I have an 8 byte array and I want to convert it to its corresponding numeric value.
e.g.
byte[] by = new byte[8]; // the byte array is stored in 'by'
// CONVERSION OPERATION
// return the numeric value
I want a method that will perform the above conversion operation.
One could use the Buffer
s that are provided as part of the java.nio
package to perform the conversion.
Here, the source byte[]
array has a of length 8, which is the size that corresponds with a long
value.
First, the byte[]
array is wrapped in a ByteBuffer
, and then the ByteBuffer.getLong
method is called to obtain the long
value:
ByteBuffer bb = ByteBuffer.wrap(new byte[] {0, 0, 0, 0, 0, 0, 0, 4});
long l = bb.getLong();
System.out.println(l);
Result
4
I'd like to thank dfa for pointing out the ByteBuffer.getLong
method in the comments.
Although it may not be applicable in this situation, the beauty of the Buffer
s come with looking at an array with multiple values.
For example, if we had a 8 byte array, and we wanted to view it as two int
values, we could wrap the byte[]
array in an ByteBuffer
, which is viewed as a IntBuffer
and obtain the values by IntBuffer.get
:
ByteBuffer bb = ByteBuffer.wrap(new byte[] {0, 0, 0, 1, 0, 0, 0, 4});
IntBuffer ib = bb.asIntBuffer();
int i0 = ib.get(0);
int i1 = ib.get(1);
System.out.println(i0);
System.out.println(i1);
Result:
1
4
Complete java converter code for all primitive types to/from arrays http://www.daniweb.com/code/snippet216874.html
If this is an 8-bytes numeric value, you can try:
BigInteger n = new BigInteger(byteArray);
If this is an UTF-8 character buffer, then you can try:
BigInteger n = new BigInteger(new String(byteArray, "UTF-8"));
You can also use BigInteger for variable length bytes. You can convert it to Long, Integer or Short, whichever suits your needs.
new BigInteger(bytes).intValue();
or to denote polarity:
new BigInteger(1, bytes).intValue();
Simply, you could use or refer to guava lib provided by google, which offers utiliy methods for conversion between long and byte array. My client code:
long content = 212000607777l;
byte[] numberByte = Longs.toByteArray(content);
logger.info(Longs.fromByteArray(numberByte));
Each cell in the array is treated as unsigned int:
private int unsignedIntFromByteArray(byte[] bytes) {
int res = 0;
if (bytes == null)
return res;
for (int i=0;i<bytes.length;i++){
res = res | ((bytes[i] & 0xff) << i*8);
}
return res;
}
public static long byteArrayToLong(byte[] bytes) {
return ((long) (bytes[0]) << 56)
+ (((long) bytes[1] & 0xFF) << 48)
+ ((long) (bytes[2] & 0xFF) << 40)
+ ((long) (bytes[3] & 0xFF) << 32)
+ ((long) (bytes[4] & 0xFF) << 24)
+ ((bytes[5] & 0xFF) << 16)
+ ((bytes[6] & 0xFF) << 8)
+ (bytes[7] & 0xFF);
}
convert bytes array (long is 8 bytes) to long
Source: Stackoverflow.com