How to Convert a Long to byte[] and Back to Long in Java

Question

How can I convert a long to a byte array and then convert it back to a long in Java?

public static byte[] longToByteArray(long value) {
    return new byte[] {
        (byte)(value >> 56),
        (byte)(value >> 48),
        (byte)(value >> 40),
        (byte)(value >> 32),
        (byte)(value >> 24),
        (byte)(value >> 16),
        (byte)(value >> 8),
        (byte)(value)
    };
}

public static long byteArrayToLong(byte[] bytes) {
    return (((long)bytes[0] << 56) | 
            ((long)(bytes[1] & 255) << 48) | 
            ((long)(bytes[2] & 255) << 40) | 
            ((long)(bytes[3] & 255) << 32) | 
            ((long)(bytes[4] & 255) << 24) | 
            ((long)(bytes[5] & 255) << 16) | 
            ((long)(bytes[6] & 255) << 8) | 
            ((long)(bytes[7] & 255))); 
}

Answer

In Java, converting a long to a byte array and subsequently back to a long can be useful for data transmission, especially over TCP connections. The byte array serves as a compact format for sending the numeric value. This guide will illustrate how you can perform these conversions effectively.

// Function to convert a long to a byte array
public static byte[] longToByteArray(long value) {
    return new byte[] {
        (byte)(value >> 56),
        (byte)(value >> 48),
        (byte)(value >> 40),
        (byte)(value >> 32),
        (byte)(value >> 24),
        (byte)(value >> 16),
        (byte)(value >> 8),
        (byte)(value)
    };
}

// Function to convert a byte array back to a long
public static long byteArrayToLong(byte[] bytes) {
    return (((long)bytes[0] << 56) | 
            ((long)(bytes[1] & 255) << 48) | 
            ((long)(bytes[2] & 255) << 40) | 
            ((long)(bytes[3] & 255) << 32) | 
            ((long)(bytes[4] & 255) << 24) | 
            ((long)(bytes[5] & 255) << 16) | 
            ((long)(bytes[6] & 255) << 8) | 
            ((long)(bytes[7] & 255))); 
}

Causes

Need to transmit data over a network efficiently.
Conforming to certain data formats that require byte arrays.
Simple storage of numeric values.

Solutions

Use bitwise operations to convert a long to a byte array.
Construct a long from a byte array using bitwise operations.

Common Mistakes

Mistake: Not handling the endianess of the data properly.

Solution: Ensure that both ends of the communication agree on the byte order (big-endian or little-endian).

Mistake: Using an incorrect array length when receiving the byte array.

Solution: Always validate the length of the byte array before converting back to long.

Helpers

convert long to byte array in Java
Java TCP byte array conversion
long byte array Java example
Java data transmission long byte array