diff --git a/hadoop-common-project/hadoop-auth/src/main/java/org/apache/hadoop/security/authentication/server/MultiSchemeAuthenticationHandler.java b/hadoop-common-project/hadoop-auth/src/main/java/org/apache/hadoop/security/authentication/server/MultiSchemeAuthenticationHandler.java
index aa491003bb..58a0adb237 100644
--- a/hadoop-common-project/hadoop-auth/src/main/java/org/apache/hadoop/security/authentication/server/MultiSchemeAuthenticationHandler.java
+++ b/hadoop-common-project/hadoop-auth/src/main/java/org/apache/hadoop/security/authentication/server/MultiSchemeAuthenticationHandler.java
@@ -186,11 +186,12 @@ public AuthenticationToken authenticate(HttpServletRequest request,
     String authorization =
         request.getHeader(HttpConstants.AUTHORIZATION_HEADER);
     if (authorization != null) {
-      for (String scheme : schemeToAuthHandlerMapping.keySet()) {
-        if (AuthenticationHandlerUtil.matchAuthScheme(scheme, authorization)) {
-          AuthenticationHandler handler =
-              schemeToAuthHandlerMapping.get(scheme);
-          AuthenticationToken token = handler.authenticate(request, response);
+      for (Map.Entry<String, AuthenticationHandler> entry :
+          schemeToAuthHandlerMapping.entrySet()) {
+        if (AuthenticationHandlerUtil.matchAuthScheme(
+            entry.getKey(), authorization)) {
+          AuthenticationToken token =
+              entry.getValue().authenticate(request, response);
           logger.trace("Token generated with type {}", token.getType());
           return token;
         }
diff --git a/hadoop-common-project/hadoop-common/dev-support/findbugsExcludeFile.xml b/hadoop-common-project/hadoop-common/dev-support/findbugsExcludeFile.xml
index cdd88f3c78..de76afbcbc 100644
--- a/hadoop-common-project/hadoop-common/dev-support/findbugsExcludeFile.xml
+++ b/hadoop-common-project/hadoop-common/dev-support/findbugsExcludeFile.xml
@@ -416,4 +416,30 @@
     <Method name="toString"/>
     <Bug pattern="DM_DEFAULT_ENCODING"/>
   </Match>
+
+  <!-- We need to make the methods public because PBHelperClient calls them. -->
+  <Match>
+    <Class name="org.apache.hadoop.crypto.CipherSuite"/>
+    <Method name="setUnknownValue"/>
+    <Bug pattern="ME_ENUM_FIELD_SETTER"/>
+  </Match>
+  <Match>
+    <Class name="org.apache.hadoop.crypto.CryptoProtocolVersion"/>
+    <Method name="setUnknownValue"/>
+    <Bug pattern="ME_ENUM_FIELD_SETTER"/>
+  </Match>
+
+  <!-- We need to make the method public for testing. -->
+  <Match>
+    <Class name="org.apache.hadoop.metrics2.lib.DefaultMetricsSystem"/>
+    <Method name="setMiniClusterMode"/>
+    <Bug pattern="ME_ENUM_FIELD_SETTER"/>
+  </Match>
+
+  <!-- Experimental interface. Ignore. -->
+  <Match>
+    <Class name="org.apache.hadoop.metrics2.lib.DefaultMetricsFactory"/>
+    <Method name="setInstance"/>
+    <Bug pattern="ME_ENUM_FIELD_SETTER"/>
+  </Match>
 </FindBugsFilter>
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FileUtil.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FileUtil.java
index 0b27a7e326..b656a878e6 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FileUtil.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FileUtil.java
@@ -115,8 +115,10 @@ public static void fullyDeleteOnExit(final File file) {
     file.deleteOnExit();
     if (file.isDirectory()) {
       File[] files = file.listFiles();
-      for (File child : files) {
-        fullyDeleteOnExit(child);
+      if (files != null) {
+        for (File child : files) {
+          fullyDeleteOnExit(child);
+        }
       }
     }
   }
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/RawLocalFileSystem.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/RawLocalFileSystem.java
index e4e0659b13..721d0c058a 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/RawLocalFileSystem.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/RawLocalFileSystem.java
@@ -384,13 +384,16 @@ public final boolean handleEmptyDstDirectoryOnWindows(Path src, File srcFile,
     // again.
     try {
       FileStatus sdst = this.getFileStatus(dst);
-      if (sdst.isDirectory() && dstFile.list().length == 0) {
-        if (LOG.isDebugEnabled()) {
-          LOG.debug("Deleting empty destination and renaming " + src + " to " +
-              dst);
-        }
-        if (this.delete(dst, false) && srcFile.renameTo(dstFile)) {
-          return true;
+      String[] dstFileList = dstFile.list();
+      if (dstFileList != null) {
+        if (sdst.isDirectory() && dstFileList.length == 0) {
+          if (LOG.isDebugEnabled()) {
+            LOG.debug("Deleting empty destination and renaming " + src +
+                " to " + dst);
+          }
+          if (this.delete(dst, false) && srcFile.renameTo(dstFile)) {
+            return true;
+          }
         }
       }
     } catch (FileNotFoundException ignored) {
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/shell/CommandWithDestination.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/shell/CommandWithDestination.java
index 578d22b48c..2a483c0a50 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/shell/CommandWithDestination.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/shell/CommandWithDestination.java
@@ -501,7 +501,7 @@ FSDataOutputStream create(PathData item, boolean lazyPersist,
                         createFlags,
                         getConf().getInt(IO_FILE_BUFFER_SIZE_KEY,
                             IO_FILE_BUFFER_SIZE_DEFAULT),
-                        lazyPersist ? 1 : getDefaultReplication(item.path),
+                        (short) 1,
                         getDefaultBlockSize(),
                         null,
                         null);
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/DoubleWritable.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/DoubleWritable.java
index 5cc326fe3c..f45ed0a82e 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/DoubleWritable.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/DoubleWritable.java
@@ -75,7 +75,7 @@ public int hashCode() {
   
