Tomcat memory leak warning on HttpURLConnection

Question

I have the following warning in Tomcat 8.5 I'm not sure I can ignore

WARNING [localhost-startStop-2] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [AppName] appears to have started a thread named [pool-20-thread-1] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.net.SocketInputStream.socketRead0(Native Method)
java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
java.net.SocketInputStream.read(SocketInputStream.java:171)
java.net.SocketInputStream.read(SocketInputStream.java:141)
sun.security.ssl.InputRecord.readFully(InputRecord.java:465)
sun.security.ssl.InputRecord.read(InputRecord.java:503)
sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:983)
sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1385)
sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1413)
sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1397)
sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:559)
sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:185)

It happens on connect in the following code:

URL url = new URL(MY_URL);
URLConnection con = url.openConnection();
HttpURLConnection http = (HttpURLConnection) con;
http.setRequestMethod("POST");
http.setDoOutput(true);
http.setFixedLengthStreamingMode(out.length);
http.setRequestProperty("Content-Type", "application/json");
http.connect();
try (OutputStream os = http.getOutputStream()) {
    os.write(out);
}

Should I add a finally with closing the InputStream:

http.getInputStream().close();

Or this code should be upgraded/converted to use URIBuilder and HttpHost?

EDIT The code executed every X seconds using Spring's @Scheduled

Answer 1

You are using @Scheduled within Tomcat to spawn threads. You must ensure that these threads will finish when the ServletContext is destroyed e.g. WAR being undeployed, Tomcat warns you about this. The HTTP request code is unrelated as URLConnection doesn't start new threads to perform the request.

One way to make Tomcat happy is to use daemon threads, as explained in this answer. This can be done with custom taskScheduler bean:

@Configuration
@EnableScheduling
public class TaskConfiguration {

  @Bean(destroyMethod = "shutdown")
  public Executor taskScheduler() {
    return Executors.Executors.newFixedThreadPool(4,
        new ThreadFactory() {
          public Thread newThread(Runnable r) {
            Thread t = Executors.defaultThreadFactory().newThread(r);
            t.setDaemon(true);
            return t;
          }
        });
  }

}