I am trying to create a Sitemap index file with JAXB. Following the requirements for creating the sitemap, I have to add the namespace attribute in the root element:
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
I would like to have a simple way to sort this out. Since this seems to be a standard procedure I would like to not do a complex workaround or add more dependencies to my project in order to solve this issue
The current output is the following:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ns2:sitemapindex xmlns:ns2="http://www.sitemaps.org/schemas/sitemap/0.9">
    <sitemap>
        <loc>https://www.example.com/sitemap-1.xml</loc>
        <lastmod>2017-05-01T15:41:17.561+01:00</lastmod>
    </sitemap>
</ns2:sitemapindex>
My SitemapIndex model is the following:
@XmlRootElement(name = "sitemapindex", namespace="http://www.sitemaps.org/schemas/sitemap/0.9")
@XmlAccessorType(XmlAccessType.FIELD)
public class SitemapIndex {
    @XmlElement(name = "sitemap")
    private List<Sitemap> sitemaps;
    public void setSitemaps(List<Sitemap> sitemaps) {
        this.sitemaps = sitemaps;
    }
    public List<Sitemap> getSitemaps() {
        return sitemaps;
    }
}
I have also tried to add the namespace field manually and it works for generating the file but I an exception is thrown when I try to read the file.
@XmlAttribute(name="xmlns")
private final String namespace ="http://www.sitemaps.org/schemas/sitemap/0.9";