Java Convert Long into Bytes

In this article, we will see how to convert a java long value into a byte array.

We may need this in many scenarios. An example would be…

In a cluster of machines, one member may want to send another member a heartbeat message containing its alive time in which case you need to convert the system time into a byte array and then send them over the wire.

Convert long to bytes

In java, long is a signed 64-bit type, which means it contains 8 bytes.
Assuming the long value is 1436808134035, Let’s start converting long value to bytes.
In the form of bits, grouped by bytes, the long value would be:
00000000 00000000 00000001 01001110 10001000 01110000 00111101 10010011
We will create an array of 8 bytes. We want each group to be assigned to one byte array element.

1. We typecast long to the last element of byte array, the lowest 8 bits will get assigned to the byte.

   b[7] = (byte) (L)

   b[7] would get 10010011

2. Now we want the next 8 bits of long to get assigned to one more element of byte array. We achieve this using unsigned right shift and reassigning the value to long.

   L >>>= 8;

   . We do unsigned right shift so that the signed bit is shifted too, replacing it with a zero bit. The long value after the unsigned right shift would be: 00000000 00000000 00000000 00000001 01001110 10001000 01110000 00111101.

3. We again follow the first step, that is, to typecast it to the next lower element of the byte array.

   b[6] = (byte) (L);

   . This will preserve the lower 8 bits of the new long value. After typecast the b[6] will get 00111101

4. Again, we do the unsigned right shift to preserve the next 8 bits of long
5. We will continue the steps from 1-2 till we reach the last 8 bits of long

LongToByteArrayExample:

package com.javarticles.io;

import java.io.IOException;

public class LongToByteArrayExample {
    public static void main(String[] args) throws IOException {
        long aliveTime = System.currentTimeMillis();
        System.out.println("Time: " + aliveTime);
    }
    
    private static void longToByteArray(long l, byte[] b) {
        b[7] = (byte) (l);
        l >>>= 8;
        b[6] = (byte) (l);
        l >>>= 8;
        b[5] = (byte) (l);
        l >>>= 8;
        b[4] = (byte) (l);
        l >>>= 8;
        b[3] = (byte) (l);
        l >>>= 8;
        b[2] = (byte) (l);
        l >>>= 8;
        b[1] = (byte) (l);
        l >>>= 8;
        b[0] = (byte) (l);
    }    
}

Output:

Time: 1436808134035

Convert bytes to long

We just need to do the reverse to convert the byte array back to long.

1. Remember, the lower 8 bits of long are stored in the 8th element of the byte array.
2. Using AND operation with the 8th element of byte array and 0xFF, we get the lower 8 bits of the long value.
3. Again, to get the next 8 bits of long follow step 2 on the next lower element of the byte array
4. Left shift the value by 8 bits and add it to the previous long value
5. Keep repeating the steps till you reach the final first element of the byte array

LongToByteArrayExample:

package com.javarticles.io;

import java.io.IOException;

public class LongToByteArrayExample {
    public static void main(String[] args) throws IOException {
        long aliveTime = System.currentTimeMillis();
        System.out.println("Time: " + aliveTime);
        byte[] longAsBytes = new byte[8];
        longToByteArray(aliveTime, longAsBytes);
        long retrievedAliveTime = byteArrayToLong(longAsBytes);
        System.out.println("Retrieved Time: " + retrievedAliveTime);
    }
    
    private static void longToByteArray(long l, byte[] b) {
        b[7] = (byte) (l);
        l >>>= 8;
        b[6] = (byte) (l);
        l >>>= 8;
        b[5] = (byte) (l);
        l >>>= 8;
        b[4] = (byte) (l);
        l >>>= 8;
        b[3] = (byte) (l);
        l >>>= 8;
        b[2] = (byte) (l);
        l >>>= 8;
        b[1] = (byte) (l);
        l >>>= 8;
        b[0] = (byte) (l);
    }
    
    private static long byteArrayToLong(byte[] b){
        return ( ( (long) b[7]) & 0xFF) +
            ( ( ( (long) b[6]) & 0xFF) << 8) +
            ( ( ( (long) b[5]) & 0xFF) << 16) +
            ( ( ( (long) b[4]) & 0xFF) << 24) +
            ( ( ( (long) b[3]) & 0xFF) << 32) +
            ( ( ( (long) b[2]) & 0xFF) << 40) +
            ( ( ( (long) b[1]) & 0xFF) << 48) +
            ( ( ( (long) b[0]) & 0xFF) << 56);
    }
}

Output:

Time: 1436808134035
Retrieved Time: 1436808134035

Download the source code

This was an example about converting java Long into Byte array and then convert the byte array back to long.