Elegant Way to Read File into Byte[] Array in Java

Elegant way to read file into byte[] array in Java

A long time ago:

Call any of these

byte[] org.apache.commons.io.FileUtils.readFileToByteArray(File file)
byte[] org.apache.commons.io.IOUtils.toByteArray(InputStream input) 

From

http://commons.apache.org/io/

If the library footprint is too big for your Android app, you can just use relevant classes from the commons-io library

Today (Java 7+ or Android API Level 26+)

Luckily, we now have a couple of convenience methods in the nio packages. For instance:

byte[] java.nio.file.Files.readAllBytes(Path path)

Javadoc here

File to byte[] in Java

It depends on what best means for you. Productivity wise, don't reinvent the wheel and use Apache Commons. Which is here FileUtils.readFileToByteArray(File input).

To convert the file into byte array

If you just want to modify your existing code to write the image to a byte array instead of a file, then replace the try block with this code:

    ByteArrayOutputStream out = new ByteArrayOutputStream();
    bmp.compress(Bitmap.CompressFormat.JPEG, 90, out);
    bytes = out.getBytes();

... where bytes has type byte[], and get rid of the code that generates the filename and deletes the existing file if it exists. Since you writing to a ByteArrayOutputStream, there is not need to call flush() or close() on out. (They won't do anything.)

Convert InputStream to byte array in Java

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.

How to read first and last 64kb of a video file in Java?

try something like this

    FileInputStream in = new FileInputStream("d:/1.avi");
    byte[] a = new byte[64 * 1024];
    in.read(a);   //head
    long p = in.getChannel().size() - 64 * 1024;
    in.getChannel().position(p);
    in.read(a);   //tail

How to pass a file (read from Java) most effectively to a native method?

Using regular arrays may be inefficient, as the VM may copy the array when passing it to native code, and may also use intermediate memory during I/O.

For the fastest IO, use ByteBuffer.allocateDirect to allocate a byte buffer. The underlying array is "special" in that it is not part of the regular JVM heap. Native code and I/O can access the array directly.

To read data into the buffer use,

ByteBuffer byteBuffer = ByteBuffer.allocateDirect(randomAccessFile.length());
RandomAccessFile.getChannel().read(byteBuffer, 0);

To get the backing array to pass to JNI use

byte[] byteArray = byteBuffer.array();

You can then pass this array and the file length to JNI.

The direct buffers are realtively heavy to create, As all your files are 1MB (or thereabouts) you should be able to reuse the same buffer on multiple files.

Hope this helps!

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