Connecting an input stream to an outputstream

Question

update in java9  https   docs oracle com javase 9 docs api java io InputStream html transferTo-java io OutputStream-  I saw some similar  but not-quite-what-i-need threads   I have a server  which will basically take input from a client  client A  and forward it  byte for byte  to another client  client B   I d like to connect my inputstream of client A with my output stream of client B   Is that possible   What are ways to do that   Also  these clients are sending each other messages  which are somewhat time sensitive  so buffering won t do   I do not want a buffer of say 500 and a client sends 499 bytes and then my server holds off on forwarding the 500 bytes because it hasn t received the last byte to fill the buffer   Right now  I am parsing each message to find its length  then reading length bytes  then forwarding them   I figured  and tested  this would be better than reading a byte and forwarding a byte over and over because that would be very slow   I also did not want to use a buffer or a timer for the reason I stated in my last paragraph     I do not want messages waiting a really long time to get through simply because the buffer isn t full   What s a good way to do this

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BUFFER SIZE is the size of chucks to read in  Should be   1kb and  lt  10MB   private static final int BUFFER SIZE   2   1024   1024  private void copy InputStream input  OutputStream output  throws IOException       try           byte   buffer   new byte BUFFER SIZE           int bytesRead   input read buffer           while  bytesRead    -1                output write buffer  0  bytesRead               bytesRead   input read buffer                   If needed  close streams        finally           input close            output close

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Asynchronous way to achieve it    void inputStreamToOutputStream final InputStream inputStream  final OutputStream out        Thread t   new Thread new Runnable              public void run                 try                   int d                  while   d   inputStream read       -1                        out write d                                   catch  IOException ex                      TODO make a callback on exception                                      t setDaemon true       t start

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Just because you use a buffer doesn t mean the stream has to fill that buffer  In other words  this should be okay   public static void copyStream InputStream input  OutputStream output      throws IOException       byte   buffer   new byte 1024      Adjust if you want     int bytesRead      while   bytesRead   input read buffer      -1                output write buffer  0  bytesRead             That should work fine - basically the read call will block until there s some data available  but it won t wait until it s all available to fill the buffer   I suppose it could  and I believe FileInputStream usually will fill the buffer  but a stream attached to a socket is more likely to give you the data immediately    I think it s worth at least trying this simple solution first

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This is a Scala version that is clean and fast  no stackoverflow      import scala annotation tailrec   import java io      implicit class InputStreamOps in  InputStream        def  gt  out  OutputStream   Unit   pipeTo out       def pipeTo out  OutputStream  bufferSize  Int   1 lt  lt 10   Unit   pipeTo out  Array ofDim Byte  bufferSize         tailrec final def pipeTo out  OutputStream  buffer  Array Byte    Unit   in read buffer  match         case n if n  gt  0   gt          out write buffer  0  n          pipeTo out  buffer        case     gt          in close           out close               This enables to use  gt  symbol e g  inputstream  gt  outputstream and also pass in custom buffers sizes

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JDK 9 has added InputStream transferTo OutputStream out  for this functionality

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Use org apache commons io IOUtils  InputStream inStream   new     OutputStream outStream   new     IOUtils copy inStream  outStream     or copyLarge for size  2GB

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In case you are into functional this is a function written in Scala showing how you could copy an input stream to an output stream using only vals  and not vars    def copyInputToOutputFunctional inputStream  InputStream  outputStream  OutputStream bufferSize  Int      val buffer   new Array Byte  bufferSize     def recurse         val len   inputStream read buffer       if  len  gt  0          outputStream write buffer take len          recurse                recurse        Note that this is not recommended to use in a java application with little memory available because with a recursive function you could easily get a stack overflow exception error

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You can use a circular buffer    Code     buffer all data in a circular buffer of infinite size CircularByteBuffer cbb   new CircularByteBuffer CircularByteBuffer INFINITE SIZE   class1 putDataOnOutputStream cbb getOutputStream     class2 processDataFromInputStream cbb getInputStream        Maven dependency   lt dependency gt       lt groupId gt org ostermiller lt  groupId gt       lt artifactId gt utils lt  artifactId gt       lt version gt 1 07 00 lt  version gt   lt  dependency gt     Mode details  http   ostermiller org utils CircularBuffer html

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How about just using  void feedInputToOutput InputStream in  OutputStream out       IOUtils copy in  out       and be done with it   from jakarta apache commons i o library which is used by a huge amount of projects already so you probably already have the jar in your classpath already

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For completeness  guava also has a handy utility for this  ByteStreams copy input  output

[java] Connecting an input stream to an outputstream

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