Reading a binary input stream into a single byte array in Java

Question

The documentation says that one should not use available   method to determine the size of an InputStream  How can I read the whole content of an InputStream into a byte array   InputStream in    assuming already present byte   data   new byte in available     in read data    now data is filled with the whole content of the InputStream   I could read multiple times into a buffer of a fixed size  but then  I will have to combine the data I read into a single byte array  which is a problem for me

User · Answer

You can read it by chunks  byte buffer     new byte 2048   and write the chunks to a ByteArrayOutputStream  From the ByteArrayOutputStream you can retrieve the contents as a byte    without needing to determine its size beforehand

User · Answer

Please keep in mind that the answers here assume that the length of the file is less than or equal to Integer MAX VALUE 2147483647    If you are reading in from a file  you can do something like this       File file   new File  myFile        byte   fileData   new byte  int  file length         DataInputStream dis   new DataInputStream new FileInputStream file        dis readFully fileData       dis close        UPDATE  May 31  2014    Java 7 adds some new features in the java nio file package that can be used to make this example a few lines shorter  See the readAllBytes   method in the java nio file Files class  Here is a short example   import java nio file FileSystems  import java nio file Files  import java nio file Path                  Path p   FileSystems getDefault   getPath      myFile            byte    fileData   Files readAllBytes p     Android has support for this starting in Api level 26  8 0 0  Oreo

User · Answer

The simplest approach IMO is to use Guava and its ByteStreams class   byte   bytes   ByteStreams toByteArray in     Or for a file   byte   bytes   Files toByteArray file     Alternatively  if you didn t want to use Guava   you could create a ByteArrayOutputStream  and repeatedly read into a byte array and write into the ByteArrayOutputStream  letting that handle resizing   then call ByteArrayOutputStream toByteArray     Note that this approach works whether you can tell the length of your input or not - assuming you have enough memory  of course

User · Answer

Max value for array index is Integer MAX INT - it s around 2Gb  2 31   2 147 483 647   Your input stream can be bigger than 2Gb  so you have to process data in chunks  sorry           InputStream is          final byte   buffer   new byte 512   1024   1024      512Mb         while true                final int read   is read buffer               if   read  lt  0                     break                               do processing

User · Answer

I believe buffer length needs to be specified  as memory is finite and you may run out of it  Example   InputStream in   new FileInputStream strFileName       long length   fileFileName length         if  length  gt  Integer MAX VALUE            throw new IOException  File is too large                byte   bytes   new byte  int  length        int offset   0      int numRead   0       while  offset  lt  bytes length  amp  amp   numRead   in read bytes  offset  bytes length - offset    gt   0            offset    numRead             if  offset  lt  bytes length            throw new IOException  Could not completely read file     fileFileName getName                in close

User · Answer

You can use Apache commons-io for this task   Refer to this method   public static byte   readFileToByteArray File file  throws IOException   Update   Java 7 way   byte   bytes   Files readAllBytes Paths get filename      and if it is a text file and you want to convert it to String  change encoding as needed    StandardCharsets UTF 8 decode ByteBuffer wrap bytes   toString

[java] Reading a binary input stream into a single byte array in Java

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