如何使用有时包含XML内容但有时不包含XML内容的JAXB编组字符串？

佟翰林

2023-03-14

问题内容：

考虑这个例子-

我有一个称为Report的类，该类具有Message类型的字段。Message类具有一个称为“ body”的字段，该字段是一个字符串。“
body”可以是任何字符串， 但有时包含格式正确的XML内容 。如何确保当“正文”包含XML内容时，序列化采用XML结构的形式而不是当前的结构？

这是带有输出的代码-

报告类别

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; }
}

讯息类别

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>&lt;rootTag&gt;&lt;body&gt;All systems online.&lt;/body&gt;&lt;/rootTag&gt;</body>
    </message>
</Report>

如您在上面的输出中看到的，对于“ body”的第二个实例，序列化产生了

 <body>&lt;rootTag&gt;&lt;body&gt;All systems online.&lt;/body&gt;&lt;/rootTag&gt;</body>

代替

<body><rootTag><body>All systems online.</body></rootTag></body>

如何解决这个问题呢？

问题答案：

注意： 我是 EclipseLink
JAXB（MOXy）的
负责人，并且是
JAXB（JSR-222）
专家组的成员。

使用@XmlAnyElement注解并指定来映射此用例DOMHandler。使用JAXB
RI执行此操作时似乎出现了错误，但是以下用例适用于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DomHandler来表示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

下面是@XmlAnyElement在Message类上指定注释的方式。

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; }
}

输出量

以下是运行your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>

想要查询更多的信息

http://blog.bdoughan.com/2011/04/xmlanyelement-and-non-dom-properties.html
http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html

注意-JAXB RI中的错误

JAXB参考实现中似乎存在一个错误，示例代码将导致如下所示的堆栈跟踪：

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

如何使用有时包含XML内容但有时不包含XML内容的JAXB编组字符串？

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