JAXB solution - a solution to my problem with https://gist.github.com/dalelane/88df784c3cb74b214d5c - using JAXB to unmarshall fragments of XML from an XMLStreamReader

JaxbSolution.java

package sandbox;

import java.io.ByteArrayInputStream;
import java.io.InputStream;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamReader;

public class JaxbProblem {

    // five items in XML fragments
    private static final String TEST1_STR = "<test key=\"one\"></test>";
    private static final String TEST2_STR = "<test key=\"two\"></test>";
    private static final String TEST3_STR = "<test key=\"three\"></test>";
    private static final String TEST4_STR = "<test key=\"four\"></test>";
    private static final String TEST5_STR = "<test key=\"five\"></test>";
    
    // combine the five items into XML documents - with and without whitespace in between
    private static final String XML_WITH_SPACES = 
            "<?xml version=\"1.0\" encoding=\"UTF-8\"?>" + 
                    "<jaxbissue>" + 
                        TEST1_STR + " " + TEST2_STR + " " + TEST3_STR + " " + TEST4_STR + " " + TEST5_STR + " " +
                    "</jaxbissue>";
    private static final String XML_WITHOUT_SPACES = 
            "<?xml version=\"1.0\" encoding=\"UTF-8\"?>" + 
                    "<jaxbissue>" + 
                        TEST1_STR + TEST2_STR + TEST3_STR + TEST4_STR + TEST5_STR + 
                    "</jaxbissue>";
    
    

    public static void main(String[] args)
    {
        String[] tests = { XML_WITH_SPACES, XML_WITHOUT_SPACES };
        for (String test : tests){
            
            System.out.println("About to process a new XML document...");
            
            try {
                // prepare a stream to read the XML document
                InputStream stream = new ByteArrayInputStream(test.getBytes());
                XMLStreamReader reader = XMLInputFactory.newInstance().createXMLStreamReader(stream);

                // prepare an unmarshaller to turn the XML into objects
                JAXBContext context = JAXBContext.newInstance(Test.class);
                Unmarshaller unmarshaller = context.createUnmarshaller();

                // get first event for the XML parsing
                int readerEvent = reader.next();
                
                // keep going until we reach the end of the document
                while (readerEvent != XMLStreamConstants.END_DOCUMENT){
                    
                    // keep unmarshalling for every element of the expected type
                    while (readerEvent == XMLStreamConstants.START_ELEMENT && reader.getLocalName().equals(Test.XMLELEMENTNAME)){
                        JAXBElement<Test> unmarshalledObj = unmarshaller.unmarshal(reader, Test.class);
                        Test item = unmarshalledObj.getValue();
                        System.out.println(">" + item.getKey());

                        // The unmarshaller will have moved the pointer in the 
                        //  stream reader - we should now be pointing at the 
                        //  next event immediately after the unmarshalled 
                        //  element. 
                        // This will either the start of the next element, or 
                        //  CHARACTERS if there is whitespace in between them, 
                        //  or something else like a comment. 
                        // We need to check this to decide whether we can 
                        //  unmarshall again, or if we need to move the 
                        //  stream reader on to get to the next element. 
                        readerEvent = reader.getEventType();
                    }

                    // move the stream reader on to the next element
                    readerEvent = reader.next();
                }
                // reached the end of the document - close the reader
                reader.close();
            }
            catch (Exception exc){
                exc.printStackTrace();
            }
        }
    }
    
    
    
    @XmlRootElement(name=Test.XMLELEMENTNAME)
    public static class Test {
        
        public static final String XMLELEMENTNAME = "test";
        
        protected String key;

        @XmlAttribute
        public String getKey() {
            return key;
        }
        public void setKey(String value) {
            this.key = value;
        }
    }
}

Hi,dalelane
I have changed your code to
if (readerEvent == XMLStreamConstants.START_ELEMENT && reader.getLocalName().equals(Test.XMLELEMENTNAME)){
JAXBElement unmarshalledObj = unmarshaller.unmarshal(reader, Test.class);
Test item = unmarshalledObj.getValue();
System.out.println(">" + item.getKey());
readerEvent = reader.getEventType();
}
else{
readerEvent = reader.next();
}
Just change the while loop to if-else block .And it also prints the same result as your original code was.I don't know is there any problem with my code,so if you find any bug in this code,please let me know .
Thanks,
Best regards.