Easy way to write contents of a Java InputStream to an OutputStream

Question

I was surprised to find today that I couldn t track down any simple way to write the contents of an InputStream to an OutputStream in Java  Obviously  the byte buffer code isn t difficult to write  but I suspect I m just missing something which would make my life easier  and the code clearer    So  given an InputStream in and an OutputStream out  is there a simpler way to write the following   byte   buffer   new byte 1024   int len   in read buffer   while  len    -1        out write buffer  0  len       len   in read buffer

User · Answer

I think this will work  but make sure to test it    minor  improvement   but it might be a bit of a cost at readability   byte   buffer   new byte 1024   int len  while   len   in read buffer      -1        out write buffer  0  len

User · Answer

I think it s better to use a large buffer  because most of the files are greater than 1024 bytes  Also it s a good practice to check the number of read bytes to be positive   byte   buffer   new byte 4096   int n  while   n   in read buffer    gt  0        out write buffer  0  n     out close

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The JDK uses the same code so it seems like there is no  easier  way without clunky third party libraries  which probably don t do anything different anyway   The following is directly copied from java nio file Files java      buffer size used for reading and writing private static final int BUFFER SIZE   8192           Reads all bytes from an input stream and writes them to an output stream       private static long copy InputStream source  OutputStream sink  throws IOException       long nread   0L      byte   buf   new byte BUFFER SIZE       int n      while   n   source read buf    gt  0            sink write buf  0  n           nread    n            return nread

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As WMR mentioned  org apache commons io IOUtils from Apache has a method called copy InputStream OutputStream  which does exactly what you re looking for   So  you have   InputStream in  OutputStream out  IOUtils copy in out   in close    out close         in your code   Is there a reason you re avoiding IOUtils

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A IMHO more minimal snippet  that also more narrowly scopes the length variable    byte   buffer   new byte 2048   for  int n   in read buffer   n  gt   0  n   in read buffer       out write buffer  0  n     As a side note  I don t understand why more people don t use a for loop  instead opting for a while with an assign-and-test expression that is regarded by some as  poor  style

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Using Java7 and try-with-resources  comes with a simplified and readable version   try InputStream inputStream   new FileInputStream  C   mov mp4        OutputStream outputStream   new FileOutputStream  D   mov mp4           byte   buffer   new byte 10 1024        for  int length   length   inputStream read buffer      -1              outputStream write buffer  0  length           catch  FileNotFoundException exception        exception printStackTrace      catch  IOException ioException        ioException printStackTrace

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Java 9  Since Java 9  InputStream provides a method called transferTo with the following signature   public long transferTo OutputStream out  throws IOException   As the documentation states  transferTo will      Reads all bytes from this input stream and writes the bytes to the   given output stream in the order that they are read  On return  this   input stream will be at end of stream  This method does not close   either stream        This method may block indefinitely reading from the   input stream  or writing to the output stream  The behavior for the   case where the input and or output stream is asynchronously closed  or   the thread interrupted during the transfer  is highly input and output   stream specific  and therefore not specified   So in order to write contents of a Java InputStream to an OutputStream  you can write   input transferTo output

User · Answer

There s no way to do this a lot easier with JDK methods  but as Apocalisp has already noted  you re not the only one with this idea  You could use IOUtils from Jakarta Commons IO  it also has a lot of other useful things  that IMO should actually be part of the JDK

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Use Commons Net s Util class   import org apache commons net io Util      Util copyStream in  out

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Another possible candidate are the Guava I O utilities   http   code google com p guava-libraries wiki IOExplained  I thought I d use these since Guava is already immensely useful in my project  rather than adding yet another library for one function

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If you are using Java 7  Files  in the standard library  is the best approach      You can get Path from file also  file toPath      Files copy InputStream in  Path target  Files copy Path source  OutputStream out    Edit  Of course it s just useful when you create one of InputStream or OutputStream from file  Use file toPath   to get path from file   To write into an existing file  e g  one created with File createTempFile     you ll need to pass the REPLACE EXISTING copy option  otherwise FileAlreadyExistsException is thrown    Files copy in  target  StandardCopyOption REPLACE EXISTING

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For those who use Spring framework there is a useful StreamUtils class   StreamUtils copy in  out     The above does not close the streams  If you want the streams closed after the copy  use FileCopyUtils class instead   FileCopyUtils copy in  out

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Not very readable  but effective  has no dependencies and runs with any java version  byte   buffer   new byte 1024   for  int n   n   inputStream read buffer      -1  outputStream write buffer  0  n

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Try Cactoos   new LengthOf new TeeInput input  output   value      More details here  http   www yegor256 com 2017 06 22 object-oriented-input-output-in-cactoos html

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public static boolean copyFile InputStream inputStream  OutputStream out        byte buf     new byte 1024       int len      long startTime System currentTimeMillis         try           while   len   inputStream read buf      -1                out write buf  0  len                      long endTime System currentTimeMillis  -startTime          Log v     Time taken to transfer all bytes is     endTime           out close            inputStream close           catch  IOException e             return false            return true

User · Answer

Here comes how I m doing with simplest for loop   private void copy final InputStream in  final OutputStream out      throws IOException       final byte   b   new byte 8192       for  int r   r   in read b      -1             out write b  0  r

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I use BufferedInputStream and BufferedOutputStream to remove the buffering semantics from the code  try  OutputStream out   new BufferedOutputStream            InputStream in     new BufferedInputStream            int ch    while   ch   in read       -1        out write ch

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This is my best shot    And do not use inputStream transferTo      because is too generic  Your code performance will be better if you control your buffer memory   public static void transfer InputStream in  OutputStream out  int buffer  throws IOException       byte   read   new byte buffer      Your buffer size      while  0  lt   buffer   in read read            out write read  0  buffer       I use it with this  improvable  method when I know in advance the size of the stream   public static void transfer int size  InputStream in  OutputStream out  throws IOException       transfer in  out              size  gt  0xFFFF   0xFFFF    16bits 65 536                       size  gt  0xFFF   0xFFF   12bits 4096                               size  lt  0xFF   0xFF    8bits 256                                       size

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PipedInputStream and PipedOutputStream should only be used when you have multiple threads  as noted by the Javadoc   Also  note that input streams and output streams do not wrap any thread interruptions with IOExceptions    So  you should consider incorporating an interruption policy to your code   byte   buffer   new byte 1024   int len   in read buffer   while  len    -1        out write buffer  0  len       len   in read buffer       if  Thread interrupted              throw new InterruptedException              This would be an useful addition if you expect to use this API for copying large volumes of data  or data from streams that get stuck for an intolerably long time

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you can use this method  public static void copyStream InputStream is  OutputStream os          final int buffer size 1024       try                 byte   bytes new byte buffer size            for                           int count is read bytes  0  buffer size              if count  -1                 break             os write bytes  0  count                          catch Exception ex

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Using Guava s ByteStreams copy     ByteStreams copy inputStream  outputStream

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PipedInputStream and PipedOutputStream may be of some use  as you can connect one to the other

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Simple Function  If you only need this for writing an InputStream to a File then you can use this simple function   private void copyInputStreamToFile  InputStream in  File file         try           OutputStream out   new FileOutputStream file           byte   buf   new byte 1024           int len          while  len in read buf   gt 0               out write buf 0 len                     out close            in close          catch  Exception e            e printStackTrace

[java] Easy way to write contents of a Java InputStream to an OutputStream

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