Find a line in a file and remove it

Question

I m looking for a small code snippet that will find a line in file and remove that line  not content but line  but could not find  So for example I have in a file following   myFile txt   aaa bbb ccc ddd   Need to have a function like this  public void removeLine String lineContent   and if I pass  removeLine  bbb    I get file like this   myFile txt   aaa ccc ddd

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public static void deleteLine String line  String filePath         File file   new File filePath        File file2   new File file getParent        temp    file getName         PrintWriter pw   null      Scanner read   null       FileInputStream fis   null      FileOutputStream fos   null      FileChannel src   null      FileChannel dest   null       try             pw   new PrintWriter file2           read   new Scanner file            while  read hasNextLine                   String currline   read nextLine                 if  line equalsIgnoreCase currline                     continue                else                   pw println currline                                    pw flush             fis   new FileInputStream file2           src   fis getChannel            fos   new FileOutputStream file           dest   fos getChannel             dest transferFrom src  0  src size             catch  IOException e            e printStackTrace          finally                pw close            read close             try               fis close                fos close                src close                dest close              catch  IOException e                e printStackTrace                       if  file2 delete                  System out println  File is deleted              else               System out println  Error occured  File      file2 getName       is not deleted

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public void removeLineFromFile String file  String lineToRemove         try          File inFile   new File file          if   inFile isFile              System out println  Parameter is not an existing file            return                   Construct the new file that will later be renamed to the original filename        File tempFile   new File inFile getAbsolutePath       tmp           BufferedReader br   new BufferedReader new FileReader file          PrintWriter pw   new PrintWriter new FileWriter tempFile           String line   null           Read from the original file and write to the new         unless content matches data to be removed        while   line   br readLine       null             if   line trim   equals lineToRemove                pw println line             pw flush                            pw close          br close             Delete the original file       if   inFile delete              System out println  Could not delete file            return                   Rename the new file to the filename the original file had        if   tempFile renameTo inFile           System out println  Could not rename file               catch  FileNotFoundException ex          ex printStackTrace              catch  IOException ex          ex printStackTrace                This I have found on the internet

User · Answer

Here you go  This solution uses a DataInputStream to scan for the position of the string you want replaced and uses a FileChannel to replace the text at that exact position  It only replaces the first occurrence of the string that it finds  This solution doesn t store a copy of the entire file somewhere   either the RAM or a temp file   it just edits the portion of the file that it finds   public static long scanForString String text  File file  throws IOException       if  text isEmpty            return file exists     0   -1         First of all  get a byte array off of this string      byte   bytes   text getBytes    StandardCharsets your charset              Next  search the file for the byte array      try  DataInputStream dis   new DataInputStream new FileInputStream file               List lt Integer gt  matches   new LinkedList lt  gt              for  long pos   0  pos  lt  file length    pos                  byte bite   dis readByte                 for  int i   0  i  lt  matches size    i                      Integer m   matches get i                   if  bytes m     bite                      matches remove i--                   else if    m    bytes length                      return pos - m   1                  else                     matches set i  m                              if  bytes 0     bite                  matches add 1                       return -1     public static void replaceText String text  String replacement  File file  throws IOException          Open a FileChannel with writing ability  You don t really need the read        ability for this specific case  but there it is in case you need it for        something else      try  FileChannel channel   FileChannel open file toPath    StandardOpenOption WRITE  StandardOpenOption READ             long scanForString   scanForString text  file           if  scanForString    -1                System out println  String not found                 return                    channel position scanForString           channel write ByteBuffer wrap replacement getBytes    StandardCharsets your charset                  Example  Input  ABCDEFGHIJKLMNOPQRSTUVWXYZ  Method Call   replaceText  QRS    000   new File  path to file      Resulting File  ABCDEFGHIJKLMNOP000TUVWXYZ

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This solution uses a RandomAccessFile to only cache the portion of the file subsequent to the string to remove  It scans until it finds the String you want to remove  Then it copies all of the data after the found string  then writes it over the found string  and everything after  Last  it truncates the file size to remove the excess data   public static long scanForString String text  File file  throws IOException       if  text isEmpty            return file exists     0   -1         First of all  get a byte array off of this string      byte   bytes   text getBytes    StandardCharsets your charset              Next  search the file for the byte array      try  DataInputStream dis   new DataInputStream new FileInputStream file               List lt Integer gt  matches   new LinkedList lt  gt              for  long pos   0  pos  lt  file length    pos                  byte bite   dis readByte                 for  int i   0  i  lt  matches size    i                      Integer m   matches get i                   if  bytes m     bite                      matches remove i--                   else if    m    bytes length                      return pos - m   1                  else                     matches set i  m                              if  bytes 0     bite                  matches add 1                       return -1     public static void remove String text  File file  throws IOException       try  RandomAccessFile rafile   new RandomAccessFile file   rw               long scanForString   scanForString text  file           if  scanForString    -1                System out println  String not found                 return                    long remainderStartPos   scanForString   text getBytes   length          rafile seek remainderStartPos           int remainderSize    int   rafile length   - rafile getFilePointer             byte   bytes   new byte remainderSize           rafile read bytes           rafile seek scanForString            rafile write bytes           rafile setLength rafile length   -  text length                Usage   File Contents  ABCDEFGHIJKLMNOPQRSTUVWXYZ  Method Call  remove  ABC   new File  Drive  Path File extension      Resulting Contents  DEFGHIJKLMNOPQRSTUVWXYZ  This solution could easily be modified to remove with a certain  specifiable cacheSize  if memory is a concern  This would just involve iterating over the rest of the file to continually replace portions of size  cacheSize  Regardless  this solution is generally much better than caching an entire file in memory  or copying it to a temporary directory  etc

