How to append text to an existing file in Java

Question

I need to append text repeatedly to an existing file in Java  How do I do that

User · Answer

Better to use try-with-resources then all that pre-java 7 finally business  static void appendStringToFile Path file  String s  throws IOException        try  BufferedWriter out   Files newBufferedWriter file  StandardCharsets UTF 8  StandardOpenOption APPEND             out append s           out newLine

User · Answer

In case you want to ADD SOME TEXT IN SPECIFIC LINES you can first read the whole file  append the text wherever you want and then overwrite everything like in the code below   public static void addDatatoFile String data1  String data2         String fullPath     home user dir file csv        File dir   new File fullPath       List lt String gt  l   new LinkedList lt String gt          try  BufferedReader br   new BufferedReader new FileReader dir              String line          int count   0           while   line   br readLine       null                if count    1                     add data at the end of second line                                     line    data1               else if count    2                     add other data at the end of third line                 line    data2                            l add line               count                      br close          catch  FileNotFoundException e            e printStackTrace          catch  IOException e            e printStackTrace                     createFileFromList l  dir      public static void createFileFromList List lt String gt  list  File f        PrintWriter writer      try           writer   new PrintWriter f   UTF-8            for  String d   list                writer println d toString                       writer close                       catch  FileNotFoundException   UnsupportedEncodingException e            e printStackTrace

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I just add small detail       new FileWriter  outfilename   true    2 nd parameter  true  is a feature  or  interface  called appendable  http   docs oracle com javase 7 docs api java lang Appendable html   It is responsible for being able to add some content to the end of particular file stream  This interface is implemented since Java 1 5  Each object  i e  BufferedWriter  CharArrayWriter  CharBuffer  FileWriter  FilterWriter  LogStream  OutputStreamWriter  PipedWriter  PrintStream  PrintWriter  StringBuffer  StringBuilder  StringWriter  Writer  with this interface can be used for adding content  In other words  you can add some content to your gzipped file  or some http process

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Make sure the stream gets properly closed in all scenarios   It s a bit alarming how many of these answers leave the file handle open in case of an error  The answer https   stackoverflow com a 15053443 2498188 is on the money but only because BufferedWriter   cannot throw  If it could then an exception would leave the FileWriter object open    A more general way of doing this that doesn t care if BufferedWriter   can throw     PrintWriter out   null    BufferedWriter bw   null    FileWriter fw   null    try       fw   new FileWriter  outfilename   true        bw   new BufferedWriter fw        out   new PrintWriter bw        out println  the text          catch  IOException e            File writing opening failed at some stage        finally       try          if  out    null               out close       Will close bw and fw too                   else if  bw    null               bw close       Will close fw too                   else if  fw    null               fw close                      else                Oh boy did it fail hard   3                       catch  IOException e               Closing the file writers failed for some obscure reason              Edit   As of Java 7  the recommended way is to use  try with resources  and let the JVM deal with it     try     FileWriter fw   new FileWriter  outfilename   true             BufferedWriter bw   new BufferedWriter fw             PrintWriter out   new PrintWriter bw         out println  the text            catch  IOException e             File writing opening failed at some stage

User · Answer

Try with bufferFileWriter append  it works with me   FileWriter fileWriter  try       fileWriter   new FileWriter file true       BufferedWriter bufferFileWriter   new BufferedWriter fileWriter       bufferFileWriter append obj toJSONString         bufferFileWriter newLine        bufferFileWriter close      catch  IOException ex        Logger getLogger JsonTest class getName    log Level SEVERE  null  ex

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Shouldn t all of the answers here with try catch blocks have the  close   pieces contained in a finally block   Example for marked answer   PrintWriter out   null  try       out   new PrintWriter new BufferedWriter new FileWriter  writePath   true         out println  the text      catch  IOException e        System err println e     finally       if  out    null            out close               Also  as of Java 7  you can use a try-with-resources statement  No finally block is required for closing the declared resource s  because it is handled automatically  and is also less verbose   try PrintWriter out   new PrintWriter new BufferedWriter new FileWriter  writePath   true           out println  the text      catch  IOException e        System err println e

