diff --git a/src/main/java/org/apache/maven/plugins/enforcer/BanDuplicateClasses.java b/src/main/java/org/apache/maven/plugins/enforcer/BanDuplicateClasses.java
index 70504c22..a527e8e7 100644
--- a/src/main/java/org/apache/maven/plugins/enforcer/BanDuplicateClasses.java
+++ b/src/main/java/org/apache/maven/plugins/enforcer/BanDuplicateClasses.java
@@ -21,6 +21,7 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.nio.file.Files;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -151,7 +152,8 @@ else if ( file.isDirectory() )
                     for ( String name : FileUtils.getFileNames( file, null, null, false ) )
                     {
                         getLog().debug( "  " + name );
-                        checkAndAddName( o, name, classesSeen, duplicateClassNames, ignorableDependencies );
+                        checkAndAddName( o, name, () -> Files.newInputStream( file.toPath().resolve( name ) ),
+                                         classesSeen, duplicateClassNames, ignorableDependencies );
                     }
                 }
                 catch ( IOException e )
@@ -170,7 +172,9 @@ else if ( isJarFile( o ) )
                         for ( JarEntry entry : Collections.list( jar.entries() ) )
                         {
                             String fileName = entry.getName();
-                            checkAndAddName( o, fileName, classesSeen, duplicateClassNames, ignorableDependencies );
+
+                            checkAndAddName( o, fileName, () -> jar.getInputStream( entry ),
+                                             classesSeen, duplicateClassNames, ignorableDependencies );
                         }
                     }
                 }
@@ -220,10 +224,10 @@ else if ( isJarFile( o ) )
 
     }
 
-    private void checkAndAddName( Artifact artifact, String pathToClassFile, Map<String,
+    private void checkAndAddName( Artifact artifact, String pathToClassFile, InputStreamSupplier inputStreamSupplier, Map<String,
                                   ClassesWithSameName> classesSeen, Set<String> duplicateClasses,
                                   Collection<IgnorableDependency> ignores )
-        throws EnforcerRuleException
+        throws EnforcerRuleException, IOException
     {
         if ( !pathToClassFile.endsWith( ".class" ) )
         {
@@ -244,7 +248,8 @@ private void checkAndAddName( Artifact artifact, String pathToClassFile, Map<Str
 
         ClassesWithSameName classesWithSameName = classesSeen.get( pathToClassFile );
         boolean isFirstTimeSeeingThisClass = ( classesWithSameName == null );
-        ClassFile classFile = new ClassFile( pathToClassFile, artifact );
+
+        ClassFile classFile = new ClassFile( pathToClassFile, artifact, inputStreamSupplier );
 
         if ( isFirstTimeSeeingThisClass )
         {
diff --git a/src/main/java/org/apache/maven/plugins/enforcer/ClassFile.java b/src/main/java/org/apache/maven/plugins/enforcer/ClassFile.java
index 64798207..18ca1e49 100644
--- a/src/main/java/org/apache/maven/plugins/enforcer/ClassFile.java
+++ b/src/main/java/org/apache/maven/plugins/enforcer/ClassFile.java
@@ -19,6 +19,10 @@
  * under the License.
  */
 
+import java.io.IOException;
+import java.io.InputStream;
+
+import org.apache.commons.codec.digest.DigestUtils;
 import org.apache.maven.artifact.Artifact;
 
 /**
@@ -44,19 +48,28 @@ public class ClassFile
     /** the path to the .class file. Example: org/apache/maven/Stuff.class */
     private final String classFilePath;
     private final Artifact artifactThisClassWasFoundIn;
-    private final Hasher hasher;
-    private String lazilyComputedHash;
+    private String hash;
 
     /**
      * Constructor.
      * @param classFilePath path to the class file. Example: org/apache/maven/Stuff.class
      * @param artifactThisClassWasFoundIn the maven artifact the class appeared in (example: a jar file)
+     * @param inputStreamSupplier a supplier for class content input stream
      */
-    public ClassFile( String classFilePath, Artifact artifactThisClassWasFoundIn )
+    public ClassFile( String classFilePath, Artifact artifactThisClassWasFoundIn, InputStreamSupplier inputStreamSupplier )
+        throws IOException
     {
         this.classFilePath = classFilePath;
         this.artifactThisClassWasFoundIn = artifactThisClassWasFoundIn;
-        this.hasher = new Hasher( classFilePath );
+        this.hash = computeHash(inputStreamSupplier);
+    }
+
+    private String computeHash( InputStreamSupplier inputStreamSupplier ) throws IOException
+    {
+        try (InputStream inputStream = inputStreamSupplier.get())
+        {
+            return DigestUtils.md5Hex( inputStream );
+        }
     }
 
