HDDS-12449. Enable UseCollectionIsEmpty check in PMD (#7995)

Author: myskov

dev-support/pmd/pmd-ruleset.xml

@@ -30,6 +30,7 @@
   <rule ref="category/java/bestpractices.xml/MissingOverride"/>
   <rule ref="category/java/bestpractices.xml/UnusedPrivateMethod"/>
   <rule ref="category/java/bestpractices.xml/UnusedPrivateField"/>
+  <rule ref="category/java/bestpractices.xml/UseCollectionIsEmpty" />
 
   <exclude-pattern>.*/generated-sources/.*</exclude-pattern>
 </ruleset>

hadoop-hdds/client/src/main/java/org/apache/hadoop/hdds/scm/storage/BlockInputStream.java

@@ -366,7 +366,7 @@ protected synchronized int readWithStrategy(ByteReaderStrategy strategy)
     int len = strategy.getTargetLength();
     while (len > 0) {
       // if we are at the last chunk and have read the entire chunk, return
-      if (chunkStreams.size() == 0 ||
+      if (chunkStreams.isEmpty() ||
           (chunkStreams.size() - 1 <= chunkIndex &&
               chunkStreams.get(chunkIndex)
                   .getRemaining() == 0)) {

hadoop-hdds/client/src/main/java/org/apache/hadoop/hdds/scm/storage/ECBlockOutputStream.java

@@ -131,7 +131,7 @@ ContainerCommandResponseProto> executePutBlock(boolean close,
         blockID = bd.getBlockID();
       }
       List<ChunkInfo> chunks = bd.getChunks();
-      if (chunks != null && chunks.size() > 0) {
+      if (chunks != null && !chunks.isEmpty()) {
         if (chunks.get(0).hasStripeChecksum()) {
           checksumBlockData = bd;
           break;

hadoop-hdds/client/src/main/java/org/apache/hadoop/hdds/scm/storage/MultipartInputStream.java

@@ -83,7 +83,7 @@ protected synchronized int readWithStrategy(ByteReaderStrategy strategy)
 
     int totalReadLen = 0;
     while (strategy.getTargetLength() > 0) {
-      if (partStreams.size() == 0 ||
+      if (partStreams.isEmpty() ||
           partStreams.size() - 1 <= partIndex &&
               partStreams.get(partIndex).getRemaining() == 0) {
         return totalReadLen == 0 ? EOF : totalReadLen;

hadoop-hdds/client/src/main/java/org/apache/hadoop/ozone/client/io/ECBlockInputStream.java

@@ -335,7 +335,7 @@ public synchronized int read(ByteBuffer byteBuffer) throws IOException {
 
   protected boolean shouldRetryFailedRead(int failedIndex) {
     Deque<DatanodeDetails> spareLocations = spareDataLocations.get(failedIndex);
-    if (spareLocations != null && spareLocations.size() > 0) {
+    if (spareLocations != null && !spareLocations.isEmpty()) {
       failedLocations.add(dataLocations[failedIndex]);
       DatanodeDetails spare = spareLocations.removeFirst();
       dataLocations[failedIndex] = spare;

hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/HddsUtils.java

@@ -207,7 +207,7 @@ public static Optional<String> getHostName(String value) {
       return Optional.empty();
     }
     String hostname = value.replaceAll("\\:[0-9]+$", "");
-    if (hostname.length() == 0) {
+    if (hostname.isEmpty()) {
       return Optional.empty();
     } else {
       return Optional.of(hostname);

hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/ha/SCMNodeInfo.java

@@ -79,7 +79,7 @@ public static List<SCMNodeInfo> buildNodeInfo(ConfigurationSource conf) {
     if (scmServiceId != null) {
       ArrayList< String > scmNodeIds = new ArrayList<>(
           HddsUtils.getSCMNodeIds(conf, scmServiceId));
-      if (scmNodeIds.size() == 0) {
+      if (scmNodeIds.isEmpty()) {
         throw new ConfigurationException(
             String.format("Configuration does not have any value set for %s " +
                     "for the SCM serviceId %s. List of SCM Node ID's should " +

hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/net/InnerNodeImpl.java

@@ -574,7 +574,7 @@ private Map<Node, Integer> getAncestorCountMap(Collection<Node> nodes,
     Preconditions.checkState(genToExclude >= 0);
     Preconditions.checkState(genToReturn >= 0);
 
-    if (nodes == null || nodes.size() == 0) {
+    if (nodes == null || nodes.isEmpty()) {
       return Collections.emptyMap();
     }
     // with the recursive call, genToReturn can be smaller than genToExclude
@@ -619,7 +619,7 @@ private Node getLeafOnLeafParent(int leafIndex, List<String> excludedScopes,
       if (excludedNodes != null && excludedNodes.contains(node)) {
         continue;
       }
-      if (excludedScopes != null && excludedScopes.size() > 0) {
+      if (excludedScopes != null && !excludedScopes.isEmpty()) {
         if (excludedScopes.stream().anyMatch(node::isDescendant)) {
           continue;
         }

hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/security/ssl/ReloadingX509KeyManager.java

@@ -221,7 +221,7 @@ private X509ExtendedKeyManager init(PrivateKey newPrivateKey, List<X509Certifica
 
   private boolean isAlreadyUsing(PrivateKey privateKey, List<X509Certificate> newTrustChain) {
     return currentPrivateKey != null && currentPrivateKey.equals(privateKey) &&
-        currentTrustChain.size() > 0 &&
+        !currentTrustChain.isEmpty() &&
         newTrustChain.size() == currentTrustChain.size() &&
         newTrustChain.stream()
             .allMatch(

hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/security/ssl/ReloadingX509TrustManager.java

@@ -161,7 +161,7 @@ private X509TrustManager init(List<X509Certificate> newRootCaCerts)
   }
 
   private boolean isAlreadyUsing(List<X509Certificate> newRootCaCerts) {
-    return newRootCaCerts.size() > 0 &&
+    return !newRootCaCerts.isEmpty() &&
         currentRootCACerts.size() == newRootCaCerts.size() &&
         newRootCaCerts.stream()
             .allMatch(