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import java io BufferedWriter  import java io FileWriter  import java io IOException  import java io PrintWriter   public class Writer         public static void main String args             doWrite  output txt   Content to be appended to file               public static void doWrite String filePath String contentToBeAppended           try              FileWriter fw   new FileWriter filePath  true               BufferedWriter bw   new BufferedWriter fw               PrintWriter out   new PrintWriter bw                                      out println contentToBeAppended                         catch  IOException e               File writing opening failed at some stage

User · Answer

FileOutputStream fos   new FileOutputStream  File Name   true   fos write data     the true allows to append the data in the existing file  If we will write  FileOutputStream fos   new FileOutputStream  File Name      It will overwrite the existing file  So go for first approach

User · Answer

Using java nio Files along with java nio file StandardOpenOption      PrintWriter out   null      BufferedWriter bufWriter       try          bufWriter               Files newBufferedWriter                  Paths get  log txt                    Charset forName  UTF8                    StandardOpenOption WRITE                   StandardOpenOption APPEND                  StandardOpenOption CREATE           out   new PrintWriter bufWriter  true        catch IOException e             Oh  no  Failed to create PrintWriter              After successful creation of PrintWriter     out println  Text to be appended           After done writing  remember to close      out close      This creates a BufferedWriter using Files  which accepts StandardOpenOption parameters  and an auto-flushing PrintWriter from the resultant BufferedWriter  PrintWriter s println   method  can then be called to write to the file   The StandardOpenOption parameters used in this code  opens the file for writing  only appends to the file  and creates the file if it does not exist   Paths get  path here   can be replaced with new File  path here   toPath    And Charset forName  charset name   can be modified to accommodate the desired Charset

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it will write content to a specified  file         param keyString     throws IOException                                                                         public static void writeToFile String keyString String textFilePAth  throws IOException          For output to file     File a   new File textFilePAth        if   a exists              a createNewFile              FileWriter fw   new FileWriter a getAbsoluteFile    true       BufferedWriter bw   new BufferedWriter fw       bw append keyString       bw newLine        bw close        end of writeToFile

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Create a function anywhere in your project and simply call that function where ever you need it   Guys you got to remember that you guys are calling active threads that you are not calling asynchronously and since it would likely be a good 5 to 10 pages to get it done right  Why not spend more time on your project and forget about writing anything already written  Properly        Adding a static modifier would make this accessible anywhere in your app      public Logger getLogger                return java util logging Logger getLogger  MyLogFileName                call the method anywhere and append what you want to log        Logger class will take care of putting timestamps for you       plus the are ansychronously done so more of the        processing power will go into your application        from inside a function body in the same class              getLogger   log Level INFO  the text you want to append                               log file resides in server root log files            three lines of code two really since the third actually appends text   P

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Sample  using Guava   File to   new File  C  test test csv     for  int i   0  i  lt  42  i          CharSequence from    some string    i     n       Files append from  to  Charsets UTF 8

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In Java-7 it also can be done such kind   import java nio file Files  import java nio file Path  import java nio file Paths  import java nio file StandardOpenOption      ---------------------  Path filePath   Paths get  someFile txt    if   Files exists filePath         Files createFile filePath     Files write filePath   Text to be added  getBytes    StandardOpenOption APPEND

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You can also try this    JFileChooser c  new JFileChooser    c showOpenDialog c   File write file   c getSelectedFile    String Content    Writing into file     what u would like to append to the file    try        RandomAccessFile raf   new RandomAccessFile write file   rw        long length   raf length          System out println length       raf setLength length   1        integer value  for spacing     raf seek raf length         raf writeBytes Content       raf close       catch  Exception e          any exception handling method of ur choice

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java 7   In my humble opinion since I am fan of plain java  I would suggest something that it is a combination of the aforementioned answers  Maybe I am late for the party  Here is the code    String sampleText    test     System getProperty  line separator     Files write Paths get filePath   sampleText getBytes StandardCharsets UTF 8     StandardOpenOption CREATE  StandardOpenOption APPEND     If the file doesn t exist  it creates it and if already exists it appends the  sampleText to the existing file  Using this  saves you from adding unnecessary libs to your classpath