     /**
@@ -81,12 +94,7 @@ public Artifact getArtifactThisClassWasFoundIn()
      */
     public String getHash()
     {
-        if ( lazilyComputedHash == null )
-        {
-            lazilyComputedHash = hasher.generateHash( artifactThisClassWasFoundIn );
-        }
-
-        return lazilyComputedHash;
+        return hash;
     }
 
 }
diff --git a/src/main/java/org/apache/maven/plugins/enforcer/Hasher.java b/src/main/java/org/apache/maven/plugins/enforcer/Hasher.java
deleted file mode 100644
index 471f1e9e..00000000
--- a/src/main/java/org/apache/maven/plugins/enforcer/Hasher.java
+++ /dev/null
@@ -1,139 +0,0 @@
-package org.apache.maven.plugins.enforcer;
-
-/*
- * Licensed to the Apache Software Foundation (ASF) under one
- * or more contributor license agreements.  See the NOTICE file
- * distributed with this work for additional information
- * regarding copyright ownership.  The ASF licenses this file
- * to you under the Apache License, Version 2.0 (the
- * "License"); you may not use this file except in compliance
- * with the License.  You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
- */
-
-import java.io.Closeable;
-import java.io.File;
-import java.io.FileInputStream;
-import java.io.IOException;
-import java.io.InputStream;
-import java.util.jar.JarFile;
-
-import org.apache.commons.codec.digest.DigestUtils;
-import org.apache.maven.artifact.Artifact;
-
-import static org.apache.maven.plugins.enforcer.JarUtils.isJarFile;
-
-/**
- * Utility class to generate hashes/checksums for binary files.
- * Typically used to generate a hashes for .class files to compare
- * those files for equality.
- */
-public class Hasher
-{
-    /** the path to the .class file. Example: org/apache/maven/Stuff.class */
-    private final String classFilePath;
-
-    /**
-     * Constructor.
-     * @param classFilePath The path to the .class file. This is the file we'll generate a hash for.
-     *                      Example: org/apache/maven/Stuff.class
-     */
-    public Hasher( String classFilePath )
-    {
-        this.classFilePath = classFilePath;
-    }
-
-    /**
-     * @param artifact The artifact (example: jar file) which contains the {@link #classFilePath}.
-     *                 We'll generate a hash for the class file inside this artifact.
-     * @return generate a hash/checksum for the .class file in the provided artifact.
-     */
-    public String generateHash( Artifact artifact )
-    {
-        File artifactFile = artifact.getFile();
-        try
-        {
-            if ( artifactFile.isDirectory() )
-            {
-                return hashForFileInDirectory( artifactFile );
-            }
-            else if ( isJarFile( artifact ) )
-            {
-                return hashForFileInJar( artifactFile );
-            }
-            else
-            {
-                throw new IllegalArgumentException(
-                  "Expected either a directory or a jar file, but instead received: " + artifactFile );
-            }
-        }
-        catch ( IOException e )
-        {
-            throw new RuntimeException( "Problem calculating hash for " + artifact + " " + classFilePath, e );
-        }
-    }
-
-    private String hashForFileInDirectory( File artifactFile ) throws IOException
-    {
-        File classFile = new File( artifactFile, classFilePath );
-        InputStream inputStream = new FileInputStream( classFile );
-        try
-        {
-            return DigestUtils.md5Hex( inputStream );
-        }
-        finally
-        {
-            closeAll( inputStream );
-        }
-      }
-
-    private String hashForFileInJar( File artifactFile ) throws IOException
-    {
-        JarFile jar = new JarFile( artifactFile );
-        InputStream inputStream = jar.getInputStream( jar.getEntry( classFilePath ) );
-        try
-        {
-            return DigestUtils.md5Hex( inputStream );
-        }
-        finally
-        {
-            closeAll( inputStream, jar );
-        }
-    }
-
-    private void closeAll( Closeable... closeables ) throws IOException
-    {
-        IOException firstException = null;
-
-        for ( Closeable closeable : closeables )
-        {
-            if ( closeable != null )
-            {
-                try
-                {
-                    closeable.close();
-                }
-                catch ( IOException exception )
-                {
-                    if ( firstException == null )
-                    {
-                        firstException = exception;
-                    }
-                }
-            }
-        }
-
-        if ( firstException != null )
-        {
-            throw firstException;
-        }
-    }
-}
diff --git a/src/main/java/org/apache/maven/plugins/enforcer/InputStreamSupplier.java b/src/main/java/org/apache/maven/plugins/enforcer/InputStreamSupplier.java
new file mode 100644
index 00000000..3f9685c1
--- /dev/null
+++ b/src/main/java/org/apache/maven/plugins/enforcer/InputStreamSupplier.java
@@ -0,0 +1,34 @@
+package org.apache.maven.plugins.enforcer;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.io.IOException;
+import java.io.InputStream;
+
+/**
+ * Supplier functional interface for InputStream with exception.
+ *
+ * @author Slawomir Jaranowski
+ */
+@FunctionalInterface
+interface InputStreamSupplier
+{
+    InputStream get() throws IOException;
+}
diff --git a/src/test/java/org/apache/maven/plugins/enforcer/ClassFileHelper.java b/src/test/java/org/apache/maven/plugins/enforcer/ClassFileHelper.java
index b41b0739..cb92878c 100644
--- a/src/test/java/org/apache/maven/plugins/enforcer/ClassFileHelper.java
+++ b/src/test/java/org/apache/maven/plugins/enforcer/ClassFileHelper.java
@@ -20,12 +20,9 @@
  */
 
