Fixes #160, ensure the java classloader is a child first one and supports to excludes some gathered classpath element to solve manually conflicts

pom.xml

@@ -184,10 +184,17 @@
       <version>1.9.0</version>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-simple</artifactId>
+      <version>${slf4j.version}</version>
+    </dependency>
   </dependencies>
 
   <properties>
     <mavenVersion>3.0</mavenVersion>
+
+    <slf4j.version>1.7.30</slf4j.version>
   </properties>
 
   <build>
@@ -269,6 +276,51 @@
           </execution>
         </executions>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-dependency-plugin</artifactId>
+        <version>3.1.2</version>
+        <executions>
+          <execution>
+            <id>copy-test-deps</id>
+            <phase>generate-test-resources</phase>
+            <goals>
+              <goal>copy</goal>
+            </goals>
+            <configuration>
+              <artifactItems>
+                <artifactItem>
+                  <groupId>org.slf4j</groupId>
+                  <artifactId>slf4j-api</artifactId>
+                  <version>${slf4j.version}</version>
+                  <type>jar</type>
+                  <overWrite>false</overWrite>
+                  <destFileName>slf4j-api.jar</destFileName>
+                </artifactItem>
+                <artifactItem>
+                  <groupId>org.slf4j</groupId>
+                  <artifactId>slf4j-simple</artifactId>
+                  <version>${slf4j.version}</version>
+                  <type>jar</type>
+                  <overWrite>false</overWrite>
+                  <destFileName>slf4j-simple.jar</destFileName>
+                </artifactItem>
+                <artifactItem>
+                  <groupId>org.slf4j</groupId>
+                  <artifactId>slf4j-jdk14</artifactId>
+                  <version>${slf4j.version}</version>
+                  <type>jar</type>
+                  <overWrite>false</overWrite>
+                  <destFileName>slf4j-jdk14.jar</destFileName>
+                </artifactItem>
+              </artifactItems>
+              <outputDirectory>${project.build.directory}/test-dependencies/</outputDirectory>
+              <overWriteReleases>false</overWriteReleases>
+              <overWriteSnapshots>true</overWriteSnapshots>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>
 

src/main/java/org/codehaus/mojo/exec/ExecJavaMojo.java

@@ -5,6 +5,7 @@
 import java.lang.invoke.MethodHandles;
 import java.lang.invoke.MethodType;
 import java.lang.reflect.InvocationTargetException;
+import java.net.URLClassLoader;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
@@ -183,6 +184,15 @@ public class ExecJavaMojo
     @Parameter
     private List<String> additionalClasspathElements;
 
+    /**
+     * List of file to exclude from the classpath.
+     * It matches the jar name, for example {@code slf4j-simple-1.7.30.jar}.
+     *
+     * @since 3.0.1
+     */
+    @Parameter
+    private List<String> classpathFilenameExclusions;
+
     /**
      * Execute goal.
      * 
@@ -270,7 +280,8 @@ public void run()
                 }
             }
         }, mainClass + ".main()" );
-        bootstrapThread.setContextClassLoader( getClassLoader() );
+        URLClassLoader classLoader = getClassLoader();
+        bootstrapThread.setContextClassLoader( classLoader );
         setSystemProperties();
 
         bootstrapThread.start();
@@ -298,6 +309,18 @@ public void run()
             }
         }
 
+        if ( classLoader != null )
+        {
+            try
+            {
+                classLoader.close();
+            }
+            catch ( IOException e )
+            {
+                getLog().error(e.getMessage(), e);
+            }
+        }
+
         if ( originalSystemProperties != null )
         {
             System.setProperties( originalSystemProperties );
@@ -485,7 +508,7 @@ private void setSystemProperties()
      * @return the classloader
      * @throws MojoExecutionException if a problem happens
      */
-    private ClassLoader getClassLoader()
+    private URLClassLoader getClassLoader()
         throws MojoExecutionException
     {
         List<Path> classpathURLs = new ArrayList<>();
@@ -495,7 +518,11 @@ private ClassLoader getClassLoader()
 
         try
         {
-            return LoaderFinder.find( classpathURLs, mainClass );
+            return URLClassLoaderBuilder.builder()
+                    .setLogger( getLog() )
+                    .setPaths( classpathURLs )
+                    .setExclusions( classpathFilenameExclusions )
+                    .build();
         }
         catch ( NullPointerException | IOException e )
         {