java中构造字节流的一种实现

import java.util.ArrayList;import java.util.List;/** * Created by kaven on 2018/4/2. */public class TestBytes {    /**     * 专门创建一个类来保存指定byte数     */    public class MyByte {        byte[] data;        MyByte(int n) {            data = new byte[n];        }        void setData(String s) {            byte[] tmp = s.getBytes();            // 提示数据超了            if (tmp.length > data.length) {                System.err.print("too many data");            }            for (int i = 0; i < this.data.length && i < tmp.length; i++) {                data[i] = tmp[i];            }        }        // 设置一个值到第一位        void setData(int i) {            data[0] = (byte) i;        }        byte[] getByte() {            return data;        }        int size() {            return data.length;        }    }    void login() {        MyByte msgType = new MyByte(1);        MyByte userId = new MyByte(16);        MyByte msg = new MyByte(12);        msgType.setData(1);        userId.setData("1");        msg.setData("222");        List
    
      list = new ArrayList();        list.add(msgType);        list.add(userId);        list.add(msg);        byte[] res = join(list);        System.out.print(res.toString());    }    /**     * 将列表中的数据合并成一个数据     * @param list     * @return     */    private byte[] join(List
     
       list) {        int count = 0;        for (int i = 0; i < list.size(); i++) {            count += list.get(i).size();        }        byte[] res = new byte[count];        int start = 0;        for (int i = 0; i < list.size(); i++) {            byte[] tmp = list.get(i).getByte();            for (int j = 0; j < tmp.length; j++) {                res[start] = tmp[j];                start += 1;            }        }        return res;    }    public static void main(String args[]) {        TestBytes a = new TestBytes();        a.login();    }}