 import java.io.File;
-import java.io.FileOutputStream;
 import java.io.FileWriter;
 import java.io.IOException;
-import java.nio.charset.StandardCharsets;
-import java.util.jar.JarEntry;
-import java.util.jar.JarOutputStream;
+import java.nio.file.Files;
 
 import org.apache.maven.artifact.Artifact;
 import org.junit.rules.TemporaryFolder;
@@ -58,31 +55,8 @@ public ClassFile createWithContent( String pathToClassFile, String fileContents
             .withType( "some type that isn't 'jar' so our code assumes it's a directory" )
             .build();
 
-        return new ClassFile( pathToClassFile, artifact );
-    }
-
-    public ClassFile createJarWithContent( String jarFileName, String pathToClassFile, String fileContents )
-        throws IOException
-    {
-        uniqueId++;
-        String uniqueIdStr = Integer.toString( uniqueId );
-
-        File tempDirectory = createTempDirectory( uniqueIdStr );
-        File tempJarFile = new File( tempDirectory, jarFileName );
-
-        try ( JarOutputStream outStream = new JarOutputStream( new FileOutputStream( tempJarFile ) ) )
-        {
-            outStream.putNextEntry( new JarEntry( pathToClassFile ) );
-            outStream.write( fileContents.getBytes( StandardCharsets.UTF_8 ) );
-        }
-
-        Artifact artifact = ArtifactBuilder.newBuilder()
-            .withFileOrDirectory( tempJarFile )
-            .withVersion( uniqueIdStr )
-            .withType( "jar" )
-            .build();
-
-        return new ClassFile( pathToClassFile, artifact );
+        return new ClassFile( pathToClassFile, artifact,
+                              () -> Files.newInputStream( tempDirectory.toPath().resolve( pathToClassFile ) ) );
     }
 
     private File createTempDirectory( String uniqueIdStr )
diff --git a/src/test/java/org/apache/maven/plugins/enforcer/HasherTest.java b/src/test/java/org/apache/maven/plugins/enforcer/HasherTest.java
deleted file mode 100644
index 7abf0318..00000000
--- a/src/test/java/org/apache/maven/plugins/enforcer/HasherTest.java
+++ /dev/null
@@ -1,53 +0,0 @@
-package org.apache.maven.plugins.enforcer;
-
-import org.apache.maven.artifact.Artifact;
-import org.junit.Before;
-import org.junit.Rule;
-import org.junit.Test;
-import org.junit.rules.TemporaryFolder;
-import org.junit.rules.TestName;
-
-import static org.junit.Assert.assertEquals;
-
-public class HasherTest
-{
-    private static final String PATH_TO_CLASS_FILE = HasherTest.class.getName().replace( '.', '/' ) + ".class";
-
-    @Rule
-    public TemporaryFolder temporaryFolder = new TemporaryFolder();
-
-    @Rule
-    public final TestName testName = new TestName();
-
-    private ClassFileHelper classFileHelper;
-
-    @Before
-    public void beforeEachTest()
-    {
-        classFileHelper = new ClassFileHelper( temporaryFolder );
-    }
-
-    @Test
-    public void generateHashReturnsCorrectHashForFileInDirectory() throws Exception
-    {
-        ClassFile classFile = classFileHelper.createWithContent( PATH_TO_CLASS_FILE, "this is the file's contents" );
-        Artifact artifact = classFile.getArtifactThisClassWasFoundIn();
-        Hasher hasher = new Hasher( PATH_TO_CLASS_FILE );
-
-        String hash = hasher.generateHash( artifact );
-
-        assertEquals( "ae23844bc5db9bfad3fbbe5426d89dd3", hash );
-    }
-
-    @Test
-    public void generateHashReturnsCorrectHashForFileInJar() throws Exception
-    {
-        ClassFile classFile = classFileHelper.createJarWithContent( "temp.jar", PATH_TO_CLASS_FILE, "this is the file's contents" );
-        Artifact artifact = classFile.getArtifactThisClassWasFoundIn();
-        Hasher hasher = new Hasher( PATH_TO_CLASS_FILE );
-
-        String hash = hasher.generateHash( artifact );
-
-        assertEquals( "ae23844bc5db9bfad3fbbe5426d89dd3", hash );
-    }
-}