At least one JAR was scanned for TLDs yet contained no TLDs

As soon as I added a jar to my Tomcat base web application, I got this new info log message.
INFO [main] org.apache.jasper.servlet.TldScanner.scanJars
At least one JAR was scanned for TLDs yet contained no TLDs
It makes sense, since it was a JDBC driver, and I would have been very surprised if it contained a TLD.

Let's see how to get rid of it.

Firstly, I read the rest of the logging message
Enable debug logging for this logger for a complete list
of JARs that were scanned but no TLDs were found in them.
Skipping unneeded JARs during scanning can
improve startup time and JSP compilation time.
Actually, I already knew the name of the JAR culprit, since I just added it, so I could have skipped directly to the second step. However, I followed the instructions and ...

Tomcat logging properties

I (temporarily) changed the for my Tomcat instance, adding this line
org.apache.jasper.servlet.TldScanner.level = FINE

After that, my log file got more interesting, and I focused my attention to this line.
FINE [main] org.apache.jasper.servlet.TldScanner$TldScannerCallback.scan
No TLD files were found in [... x.jar] Consider adding the
JAR to the tomcat.util.scan.StandardJarScanFilter.jarsToSkip
property in CATALINA_BASE/conf/ file.
Very clear indeed.

Tomcat Catalina properties

I easily found the tomcat.util.scan.StandardJarScanFilter.jarsToSkip property in file from my Tomcat configuration folder. It is a longish comma separated string containing a list of JAR that are known not to contain TLD.

I just added the name of my JAR to it, and the case was closed.

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Testing Spring Boot with JUnit5

I decided that is time to move my tests in Spring app from JUnit 4 to Jupiter. It is not too complicated, given that Spring is already supporting JUnit 5, even though the default is still the previous version. However it requires being careful in a couple of steps.

Firstly, I have changed the POM in this way:
            <!-- get rid of JUnit 4 -->

<!-- using JUnit 5 instead -->
    <!-- using the version set by Spring -->
I have excluded JUnit 4 from the spring-boot-starter-test dependency, and then I have inserted a new dependency for Jupiter, all of them are obviously in the test scope. Notice that I didn't set the version for JUnit 5, accepting instead the one proposed by Spring. Just to stay on the safe side.

The changes in "normal" testing are quite simple, usually limited in using the right imports for the new library. Something a bit more engaging is to be done for Spring Application test. What I had for JUnit 4 was something like this
public class MyApplicationTests {
    // ...
In Jupiter, however, the annotation RunWith has been replaced with the more powerful ExtendWith, so the code has to be changed to
public class MyApplicationTests {
    // ...
Not too bad, isn't it?

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