User · Answer

You want to do something like the following    Open the old file for reading Open a new  temporary  file for writing Iterate over the lines in the old file  probably using a BufferedReader    For each line  check if it matches what you are supposed to remove If it matches  do nothing If it doesn t match  write it to the temporary file  When done  close both files Delete the old file Rename the temporary file to the name of the original file    I won t write the actual code  since this looks like homework  but feel free to post other questions on specific bits that you have trouble with

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Using apache commons-io and Java 8 you can use   List lt String gt  lines   FileUtils readLines file    List lt String gt  updatedLines   lines stream   filter s - gt   s contains searchString   collect Collectors toList      FileUtils writeLines file  updatedLines  false

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This solution may not be optimal or pretty  but it works  It reads in an input file line by line  writing each line out to a temporary output file  Whenever it encounters a line that matches what you are looking for  it skips writing that one out  It then renames the output file  I have omitted error handling  closing of readers writers  etc  from the example  I also assume there is no leading or trailing whitespace in the line you are looking for  Change the code around trim   as needed so you can find a match   File inputFile   new File  myFile txt    File tempFile   new File  myTempFile txt     BufferedReader reader   new BufferedReader new FileReader inputFile    BufferedWriter writer   new BufferedWriter new FileWriter tempFile     String lineToRemove    bbb   String currentLine   while  currentLine   reader readLine       null           trim newline when comparing with lineToRemove     String trimmedLine   currentLine trim        if trimmedLine equals lineToRemove   continue      writer write currentLine   System getProperty  line separator       writer close     reader close     boolean successful   tempFile renameTo inputFile

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This solution requires the Apache Commons IO library to be added to the build path  It works by reading the entire file and writing each line back but only if the search term is not contained   public static void removeLineFromFile File targetFile  String searchTerm          throws IOException       StringBuffer fileContents   new StringBuffer              FileUtils readFileToString targetFile        String   fileContentLines   fileContents toString   split              System lineSeparator          emptyFile targetFile       fileContents   new StringBuffer         for  int fileContentLinesIndex   0  fileContentLinesIndex  lt  fileContentLines length  fileContentLinesIndex                  if  fileContentLines fileContentLinesIndex  contains searchTerm                         continue                     fileContents append fileContentLines fileContentLinesIndex    System lineSeparator                FileUtils writeStringToFile targetFile  fileContents toString   trim        private static void emptyFile File targetFile  throws FileNotFoundException          IOException       RandomAccessFile randomAccessFile   new RandomAccessFile targetFile   rw         randomAccessFile setLength 0       randomAccessFile close

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Try this   public static void main String   args  throws IOException        File file   new File  file csv         CSVReader csvFileReader   new CSVReader new FileReader file         List lt String   gt  list   csvFileReader readAll         for  int i   0  i  lt  list size    i              String   filter   list get i           if  filter 0  equalsIgnoreCase  bbb                  list remove i                       csvFileReader close        CSVWriter csvOutput   new CSVWriter new FileWriter file         csvOutput writeAll list       csvOutput flush         csvOutput close

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I refactored the solution that Narek had to create  according to me  a slightly more efficient and easy to understand code  I used embedded Automatic Resource Management  a recent feature in Java and used a Scanner class which according to me is more easier to understand and use    Here is the code with edited Comments   public class RemoveLineInFile        private static File file       public static void main String   args              create a new File         file   new File  hello txt              takes in String that you want to get rid off         removeLineFromFile  Hello                public static void removeLineFromFile String lineToRemove                if file does not exist  a file is created              if   file exists                      try                       file createNewFile                      catch  IOException e                        System out println  File   file getName     not created successfully                                                    Construct the new temporary file that will later be renamed to the original                filename              File tempFile   new File file getAbsolutePath       tmp                  Two Embedded Automatic Resource Managers used                to effectivey handle IO Responses           try Scanner scanner   new Scanner file                   try  PrintWriter pw   new PrintWriter new FileWriter tempFile                           a declaration of a String Line Which Will Be assigned Later                   String line                        Read from the original file and write to the new                      unless content matches data to be removed                    while  scanner hasNextLine                            line   scanner nextLine                          if   line trim   equals lineToRemove                                pw println line                             pw flush                                                                     Delete the original file                   if   file delete                            System out println  Could not delete file                          return                                            Rename the new file to the filename the original file had                    if   tempFile renameTo file                         System out println  Could not rename file                                        catch  IOException e                        System out println  IO Exception Occurred

