Convert InputStream to byte array in Java

Question

How do I read an entire InputStream into a byte array?

Answer 1

Safe solution (with capability of close streams correctly):

• Java 9+:

   final byte[] bytes;
   try (inputStream) {
       bytes = inputStream.readAllBytes();
   }
  

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• Java 8:

   public static byte[] readAllBytes(InputStream inputStream) throws IOException {
       final int bufLen = 4 * 0x400; // 4KB
       byte[] buf = new byte[bufLen];
       int readLen;
       IOException exception = null;
  
       try {
           try (ByteArrayOutputStream outputStream = new ByteArrayOutputStream()) {
               while ((readLen = inputStream.read(buf, 0, bufLen)) != -1)
                   outputStream.write(buf, 0, readLen);
  
               return outputStream.toByteArray();
           }
       } catch (IOException e) {
           exception = e;
           throw e;
       } finally {
           if (exception == null) inputStream.close();
           else try {
               inputStream.close();
           } catch (IOException e) {
               exception.addSuppressed(e);
           }
       }
   }
  

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• Kotlin (when Java 9+ isn't accessible):

   @Throws(IOException::class)
   fun InputStream.readAllBytes(): ByteArray {
       val bufLen = 4 * 0x400 // 4KB
       val buf = ByteArray(bufLen)
       var readLen: Int = 0
  
       ByteArrayOutputStream().use { o ->
           this.use { i ->
               while (i.read(buf, 0, bufLen).also { readLen = it } != -1)
                   o.write(buf, 0, readLen)
           }
  
           return o.toByteArray()
       }
   }
  

  To avoid nested use see here.

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• Scala (when Java 9+ isn't accessible) (By @Joan. Thx):

  def readAllBytes(inputStream: InputStream): Array[Byte] =
    Stream.continually(inputStream.read).takeWhile(_ != -1).map(_.toByte).toArray