public class ByteConvert {
/**
 * 整型转化为字节数组
 * @param id
 * @return
 */
    public byte[] int2Byte(int id){
        byte[] arr=new byte[4];
        for(int i=0;i<4;i++){
            arr[i]=(byte)((id>>i*8)&0xff);
        }
        return arr;
    }
    /*
     * 字节数组转化为整型
     */
    public int byte2Int(byte[] arr){
        int count=0;
        for(int i=0;i<4;i++){
            int add=(int)((arr[i]&0xff)<<(i*8));
            count+=add;
        }
        return count;
    }

    //long型转化为byte[]
    public byte[] long2Byte(long id){
        byte[] arr=new byte[8];
        for(int i=0;i<arr.length;i++){
            arr[i]=(byte)((id>>i*8)&0xff);
        }
        return arr;
    }

    //byte[]转化为long
    public long byte2long(byte[] arr){
        long result=0;
        for(int i=0;i<arr.length;i++){
            long add=(long)((arr[i]&0xff)<<i*8);
            result+=add;
        }
        return result;
    }

    public static void main(String[] args) {
        ByteConvert bc=new ByteConvert();

        //int转化为byte[]
        byte[] arr=bc.int2Byte(8143);
        for(byte one:arr){
            System.out.println(one);
        }

        //测试从字节数组转化为整型
        System.out.println(bc.byte2Int(arr));

        //long转化为byte[]
        byte[] arr2=bc.long2Byte(8143);
        for(byte one:arr2){
            System.out.println(one);
        }

        //byte[]转化为long
        System.out.println(bc.byte2long(arr2));

        //String转化为byte[]
        String str="我是lcc";
        byte[] arr3=str.getBytes();
        //byte[]转化为String
        String str2=new String(arr3);
        System.out.println(str2);

    }

运行结果：
-49
31
0
0
8143
-49
31
0
0
0
0
0
0
8143
我是lcc