add comments as reviewer suggested

src/main/java/au/csiro/variantspark/utils/FileUtils.java

@@ -20,37 +20,11 @@ public static boolean isBGZFile(String filePath) {
 		 * .vcf is not GZP file and get htsjdk.samtools.SAMFormatException: at header from java.io.BufferedReader.readLine(BufferedReader.java:389)
 		*/
 	    try (BufferedInputStream bufferedInputStream = new BufferedInputStream(new FileInputStream(filePath))) {
-	        //bufferedInputStream.mark(100); // mark the current position
 	        boolean isValid = BlockCompressedInputStream.isValidFile(bufferedInputStream);
-	        //bufferedInputStream.reset(); // reset back to the marked position
 	        return isValid;
 	    } catch (IOException e) {
-	        // Handle the exception
+	        //handle exception for non proper bgzip file
 	        return false;
 	    }
 	}
-
-	/**
-	 * 
-	 * @param file: an input file
-	 * @return true if input file is Gzip by check the first two byte of input file 
-	 * @throws IOException
-	 */
-	public static boolean isInputGZip(final File file) throws IOException {
-		//final PushbackInputStream pb = new PushbackInputStream(input, 2);
-
-		try(final InputStream input = new FileInputStream(file)){
-			int header = input.read(); //read ID1
-	        if(header == -1)   return false;	        
-
-	        int b = input.read(); //read ID2
-	        if(b == -1)  return false;
-
-	        //ID2 * 256 + ID1 = 35615
-	        if( ( (b << 8) | header) == GZIPInputStream.GZIP_MAGIC) 
-	            return true;	         
-		}
-
-		return false;		
-	} 
 }

src/main/scala/au/csiro/variantspark/cli/args/SparkArgs.scala

@@ -2,7 +2,7 @@ package au.csiro.variantspark.cli.args
 
 import org.kohsuke.args4j.Option
 import au.csiro.pbdava.ssparkle.spark.SparkApp
-import au.csiro.variantspark.utils._
+import au.csiro.variantspark.utils.FileUtils
 import org.apache.spark.rdd.RDD
 import htsjdk.samtools.util.BlockCompressedInputStream
 import org.apache.hadoop.fs.Path
@@ -18,11 +18,15 @@ trait SparkArgs extends SparkApp {
     val isBGZ = FileUtils.isBGZFile(inputFile)
     println(inputFile + " is loading to spark RDD, isBGZFile: " + isBGZ)
     if (isBGZ) {
+      // BGZIP file is compressed as blocks, requires specialized libraries htsjdk
       val path = new Path(inputFile)
       val fs = path.getFileSystem(sc.hadoopConfiguration)
       val bgzInputStream = new BlockCompressedInputStream(fs.open(path))
+      // each blocks can be decompressed independently and to be read in parallel
       sc.parallelize(Stream.continually(bgzInputStream.readLine()).takeWhile(_ != null).toList)
     } else {
+      // The standard GZIP libraries can handle files compressed as a whole
+      // load .vcf, .vcf.gz or .vcf.bz2 to RDD
       sc.textFile(inputFile, if (sparkPar > 0) sparkPar else sc.defaultParallelism)
     }
   }