Most efficient way to check if a file is empty in Java on Windows

Question

I am trying to check if a log file is empty  meaning no errors  or not  in Java  on Windows  I have tried using 2 methods so far   Method 1  Failure   FileInputStream fis   new FileInputStream new File sLogFilename      int iByteCount   fis read      if  iByteCount    -1        System out println  NO ERRORS     else     System out println  SOME ERRORS       Method 2  Failure   File logFile   new File sLogFilename   if logFile length      0      System out println  NO ERRORS     else     System out println  SOME ERRORS       Now both these methods fail at times when the log file is empty  has no content   yet the file size is not zero  2 bytes    What is the most efficient and accurate method to check if the file is empty  I asked for efficiency  as I have to keep checking the file size thousands of times  in a loop   Note  The file size would hover around a few to 10 KB only   Method 3  Failure   Following  Cygnusx1 s suggestion  I had tried using a FileReader too  without success  Here s the snippet  if anyone s interested   Reader reader   new FileReader sLogFilename   int readSize   reader read    if  readSize    -1      System out println  NO ERRORS     else     System out println  SOME ERRORS

User · Answer

You can choose try the FileReader approach but it may not be time to give up just yet. If is the BOM field destroying for you try this solution posted here at stackoverflow.

Byte order mark screws up file reading in Java

User · Answer

String line   br readLine    String   splitted   line split  anySplitCharacter    if splitted length    0        file is empty else       file is not empty   I had the same problem with my text file  Although it was empty  the value being returned by the readLine method was not null  Therefore  I tried to assign its value to the String array which I was using to access the splitted attributes of my data  It did work for me  Try this out and tell me if it works for u as well

User · Answer

Another way to do this is  using Apache Commons FileUtils  -  private void printEmptyFileName final File file  throws IOException       if  FileUtils readFileToString file  trim   isEmpty              System out println  File is empty      file getName

User · Answer

Now both these methods fail at times when the log file is empty  has no content   yet the file size is not zero  2 bytes     Actually  I think you will find that the file is NOT empty   Rather I think that you will find that those two characters are a CR and a NL  i e  the file consists of one line that is empty   If you want to test if a file is either empty or has a single empty line then a simple  relatively efficient way is   try  BufferedReader br   new BufferedReader FileReader fileName          String line   br readLine        if  line    null              line length      0  amp  amp  br readLine      null             System out println  NO ERRORS           else           System out println  SOME ERRORS               Can we do this more efficiently   Possibly   It depends on how often you have to deal with the three different cases    a completely empty file a file consisting of a single empty line a file with a non-empty line  or multiple lines    You can probably do better by using Files length   and   or reading just the first two bytes   However  the problems include    If you both test the file size AND read the first few bytes then you are making 2 syscalls  The actual line termination sequence could be CR  NL or CR NL  depending on the platform    I know you say this is for Windows  but what happens if you need to port your application   Or if someone sends you a non-Windows file   It would be nice to avoid setting up stream   reader stack  but the file s character encoding could map CR and NL to something other than the bytes 0x0d and 0x0a    For example     UTF-16  Then there s the annoying habit of some Windows utilities have putting BOM markers into UTF-8 encoded files    This would even mess up the simple version above     All of this means that the most efficient possible solution is going to be rather complicated

User · Answer

I think the best way is to use file length    0   It is sometimes possible that the first line is empty

User · Answer

Check if the first line of file is empty   BufferedReader br   new BufferedReader new FileReader  path to some file          if  br readLine      null        System out println  No errors  and file empty

User · Answer

Try FileReader  this reader is meant to read stream of character  while FileInputStream is meant to read raw data   From the Javadoc      FileReader is meant for reading streams of characters  For reading   streams of raw bytes  consider using a FileInputStream    Since you wanna read a log file  FileReader is the class to use IMO

User · Answer

Stolen from http   www coderanch com t 279224 Streams java Checking-empty-file  FileInputStream fis   new FileInputStream new File  file name       int b   fis read      if  b    -1          System out println    File     file name     emty              Updated  My first answer was premature and contained a bug

User · Answer

This is an improvement of Saik0 s answer based on Anwar Shaikh s comment that too big files  above available memory  will throw an exception   Using Apache Commons FileUtils  private void printEmptyFileName final File file  throws IOException         Arbitrary big-ish number that definitely is not an empty file       int limit   4096      if file length  lt  limit  amp  amp  FileUtils readFileToString file  trim   isEmpty              System out println  File is empty      file getName

User · Answer

The idea of your first snippet is right  You probably meant to check iByteCount    -1  whether the file has at least one byte   if  iByteCount    -1        System out println  NO ERRORS     else     System out println  SOME ERRORS

User · Answer

Why not just use   File file   new File  test txt     if  file length      0           file empty   else          not empty     Is there something wrong with it

User · Answer

I combined the two best solutions to cover all the possibilities   BufferedReader br   new BufferedReader new FileReader fileName         File file   new File fileName   if  br readLine      null  amp  amp  file length      0        System out println  No errors  and file empty                      else       System out println  File contains something

[java] Most efficient way to check if a file is empty in Java on Windows

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