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FileOutputStream stream   new FileOutputStream path  true   try        stream write           string getBytes  UTF-8      Choose your encoding             finally       stream close        Then catch an IOException somewhere upstream

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The following method let s you append text to some file   private void appendToFile String filePath  String text        PrintWriter fileWriter   null       try               fileWriter   new PrintWriter new BufferedWriter new FileWriter                  filePath  true              fileWriter println text         catch  IOException ioException                ioException printStackTrace          finally               if  fileWriter    null                        fileWriter close                        Alternatively using FileUtils   public static void appendToFile String filePath  String text  throws IOException       File file   new File filePath        if  file exists                  file createNewFile               String fileContents   FileUtils readFileToString file        if file length      0                fileContents   fileContents concat System lineSeparator                fileContents   fileContents concat text        FileUtils writeStringToFile file  fileContents       It is not efficient but works fine  Line breaks are handled correctly and a new file is created if one didn t exist yet

User · Answer

You can use fileWriter with a flag set to true   for appending   try       String filename   MyFile txt       FileWriter fw   new FileWriter filename true     the true will append the new data     fw write  add a line n     appends the string to the file     fw close      catch IOException ioe        System err println  IOException      ioe getMessage

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1 7 Approach   void appendToFile String filePath  String content  throws IOException       Path path   Paths get filePath        try  BufferedWriter writer                Files newBufferedWriter path                       StandardOpenOption APPEND             writer newLine            writer append content                       Alternative      try  BufferedWriter bWriter                Files newBufferedWriter path                       StandardOpenOption WRITE  StandardOpenOption APPEND               PrintWriter pWriter   new PrintWriter bWriter                          pWriter println     to have println   style instead of newLine               pWriter append content    Also  bWriter append content

User · Answer

Using Apache Commons 2 1  FileUtils writeStringToFile file   quot String to append quot   true

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For JDK version  gt   7 You can utilise this simple method which appends the given content to the specified file  void appendToFile String filePath  String content      try  FileWriter fw   new FileWriter filePath  true         fw write content   System lineSeparator         catch  IOException e            TODO handle exception        We are constructing a FileWriter object in append mode

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String str      String path    C  Users    the path     iin txt      you can input also  i created this way  P      BufferedReader br   new BufferedReader new InputStreamReader System in        PrintWriter pw   new PrintWriter new FileWriter path  true         try               while true                        System out println  Enter the text                   str   br readLine                if str equalsIgnoreCase  exit                    break              else                 pw println str                        catch  Exception e                   oh noes            finally               pw close                     this will do what you intend for

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My answer   JFileChooser chooser  new JFileChooser    chooser showOpenDialog chooser   File file   chooser getSelectedFile    String Content    What you want to append to file    try        RandomAccessFile random   new RandomAccessFile file   rw        long length   random length        random setLength length   1       random seek random length         random writeBytes Content       random close       catch  Exception exception          exception handling

User · Answer

This can be done in one line of code  Hope this helps     Files write Paths get fileName   msg getBytes    StandardOpenOption APPEND

