refs PR 112 - fixed threading issue when creating list of exceptions

Author: johnscancella

src/main/java/gov/loc/repository/bagit/verify/BagVerifier.java

@@ -3,9 +3,10 @@
 import java.io.IOException;
 import java.nio.file.Path;
 import java.util.ArrayList;
-import java.util.List;
-import java.util.ResourceBundle;
+import java.util.Collection;
+import java.util.Collections;
 import java.util.Map.Entry;
+import java.util.ResourceBundle;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -151,10 +152,8 @@ public void isValid(final Bag bag, final boolean ignoreHiddenFiles) throws IOExc
   void checkHashes(final Manifest manifest) throws CorruptChecksumException, InterruptedException, VerificationException{
     final CountDownLatch latch = new CountDownLatch( manifest.getFileToChecksumMap().size());
 
-    //TODO maybe return all of these at some point... 
-    //if that is ever the case make sure to use Collections.synchronizedCollection(new ArrayList<>())
-    //we aren't doing it now because it is a huge performance hit for little value
-    final List<Exception> exceptions = new ArrayList<>(); 
+    //TODO maybe return all of these at some point...
+    final Collection<Exception> exceptions = Collections.synchronizedCollection(new ArrayList<>());
 
     for(final Entry<Path, String> entry : manifest.getFileToChecksumMap().entrySet()){
       executor.execute(new CheckManifestHashesTask(entry, manifest.getAlgorithm().getMessageDigestName(), latch, exceptions));
@@ -163,7 +162,7 @@ void checkHashes(final Manifest manifest) throws CorruptChecksumException, Inter
     latch.await();
 
     if(!exceptions.isEmpty()){
-      final Exception e = exceptions.get(0);
+      final Exception e = exceptions.iterator().next();
       if(e instanceof CorruptChecksumException){
         logger.debug(messages.getString("checksums_not_matching_error"), exceptions.size());
         throw (CorruptChecksumException)e;

src/main/java/gov/loc/repository/bagit/verify/CheckManifestHashesTask.java

@@ -5,9 +5,9 @@
 import java.nio.file.Path;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
-import java.util.List;
-import java.util.ResourceBundle;
+import java.util.Collection;
 import java.util.Map.Entry;
+import java.util.ResourceBundle;
 import java.util.concurrent.CountDownLatch;
 
 import org.slf4j.Logger;
@@ -27,10 +27,10 @@ public class CheckManifestHashesTask implements Runnable {
 
   private final Entry<Path, String> entry;
   private final CountDownLatch latch;
-  private final List<Exception> exceptions;
+  private final Collection<Exception> exceptions;
   private final String algorithm;
 
-  public CheckManifestHashesTask(final Entry<Path, String> entry, final String algorithm, final CountDownLatch latch, final List<Exception> exceptions) {
+  public CheckManifestHashesTask(final Entry<Path, String> entry, final String algorithm, final CountDownLatch latch, final Collection<Exception> exceptions) {
     this.entry = entry;
     this.algorithm = algorithm;
     this.latch = latch;
@@ -68,7 +68,7 @@ public CountDownLatch getLatch() {
     return latch;
   }
 
-  public List<Exception> getExceptions() {
+  public Collection<Exception> getExceptions() {
     return exceptions;
   }