Namespace with no prefix in JAXB

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";

Solution

You can use @XmlSchema [1] package level annotation in order to set prefix. In your case, we just set empty prefix.

Simply create package-info.java file in your package e.g. com.stackoverflow.jaxb, with similar content.

package-info.java

@XmlSchema(namespace = "http://www.sitemaps.org/schemas/sitemap/0.9",
           xmlns = {@XmlNs(prefix = "",
                           namespaceURI = "http://www.sitemaps.org/schemas/sitemap/0.9")},
           elementFormDefault = XmlNsForm.QUALIFIED)
package com.stackoverflow.jaxb;

import javax.xml.bind.annotation.XmlNs;
import javax.xml.bind.annotation.XmlNsForm;
import javax.xml.bind.annotation.XmlSchema;

Note, that you can remove namespace attribute from @XmlRootElement annotation.

[1] https://jaxb.java.net/nonav/2.2.4/docs/api/javax/xml/bind/annotation/XmlSchema.html