   @Override
   public int compareTo(DoubleWritable o) {
-    return (value < o.value ? -1 : (value == o.value ? 0 : 1));
+    return Double.compare(value, o.value);
   }
   
   @Override
@@ -94,7 +94,7 @@ public int compare(byte[] b1, int s1, int l1,
                        byte[] b2, int s2, int l2) {
       double thisValue = readDouble(b1, s1);
       double thatValue = readDouble(b2, s2);
-      return (thisValue < thatValue ? -1 : (thisValue == thatValue ? 0 : 1));
+      return Double.compare(thisValue, thatValue);
     }
   }
 
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/FloatWritable.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/FloatWritable.java
index 21e4cc4f5b..367fc946da 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/FloatWritable.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/FloatWritable.java
@@ -66,9 +66,7 @@ public int hashCode() {
   /** Compares two FloatWritables. */
   @Override
   public int compareTo(FloatWritable o) {
-    float thisValue = this.value;
-    float thatValue = o.value;
-    return (thisValue<thatValue ? -1 : (thisValue==thatValue ? 0 : 1));
+    return Float.compare(value, o.value);
   }
 
   @Override
@@ -86,7 +84,7 @@ public int compare(byte[] b1, int s1, int l1,
                        byte[] b2, int s2, int l2) {
       float thisValue = readFloat(b1, s1);
       float thatValue = readFloat(b2, s2);
-      return (thisValue<thatValue ? -1 : (thisValue==thatValue ? 0 : 1));
+      return Float.compare(thisValue, thatValue);
     }
   }
 
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/IOUtils.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/IOUtils.java
index 459014ba72..e24f1960ac 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/IOUtils.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/IOUtils.java
@@ -371,9 +371,12 @@ public static List<String> listDirectory(File dir, FilenameFilter filter)
     try (DirectoryStream<Path> stream =
              Files.newDirectoryStream(dir.toPath())) {
       for (Path entry: stream) {
-        String fileName = entry.getFileName().toString();
-        if ((filter == null) || filter.accept(dir, fileName)) {
-          list.add(fileName);
+        Path fileName = entry.getFileName();
+        if (fileName != null) {
+          String fileNameStr = fileName.toString();
+          if ((filter == null) || filter.accept(dir, fileNameStr)) {
+            list.add(fileNameStr);
+          }
         }
       }
     } catch (DirectoryIteratorException e) {
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/ECSchema.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/ECSchema.java
index e55fbdd876..4d66019a35 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/ECSchema.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/ECSchema.java
@@ -189,8 +189,8 @@ public String toString() {
     sb.append((extraOptions.isEmpty() ? "" : ", "));
 
     int i = 0;
-    for (String opt : extraOptions.keySet()) {
-      sb.append(opt + "=" + extraOptions.get(opt) +
+    for (Map.Entry<String, String> entry : extraOptions.entrySet()) {
+      sb.append(entry.getKey() + "=" + entry.getValue() +
           (++i < extraOptions.size() ? ", " : ""));
     }
 
