Check line for unprintable characters while reading text file

Question

My program must read text files - line by line  Files in UTF-8  I am not sure that files are correct - can contain unprintable characters  Is possible check for it without going to byte level  Thanks

User · Answer

How about below           FileReader fileReader   new FileReader new File  test txt       BufferedReader br   new BufferedReader fileReader     String line   null      if no more lines the readLine   returns null  while   line   br readLine       null             reading lines until the end of the file       Source  http   devmain blogspot co uk 2013 10 java-quick-way-to-read-or-write-to-file html

User · Answer

I can find following ways to do   private static final String fileName    C  Input txt    public static void main String   args  throws IOException       Stream lt String gt  lines   Files lines Paths get fileName        lines toArray String    new        List lt String gt  readAllLines   Files readAllLines Paths get fileName        readAllLines forEach s - gt  System out println s         File file   new File fileName       Scanner scanner   new Scanner file       while  scanner hasNext              System out println scanner next

User · Answer

Open the file with a FileInputStream  then use an InputStreamReader with the UTF-8 Charset to read characters from the stream  and use a BufferedReader to read lines  e g  via BufferedReader readLine  which will give you a string  Once you have the string  you can check for characters that aren t what you consider to be printable   E g   without error checking   using try-with-resources  which is in vaguely modern Java version      String line  try       InputStream fis   new FileInputStream  the file name        InputStreamReader isr   new InputStreamReader fis  Charset forName  UTF-8         BufferedReader br   new BufferedReader isr           while   line   br readLine       null               Deal with the line

User · Answer

If every char in the file is properly encoded in UTF-8  you won t have any problem reading it using a reader with the UTF-8 encoding  Up to you to check every char of the file and see if you consider it printable or not

User · Answer

The answer by  T J Crowder is Java 6 - in java 7 the valid answer is the one by  McIntosh - though its use of Charset for name for UTF -8 is discouraged   List lt String gt  lines   Files readAllLines Paths get   tmp test csv        StandardCharsets UTF 8   for String line  lines      DO        Reminds a lot of the Guava way posted by Skeet above - and of course same caveats apply  That is  for big files  Java 7    BufferedReader reader   Files newBufferedReader path  StandardCharsets UTF 8   for  String line   reader readLine    line    null  line   reader readLine

User · Answer

Just found out that with the Java NIO  java nio file    you can easily write   List lt String gt  lines Files readAllLines Paths get   tmp test csv    StandardCharsets UTF 8   for String line lines     System out println line       instead of dealing with FileInputStreams and  BufferedReaders

User · Answer

While it s not hard to do this manually using BufferedReader and InputStreamReader  I d use Guava   List lt String gt  lines   Files readLines file  Charsets UTF 8     You can then do whatever you like with those lines   EDIT  Note that this will read the whole file into memory in one go  In most cases that s actually fine - and it s certainly simpler than reading it line by line  processing each line as you read it  If it s an enormous file  you may need to do it that way as per T J  Crowder s answer

User · Answer

If you want to check a string has unprintable characters you can use a regular expression      p Print

[java] Check line for unprintable characters while reading text file

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