Excluding package with maven-compiler-plugin works for one package but doesn't work for another

Question

My project has the following package structure:

src/
  com.my.app.school.course
    -Course.java
    ...

  com.my.app.school.course.free
    -CourseFree.java  

I use Maven to build the project, in my pom.xml, I defined maven-compiler-plugin to test excluding a package with all its java classes.

I first tried following way to exclude package com.my.app.school.course.free :

<build>
   <plugins>
       <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>2.3.2</version>
            <configuration>
                <excludes>
                    <exclude>**/com/my/app/school/course/free/*</exclude>
                </excludes>
             </configuration>
        </plugin>
    </plugins>
</build>

It works! I mean after run mvn clean install , the final build under target/classes/ doesn't have the package com/my/app/school/course/free .

Then, I tried to exclude package com.my.app.school.course . I simply replace the above <exclude> tag with value <exclude>**/com/my/app/school/course/*</exclude> . I thought it should work too , but it doesnt! Under target/classes/ I see all packages, no package is excluded. Why?

What I want to achieve is to exclude package com.my.app.school.course but keep pacakge com.my.app.school.course.free , how to achieve this?

======== update ========

I feel it might be because the package I tried to exclude contain java classes that have been used in other packages. I will verify my guess.

Answer 1

Ok, I found the reason why the exclusion doesn't work.

Because some java classes under the package which I tried to exclude have been used in other packages. Seems maven-compiler-plugin is smart to detect that.

Answer 2

As you note, the problem is that your other sources depend on some of the sources you've excluded: Because Maven passes -sourcepath to javac, javac can find and compile those "missing" sources.

If you want the build to fail in that case, you can explicitly specify a dummy value for -sourcepath :

<plugin>
  <artifactId>maven-compiler-plugin</artifactId>
  <version>3.8.1</version>
  <configuration>
    <compilerArgs>
      <arg>-sourcepath</arg>
      <arg>doesnotexist</arg>
    </compilerArgs>
  </configuration>
</plugin>

See MCOMPILER-174 and this longer explanation of how javac handles -sourcepath and other arguments .

Answer 3

configuring the exclusion in the jar or war plugins seems to be a good technique to not disturb JUnit testing and compilation:

maven-jar-plugin / exclude

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-jar-plugin</artifactId>
  <version>3.2.0</version>
  <configuration>
    <excludes>
      <exclude>**/service/*</exclude>
    </excludes>
  </configuration>
</plugin>

maven-war-plugin / exclude

<plugin>
  <artifactId>maven-war-plugin</artifactId>
  <version>3.3.1</version>
  <configuration>
    <packagingExcludes>
      WEB-INF/lib/commons-logging-*.jar,
      %regex[WEB-INF/lib/log4j-(?!over-slf4j).*.jar]
    </packagingExcludes>
  </configuration>
</plugin>