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/file/tfile/Utils.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/file/tfile/Utils.java
index 5743c66798..8cb6e0d95c 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/file/tfile/Utils.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/file/tfile/Utils.java
@@ -395,7 +395,7 @@ public boolean equals(Object other) {
 
     @Override
     public int hashCode() {
-      return (major << 16 + minor);
+      return (major << 16) + minor;
     }
   }
 
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/token/delegation/ZKDelegationTokenSecretManager.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/token/delegation/ZKDelegationTokenSecretManager.java
index 4a7ddb2465..88bd29bd73 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/token/delegation/ZKDelegationTokenSecretManager.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/token/delegation/ZKDelegationTokenSecretManager.java
@@ -881,11 +881,9 @@ private void addOrUpdateToken(TokenIdent ident,
     String nodeCreatePath =
         getNodePath(ZK_DTSM_TOKENS_ROOT, DELEGATION_TOKEN_PREFIX
             + ident.getSequenceNumber());
-    ByteArrayOutputStream tokenOs = new ByteArrayOutputStream();
-    DataOutputStream tokenOut = new DataOutputStream(tokenOs);
-    ByteArrayOutputStream seqOs = new ByteArrayOutputStream();
 
-    try {
+    try (ByteArrayOutputStream tokenOs = new ByteArrayOutputStream();
+         DataOutputStream tokenOut = new DataOutputStream(tokenOs)) {
       ident.write(tokenOut);
       tokenOut.writeLong(info.getRenewDate());
       tokenOut.writeInt(info.getPassword().length);
@@ -902,8 +900,6 @@ private void addOrUpdateToken(TokenIdent ident,
         zkClient.create().withMode(CreateMode.PERSISTENT)
             .forPath(nodeCreatePath, tokenOs.toByteArray());
       }
-    } finally {
-      seqOs.close();
     }
   }
 
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/SysInfoWindows.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/SysInfoWindows.java
index 8b4ea54602..bce2d6d3b8 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/SysInfoWindows.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/SysInfoWindows.java
@@ -169,7 +169,7 @@ public long getAvailablePhysicalMemorySize() {
 
   /** {@inheritDoc} */
   @Override
-  public int getNumProcessors() {
+  public synchronized int getNumProcessors() {
     refreshIfNeeded();
     return numProcessors;
   }
@@ -196,7 +196,7 @@ public long getCumulativeCpuTime() {
 
   /** {@inheritDoc} */
   @Override
-  public float getCpuUsagePercentage() {
+  public synchronized float getCpuUsagePercentage() {
     refreshIfNeeded();
     float ret = cpuUsage;
     if (ret != -1) {
@@ -207,7 +207,7 @@ public float getCpuUsagePercentage() {
 
   /** {@inheritDoc} */
   @Override
-  public float getNumVCoresUsed() {
+  public synchronized float getNumVCoresUsed() {
     refreshIfNeeded();
     float ret = cpuUsage;
     if (ret != -1) {
diff --git a/hadoop-common-project/hadoop-minikdc/src/main/java/org/apache/hadoop/minikdc/MiniKdc.java b/hadoop-common-project/hadoop-minikdc/src/main/java/org/apache/hadoop/minikdc/MiniKdc.java
index fe194c00e4..6f91018adb 100644
--- a/hadoop-common-project/hadoop-minikdc/src/main/java/org/apache/hadoop/minikdc/MiniKdc.java
+++ b/hadoop-common-project/hadoop-minikdc/src/main/java/org/apache/hadoop/minikdc/MiniKdc.java
@@ -365,8 +365,11 @@ private void delete(File f) {
         LOG.warn("WARNING: cannot delete file " + f.getAbsolutePath());
       }
     } else {
-      for (File c: f.listFiles()) {
-        delete(c);
+      File[] fileList = f.listFiles();
+      if (fileList != null) {
+        for (File c : fileList) {
+          delete(c);
+        }
       }
       if (! f.delete()) {
         LOG.warn("WARNING: cannot delete directory " + f.getAbsolutePath());