Convert InputStream to byte array in Java

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

Solution 1:

You can use Apache Commons IO to handle this and similar tasks.

The IOUtils type has a static method to read an InputStream and return a byte[].

InputStream is;
byte[] bytes = IOUtils.toByteArray(is);

Internally this creates a ByteArrayOutputStream and copies the bytes to the output, then calls toByteArray(). It handles large files by copying the bytes in blocks of 4KiB.

Solution 2:

You need to read each byte from your InputStream and write it to a ByteArrayOutputStream.

You can then retrieve the underlying byte array by calling toByteArray():

InputStream is = ...
ByteArrayOutputStream buffer = new ByteArrayOutputStream();

int nRead;
byte[] data = new byte[16384];

while ((nRead = is.read(data, 0, data.length)) != -1) {
  buffer.write(data, 0, nRead);
}

return buffer.toByteArray();

Solution 3:

Finally, after twenty years, there’s a simple solution without the need for a 3rd party library, thanks to Java 9:

InputStream is;
…
byte[] array = is.readAllBytes();

Note also the convenience methods readNBytes(byte[] b, int off, int len) and transferTo(OutputStream) addressing recurring needs.