Optimization of computing hash for classes in BanDuplicateClasses

hash is calculated during jar scanning,
before was calculated during class compare
which cause to open and read jars again - now jar is opened once

close #122

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 )
         {

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;
     }
 
 }

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;
+}

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 )