Find and replace words lines in a file

Question

I have a file  more specifically  a log4j configuration file  and I want to be able to read in the file and pick out certain lines in the code and replace them  For example  within the file there is a string of text that indicates the directory it is stored in  or the level of the logger  I want to be able to replace those string of text without reading in the file  writing it to another file  and deleting the original file  Is there a more efficient way of doing find and replace texts in a file using Java   Here is an example of the text file I m trying to work with   log4j rootLogger DEBUG  A0  log4j appender A0 org apache log4j RollingFileAppender log4j appender A0 File C  log txt log4j appender A0 MaxFileSize 100KB log4j appender A0 MaxBackupIndex 1  log4j appender A0 layout org apache log4j RollingFileAppender log4j appender A0 layout ConversionPattern  -4r   t   -5p   c  x -  m n   I want to be able to read the file and replace  DEBUG  with another level or replace the file directory name  C  log txt   The log configuration file is also written in xml  An example of that is featured below    lt  xml version  1 0  encoding  UTF-8  standalone  no   gt   lt  DOCTYPE log4j configuration SYSTEM  log4j dtd  gt   lt log4j configuration gt       lt appender class  org apache log4j RollingFileAppender  name  A0  gt           lt param name  append  value  false   gt           lt param name  File  value  C  log  txt   gt           lt param name  MaxBackupIndex  value  1   gt           lt param name  MaxFileSize  value  100KB   gt           lt layout class  org apache log4j PatternLayout  gt               lt param name  ConversionPattern  value   -4r   t   -5p   c  x -  m n   gt           lt  layout gt       lt  appender gt       lt root gt           lt level value  DEBUG   gt           lt appender-ref ref  A0   gt       lt  root gt   lt  log4j configuration gt    I m thinking it may be possible to use a hash map for this type of implementation

User · Answer

You can use Java s Scanner class to parse words of a file and process them in your application  and then use a BufferedWriter or FileWriter to write back to the file  applying the changes   I think there is a more efficient way of getting the iterator s position of the scanner at some point  in order to better implement editting  But since files are either open for reading  or writing  I m not sure regarding that   In any case  you can use libraries already available for parsing of XML files  which have all of this implemented already and will allow you to do what you want easily

User · Answer

This is the sort of thing I d normally use a scripting language for  It s very useful to have the ability to perform these sorts of transformations very simply using something like Ruby Perl Python  insert your favorite scripting language here    I wouldn t normally use Java for this since it s too heavyweight in terms of development cycle typing etc   Note that if you want to be particular in manipulating XML  it s advisable to read the file as XML and manipulate it as such  the above scripting languages have very useful and simple APIs for doing this sort of work   A simple text search replace can invalidate your file in terms of character encoding etc  As always  it depends on the complexity of your search replace requirements

User · Answer

public static void replaceFileString String old  String new  throws IOException       String fileName   Settings getValue  fileDirectory        FileInputStream fis   new FileInputStream fileName       String content   IOUtils toString fis  Charset defaultCharset         content   content replaceAll old  new       FileOutputStream fos   new FileOutputStream fileName       IOUtils write content  new FileOutputStream fileName   Charset defaultCharset         fis close        fos close        above is my implementation of Meriton s example that works for me  The fileName is the directory  ie  D  utilities settings txt   I m not sure what character set should be used  but I ran this code on a Windows XP machine just now and it did the trick without doing that temporary file creation and renaming stuff

User · Answer

You might want to use Scanner to parse through and find the specific sections you want to modify   There s also Split and StringTokenizer that may work  but at the level you re working at Scanner might be what s needed     Here s some additional info on what the difference is between them  Scanner vs  StringTokenizer vs  String Split

User · Answer

Any decent text editor has a search amp replace facility that supports regular expressions    If however  you have reason to reinvent the wheel in Java  you can do   Path path   Paths get  test txt    Charset charset   StandardCharsets UTF 8   String content   new String Files readAllBytes path   charset   content   content replaceAll  foo    bar    Files write path  content getBytes charset      This only works for Java 7 or newer  If you are stuck on an older Java  you can do   String content   IOUtils toString new FileInputStream myfile   myencoding   content   content replaceAll myPattern  myReplacement   IOUtils write content  new FileOutputStream myfile   myencoding     In this case  you ll need to add error handling and close the streams after you are done with them   IOUtils is documented at http   commons apache org proper commons-io javadocs api-release org apache commons io IOUtils html

User · Answer

After visiting this question and noting the initial concerns of the chosen solution  I figured I d contribute this one for those not using Java 7 which uses FileUtils instead of IOUtils from Apache Commons   The advantage here is that the readFileToString and the writeStringToFile handle the issue of closing the files for you automatically    writeStringToFile doesn t document it but you can read the source    Hopefully this recipe simplifies things for anyone new coming to this problem     try        String content   FileUtils readFileToString new File  InputFile     UTF-8         content   content replaceAll  toReplace    replacementString         File tempFile   new File  OutputFile         FileUtils writeStringToFile tempFile  content   UTF-8        catch  IOException e           Simple exception handling  replace with what s necessary for your use case       throw new RuntimeException  Generating file failed   e

[java] Find and replace words/lines in a file

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