File to byte in Java

Question

How do I convert a java io File to a byte

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Simplest Way for reading bytes from file  import java io     class ReadBytesFromFile       public static void main String args    throws Exception              getBytes from anyWhere            I m getting byte array from File         File file   null          FileInputStream fileStream   new FileInputStream file   new File  ByteArrayInputStreamClass java                 Instantiate array         byte   arr   new byte  int  file length                 read All bytes of File stream         fileStream read arr  0  arr length            for  int X   arr                System out print  char  X

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I belive this is the easiest way   org apache commons io FileUtils readFileToByteArray file

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Try this    import sun misc IOUtils  import java io IOException   try       String path         InputStream inputStream new FileInputStream path       byte   data IOUtils readFully inputStream -1 false     catch  IOException e        System out println e

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Returns the contents of the file in a byte array      public static byte   getBytesFromFile File file  throws IOException                      Get the size of the file         long length   file length                You cannot create an array using a long type             It needs to be an int type             Before converting to an int type  check            to ensure that file is not larger than Integer MAX VALUE          if  length  gt  Integer MAX VALUE                   File is too large             throw new IOException  File is too large                           Create the byte array to hold the data         byte   bytes   new byte  int length               Read in the bytes         int offset   0          int numRead   0           InputStream is   new FileInputStream file           try               while  offset  lt  bytes length                     amp  amp   numRead is read bytes  offset  bytes length-offset    gt   0                    offset    numRead                          finally               is close                          Ensure all the bytes have been read in         if  offset  lt  bytes length                throw new IOException  Could not completely read file   file getName                       return bytes

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ReadFully Reads b length bytes from this file into the byte array  starting at the current file pointer  This method reads repeatedly from the file until the requested number of bytes are read  This method blocks until the requested number of bytes are read  the end of the stream is detected  or an exception is thrown   RandomAccessFile f   new RandomAccessFile fileName   r    byte   b   new byte  int f length     f readFully b

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Let me add another solution without using third-party libraries  It re-uses an exception handling pattern that was proposed by Scott  link   And I moved the ugly part into a separate message  I would hide in some FileUtils class       public void someMethod         final byte   buffer   read new File  test txt        private byte   read final File file        if  file isDirectory            throw new RuntimeException  Unsupported operation  file                     file getAbsolutePath       is a directory        if  file length     Integer MAX VALUE          throw new RuntimeException  Unsupported operation  file                     file getAbsolutePath       is too big         Throwable pending   null      FileInputStream in   null      final byte buffer     new byte  int  file length         try           in   new FileInputStream file           in read buffer         catch  Exception e            pending   new RuntimeException  Exception occured on reading file                     file getAbsolutePath    e         finally           if  in    null                try                   in close                  catch  Exception e                    if  pending    null                        pending   new RuntimeException                           Exception occured on closing file                                  file getAbsolutePath    e                                                     if  pending    null                throw new RuntimeException pending                       return buffer

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If you don t have Java 8  and agree with me that including a massive library to avoid writing a few lines of code is a bad idea   public static byte   readBytes InputStream inputStream  throws IOException       byte   b   new byte 1024       ByteArrayOutputStream os   new ByteArrayOutputStream        int c      while   c   inputStream read b      -1            os write b  0  c             return os toByteArray        Caller is responsible for closing the stream

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Basically you have to read it in memory  Open the file  allocate the array  and read the contents from the file into the array    The simplest way is something similar to this    public byte   read File file  throws IOException  FileTooBigException       if  file length    gt  MAX FILE SIZE            throw new FileTooBigException file             ByteArrayOutputStream ous   null      InputStream ios   null      try           byte   buffer   new byte 4096           ous   new ByteArrayOutputStream            ios   new FileInputStream file           int read   0          while   read   ios read buffer      -1                ous write buffer  0  read                  finally           try               if  ous    null                  ous close              catch  IOException e                       try               if  ios    null                  ios close              catch  IOException e                        return ous toByteArray        This has some unnecessary copying of the file content  actually the data is copied three times  from file to buffer  from buffer to ByteArrayOutputStream  from ByteArrayOutputStream to the actual resulting array    You also need to make sure you read in memory only files up to a certain size  this is usually application dependent   -     You also need to treat the IOException outside the function   Another way is this    public byte   read File file  throws IOException  FileTooBigException       if  file length    gt  MAX FILE SIZE            throw new FileTooBigException file              byte   buffer   new byte  int  file length         InputStream ios   null      try           ios   new FileInputStream file           if  ios read buffer     -1                throw new IOException                       EOF reached while trying to read the whole file                    finally           try               if  ios    null                  ios close              catch  IOException e                        return buffer      This has no unnecessary copying   FileTooBigException is a custom application exception   The MAX FILE SIZE constant is an application parameters   For big files you should probably think a stream processing algorithm or use memory mapping  see java nio

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Another Way for reading bytes from file  Reader reader   null      try           reader   new FileReader file           char buf     new char 8192           int len          StringBuilder s   new StringBuilder            while   len   reader read buf    gt   0                s append buf  0  len               byte   byteArray   s toString   getBytes                    catch FileNotFoundException ex          catch IOException e              finally           if  reader    null                reader close

