读取文件的前4个字节

Question

I'm used to C#, but I'm trying to make an app which reads the first 4 bytes into an array, but I have been unsuccessful. I also need to reverse the Endian on the file which I don't know how in Java, in C# it is Array.Reverse(bytes); . I've tried reading the file into an Int32, but from there I cannot get it into an array for some reason.

Answer 1

Like that :

byte[] buffer = new byte[4];
InputStream is = new FileInputStream("somwhere.in.the.dark");
if (is.read(buffer) != buffer.length) { 
    // do something 
}
is.close();
// at this point, the buffer contains the 4 bytes...

Answer 2

You can change the Endianness with ByteBuffer

FileChannel fc = new FileInputStream(filename).getChannel();
ByteBuffer bb = ByteBuffer.allocate(4);
bb.order(ByteBuffer.nativeOrder()); // or whatever you want.
fc.read(bb);
bb.flip();
int n = bb.getInt();

The simple way to reverse the byte of an Integer

int n = ...
int r = Integer.reverseByte(n);

similarly

long l = Long.reverseBytes(n);