HADOOP-17686. Avoid potential NPE by using Path#getParentPath API in hadoop-huaweicloud (#2990)

Signed-off-by: Takanobu Asanuma <tasanuma@apache.org>

hadoop-cloud-storage-project/hadoop-huaweicloud/src/main/java/org/apache/hadoop/fs/obs/OBSObjectBucketUtils.java

@@ -55,6 +55,7 @@ import java.util.Collections;
 import java.util.Comparator;
 import java.util.LinkedList;
 import java.util.List;
+import java.util.Optional;
 import java.util.Set;
 import java.util.TreeSet;
 import java.util.concurrent.ExecutionException;
@@ -872,8 +873,12 @@ final class OBSObjectBucketUtils {
       directories.add(p.toString());
     }
     while (p.compareTo(sourcePath) > 0) {
-      p = p.getParent();
-      if (p.isRoot() || p.compareTo(sourcePath) == 0) {
+      Optional<Path> parent = p.getOptionalParentPath();
+      if (!parent.isPresent()) {
+        break;
+      }
+      p = parent.get();
+      if (p.compareTo(sourcePath) == 0) {
         break;
       }
       directories.add(p.toString());

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/Path.java

@@ -24,6 +24,7 @@ import java.io.ObjectInputValidation;
 import java.io.Serializable;
 import java.net.URI;
 import java.net.URISyntaxException;
+import java.util.Optional;
 import java.util.regex.Pattern;
 
 import org.apache.avro.reflect.Stringable;
@@ -420,22 +421,39 @@ public class Path
   }
 
   /**
-   * Returns the parent of a path or null if at root.
+   * Returns the parent of a path or null if at root. Better alternative is
+   * {@link #getOptionalParentPath()} to handle nullable value for root path.
+   *
    * @return the parent of a path or null if at root
    */
   public Path getParent() {
+    return getParentUtil();
+  }
+
+  /**
+   * Returns the parent of a path as {@link Optional} or
+   * {@link Optional#empty()} i.e an empty Optional if at root.
+   *
+   * @return Parent of path wrappen in {@link Optional}.
+   * {@link Optional#empty()} i.e an empty Optional if at root.
+   */
+  public Optional<Path> getOptionalParentPath() {
+    return Optional.ofNullable(getParentUtil());
+  }
+
+  private Path getParentUtil() {
     String path = uri.getPath();
     int lastSlash = path.lastIndexOf('/');
     int start = startPositionWithoutWindowsDrive(path);
     if ((path.length() == start) ||               // empty path
-        (lastSlash == start && path.length() == start+1)) { // at root
+        (lastSlash == start && path.length() == start + 1)) { // at root
       return null;
     }
     String parent;
-    if (lastSlash==-1) {
+    if (lastSlash == -1) {
       parent = CUR_DIR;
     } else {
-      parent = path.substring(0, lastSlash==start?start+1:lastSlash);
+      parent = path.substring(0, lastSlash == start ? start + 1 : lastSlash);
     }
     return new Path(uri.getScheme(), uri.getAuthority(), parent);
   }