Using Tomcat I try to shutdown the DNS-Thread. Using this code: ``` package de.e_nexus.web.rm.mail.veto.dnsbl; import java.util.logging.Level; import java.util.logging.Logger; import javax.annotation.PreDestroy; import javax.inject.Named; import org.xbill.DNS.NioClient; @Named public class DNSThreadStopper { public static final Logger LOG = Logger.getLogger(DNSThreadStopper.class.getCanonicalName()); @PreDestroy public void stopDNSThreads() { LOG.info("Stopping thread [dnsjava NIO selector] in order to clean shutdown."); try { NioClient.close(); LOG.info("Finished thread [dnsjava NIO selector], clean shutdown possible now."); } catch (Exception e) { LOG.log(Level.SEVERE, "Could not shutdown [dnsjava NIO selector]!", e); } } } ``` This is the Stacktrace: ```31-Mar-2024 08:23:02.704 SCHWERWIEGEND [http-nio-8080-exec-25] de.e_nexus.web.rm.mail.veto.dnsbl.DNSThreadStopper.stopDNSThreads Could not shutdown [dnsjava NIO selector]! java.lang.NullPointerException: Cannot invoke "java.nio.channels.Selector.wakeup()" because "org.xbill.DNS.NioClient.selector" is null at org.xbill.DNS.NioClient.close(NioClient.java:89) at org.xbill.DNS.NioClient.close(NioClient.java:67) at de.e_nexus.web.rm.mail.veto.dnsbl.DNSThreadStopper.stopDNSThreads(DNSThreadStopper.java:29) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 31-Mar-2024 08:23:50.761 WARNUNG [http-nio-8080-exec-25] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [ROOT] appears to have started a thread named [dnsjava NIO selector] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread: java.base@17.0.6/sun.nio.ch.EPoll.wait(Native Method) java.base@17.0.6/sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:118) java.base@17.0.6/sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:129) java.base@17.0.6/sun.nio.ch.SelectorImpl.select(SelectorImpl.java:141) org.xbill.DNS.NioClient.runSelector(NioClient.java:113) org.xbill.DNS.NioClient$$Lambda$5994/0x0000000807912710.run(Unknown Source) java.base@17.0.6/java.lang.Thread.run(Thread.java:833) ```