Maven compile fails silently - Unresolved compilation problems

Question

I have an interesting problem with a spring webapp maven build. When being built inside eclipse everything is fine yet when built via maven and deployed to a tomcat 8 container the webapp fails on startup with the following error:

Caused by: java.lang.NoClassDefFoundError: FilterConfig

Now I tried all the obvious and well documented dependency issues (setting scope provided on the javax.servlet-api & jsp-api import and making sure they are of the latest versions as this is a Java 8 project). I have made sure all of the complier plugins are of the latest versions:

maven-war-plugin 3.1.0

maven-compiler-plugin 3.6.1

yet the webapp fails to start with no errors being shown in the maven build console output. After much head-scratching and painstaking comparison between the (working) eclipse build and the mysteriously failing maven equivalent it was discovered that inside some of the class files generated by maven were texts describing compilation problems. (The following was extracted from the "Open With > Text Editor" option in eclipse against the .class file - some of the characters had to be omitted as they wouldn't copy correctly)

Unresolved compilation problems: 
    The import javax.servlet.Filter cannot be resolved
    The import javax.servlet.FilterChain cannot be resolved
    The import javax.servlet.FilterConfig cannot be resolved
    The import javax.servlet.ServletException cannot be resolved
    The import javax.servlet.ServletRequest cannot be resolved
    The import javax.servlet.ServletResponse cannot be resolved
    The import javax.servlet.http.HttpServletRequest cannot be resolved
    The import javax.servlet.http.HttpSession cannot be resolved
    Filter cannot be resolved to a type
    FilterConfig cannot be resolved to a type
    ServletException cannot be resolved to a type
    ServletRequest cannot be resolved to a type
    ServletResponse cannot be resolved to a type
    FilterChain cannot be resolved to a type
    ServletException cannot be resolved to a type
    HttpServletRequest cannot be resolved to a type
    HttpServletRequest cannot be resolved to a type
    HttpSession cannot be resolved to a type

I cannot understand how the maven process appears to complete successfully and that no errors are shown with any of the mvn goals I've tried

mvn complier:compile

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building xxxx 2.0.1
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ EBPP ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 5 resources
[INFO]
[INFO] --- maven-compiler-plugin:3.6.1:compile (default-compile) @ EBPP ---
[INFO] Nothing to compile - all classes are up to date
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.413 s
[INFO] Finished at: 2017-06-28T15:11:45+01:00
[INFO] Final Memory: 9M/213M
[INFO] ------------------------------------------------------------------------

the above but with the -x showed a lot of debugging output but nothing to suggest compile problems, in fact it states that the class-file identified unresolved dependencies are included

...
[DEBUG]    javax.servlet:javax.servlet-api:jar:3.1.0:provided  
[DEBUG]    org.apache.velocity:velocity:jar:1.7:compile
[DEBUG]    commons-collections:commons-collections:jar:3.2.1:compile 
[DEBUG]    commons-lang:commons-lang:jar:2.4:compile 
[DEBUG]    javax.servlet.jsp:jsp-api:jar:2.2:provided 
...

