What's the difference between WebappClassLoader and StandardJarScanner? - maven

Question

I'm using the tomcat7-maven-plugin to launch a web application from Maven during the pre-integration-test lifecycle phase so that I can run tests against it locally during the integration-test phase.
I haven't worked much on the web application itself, but for the record it uses JSP and Java controllers which are tied together using Spring MVC 3.0.
When I run Maven (mvn clean verify) on my own machine I see the following output for the plugin:
[INFO] --- tomcat7-maven-plugin:2.2:run-war-only (start-tomcat) # MyProject ---
[INFO] Running war on http://localhost:8080/contentmain
[INFO] Using existing Tomcat server configuration at /Users/alexjohnson/MyWorkspace/MyProject/src/test/resources/com/MyCompany/MyProject/ui/automation/tomcat7
Jan 27, 2015 2:18:54 PM org.apache.catalina.core.AprLifecycleListener init
INFO: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: /Users/alexjohnson/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:.
Jan 27, 2015 2:18:54 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-bio-8080"]
Jan 27, 2015 2:18:54 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["ajp-bio-8009"]
Jan 27, 2015 2:18:54 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-bio-8443"]
Jan 27, 2015 2:18:54 PM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 425 ms
Jan 27, 2015 2:18:54 PM org.apache.catalina.core.StandardService startInternal
INFO: Starting service Catalina
Jan 27, 2015 2:18:54 PM org.apache.catalina.core.StandardEngine startInternal
INFO: Starting Servlet Engine: Apache Tomcat/7.0.53
Jan 27, 2015 2:18:55 PM org.apache.catalina.loader.WebappClassLoader validateJarFile
// More startup stuff
This is working as expected. Note that WebappClassLoader.validateJarFile is called. Also note that the APR info message is expected since we aren't using these libraries in the test environment.
When I run Maven on our build server (mvn clean verify) I see the following output for the plugin:
[INFO] --- tomcat7-maven-plugin:2.2:run-war-only (start-tomcat) # MyProject ---
[INFO] Running war on http://localhost:8080/contentmain
[INFO] Using existing Tomcat server configuration at /opt/jenkins/workspace/BuildServerWorkspace/src/test/resources/com/MyCompany/MyProject/ui/automation/tomcat7
Jan 27, 2015 2:30:09 PM org.apache.catalina.core.AprLifecycleListener init
INFO: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: /usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib
Jan 27, 2015 2:30:09 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-bio-8080"]
Jan 27, 2015 2:30:09 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["ajp-bio-8009"]
Jan 27, 2015 2:30:09 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-bio-8443"]
Jan 27, 2015 2:30:09 PM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 823 ms
Jan 27, 2015 2:30:09 PM org.apache.catalina.core.StandardService startInternal
INFO: Starting service Catalina
Jan 27, 2015 2:30:09 PM org.apache.catalina.core.StandardEngine startInternal
INFO: Starting Servlet Engine: Apache Tomcat/7.0.53
Jan 27, 2015 2:30:10 PM org.apache.tomcat.util.scan.StandardJarScanner scan
WARNING: Failed to scan JAR [file:/opt/jenkins/BuildServerWorkspace/src/test/resources/com/MyCompany/MyProject/ui/automation/tomcat7/webapps/../../../../../../../../../../../target/MyProject/WEB-INF/lib/openws-1.5.1.jar] from WEB-INF/lib
java.io.FileNotFoundException: /opt/jenkins/BuildServerWorkspace/src/test/resources/com/MyCompany/MyProject/ui/automation/tomcat7/webapps/../../../../../../../../../../../target/MyProject/WEB-INF/lib/openws-1.5.1.jar (No such file or directory)
// Hundreds more FileNotFoundExceptions for JAR files.
This is not working. Note that this time StandardJarScanner.scan is called. Also note that the missing JAR files appear to have been created during the build on my local machine at the same relative path (11 directories out from webapps and 5 more into the target directory). I believe all of these JAR files are for third-party Maven dependencies.
I've read the official JavaDocs, but I can't find a helpful description of the WebappClassLoader or the StandardJarScanner. All I can really gather is that they're both used for loading classes from JAR files when Tomcat starts up.
What I'd like to know:
What are WebappClassLoader and StandardJarScanner specifically being used for in this context?
What are the key differences between WebappClassLoader and StandardJarScanner?
What sort of configuration could be different on the build server that causes it to use the StandardJarScanner instead of the WebappClassLoader when running Maven there (All of the environment variables and Maven parameters which I know of are already the same)?

Answer 1

have a look at this issue https://issues.apache.org/jira/browse/MTOMCAT-239
Sounds like some weird paths from jenkins, I can't figure out why..

Answer 2

WebAppClassLoader and StandardJarScanner are apples and oranges. StandardJarScanner always runs before WebAppClassLoader but only produces log statements if something goes wrong. This means that the StandardJarScanner log statements were appearing at the same point in the failing build as the WebAppClassLoader log statements in the passing build.
Since I was mis-reading these log statements I ended up asking the wrong question. My original problem still stands. I've opened a new question for it at Why is Tomcat throwing FileNotFoundExceptions for existing JAR files?.