我的问题与How to prevent marshalling empty tags in JAXB when string is empty but not null
非常相似不同之处在于我无法将注释添加到package-info.java,因为我们的所有JAXB类型都是从每次构建的模式生成的。 如果可能,我也更愿意不更改JAXB提供程序。
我想要实现的是设置一个空String不会创建该元素,但我需要为许多模式中的所有生成的JAXB类型设置它。有没有办法将它应用于所有生成的JAXB类中的所有String字段?
更新 我已经设法通过进行以下更改来为模式中的所有字符串生成XML适配器:
在项目POM中,我将其添加到maven-jaxb2-plugin:
<bindingDirectory>src/main/resources</bindingDirectory>
<bindingIncludes>
<include>bindings.xjb</include>
</bindingIncludes>
这是我的bindings.xjb文件:
<jxb:bindings xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:jxb="http://java.sun.com/xml/ns/jaxb" version="2.1">
<jxb:globalBindings>
<jxb:javaType name="java.lang.String" xmlType="xs:token"
parseMethod="com.project.Formatter.parseString"
printMethod="com.project.Formatter.printString"/>
</jxb:globalBindings>
</jxb:bindings>
格式化方法:
public static String printString(final String value)
{
if (StringUtils.isBlank(value))
{
return null;
}
return value;
}
问题是这会导致JAXB内部出现空指针异常。这是堆栈跟踪:
Caused by: java.lang.NullPointerException
at com.sun.xml.bind.v2.runtime.output.SAXOutput.text(SAXOutput.java:158)
at com.sun.xml.bind.v2.runtime.XMLSerializer.leafElement(XMLSerializer.java:321)
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:322)
at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsXsiType(XMLSerializer.java:681)
at com.sun.xml.bind.v2.runtime.property.SingleElementNodeProperty.serializeBody(SingleElementNodeProperty.java:150)
at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:322)
at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsXsiType(XMLSerializer.java:681)
at com.sun.xml.bind.v2.runtime.property.ArrayElementNodeProperty.serializeItem(ArrayElementNodeProperty.java:65)
at com.sun.xml.bind.v2.runtime.property.ArrayElementProperty.serializeListBody(ArrayElementProperty.java:168)
at com.sun.xml.bind.v2.runtime.property.ArrayERProperty.serializeBody(ArrayERProperty.java:152)
at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:322)
at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsXsiType(XMLSerializer.java:681)
at com.sun.xml.bind.v2.runtime.property.SingleElementNodeProperty.serializeBody(SingleElementNodeProperty.java:150)
at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:322)
at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsXsiType(XMLSerializer.java:681)
at com.sun.xml.bind.v2.runtime.property.SingleElementNodeProperty.serializeBody(SingleElementNodeProperty.java:150)
at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:322)
at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsXsiType(XMLSerializer.java:681)
at com.sun.xml.bind.v2.runtime.property.SingleElementNodeProperty.serializeBody(SingleElementNodeProperty.java:150)
at com.sun.xml.bind.v2.runtime.ElementBeanInfoImpl$1.serializeBody(ElementBeanInfoImpl.java:156)
at com.sun.xml.bind.v2.runtime.ElementBeanInfoImpl$1.serializeBody(ElementBeanInfoImpl.java:185)
at com.sun.xml.bind.v2.runtime.ElementBeanInfoImpl.serializeBody(ElementBeanInfoImpl.java:305)
at com.sun.xml.bind.v2.runtime.ElementBeanInfoImpl.serializeRoot(ElementBeanInfoImpl.java:312)
at com.sun.xml.bind.v2.runtime.ElementBeanInfoImpl.serializeRoot(ElementBeanInfoImpl.java:71)
at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsRoot(XMLSerializer.java:490)
at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:328)
at com.sun.xml.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:257)
at javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(AbstractMarshallerImpl.java:103)
此问题的原因归结为此方法:
com.sun.xml.bind.v2.runtime.reflect.TransducedAccessor.CompositeTransducedAccessorImpl.hasValue(BeanT)
如果在运行任何适配器之前值
有没有办法覆盖JAXB中使用的Accessor,以便在确定是否呈现元素之前运行适配器?还有另一种方法可以达到我的目的吗?