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From JDK 7 you can use Files readAllBytes Path    Example   import java io File  import java nio file Files   File file         file is initialised     byte   fileContent   Files readAllBytes file toPath

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As someone said  Apache Commons File Utils might have what you are looking for  public static byte   readFileToByteArray File file  throws IOException   Example use  Program java    import org apache commons io FileUtils  public class Program       public static void main String   args  throws IOException           File file   new File args 0        assume args 0  is the path to file         byte   data   FileUtils readFileToByteArray file

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It depends on what best means for you  Productivity wise  don t reinvent the wheel and use Apache Commons  Which is here FileUtils readFileToByteArray File input

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Can be done as simple as this  Kotlin version  val byteArray   File path  inputStream   readBytes    EDIT  I ve read docs of readBytes method  It says   Reads this stream completely into a byte array  Note  It is the caller s responsibility to close this stream   So to be able to close the stream  while keeping everything clean  use the following code  val byteArray   File path  inputStream   use   it readBytes      Thanks to  user2768856 for pointing this out

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Since JDK 7 - one liner   byte   array   Files readAllBytes Paths get   path to file       No external dependencies needed

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Simple way to do it   File fff   new File   path to file    FileInputStream fileInputStream   new FileInputStream fff       int byteLength   fff length         In android the result of file length   is long long byteLength   fff length       byte count of the file-content  byte   filecontent   new byte  int  byteLength   fileInputStream read filecontent  0   int  byteLength

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If you want to read bytes into a pre-allocated byte buffer  this answer may help   Your first guess would probably be to use InputStream read byte     However  this method has a flaw that makes it unreasonably hard to use  there is no guarantee that the array will actually be completely filled  even if no EOF is encountered   Instead  take a look at DataInputStream readFully byte     This is a wrapper for input streams  and does not have the above mentioned issue  Additionally  this method throws when EOF is encountered  Much nicer

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Using the same approach as the community wiki answer  but cleaner and compiling out of the box  preferred approach if you don t want to import Apache Commons libs  e g  on Android    public static byte   getFileBytes File file  throws IOException       ByteArrayOutputStream ous   null      InputStream ios   null      try           byte   buffer   new byte 4096           ous   new ByteArrayOutputStream            ios   new FileInputStream file           int read   0          while   read   ios read buffer      -1              ous write buffer  0  read         finally           try               if  ous    null                  ous close              catch  IOException e                   swallow  since not that important                   try               if  ios    null                  ios close              catch  IOException e                   swallow  since not that important                     return ous toByteArray

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public static byte   readBytes InputStream inputStream  throws IOException       byte   buffer   new byte 32   1024       int bufferSize   0      for                int read   inputStream read buffer  bufferSize  buffer length - bufferSize           if  read    -1                return Arrays copyOf buffer  bufferSize                     bufferSize    read          if  bufferSize    buffer length                buffer   Arrays copyOf buffer  bufferSize   2

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import java io File  import java nio file Files  import java nio file Path   File file   getYourFile    Path path   file toPath    byte   data   Files readAllBytes path

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The file that you wanna convert into byte   File file new File   storage 0CE2-EA3D DCIM Camera VID 20190822 205931 mp4      FileInputStream fileInputStream new FileInputStream file   byte   data new byte  int  file length     BufferedInputStream bufferedInputStream new BufferedInputStream fileInputStream   bufferedInputStream read data 0 data length      Now the bytes of the file are contain in the  byte   data

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In JDK8  Stream lt String gt  lines   Files lines path   String data   lines collect Collectors joining   n     lines close

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Guava has Files toByteArray   to offer you  It has several advantages    It covers the corner case where files report a length of 0 but still have content It s highly optimized  you get a OutOfMemoryException if trying to read in a big file before even trying to load the file   Through clever use of file length    You don t have to reinvent the wheel

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You can use the NIO api as well to do it  I could do this with this code as long as the total file size  in bytes  would fit in an int   File f   new File  c   wscp script    FileInputStream fin   null  FileChannel ch   null  try       fin   new FileInputStream f       ch   fin getChannel        int size    int  ch size        MappedByteBuffer buf   ch map MapMode READ ONLY  0  size       byte   bytes   new byte size       buf get bytes      catch  IOException e           TODO Auto-generated catch block     e printStackTrace      finally       try           if  fin    null                fin close                      if  ch    null                ch close                    catch  IOException e            e printStackTrace              I think its very fast since its using MappedByteBuffer

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Not only does the following way convert a java io File to a byte    I also found it to be the fastest way to read in a file  when testing many different Java file reading methods against each other   java nio file Files readAllBytes    import java io File  import java io IOException  import java nio file Files   public class ReadFile Files ReadAllBytes     public static void main String    pArgs  throws IOException       String fileName    c   temp  sample-10KB txt       File file   new File fileName        byte    fileBytes   Files readAllBytes file toPath         char singleChar      for byte b   fileBytes          singleChar    char  b        System out print singleChar

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import java io RandomAccessFile  RandomAccessFile f   new RandomAccessFile fileName   r    byte   b   new byte  int f length     f readFully b     Documentation for Java 8  http   docs oracle com javase 8 docs api java io RandomAccessFile html

[java] File to byte[] in Java

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