前言

最近在工作中，遇到一个需要通过 byte[] 类型发送控制指令的需求

过程分析

此次用到了两个简易的位运算和一个小常识

1. 按位与（&）：两个操作数按位进行与运算

2. 按位或（|）：两个操作数按位进行或运算

3. 按位与（&）1 数据保持不变，按位或（|）0 数据将强制变为 0

结论

通过约定，首位作为是否切换的布尔值，其余位作为附加数据，可以在一个字节内编码一些简单的配置项信息

import java.util.Arrays;

public class Command {
    private boolean mSwitchCamera;

    private byte mSwitchCameraId;

    private boolean mSwitchQuality;

    private byte mSwitchQualityId;

    private Command() {
    }

    public Command(boolean mSwitchCamera, byte mSwitchCameraId, boolean mSwitchQuality, byte mSwitchQualityId) {
        this.mSwitchCamera = mSwitchCamera;
        this.mSwitchCameraId = mSwitchCameraId;
        this.mSwitchQuality = mSwitchQuality;
        this.mSwitchQualityId = mSwitchQualityId;
    }

    public static Command parse(byte[] dataArray) {
        Command command = null;
        if (dataArray != null && dataArray.length > 0) {
            command = new Command();
            command.mSwitchCamera = (dataArray[0] & -128) == -128;
            command.mSwitchCameraId = (byte) (dataArray[0] & 127);
            command.mSwitchQuality = (dataArray[1] & -128) == -128;
            command.mSwitchQualityId = (byte) (dataArray[1] & 127);
        }
        return command;
    }

    public static byte[] compact(Command command) {
        byte[] data = null;
        if (command != null) {
            data = new byte[2];
            data[0] = (byte) (command.mSwitchCameraId & 127);
            if (command.mSwitchCamera) {
                data[0] |= -128;
            }
            data[1] = (byte) (command.mSwitchQualityId & 127);
            if (command.mSwitchQuality) {
                data[1] |= -128;
            }
        }
        return data;
    }

    public boolean isSwitchCamera() {
        return mSwitchCamera;
    }

    public byte getSwitchCameraId() {
        return mSwitchCameraId;
    }

    public boolean isSwitchQuality() {
        return mSwitchQuality;
    }

    public byte getSwitchQualityId() {
        return mSwitchQualityId;
    }

    @Override
    public String toString() {
        return "Command{" + "mSwitchCamera=" + mSwitchCamera + ", mSwitchCameraId=" + mSwitchCameraId + ", mSwitchQuality=" + mSwitchQuality + ", mSwitchQualityId=" + mSwitchQualityId + '}';
    }

    public static void main(String[] args) {
        Command command = new Command(true, (byte) 3, false, (byte) 66);
        byte[] data = compact(command);
        System.out.println(Arrays.toString(data));
        System.out.println(parse(data));
    }
}