How do I convert Long to byte[] and back in java

public byte[] longToBytes(long x) {    ByteBuffer buffer = ByteBuffer.allocate(Long.BYTES);    buffer.putLong(x);    return buffer.array();}public long bytesToLong(byte[] bytes) {    ByteBuffer buffer = ByteBuffer.allocate(Long.BYTES);    buffer.put(bytes);    buffer.flip();//need flip     return buffer.getLong();}

Or wrapped in a class to avoid repeatedly creating ByteBuffers:

public class ByteUtils {    private static ByteBuffer buffer = ByteBuffer.allocate(Long.BYTES);        public static byte[] longToBytes(long x) {        buffer.putLong(0, x);        return buffer.array();    }    public static long bytesToLong(byte[] bytes) {        buffer.put(bytes, 0, bytes.length);        buffer.flip();//need flip         return buffer.getLong();    }}

Since this is getting so popular, I just want to mention that I think you're better off using a library like Guava in the vast majority of cases. And if you have some strange opposition to libraries, you should probably consider this answer first for native java solutions. I think the main thing my answer really has going for it is that you don't have to worry about the endian-ness of the system yourself.

You could use the Byte conversion methods from Google Guava.

Example:

byte[] bytes = Longs.toByteArray(12345L);

I tested the ByteBuffer method against plain bitwise operations but the latter is significantly faster.

public static byte[] longToBytes(long l) {    byte[] result = new byte[8];    for (int i = 7; i >= 0; i--) {        result[i] = (byte)(l & 0xFF);        l >>= 8;    }    return result;}public static long bytesToLong(final byte[] b) {    long result = 0;    for (int i = 0; i < 8; i++) {        result <<= 8;        result |= (b[i] & 0xFF);    }    return result;}

For Java 8+ we can use the static variables that were added:

public static byte[] longToBytes(long l) {    byte[] result = new byte[Long.BYTES];    for (int i = Long.BYTES - 1; i >= 0; i--) {        result[i] = (byte)(l & 0xFF);        l >>= Byte.SIZE;    }    return result;}public static long bytesToLong(final byte[] b) {    long result = 0;    for (int i = 0; i < Long.BYTES; i++) {        result <<= Byte.SIZE;        result |= (b[i] & 0xFF);    }    return result;}