User · Answer

Are you doing this for logging purposes   If so there are several libraries for this  Two of the most popular are Log4j and Logback  Java 7  For a one-time task  the Files class makes this easy  try       Files write Paths get  quot myfile txt quot     quot the text quot  getBytes    StandardOpenOption APPEND    catch  IOException e          exception handling left as an exercise for the reader    Careful  The above approach will throw a NoSuchFileException if the file does not already exist  It also does not append a newline automatically  which you often want when appending to a text file   Another approach is to pass both CREATE and APPEND options  which will create the file first if it doesn t already exist  private void write final String s  throws IOException       Files writeString          Path of System getProperty  quot java io tmpdir quot     quot filename txt quot            s   System lineSeparator            CREATE  APPEND           However  if you will be writing to the same file many times  the above snippets must open and close the file on the disk many times  which is a slow operation  In this case  a BufferedWriter is faster  try FileWriter fw   new FileWriter  quot myfile txt quot   true       BufferedWriter bw   new BufferedWriter fw       PrintWriter out   new PrintWriter bw         out println  quot the text quot          more code     out println  quot more text quot          more code   catch  IOException e          exception handling left as an exercise for the reader    Notes   The second parameter to the FileWriter constructor will tell it to append to the file  rather than writing a new file   If the file does not exist  it will be created   Using a BufferedWriter is recommended for an expensive writer  such as FileWriter   Using a PrintWriter gives you access to println syntax that you re probably used to from System out  But the BufferedWriter and PrintWriter wrappers are not strictly necessary    Older Java try       PrintWriter out   new PrintWriter new BufferedWriter new FileWriter  quot myfile txt quot   true         out println  quot the text quot        out close      catch  IOException e          exception handling left as an exercise for the reader     Exception Handling If you need robust exception handling for older Java  it gets very verbose  FileWriter fw   null  BufferedWriter bw   null  PrintWriter out   null  try       fw   new FileWriter  quot myfile txt quot   true       bw   new BufferedWriter fw       out   new PrintWriter bw       out println  quot the text quot        out close      catch  IOException e          exception handling left as an exercise for the reader   finally       try           if out    null              out close          catch  IOException e              exception handling left as an exercise for the reader           try           if bw    null              bw close          catch  IOException e              exception handling left as an exercise for the reader           try           if fw    null              fw close          catch  IOException e              exception handling left as an exercise for the reader

User · Answer

This code will fulifil your need      FileWriter fw new FileWriter  C   file json  true      fw write  ssssss       fw close

User · Answer

You can use the follong code to append the content in the file    String fileName   home shriram Desktop Images    test txt     FileWriter fw new FileWriter fileName true         fw write  here will be you content to insert or append in file          fw close       FileWriter fw1 new FileWriter fileName true        fw1 write  another content will be here to be append in the same file         fw1 close

User · Answer

Slightly expanding on Kip s answer  here is a simple Java 7  method to append a new line to a file  creating it if it doesn t already exist  try       final Path path   Paths get  quot path to filename txt quot        Files write path  Arrays asList  quot New line to append quot    StandardCharsets UTF 8          Files exists path    StandardOpenOption APPEND   StandardOpenOption CREATE     catch  final IOException ioe           Add your own exception handling       Further notes   The above uses the Files write overload that writes lines of text to a file  i e  similar to a println command   To just write text to the end  i e  similar to a print command   an alternative Files write overload can be used  passing in a byte array  e g   quot mytext quot  getBytes StandardCharsets UTF 8     The CREATE option will only work if the specified directory already exists - if it doesn t  a NoSuchFileException is thrown  If required  the following code could be added after setting path to create the directory structure  Path pathParent   path getParent    if   Files exists pathParent         Files createDirectories pathParent

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I might suggest the apache commons project  This project already provides a framework for doing what you need  i e  flexible filtering of collections

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Library   import java io BufferedWriter  import java io File  import java io FileWriter  import java io IOException       Code   public void append         try               String path    D  sample txt            File file   new File path            FileWriter fileWriter   new FileWriter file true            BufferedWriter bufferFileWriter    new BufferedWriter fileWriter            fileWriter append  Sample text in the file to append             bufferFileWriter close             System out println  User Registration Completed          catch Exception ex                System out println ex

User · Answer

If we are using Java 7 and above and also know the content to be added  appended  to the file we can make use of newBufferedWriter method in NIO package   public static void main String   args        Path FILE PATH   Paths get  C  temp    temp txt        String text     n Welcome to Java 8          Writing to the file temp txt     try  BufferedWriter writer   Files newBufferedWriter FILE PATH  StandardCharsets UTF 8  StandardOpenOption APPEND             writer write text         catch  IOException e            e printStackTrace              There are few points to note    It is always a good habit to specify charset encoding and for that we have constant in class StandardCharsets  The code uses try-with-resource statement in which resources are automatically closed after the try    Though OP has not asked but just in case we want to search for lines having some specific keyword e g  confidential we can make use of stream APIs in Java     Reading from the file the first line which contains word  confidential  try       Stream lt String gt  lines   Files lines FILE PATH       Optional lt String gt  containsJava   lines filter l- gt l contains  confidential    findFirst        if containsJava isPresent             System out println containsJava get             catch  IOException e        e printStackTrace

[java] How to append text to an existing file in Java?

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