Can a piece of XML be distributed using JAXB (or JAXB + StAX)?
I have an XML structure that is very huge. I want to update parts of this XML by parsing one element and then applying business logic.
I can unbind a child in a POJO. I want to modify this POJO in Java and then update it to XML in the same place.
Is this possible in JAXB? Or using the JAXB + StAX combination.
Structure example:
<folder id="c5718b36-bab1-4c08-8f75-8e2f9aee42c5" name="Folder-1">
<description> folder Desc</description>
<createdBy>User2</createdBy>
<hidden>false</hidden>
<file id="4f2efb42-0604-4878-9e1e-ae90d66fb836" name="File-1">
<description>file desc</description>
<createdBy>User1</createdBy>
<hidden>false</hidden>
</file>
</folder>
In the above example, I can unbind the "file" element in the POJO. I want to make changes to this POJO and then update them in the XML file in the correct location.
How can i do this?
Please help me. Thank.
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2 answers
You can do the following with JAXB and StAX:
import javax.xml.bind.*;
import javax.xml.stream.*;
import javax.xml.stream.events.XMLEvent;
import java.io.*;
public class Demo {
public static void main(String[] args) throws Exception {
XMLInputFactory xif = XMLInputFactory.newFactory();
XMLOutputFactory xof = XMLOutputFactory.newFactory();
try(
FileInputStream in = new FileInputStream("in.xml");
FileOutputStream out = new FileOutputStream("out.xml");
) {
XMLEventReader xer = xif.createXMLEventReader(in);
XMLEventWriter xew = xof.createXMLEventWriter(out);
JAXBContext jc = JAXBContext.newInstance(File.class);
Unmarshaller unmarshaller = jc.createUnmarshaller();
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FRAGMENT, true);
while(xer.hasNext()) {
if(xer.peek().isStartElement() && xer.peek().asStartElement().getName().getLocalPart().equals("file")) {
// Unmarshal the File object from the XMLEventReader
File file = (File) unmarshaller.unmarshal(xer);
// Modify the File object
file.description = "NEW DESCRIPTION";
// Marshal the File object to the XMLEventWriter
marshaller.marshal(file, xew);
} else {
// Copy node from reader to writer
xew.add(xer.nextEvent());
}
}
}
}
}
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If you want StAX see methods:
-
javax.xml.bind.Unmarshaller.unmarshal(XMLStreamReader, Class<T>)
-
javax.xml.bind.Marshaller.marshal(Object, XMLStreamWriter)
You can decouple the known class from the stream, process it, and return the marshal. This can even be done in a "filtration" process. I.e:.
- You are parsing your XML through StAX.
- You check upcoming events until you see what you want to handle.
- Unacceptable events are passed on.
- When you receive the appropriate event, you unmount your class with JAXB, handle the pojo, and send it back to the author of the stream.
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