UTF-8 byte to String

Question

Let s suppose I have just used a BufferedInputStream to read the bytes of a UTF-8 encoded text file into a byte array  I know that I can use the following routine to convert the bytes to a string  but is there a more efficient smarter way of doing this than just iterating through the bytes and converting each one    public String openFileToString byte    bytes        String file string            for int i   0  i  lt   bytes length  i                  file string     char  bytes i              return file string

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String has a constructor that takes byte   and charsetname as parameters

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I use this way  String strIn   new String  bytes  0  numBytes

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Look at the constructor for String  String str   new String bytes  StandardCharsets UTF 8     And if you re feeling lazy  you can use the Apache Commons IO library to convert the InputStream to a String directly   String str   IOUtils toString inputStream  StandardCharsets UTF 8

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Why not get what you are looking for from the get go and read a string from the file instead of an array of bytes   Something like   BufferedReader in   new BufferedReader new InputStreamReader  new FileInputStream   foo txt    Charset forName   UTF-8       then readLine from in until it s done

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Here s a simplified function that will read in bytes and create a string  It assumes you probably already know what encoding the file is in  and otherwise defaults    static final int BUFF SIZE   2048  static final String DEFAULT ENCODING    utf-8    public static String readFileToString String filePath  String encoding  throws IOException        if  encoding    null    encoding length      0          encoding   DEFAULT ENCODING       StringBuffer content   new StringBuffer         FileInputStream fis   new FileInputStream new File filePath        byte   buffer   new byte BUFF SIZE        int bytesRead   0      while   bytesRead   fis read buffer      -1          content append new String buffer  0  bytesRead  encoding         fis close                return content toString

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Java String class has a built-in-constructor for converting byte array to string   byte   byteArray   new byte    87  79  87  46  46  46    String value   new String byteArray   UTF-8

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To convert utf-8 data  you can t assume a 1-1 correspondence between bytes and characters  Try this   String file string   new String bytes   UTF-8       Bah  I see I m way to slow in hitting the Post Your Answer button    To read an entire file as a String  do something like this   public String openFileToString String fileName  throws IOException       InputStream is   new BufferedInputStream new FileInputStream fileName         try           InputStreamReader rdr   new InputStreamReader is   UTF-8            StringBuilder contents   new StringBuilder            char   buff   new char 4096           int len   rdr read buff           while  len  gt   0                contents append buff  0  len                     return buff toString          finally           try               is close              catch  Exception e                   log error in closing the file

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You could use the methods described in this question  especially since you start off with an InputStream   Read convert an InputStream to a String  In particular  if you don t want to rely on external libraries  you can try this answer  which reads the InputStream via an InputStreamReader into a char   buffer and appends it into a StringBuilder

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This also involves iterating  but this is much better than concatenating strings as they are very very costly   public String openFileToString String fileName        StringBuilder s   new StringBuilder  bytes length        for int i   0  i  lt   bytes length  i                  s append  char  bytes i               return s toString

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Knowing that you are dealing with a UTF-8 byte array  you ll definitely want to use the String constructor that accepts a charset name  Otherwise you may leave yourself open to some charset encoding based security vulnerabilities  Note that it throws UnsupportedEncodingException which you ll have to handle  Something like this   public String openFileToString String fileName        String file string      try           file string   new String  bytes   UTF-8          catch  UnsupportedEncodingException e               this should never happen because  UTF-8  is hard-coded          throw new IllegalStateException e             return file string

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You can use the String byte   bytes   constructor for that  See this link for details  EDIT You also have to consider your plateform s default charset as per the java doc      Constructs a new String by decoding the specified array of bytes using   the platform s default charset  The length of the new String is a   function of the charset  and hence may not be equal to the length of   the byte array  The behavior of this constructor when the given bytes   are not valid in the default charset is unspecified  The   CharsetDecoder class should be used when more control over the   decoding process is required

[java] UTF-8 byte[] to String

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