答案 0 :(得分:13)
注意:我是EclipseLink JAXB (MOXy)主管,是JAXB (JSR-222)专家组的成员。
你所做的是对的,你看到的错误是由于我认为是JAXB reference implementation中的错误。 JAXB RI应该能够处理从XmlAdapter
返回的空值。这个用例适用于EclipseLink JAXB(MOXy),我将在下面举例说明。
<强> StringAdapter 强>
下面是一个implmentation,它大致与您从XML模式生成Java模型后的内容大致相同(参见http://blog.bdoughan.com/2011/08/xml-schema-to-java-generating.html)。
package forum11894193;
import javax.xml.bind.annotation.adapters.XmlAdapter;
public class StringAdapter extends XmlAdapter<String, String> {
@Override
public String marshal(String string) throws Exception {
if("".equals(string)) {
return null;
}
return string;
}
@Override
public String unmarshal(String string) throws Exception {
return string;
}
}
<强>包信息强>
由于您正在注册全局适配器,因此将从package-info
类引用它,如下所示(请参阅:http://blog.bdoughan.com/2012/02/jaxb-and-package-level-xmladapters.html)。
@XmlJavaTypeAdapters({
@XmlJavaTypeAdapter(value=StringAdapter.class, type=String.class)
})
package forum11894193;
import javax.xml.bind.annotation.adapters.*;
<强>根强>
以下是一个包含几个String
字段的示例域类。由于XmlAdapter
已在包级别注册,因此它将应用于该包中的所有映射的字符串字段/属性。
package forum11894193;
import javax.xml.bind.annotation.*;
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Root {
String a;
String b;
String c;
}
<强>演示强>
在下面的演示代码中,我们将创建一个Root
的实例,将几个字段设置为""
,然后将其编组为XML。
package forum11894193;
import javax.xml.bind.*;
public class Demo {
public static void main(String[] args) throws Exception {
JAXBContext jc = JAXBContext.newInstance(Root.class);
Root root = new Root();
root.a = "";
root.b = "b";
root.c = "";
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(root, System.out);
}
}
使用JAXB RI输出
在此示例中使用JAXB RI会生成NPE。堆栈跟踪是不同的,但我们最有可能使用不同的编组方法。我还使用JDK中包含的JAXB RI版本,该版本重新打包到com.sun.xml.internal.bind.v2
。
Exception in thread "main" java.lang.NullPointerException
at com.sun.xml.internal.bind.v2.runtime.output.Encoded.setEscape(Encoded.java:96)
at com.sun.xml.internal.bind.v2.runtime.output.UTF8XmlOutput.doText(UTF8XmlOutput.java:294)
at com.sun.xml.internal.bind.v2.runtime.output.UTF8XmlOutput.text(UTF8XmlOutput.java:283)
at com.sun.xml.internal.bind.v2.runtime.output.IndentingUTF8XmlOutput.text(IndentingUTF8XmlOutput.java:141)
at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.leafElement(XMLSerializer.java:293)
at com.sun.xml.internal.bind.v2.model.impl.RuntimeBuiltinLeafInfoImpl$1.writeLeafElement(RuntimeBuiltinLeafInfoImpl.java:179)
at com.sun.xml.internal.bind.v2.model.impl.RuntimeBuiltinLeafInfoImpl$1.writeLeafElement(RuntimeBuiltinLeafInfoImpl.java:166)
at com.sun.xml.internal.bind.v2.runtime.reflect.TransducedAccessor$CompositeTransducedAccessorImpl.writeLeafElement(TransducedAccessor.java:239)
at com.sun.xml.internal.bind.v2.runtime.property.SingleElementLeafProperty.serializeBody(SingleElementLeafProperty.java:87)
at com.sun.xml.internal.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:306)
at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.childAsSoleContent(XMLSerializer.java:561)
at com.sun.xml.internal.bind.v2.runtime.ClassBeanInfoImpl.serializeRoot(ClassBeanInfoImpl.java:290)
at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.childAsRoot(XMLSerializer.java:462)
at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:314)
at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:243)
at javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(AbstractMarshallerImpl.java:75)
at forum11894193.Demo.main(Demo.java:17)
使用EclipseLink JAXB(MOXy)输出
当MOXy用作JAXB提供程序时,您将获得所需的输出。有关将MOXy指定为JAXB提供程序的信息,请参阅:http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html。
<?xml version="1.0" encoding="UTF-8"?>
<root>
<b>b</b>
</root>
答案 1 :(得分:0)
空字符串仍然是值。这就是元素创建的原因。如上所述,如果字符串为空,在setter方法中将变量设置为null?
另外,请检查此帖子 JAXB: how to make JAXB NOT to unmarshal empty string to 0
答案 2 :(得分:0)
将以下代码用于Marshall课程
public static String toXml(Object o, Class clazz, boolean isFormatted, boolean isEmptyNodes) {
try {
Map<String, Object> properties = new HashMap<String, Object>(1);
if(isEmptyNodes) {
SessionEventListener sessionEventListener = new NullPolicySessionEventListener();
properties.put(JAXBContextProperties.SESSION_EVENT_LISTENER, sessionEventListener);
} else {
SessionEventListener sessionEventListener = new DiscardEmptyTagSessionEventListener();
properties.put(JAXBContextProperties.SESSION_EVENT_LISTENER, sessionEventListener);
}
// Create a JaxBContext
JAXBContext jc = JAXBContext.newInstance(new Class[] {clazz}, properties);
StringWriter sw = new StringWriter();
// Create the UnMarshaller Object using the JaxB Context
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, isFormatted);
// remove the xml version line from the output
marshaller.setProperty("com.sun.xml.bind.xmlDeclaration", Boolean.FALSE);
// Marshal the employee object to XML and print the output to console
marshaller.marshal(o, sw);
return sw.toString();
} catch (JAXBException e) {
throw new RuntimeException(e.getMessage(), e);
}
}