RocketMQ消息

引言

用戶發送消息封裝類是Message和MessageBatch，分別是普通消息和批量消息

主要屬性

private String topic;
    private int flag;
    private Map<String, String> properties;
    private byte[] body;
    private String transactionId;

Properties中的主要屬性：

• TAGS： topic下的子標籤，用於過濾消息
• KEYS：消息索引鍵，多個使用空格隔開，rocketmq可以根據這些key快速檢索到消息
• DELAY：消息延遲級別，用於定時消息或消息重試
• WAIT：消息發送時，是否等待消息存儲完成再返回
• INSTANCE_ID：生產者的實例id
• BUYER_ID：買家？？？ 看着像業務屬性
• UNIQ_KEY：批量消息的唯一鍵

MessageBatch

• 不支持延遲消息
• 不支持重試消息
• 不支持壓縮
• 消息的topic要相同
• waitStoreMsgOK要一致

public class MessageBatch extends Message implements Iterable<Message> {

    private static final long serialVersionUID = 621335151046335557L;
    private final List<Message> messages;

    private MessageBatch(List<Message> messages) {
        this.messages = messages;
    }

	// 批量消息轉換成byte
    public byte[] encode() {
    	// 按單個轉換處理，合併byte數組
        return MessageDecoder.encodeMessages(messages);
    }

    public Iterator<Message> iterator() {
        return messages.iterator();
    }

    public static MessageBatch generateFromList(Collection<Message> messages) {
        assert messages != null;
        assert messages.size() > 0;
        List<Message> messageList = new ArrayList<Message>(messages.size());
        Message first = null;
        for (Message message : messages) {
            if (message.getDelayTimeLevel() > 0) {
                throw new UnsupportedOperationException("TimeDelayLevel is not supported for batching");
            }
            if (message.getTopic().startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX)) {
                throw new UnsupportedOperationException("Retry Group is not supported for batching");
            }
            if (first == null) {
                first = message;
            } else {
                if (!first.getTopic().equals(message.getTopic())) {
                    throw new UnsupportedOperationException("The topic of the messages in one batch should be the same");
                }
                if (first.isWaitStoreMsgOK() != message.isWaitStoreMsgOK()) {
                    throw new UnsupportedOperationException("The waitStoreMsgOK of the messages in one batch should the same");
                }
            }
            messageList.add(message);
        }
        MessageBatch messageBatch = new MessageBatch(messageList);

        messageBatch.setTopic(first.getTopic());
        messageBatch.setWaitStoreMsgOK(first.isWaitStoreMsgOK());
        return messageBatch;
    }

}

消息的編碼接碼

MessageDecoder

• 這樣編碼方便使用netty的定長解碼器
• todo

public static byte[] encodeMessage(Message message) {
        //only need flag, body, properties
        byte[] body = message.getBody();
        int bodyLen = body.length;
        String properties = messageProperties2String(message.getProperties());
        byte[] propertiesBytes = properties.getBytes(CHARSET_UTF8);
        //note properties length must not more than Short.MAX
        short propertiesLength = (short) propertiesBytes.length;
        int sysFlag = message.getFlag();
        int storeSize = 4 // 1 TOTALSIZE
            + 4 // 2 MAGICCOD
            + 4 // 3 BODYCRC
            + 4 // 4 FLAG
            + 4 + bodyLen // 4 BODY
            + 2 + propertiesLength;
        ByteBuffer byteBuffer = ByteBuffer.allocate(storeSize);
        // 1 TOTALSIZE
        byteBuffer.putInt(storeSize);

        // 2 MAGICCODE
        byteBuffer.putInt(0);

        // 3 BODYCRC
        byteBuffer.putInt(0);

        // 4 FLAG
        int flag = message.getFlag();
        byteBuffer.putInt(flag);

        // 5 BODY
        byteBuffer.putInt(bodyLen);
        byteBuffer.put(body);

        // 6 properties
        byteBuffer.putShort(propertiesLength);
        byteBuffer.put(propertiesBytes);

        return byteBuffer.array();
    }

    public static Message decodeMessage(ByteBuffer byteBuffer) throws Exception {
        Message message = new Message();

        // 1 TOTALSIZE
        byteBuffer.getInt();

        // 2 MAGICCODE
        byteBuffer.getInt();

        // 3 BODYCRC
        byteBuffer.getInt();

        // 4 FLAG
        int flag = byteBuffer.getInt();
        message.setFlag(flag);

        // 5 BODY
        int bodyLen = byteBuffer.getInt();
        byte[] body = new byte[bodyLen];
        byteBuffer.get(body);
        message.setBody(body);

        // 6 properties
        short propertiesLen = byteBuffer.getShort();
        byte[] propertiesBytes = new byte[propertiesLen];
        byteBuffer.get(propertiesBytes);
        message.setProperties(string2messageProperties(new String(propertiesBytes, CHARSET_UTF8)));

        return message;
    }