuntimeBuiltinLeafInfoImpl.java:210) at com.sun.xml.bind.v2.model.impl.RuntimeBuiltinLeafInfoImpl$1.writeLeafElement(RuntimeBuiltinLeafInfoImpl.java:209) at com.sun.xml.bind.v2.runtime.reflect.TransducedAccessor$CompositeTransducedAccessorImpl.writeLeafElement(TransducedAccessor.java:250) at com.sun.xml.bind.v2.runtime.property.SingleElementLeafProperty.serializeBody(SingleElementLeafProperty.java:98) at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:340) at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsSoleContent(XMLSerializer.java:593) at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeRoot(ClassBeanInfoImpl.java:324) at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsRoot(XMLSerializer.java:494) at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:315) at com.sun.xml.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:244) at javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(AbstractMarshallerImpl.java:75) at example.Demo.main(Demo.java:18)

当字符串为空但不为null时，如何防止在JAXB中编组空标记

1 个答案: