Question

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？

以下是带输出的代码 -

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>&lt;rootTag&gt;&lt;body&gt;All systems online.&lt;/body&gt;&lt;/rootTag&gt;</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，序列化产生了

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

而不是

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

如何解决这个问题？

Answer 1

注意：我是EclipseLink JAXB (MOXy)主管，是JAXB (JSR-222)专家组的成员。

使用@XmlAnyElement注释并指定DOMHandler来映射此用例。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）。

<强> BodyDomHandler

默认情况下，JAXB实现将未映射的内容表示为DOM节点。您可以将DomHandler用于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);
        }
    }

}

<强>消息

以下是在@XmlAnyElement课程中指定Message注释的方法。

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; }
}

<强>输出

以下是运行SerialziationTest：

的输出

<?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>

了解更多信息

注意 - JAXB RI中的错误

JAXB参考实现中似乎存在一个错误，示例代码将产生如下堆栈跟踪：

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

Answer 2

如果仅用于编组，并忽略＆lt;和＆gt ;, 我们可以使用以下内容：

marshaller.setProperty("com.sun.xml.bind.marshaller.CharacterEscapeHandler",
                new CharacterEscapeHandler() {
                    @Override
                    public void escape(char[] ac, int i, int j, boolean flag,
                            Writer writer) throws IOException {
                        writer.write(ac, i, j);
                    }
                });

Answer 3

3种不同的解决方案1），2）3），如下：

1）以下帖子是您的解决方案Loresh的描述：

http://anna-safronova.livejournal.com/2524.html?thread=9180

这仍然缺少限制细节。

使用嵌入式html，我们需要<![CDATA块
JAXB的依赖

com.sun.xml.bind.marshaller.CharacterEscapeHandler

需要导入jaxb-impl进行编译/可能需要执行，例如：

<groupId>com.sun.xml.bind</groupId>
<artifactId>jaxb-impl</artifactId>  
 <version>2.2.4</version>

限制：此解决方案特定于Container，因类加载策略而无法运行。

2）另一种类似的方法是JDK的rt.jar依赖

com.sun.xml.internal.bind.CharacterEscapeHandler

http://theopentutorials.com/tutorials/java/jaxb/jaxb-marshalling-and-unmarshalling-cdata-block/

相同的限制/取决于目标JDK，并且必须对Eclipse / Maven进行一些调整（糟糕的替代/我的意见）

3）最后，在Reg Whitton的另一篇文章中找到了最佳解决方案：

https://stackoverflow.com/a/12637295/560410

这是详细的reciepe：

http://javacoalface.blogspot.co.uk/2012/09/outputting-cdata-sections-with-jaxb.html

对我来说很完美！

如何使用有时包含XML内容的JAXB来编组字符串，有时却不包含？

3 个答案: