'How to read/write a file in Java

I would like to replace some items in a file, based on some regular expressions. In order to do that:

  • I read the file line per line
  • For every line, I check for the regular expression and I perform the replacement
  • Every line gets written in an array of strings

When all this is finished, I try to delete the file (in order to recreate it again with the replaced lines).

For some reason this does not work: it seems that Java keeps a handle on that file, even after the BufferedReader has been closed.

Does anybody have a solution for this (newbie) question?

Code excerpt:

      Pattern oDatePattern   = Pattern.compile("at \\d{2}:\\d{2}:\\d{2} "); // meaning: "at xx:xx:xx"
      Pattern oTimePattern   = Pattern.compile("Kernel time [0-9]*\\.?[0-9]+ User time: [0-9]*\\.?[0-9]+"); // "[0-9]*\.?[0-9]+" stands for any floating point number
      Pattern oMemoryPattern = Pattern.compile("\\([0-9,A-F]*\\)"); // "[0-9,A-F]*" stands for any hexadecimal number 
      Matcher oDateMatcher;
      Matcher oTimeMatcher;
      Matcher oMemoryMatcher;

      List<String> sLog_Content = new ArrayList<String>();

      BufferedReader br = new BufferedReader(new FileReader(sLp_LogFile));
      try {
        String sLine = br.readLine();

        while (sLine != null) {
          System.out.println("ORIG : " + sLine);
          oDateMatcher = oDatePattern.matcher(sLine);
          sLine        = oDateMatcher.replaceAll("at <timestamp> ");
          oTimeMatcher = oTimePattern.matcher(sLine);
          sLine        = oTimeMatcher.replaceAll("Kernel time <Kernel_Time_usage> User time: <User_Time_usage>");
          oMemoryMatcher = oMemoryPattern.matcher(sLine);
          sLine          = oMemoryMatcher.replaceAll("<Memory_Address>");
          System.out.println("REPL : " + sLine);
          sLog_Content.add(sLine);
          sLine = br.readLine();
        }
      } finally {
        br.close();
      }

      System.out.println("All lines are read and regex replaced, try to delete the file");

      File tst_File = new File(sLp_LogFile);
      if (tst_File.exists()) {
        System.out.println(sLp_LogFile + " exists");
      } else {
        System.out.println(sLp_LogFile + " does not exist");
      }

      if (tst_File.delete()) {
        System.out.println(sLp_LogFile + " is deleted");
      } else {
        System.out.println(sLp_LogFile + " is not deleted");
      }

Output logs:

ORIG : Reading buffer 1 (0000000002ED0070) at 15:40:44 (index 125999, size 4410000 lines 126000, total lines read 126000)
REPL : Reading buffer 1 <Memory_Address> at <timestamp> (index 125999, size 4410000 lines 126000, total lines read 126000)
...
ORIG : Sending buffer 1 (0000000002ED0070) at 15:40:44 (index 125999, size 4410000, lines 126000, total lines sent 126000)
REPL : Sending buffer 1 <Memory_Address> at <timestamp> (index 125999, size 4410000, lines 126000, total lines sent 126000)
...
ORIG : Kernel time 0.2808 User time: 0.312
REPL : Kernel time <Kernel_Time_usage> User time: <User_Time_usage>
...
All lines are read and regex replaced, try to delete the file
D:\Logfile_lp.log exists
D:\Logfile_lp.log is not deleted
javaiofile-handling


Solution 1:[1]

Good afternoon, I would like to thank you all for having searched for a solution of this problem. Unfortunately the problem is not Java based: the file I'm trying to write to is created by a redirection cmd /c <program>.exe >> <output>.log, and it seems that Windows has not fully flushed the output buffer towards the output file, creating the problem.

I am currently using following (very dirty) work-around for this issue:

boolean bFile_can_be_opened = false;
while (!bFile_can_be_opened) {
  try {
    fwLog2 = new FileWriter(sLp_LogFile, true);
    bFile_can_be_opened = true;
  }
  catch (Exception e)
  {}
}

Further information on this issue can be found under the following new StackOverflow question: How to release a file, locked by the application, in Java

Solution 2:[2]

One possible explanation is that your application has the file open somewhere else.

Or it could be another application that has the file open.

Or maybe the application / user has permission to read the file but not to delete it.

I concur with the suggestion of using Files.delete ..

Solution 3:[3]

I see no issues in your code.

Seemingly closing the BufferReader ensure the file is closed. (cf this response).

Maybe you can give a try to Files.delete cf this response.
It will give more information about the deletion fail by throwing different exceptions.

Solution 4:[4]

I'm a beginner, I do not know as much things as you. But if I am right you should save your changes first a temp file. Afterwards you will read again the temp file and later you'll write to your real file. I hope my comment will help you.

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Community
Solution 2 Stephen C
Solution 3 Community
Solution 4 Dominique

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