address comments

parquet-hadoop/src/main/java/org/apache/parquet/hadoop/ParquetOutputFormat.java

@@ -224,12 +224,12 @@ public static int getBloomFilterMaxBytes(Configuration conf) {
       ParquetProperties.DEFAULT_MAX_BLOOM_FILTER_BYTES);
   }
 
-  public static Set getBloomFilterColumns(Configuration conf) {
+  public static Set<String> getBloomFilterColumns(Configuration conf) {
     String columnNames = conf.get(BLOOM_FILTER_COLUMN_NAMES);
     if (columnNames != null) {
       return new HashSet<>(Arrays.asList(columnNames.split(",")));
     } else {
-      return new HashSet();
+      return new HashSet<>();
     }
   }
 

parquet-hadoop/src/main/java/org/apache/parquet/hadoop/ParquetWriter.java

@@ -1,14 +1,14 @@
-/* 
+/*
  * Licensed to the Apache Software Foundation (ASF) under one
  * or more contributor license agreements.  See the NOTICE file
  * distributed with this work for additional information
  * regarding copyright ownership.  The ASF licenses this file
  * to you under the Apache License, Version 2.0 (the
  * "License"); you may not use this file except in compliance
  * with the License.  You may obtain a copy of the License at
- * 
+ *
  *   http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing,
  * software distributed under the License is distributed on an
  * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
@@ -544,10 +544,10 @@ public SELF withPageWriteChecksumEnabled(boolean enablePageWriteChecksum) {
      *
      * @return this builder for method chaining.
      */
-    public SELF withBloomFilterColumnNames(String columnNames) {
+    public SELF withBloomFilterColumnNames(String... columnNames) {
       if (columnNames != null) {
         encodingPropsBuilder.withBloomFilterColumnNames(
-          new HashSet<>(Arrays.asList(columnNames.split(",")))
+          new HashSet<>(Arrays.asList(columnNames))
         );
       }