mysql客户端与mysql服务端交互过程中，如果服务端遇到错误需要告知客户端则返回错误包。

mysql通信报文结构

错误包

Payload

错误包操作

1. 错误包类

/**
 * 
 * @author seaboat
 * @date 2016-09-25
 * @version 1.0
 * <pre><b>email: </b>849586227@qq.com</pre>
 * <pre><b>blog: </b>http://blog.csdn.net/wangyangzhizhou</pre>
 * <p>mysql error packet.</p>
 */
public class ErrorPacket extends MySQLPacket {
    public static final byte header = (byte) 0xff;
    private static final byte SQLSTATE_MARKER = (byte) '#';
    private static final byte[] DEFAULT_SQLSTATE = "HY000".getBytes();

    public int errno;
    public byte mark = SQLSTATE_MARKER;
    public byte[] sqlState = DEFAULT_SQLSTATE;
    public byte[] message;

    public void read(byte[] data) {
        MySQLMessage mm = new MySQLMessage(data);
        packetLength = mm.readUB3();
        packetId = mm.read();
        mm.read();
        errno = mm.readUB2();
        if (mm.hasRemaining() && (mm.read(mm.position()) == SQLSTATE_MARKER)) {
            mm.read();
            sqlState = mm.readBytes(5);
        }
        message = mm.readBytes();
    }

    public void write(ByteBuffer buffer) {
        int size = calcPacketSize();
        BufferUtil.writeUB3(buffer, size);
        buffer.put(packetId);
        buffer.put(header);
        BufferUtil.writeUB2(buffer, errno);
        buffer.put(mark);
        buffer.put(sqlState);
        buffer.put(message);
    }

    @Override
    public int calcPacketSize() {
        int size = 9;// 1 + 2 + 1 + 5
        if (message != null) {
            size += message.length;
        }
        return size;
    }

    @Override
    protected String getPacketInfo() {
        return "MySQL Error Packet";
    }

}

1. 十六进制转换工具

/**
 * 
 * @author seaboat
 * @date 2016-09-25
 * @version 1.0
 */
public class HexUtil {
    private final static byte[] hex = "0123456789ABCDEF".getBytes();

    public static String Bytes2HexString(byte[] b) {
        byte[] buff = new byte[2 * b.length];
        for (int i = 0; i < b.length; i++) {
            buff[2 * i] = hex[(b[i] >> 4) & 0x0f];
            buff[2 * i + 1] = hex[b[i] & 0x0f];
        }
        return new String(buff);
    }

    public static String str2HexStr(String str) {
        char[] chars = "0123456789ABCDEF".toCharArray();
        StringBuilder sb = new StringBuilder("");
        byte[] bs = str.getBytes();
        int bit;
        for (int i = 0; i < bs.length; i++) {
            bit = (bs[i] & 0x0f0) >> 4;
            sb.append(chars[bit]);
            bit = bs[i] & 0x0f;
            sb.append(chars[bit]);
        }
        return sb.toString();
    }
}

1. 错误包生成测试

/**
 * 
 * @author seaboat
 * @date 2016-09-25
 * @version 1.0
 */
public class ErrorPacketTest {
    @Test
    public void produce() {
        ErrorPacket err = new ErrorPacket();
        err.packetId = 1;
        err.errno = 32322;
        err.message = "sorry".getBytes();
        ByteBuffer buffer = ByteBuffer.allocate(256);
        err.write(buffer);
        buffer.flip();
        byte[] bytes = new byte[buffer.remaining()];
        buffer.get(bytes, 0, bytes.length);
        String result = HexUtil.Bytes2HexString(bytes);
        System.out.println(result);
        assertTrue(Integer.valueOf(result.substring(0, 2), 16) == result
                .length() / 2 - 4);

        ErrorPacket err2 = new ErrorPacket();
        err2.read(bytes);
        assertTrue(err2.errno == 32322);
        assertTrue(err2.message.length == "sorry".getBytes().length);
    }

}