GH-3168: Fix FtpSession warning on logout

Fixes #3168

* Call `this.client.noop()` instead of `this.client.isConnected()` to really
check that client has a live connection with the server before calling a `this.client.logout()`
* Wrap `this.client.logout()` into a `try..catch` to be sure that we wil call a
`this.client.disconnect()` even if `logout()` fails for some reason.
* Change `WARN` logs about `Session.close()` into a `DEBUG` level -
when we have a problem with closing session because of server disconnect reason
we have no any control to do with a situation

**Cherry-pick to 5.2.x**

Author: artembilan

spring-integration-ftp/src/main/java/org/springframework/integration/ftp/session/FtpSession.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -152,16 +152,21 @@ public void append(InputStream inputStream, String path) throws IOException {
 	@Override
 	public void close() {
 		try {
-			if (this.readingRaw.get() && !finalizeRaw() && LOGGER.isWarnEnabled()) {
-				LOGGER.warn("Finalize on readRaw() returned false for " + this);
+			if (this.readingRaw.get() && !finalizeRaw() && LOGGER.isDebugEnabled()) {
+				LOGGER.debug("Finalize on readRaw() returned false for " + this);
 			}
-			if (this.client.isConnected()) {
-				this.client.logout();
+			if (isOpen()) {
+				try {
+					this.client.logout();
+				}
+				catch (IOException ex) {
+					LOGGER.debug("failed to logout FTPClient", ex);
+				}
 			}
 			this.client.disconnect();
 		}
-		catch (Exception e) {
-			LOGGER.warn("failed to disconnect FTPClient", e);
+		catch (Exception ex) {
+			LOGGER.debug("failed to disconnect FTPClient", ex);
 		}
 	}
 
@@ -170,7 +175,8 @@ public boolean isOpen() {
 		try {
 			this.client.noop();
 		}
-		catch (Exception e) {
+		catch (Exception ex) {
+			LOGGER.debug("failed to noop FTPClient", ex);
 			return false;
 		}
 		return true;

spring-integration-ftp/src/test/java/org/springframework/integration/ftp/session/SessionFactoryTests.java

@@ -21,7 +21,9 @@
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 import static org.assertj.core.api.Assertions.fail;
 import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.doThrow;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 
 import java.lang.reflect.Field;
@@ -69,7 +71,6 @@ protected FTPClient createClientInstance() {
 		sessionFactory.setDataTimeout(789);
 		doReturn(200).when(client).getReplyCode();
 		doReturn(true).when(client).login("foo", null);
-		doReturn(true).when(client).isConnected();
 		FtpSession session = sessionFactory.getSession();
 		verify(client).setConnectTimeout(123);
 		verify(client).setDefaultTimeout(456);
@@ -79,6 +80,13 @@ protected FTPClient createClientInstance() {
 
 		verify(client).logout();
 		verify(client).disconnect();
+
+		doThrow(RuntimeException.class).when(client).noop();
+
+		session.close();
+
+		verify(client).logout();
+		verify(client, times(2)).disconnect();
 	}
 
 	@Test