对象类型为的java JAXB属性引发空指针异常？

Question

我试图注释一个java类，用一个属性为value的元素创建一个JAXB模式。代码如下：

    @XmlAttribute(name="value")
    public Object getSettingValue() {
        return this.settingValue;
    }

    public void setSettingValue( final Object settingValue ) {
        this.settingValue = settingValue;
    }

当我尝试生成模式（使用Eclipse的非Moxy实现）时，我得到了以下空指针异常：

Exception in thread "main" java.lang.NullPointerException
    at com.sun.xml.internal.bind.v2.runtime.reflect.TransducedAccessor.get(TransducedAccessor.java:154)
    at com.sun.xml.internal.bind.v2.runtime.property.AttributeProperty.<init>(AttributeProperty.java:56)
    at com.sun.xml.internal.bind.v2.runtime.property.PropertyFactory.create(PropertyFactory.java:93)
    at com.sun.xml.internal.bind.v2.runtime.ClassBeanInfoImpl.<init>(ClassBeanInfoImpl.java:145)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.getOrCreate(JAXBContextImpl.java:479)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:305)
    at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(JAXBContextImpl.java:1100)
    at com.sun.xml.internal.bind.v2.ContextFactory.createContext(ContextFactory.java:143)
    at com.sun.xml.internal.bind.v2.ContextFactory.createContext(ContextFactory.java:110)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:202)
    at javax.xml.bind.ContextFinder.find(ContextFinder.java:376)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:574)
    at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:522)
    at org.eclipse.jpt.jaxb.core.schemagen.Main.buildJaxbContext(Main.java:95)
    at org.eclipse.jpt.jaxb.core.schemagen.Main.generate(Main.java:76)
    at org.eclipse.jpt.jaxb.core.schemagen.Main.execute(Main.java:62)
    at org.eclipse.jpt.jaxb.core.schemagen.Main.main(Main.java:47)

当我将其设置为@XmlElement而不是属性时，生成的模式没有任何问题，因此它一定与此有关。有什么想法吗

Answer 1

您看到的NullPointerException似乎是由于JAXB参考实现中的错误造成的。您可以使用以下链接输入错误

• http://java.net/jira/browse/JAXB/

使用EclipseLink JAXB (MOXy)作为JAXB提供程序时，不会出现类似的异常

解决方法

您可以将属性改为String类型。类型为Object的属性无论如何都不会往返，因为与元素不同，属性没有任何包含类型信息的机制

---

When I made this an @XmlElement instead of an attribute, the schema was generated with no issues, so it must have to do with that.

Java模型（根）

对象映射到XML元素时是有效的属性类型

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Root {

    private Object settingValue;

    public Object getSettingValue() {
        return settingValue;
    }

    public void setSettingValue(final Object settingValue) {
        this.settingValue = settingValue;
    }

}

这是因为XML元素可以包含xsi:type属性形式的类型信息

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<root>
    <settingValue 
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
        xmlns:xs="http://www.w3.org/2001/XMLSchema" 
        xsi:type="xs:int">123</settingValue>
</root>