Remove 'standalone="yes"' from generated XML

This property:

marshaller.setProperty("com.sun.xml.bind.xmlDeclaration", false);

...can be used to have no:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>

However, I wouldn't consider this best practice.

If you make document dependent on DOCTYPE (e.g. use named entities) then it will stop being standalone, thus standalone="yes" won't be allowed in XML declaration.

However standalone XML can be used anywhere, while non-standalone is problematic for XML parsers that don't load externals.

I don't see how this declaration could be a problem, other than for interoperability with software that doesn't support XML, but some horrible regex soup.

I'm using Java 1.8 and JAXB 2.3.1

First, be sure to be using java 1.8 in pom.xml

<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>

Then in source code I used: (the key was the internal part)

// remove standalone=yes
marshaller.setProperty(Marshaller.JAXB_FRAGMENT, true);
marshaller.setProperty("com.sun.xml.internal.bind.xmlHeaders", "<?xml version=\"1.0\" encoding=\"UTF-8\"?>");

In case you are getting property exception, add the following configuration:

jaxbMarshaller.setProperty("com.sun.xml.internal.bind.xmlHeaders",
              "<?xml version=\"1.0\" encoding=\"UTF-8\"?>");
jaxbMarshaller.setProperty("com.sun.xml.internal.bind.xmlDeclaration", Boolean.FALSE);
jaxbMarshaller.setProperty(Marshaller.JAXB_FRAGMENT, Boolean.TRUE);  

just try

private String marshaling2(Object object) throws JAXBException, XMLStreamException {
    JAXBContext jaxbContext = JAXBContext.newInstance(object.getClass());
    Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
    jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
    jaxbMarshaller.setProperty(Marshaller.JAXB_FRAGMENT, Boolean.TRUE);
    StringWriter writer = new StringWriter();
    writer.write("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n");
    jaxbMarshaller.marshal(object, writer);
    return writer.toString();
  }

If you have <?xml version="1.0" encoding="UTF-8" standalone="yes"?>

but want this: <?xml version="1.0" encoding="UTF-8"?>

Just do:

marshaller.setProperty(Marshaller.JAXB_FRAGMENT, Boolean.TRUE);
marshaller.setProperty("com.sun.xml.internal.bind.xmlHeaders", "<?xml version=\"1.0\" encoding=\"UTF-8\"?>");