mvn dependency:build-classpath

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building xxxx 2.0.1
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-dependency-plugin:2.8:build-classpath (default-cli) @ EBPP ---
[INFO] Dependencies classpath:
C:\Users\xxxxxx\.m2\repository\org\springframework\webflow\spring-webflow\2.4.5.RELEASE\spring-webflow-2.4.5.RELEASE.jar;C:\Users\xxxxxx\.m2\repository\commons-logging\commons-logging\1.2\commons-logging-1.2.jar;C:\Users\xxxxxx\.m2\repository\opensymphony\ognl\2.6.11\ognl-2.6.11.jar;C:\Users\xxxxxx\.m2\repository\org\springframework\webflow\spring-binding\2.4.5.RELEASE\spring-binding-2.4.5.RELEASE.jar;C:\Users\xxxxxx\.m2\repository\org\springframework\webflow\spring-js\2.4.5.RELEASE\spring-js-2.4.5.RELEASE.jar;C:\Users\xxxxxx\.m2\repository\org\springframework\webflow\spring-js-resources\2.4.5.RELEASE\spring-js-resources-2.4.5.RELEASE.jar;C:\Users\xxxxxx\.m2\repository\org\springframework\spring-beans\4.3.0.RELEASE\spring-beans-4.3.0.RELEASE.jar;C:\Users\xxxxxx\.m2\repository\org\springframework\spring-context\4.3.0.RELEASE\spring-context-4.3.0.RELEASE.jar;C:\Users\xxxxxx\.m2\repository\org\springframework\spring-aop\4.3.0.RELEASE\spring-aop-4.3.0.RELEASE.jar;C:\Users\xxxxxx\.m2\repository\org\springframework\spring-expression\4.3.0.RELEASE\spring-expression-4.3.0.RELEASE.jar;C:\Users\xxxxxx\.m2\repository\org\springframework\spring-web\4.3.0.RELEASE\spring-web-4.3.0.RELEASE.jar;C:\Users\xxxxxx\.m2\repository\org\springframework\spring-webmvc\4.3.0.RELEASE\spring-webmvc-4.3.0.RELEASE.jar;C:\Users\xxxxxx\.m2\repository\org\springframework\spring-core\4.3.9.RELEASE\spring-core-4.3.9.RELEASE.jar;C:\Users\xxxxxx\.m2\repository\com\xxxxxxx\ebpp\JComms\2.0.1\JComms-2.0.1.jar;C:\Users\xxxxxx\.m2\repository\log4j\log4j\1.2.17\log4j-1.2.17.jar;C:\Users\xxxxxx\.m2\repository\javax\mail\mail\1.4.7\mail-1.4.7.jar;C:\Users\xxxxxx\.m2\repository\javax\activation\activation\1.1\activation-1.1.jar;C:\Users\xxxxxx\.m2\repository\org\apache\httpcomponents\httpclient\4.5.1\httpclient-4.5.1.jar;C:\Users\xxxxxx\.m2\repository\org\apache\httpcomponents\httpcore\4.4.3\httpcore-4.4.3.jar;C:\Users\xxxxxx\.m2\repository\commons-codec\commons-codec\1.9\commons-codec-1.9.jar;C:\Users\xxxxxx\.m2\repository\commons-httpclient\commons-httpclient\3.1\commons-httpclient-3.1.jar;C:\Users\xxxxxx\.m2\repository\com\xxxxxxx\ebpp\JCore\2.0.1\JCore-2.0.1.jar;C:\Users\xxxxxx\.m2\repository\javax\servlet\javax.servlet-api\3.1.0\javax.servlet-api-3.1.0.jar;C:\Users\xxxxxx\.m2\repository\org\apache\velocity\velocity\1.7\velocity-1.7.jar;C:\Users\xxxxxx\.m2\repository\commons-collections\commons-collections\3.2.1\commons-collections-3.2.1.jar;C:\Users\xxxxxx\.m2\repository\commons-lang\commons-lang\2.4\commons-lang-2.4.jar;C:\Users\xxxxxx\.m2\repository\javax\servlet\jsp\jsp-api\2.2\jsp-api-2.2.jar;C:\Users\xxxxxx\.m2\repository\junit\junit\3.8.2\junit-3.8.2.jar;C:\Users\xxxxxx\.m2\repository\org\springframework\spring-context-support\4.3.9.RELEASE\spring-context-support-4.3.9.RELEASE.jar;C:\Users\xxxxxx\.m2\repository\com\xxxxxxx\xxxxxxx\440\xxxxxxx-440.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.331 s
[INFO] Finished at: 2017-06-28T15:13:05+01:00
[INFO] Final Memory: 13M/213M
[INFO] ------------------------------------------------------------------------

mvn validate

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building xxx 2.0.1
[INFO] ------------------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.109 s
[INFO] Finished at: 2017-06-28T15:15:32+01:00
[INFO] Final Memory: 7M/213M
[INFO] ------------------------------------------------------------------------

I really am stumped. I'm presuming maven is using a different compiler from eclipse but I really have run out of ideas.

Has anyone else encountered this before?

Thanks in advance.

Answer 1

I suspect it's a combination of eclipse building your files with compilation errors (yes, Eclipse can do that: if you never reach the un-compilable code, then you don't even get errors) and Maven not cleaning the output of Eclipse first.

Then Maven sees that the file is up-to-date, and doesn't overwrite it.

I suggest the following (to check if I'm right):

• Turn off Eclipse's automatic build (or stop eclipse altogether).
• Run a Maven target, such as package but also run clean (i.e. mvn clean package); the point is to be 100% sure that Maven builds those files and not Eclipse.
• Maven should now report compilation errors.

As for the error itself, it looks like you are indeed missing a dependency (but probably in Eclipse's classpath, not Maven's).

Answer 2

So when comparing this project to another successful project (that were both converted from Java 4), on the hunch that using non standard directory names was the cause for mavens erratic behavior (while copying the warSourceDirectory). I analysed the (now called) WebRoot > WEB-INF > classes directory and discovered that for the problematic app this had been populated, with you've guessed it - incorrectly compiled class files! Clearly the war plugin copied these bad files over the top of the files Maven had, in the same build process just successfully complied - hence no error.

I am unsure why the bad files were there as they were not in the old Java 4 project. I suspect that they must have been created somehow during a previous failed maven build using incorrect settings.