JAXB通用@XmlValue [英] JAXB generic @XmlValue
问题描述
目标是使用 JAXB 制作以下XML
< foo>
< bar>字符串数据< / bar>
< bar>二进制数据< / bar>
< / foo>
是否有解决方法允许通用 @XmlValue 字段（我需要存储 byte [] 和 String data）？以下是我的愿望：
@XmlRootElement
公共类Foo {
私有@XmlElement列表< Bar> ;酒吧;
}
@XmlRootElement
public class Bar< T> {
private @XmlValue T值; //（*）
}
但是我得到这个异常
$ b $
（*）IllegalAnnotationException：
@ XmlAttribute / @ XmlValue需要引用映射到XML文本的Java类型。
您可以利用 XmlAdapter 而不是 @XmlValue ：
BarAdapter
package forum8807296;
import javax.xml.bind.annotation.adapters.XmlAdapter;
public class BarAdapter extends XmlAdapter< Object，Bar<？>> {
@Override
public Bar<？> unmarshal（Object v）抛出Exception {
if（null == v）{
return null;
}
Bar< Object> bar = new Bar< Object>（）;
bar.setValue（v）;
返回栏;
}
@Override
public Object marshal（Bar<> v）抛出Exception {
if（null == v）{
return空值;
}
return v.getValue（）;
}
}
Foo
$ b
XmlAdapter 与 bars 属性相关联使用 @XmlJavaTypeAdapter 注解：
package forum8807296;
import java.util.List;
import javax.xml.bind.annotation。*;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
@XmlRootElement
公共类Foo {
私人列表< Bar>酒吧;
@XmlElement（name =bar）
@XmlJavaTypeAdapter（BarAdapter.class）
public List< Bar> getBars（）{
返回酒吧;
}
public void setBars（List< Bar> bars）{
this.bars = bars;
}
}
Bar
package forum8807296;
公开课Bar< T> {
私人T值;
public T getValue（）{
返回值;
}
public void setValue（T value）{
this.value = value;
}
}
演示
您可以使用以下演示代码测试此示例：
package forum8807296;
import java.util.ArrayList;
import java.util.List;
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（Foo.class）;
Foo foo = new Foo（）;
列表< Bar> bars = new ArrayList< Bar>（）;
foo.setBars（bars）;
Bar< String> stringBar = new Bar< String>（）;
stringBar.setValue（string data）;
bars.add（stringBar）;
Bar< byte []> binaryBar = new Bar< byte []>（）;
binaryBar.setValue（binary data.getBytes（））;
bars.add（binaryBar）;
Marshaller marshaller = jc.createMarshaller（）;
marshaller.setProperty（Marshaller.JAXB_FORMATTED_OUTPUT，true）;
marshaller.marshal（foo，System.out）;
}
}
输出 xsi：type 属性来保留值的类型。您可以通过让 XmlAdapter 返回字符串来消除 xsi：type 属性c $ c>而不是 Object ，如果你这样做，你需要处理从 String 到相应类型的转换你自己的解组操作：
<？xml version =1.0encoding =UTF-8standalone =yes >？;
< foo>
< bar xmlns：xsi =http://www.w3.org/2001/XMLSchema-instancexmlns：xs =http://www.w3.org/2001/XMLSchemaxsi：type =xs：string>字符串数据< / bars>
< bar xmlns：xsi =http://www.w3.org/2001/XMLSchema-instancexmlns：xs =http://www.w3.org/2001/XMLSchemaxsi：type = XS：base64Binary的 > YmluYXJ5IGRhdGE = LT; /棒>
< / foo>
The goal is to produce the following XML with JAXB
<foo>
<bar>string data</bar>
<bar>binary data</bar>
</foo>
Is there a workaround to allow generic @XmlValue fields (I need to store byte[] and String data)? Below is what I desire:
@XmlRootElement
public class Foo {
private @XmlElement List<Bar> bars;
}
@XmlRootElement
public class Bar<T> {
private @XmlValue T value; // (*)
}
But I get this exception
(*) IllegalAnnotationException:
@XmlAttribute/@XmlValue need to reference a Java type that maps to text in XML.
You could leverage an XmlAdapter for this use case instead of @XmlValue:
BarAdapter
package forum8807296;
import javax.xml.bind.annotation.adapters.XmlAdapter;
public class BarAdapter extends XmlAdapter<Object, Bar<?>> {
@Override
public Bar<?> unmarshal(Object v) throws Exception {
if(null == v) {
return null;
}
Bar<Object> bar = new Bar<Object>();
bar.setValue(v);
return bar;
}
@Override
public Object marshal(Bar<?> v) throws Exception {
if(null == v) {
return null;
}
return v.getValue();
}
}
Foo
The XmlAdapter is associated with the bars property using the @XmlJavaTypeAdapter annotation:
package forum8807296;
import java.util.List;
import javax.xml.bind.annotation.*;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
@XmlRootElement
public class Foo {
private List<Bar> bars;
@XmlElement(name="bar")
@XmlJavaTypeAdapter(BarAdapter.class)
public List<Bar> getBars() {
return bars;
}
public void setBars(List<Bar> bars) {
this.bars = bars;
}
}
Bar
package forum8807296;
public class Bar<T> {
private T value;
public T getValue() {
return value;
}
public void setValue(T value) {
this.value = value;
}
}
Demo
You can test this example using the following demo code:
package forum8807296;
import java.util.ArrayList;
import java.util.List;
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(Foo.class);
Foo foo = new Foo();
List<Bar> bars = new ArrayList<Bar>();
foo.setBars(bars);
Bar<String> stringBar = new Bar<String>();
stringBar.setValue("string data");
bars.add(stringBar);
Bar<byte[]> binaryBar = new Bar<byte[]>();
binaryBar.setValue("binary data".getBytes());
bars.add(binaryBar);
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(foo, System.out);
}
}
Output
Note how the output includes the xsi:type attributes to preserve the type of the value. You can eliminate the the xsi:type attribute by having your XmlAdapter return String instead of Object, if you do this you will need handle the conversion from String to the appropriate type yourself for the unmarshal operation:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<foo>
<bar xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:string">string data</bars>
<bar xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:base64Binary">YmluYXJ5IGRhdGE=</bars>
</foo>
这篇关于JAXB通用@XmlValue的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
