HDDS-12065. Checkpoint directory should be cleared on startup

Change-Id: Ie840ca2d5ccbce02f7a19c66f10eb7b7f810d9f6

hadoop-hdds/framework/src/main/java/org/apache/hadoop/hdds/utils/DBCheckpointServlet.java

@@ -24,9 +24,12 @@
 import java.io.File;
 import java.io.IOException;
 import java.io.OutputStream;
+import java.nio.file.FileVisitResult;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.nio.file.SimpleFileVisitor;
+import java.nio.file.attribute.BasicFileAttributes;
 import java.time.Duration;
 import java.time.Instant;
 import java.util.ArrayList;
@@ -107,6 +110,13 @@ public void initialize(DBStore store, DBCheckpointMetrics metrics,
     }
     bootstrapTempData = Paths.get(tempData,
         "temp-bootstrap-data").toFile();
+    if (bootstrapTempData.exists()) {
+      try {
+        deleteContents(bootstrapTempData.toPath());
+      } catch (IOException e) {
+        throw new ServletException(e);
+      }
+    }
     if (!bootstrapTempData.exists() &&
         !bootstrapTempData.mkdirs()) {
       throw new ServletException("Failed to make:" + bootstrapTempData);
@@ -123,6 +133,24 @@ private boolean hasPermission(UserGroupInformation user) {
     }
   }
 
+  private void deleteContents(Path directory) throws IOException {
+    Files.walkFileTree(directory, new SimpleFileVisitor<Path>() {
+      @Override
+      public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
+        Files.delete(file); // Delete file
+        return FileVisitResult.CONTINUE;
+      }
+
+      @Override
+      public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
+        if (!dir.equals(directory)) { // Skip deleting the root directory
+          Files.delete(dir);
+        }
+        return FileVisitResult.CONTINUE;
+      }
+    });
+  }
+
   /**
    * Generates Snapshot checkpoint as tar ball.
    * @param request the HTTP servlet request