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


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()];;//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.

This question is tagged with java inputstream

~ Asked on 2011-08-30 21:50:25

The Best Answer is


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.

~ Answered on 2011-08-30 21:53:54


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));

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).

~ Answered on 2011-08-30 21:55:20

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