<newRule pattern="/configuration/xmlProperty" actionClass="ch.qos.logback.core.joran.action.XmlPropertyAction"/>
<xmlProperty file="/path/to/property_file.xml"/>

package ch.qos.logback.core.joran.action;

import ch.qos.logback.core.joran.spi.InterpretationContext;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class XmlPropertyAction extends PropertyAction {
    void loadAndSetProperties(InterpretationContext ec, InputStream istream, ActionUtil.Scope scope) throws IOException {
        Properties props = new Properties();
        props.loadFromXML(istream);
        istream.close();
        ActionUtil.setProperties(ec, props, scope);
    }
}