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package com ncs cache   import java io BufferedReader  import java io FileReader  import java io File  import java io FileWriter  import java io FileNotFoundException  import java io IOException  import java io PrintWriter   public class FileUtil        public void removeLineFromFile String file  String lineToRemove             try                File inFile   new File file                if   inFile isFile                      System out println  Parameter is not an existing file                    return                                Construct the new file that will later be renamed to the original                filename              File tempFile   new File inFile getAbsolutePath       tmp                 BufferedReader br   new BufferedReader new FileReader file                PrintWriter pw   new PrintWriter new FileWriter tempFile                 String line   null                  Read from the original file and write to the new                unless content matches data to be removed              while   line   br readLine       null                     if   line trim   equals lineToRemove                          pw println line                       pw flush                                                pw close                br close                    Delete the original file             if   inFile delete                      System out println  Could not delete file                    return                                Rename the new file to the filename the original file had              if   tempFile renameTo inFile                   System out println  Could not rename file               catch  FileNotFoundException ex                ex printStackTrace              catch  IOException ex                ex printStackTrace                         public static void main String   args            FileUtil util   new FileUtil            util removeLineFromFile  test txt    bbbbb              src   http   www javadb com remove-a-line-from-a-text-file

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Old question  but an easy way is to    Iterate through file  adding each line to an new array list iterate through the array  find matching String  then call the remove method  iterate through array again  printing each line to the file  boolean for append should be false  which basically replaces the file

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public static void deleteLine   throws IOException           RandomAccessFile file   new RandomAccessFile  me txt    rw            String delete          String task             byte   tasking          while   delete   file readLine       null                if  delete startsWith  BAD                      continue                            task  delete   n                     System out println task           BufferedWriter writer   new BufferedWriter new FileWriter  me txt             writer write task           file close            writer close

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Here is the complete Class  In the below file  somelocation  refers to the actual path of the file   import java io BufferedReader  import java io BufferedWriter  import java io File  import java io FileReader  import java io FileWriter  import java io IOException     public class FileProcess         public static void main String   args  throws IOException               File inputFile   new File  C   somelocation  Demographics txt            File tempFile   new File  C   somelocation  Demographics report txt             BufferedReader reader   new BufferedReader new FileReader inputFile            BufferedWriter writer   new BufferedWriter new FileWriter tempFile             String currentLine           while  currentLine   reader readLine       null                if null  currentLine  amp  amp   currentLine equalsIgnoreCase  BBB                     writer write currentLine   System getProperty  line separator                                     writer close             reader close             boolean successful   tempFile renameTo inputFile           System out println successful

User · Answer

This solution reads in an input file line by line  writing each line out to a StringBuilder variable  Whenever it encounters a line that matches what you are looking for  it skips writing that one out  Then it deletes file content and put the StringBuilder variable content   public void removeLineFromFile String lineToRemove  File f  throws FileNotFoundException  IOException        Reading File Content and storing it to a StringBuilder variable   skips lineToRemove      StringBuilder sb   new StringBuilder        try  Scanner sc   new Scanner f             String currentLine          while sc hasNext                 currentLine   sc nextLine                if currentLine equals lineToRemove                    continue    skips lineToRemove                           sb append currentLine  append   n                          Delete File Content     PrintWriter pw   new PrintWriter f       pw close         BufferedWriter writer   new BufferedWriter new FileWriter f  true        writer append sb toString         writer close

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So  whenever I hear someone mention that they want to filter out text  I immediately think to go to Streams  mainly because there is a method called filter which filters exactly as you need it to   Another answer mentions using Streams with the Apache commons-io library  but I thought it would be worthwhile to show how this can be done in standard Java 8  Here is the simplest form   public void removeLine String lineContent  throws IOException       File file   new File  myFile txt        List lt String gt  out   Files lines file toPath                             filter line - gt   line contains lineContent                            collect Collectors toList         Files write file toPath    out  StandardOpenOption WRITE  StandardOpenOption TRUNCATE EXISTING       I think there isn t too much to explain there  basically Files lines gets a Stream lt String gt  of the lines of the file  filter takes out the lines we don t want  then collect puts all of the lines of the new file into a List  We then write the list over top of the existing file with Files write  using the additional option TRUNCATE so the old contents of the file are replaced   Of course  this approach has the downside of loading every line into memory as they all get stored into a List before being written back out  If we wanted to simply modify without storing  we would need to use some form of OutputStream to write each new line to a file as it passes through the stream  like this   public void removeLine String lineContent  throws IOException       File file   new File  myFile txt        File temp   new File   temp         PrintWriter out   new PrintWriter new FileWriter temp        Files lines file toPath             filter line - gt   line contains lineContent            forEach out  println       out flush        out close        temp renameTo file       Not much has been changed in this example  Basically  instead of using collect to gather the file contents into memory  we use forEach so that each line that makes it through the filter gets sent to the PrintWriter to be written out to the file immediately and not stored  We have to save it to a temporary file  because we can t overwrite the existing file at the same time as we are still reading from it  so then at the end  we rename the temp file to replace the existing file

[java] Find a line in a file and remove it

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