Cod*_*lue 4 java serialization jaxb
考虑这个例子 -
我有一个名为Report的类,它有一个Message类型的字段.Message类有一个名为"body"的字段,它是一个字符串."body"可以是任何字符串,但有时它包含格式正确的XML内容.我怎样才能确保当"body"包含XML内容时,序列化采用XML结构的形式而不是目前提供的形式？
这是输出的代码 -
报告类
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;
@XmlRootElement(name = "Report")
@XmlType(propOrder = { "message"})
public class Report
{
private Message message;
public Message getMessage() { return message; }
public void setMessage(Message m) { message = m; }
}
消息类
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlType;
@XmlType(propOrder = { "body" })
public class Message
{
private String body;
public String getBody() { return body; }
@XmlElement
public void setBody(String body) { this.body = body; }
}
主要
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
public class SerializationTest
{
public static void main(String args[]) throws Exception
{
JAXBContext jaxbContext = JAXBContext.newInstance(Report.class);
Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
Report report = new Report();
Message message = new Message();
message.setBody("Sample report message.");
report.setMessage(message);
jaxbMarshaller.marshal(report, System.out);
message.setBody("<rootTag><body>All systems online.</body></rootTag>");
report.setMessage(message);
jaxbMarshaller.marshal(report, System.out);
}
}
输出如下 -
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Report>
<message>
<body>Sample report message.</body>
</message>
</Report>
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Report>
<message>
<body><rootTag><body>All systems online.</body></rootTag></body>
</message>
</Report>
正如您在上面的输出中所看到的,对于"body"的第二个实例,生成了序列化
<body><rootTag><body>All systems online.</body></rootTag></body>
代替
<body><rootTag><body>All systems online.</body></rootTag></body>
如何解决这个问题呢？
注意: 我是EclipseLink JAXB(MOXy)的负责人,也是JAXB(JSR-222)专家组的成员.
此用例使用@XmlAnyElement注释进行映射并指定a DOMHandler.使用JAXB RI执行此操作时似乎存在错误,但以下用例适用于EclipseLink JAXB(MOXy).
BodyDomHandler
默认情况下,JAXB实现将未映射的内容表示为DOM节点.您可以利用a DomHandler来替代DOM的替代表示.在这种情况下,我们将DOM表示为String.
import java.io.*;
import javax.xml.bind.ValidationEventHandler;
import javax.xml.bind.annotation.DomHandler;
import javax.xml.transform.Source;
import javax.xml.transform.stream.*;
public class BodyDomHandler implements DomHandler<String, StreamResult> {
private static final String BODY_START_TAG = "<body>";
private static final String BODY_END_TAG = "</body>";
private StringWriter xmlWriter = new StringWriter();
public StreamResult createUnmarshaller(ValidationEventHandler errorHandler) {
return new StreamResult(xmlWriter);
}
public String getElement(StreamResult rt) {
String xml = rt.getWriter().toString();
int beginIndex = xml.indexOf(BODY_START_TAG) + BODY_START_TAG.length();
int endIndex = xml.indexOf(BODY_END_TAG);
return xml.substring(beginIndex, endIndex);
}
public Source marshal(String n, ValidationEventHandler errorHandler) {
try {
String xml = BODY_START_TAG + n.trim() + BODY_END_TAG;
StringReader xmlReader = new StringReader(xml);
return new StreamSource(xmlReader);
} catch(Exception e) {
throw new RuntimeException(e);
}
}
}
信息
以下是如何@XmlAnyElement在Message类上指定注释.
import javax.xml.bind.annotation.XmlAnyElement;
import javax.xml.bind.annotation.XmlType;
@XmlType(propOrder = { "body" })
public class Message
{
private String body;
public String getBody() { return body; }
@XmlAnyElement(BodyDomHandler.class)
public void setBody(String body) { this.body = body; }
}
产量
以下是运行您的输出SerialziationTest:
<?xml version="1.0" encoding="UTF-8"?>
<Report>
<message>
<body>Sample report message.</body>
</message>
</Report>
<?xml version="1.0" encoding="UTF-8"?>
<Report>
<message>
<body>
<rootTag>
<body>All systems online.</body>
</rootTag>
</body>
</message>
</Report>
欲获得更多信息
注 - JAXB RI中的错误
JAXB参考实现中似乎存在错误,示例代码将导致堆栈跟踪,如下所示:
Exception in thread "main" javax.xml.bind.MarshalException
- with linked exception:
[com.sun.istack.internal.SAXException2: unable to marshal type "java.lang.String" as an element because it is missing an @XmlRootElement annotation]
at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:317)
at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:243)
at javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(AbstractMarshallerImpl.java:75)
at forum12428727.SerializationTest.main(SerializationTest.java:20)
Caused by: com.sun.istack.internal.SAXException2: unable to marshal type "java.lang.String" as an element because it is missing an @XmlRootElement annotation
at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.reportError(XMLSerializer.java:216)
at com.sun.xml.internal.bind.v2.runtime.LeafBeanInfoImpl.serializeRoot(LeafBeanInfoImpl.java:126)
at com.sun.xml.internal.bind.v2.runtime.property.SingleReferenceNodeProperty.serializeBody(SingleReferenceNodeProperty.java:100)
at com.sun.xml.internal.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:306)
at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.childAsXsiType(XMLSerializer.java:664)
at com.sun.xml.internal.bind.v2.runtime.property.SingleElementNodeProperty.serializeBody(SingleElementNodeProperty.java:141)
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)
... 3 more