一. 概念
1. msgId(uniqId)
由 producer客户端 生成,调用方法MessageClientIDSetter.createUniqID()生成全局唯一的Id
private static final int LEN;
private static final String FIX_STRING;
private static final AtomicInteger COUNTER;
private static long startTime;
private static long nextStartTime;
public static String createUniqID() {
StringBuilder sb = new StringBuilder(LEN * 2);
sb.append(FIX_STRING); // 固定值,程序启动时生成
sb.append(UtilAll.bytes2string(createUniqIDBuffer())); // 变化值 根据时间差+自增长生成
return sb.toString();
}
- FIX_STRING 固定前缀
- 生成规则:客户端的IP、进程ID、MessageClientIDSetter类加载器的hashcode
static {
byte[] ip;
try {
ip = UtilAll.getIP();
} catch (Exception e) {
ip = createFakeIP();
}
LEN = ip.length + 2 + 4 + 4 + 2;
ByteBuffer tempBuffer = ByteBuffer.allocate(ip.length + 2 + 4);
tempBuffer.put(ip); // 客户端IP
tempBuffer.putShort((short) UtilAll.getPid()); // 进程ID
tempBuffer.putInt(MessageClientIDSetter.class.getClassLoader().hashCode()); // 类加载器hashCode
FIX_STRING = UtilAll.bytes2string(tempBuffer.array());
setStartTime(System.currentTimeMillis());
COUNTER = new AtomicInteger(0);
}
private synchronized static void setStartTime(long millis) {
Calendar cal = Calendar.getInstance();
cal.setTimeInMillis(millis);
cal.set(Calendar.DAY_OF_MONTH, 1);
cal.set(Calendar.HOUR_OF_DAY, 0);
cal.set(Calendar.MINUTE, 0);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);
startTime = cal.getTimeInMillis();
cal.add(Calendar.MONTH, 1);
nextStartTime = cal.getTimeInMillis();
}
// 获取进程ID
public static int getPid() {
RuntimeMXBean runtime = ManagementFactory.getRuntimeMXBean();
String name = runtime.getName(); // format: "pid@hostname"
try {
return Integer.parseInt(name.substring(0, name.indexOf(‘@‘)));
} catch (Exception e) {
return -1;
}
}
- createUniqIDBuffer 变化值
- 生成规则:当前时间与系统启动时间的差值,以及自增序号
private static byte[] createUniqIDBuffer() {
ByteBuffer buffer = ByteBuffer.allocate(4 + 2);
long current = System.currentTimeMillis();
// 每月1号重新计算 startTime,避免时间戳差值无限增加
if (current >= nextStartTime) {
setStartTime(current);
}
// 时间差值(当前时间戳-系统启动时时间戳)
buffer.putInt((int) (System.currentTimeMillis() - startTime));
// 1. short:毫秒内自增长,几万够了
// 2. COUNTER达到最大值后,会从最大的负数开始递增,如-2147483648 -2147483647
buffer.putShort((short) COUNTER.getAndIncrement());
return buffer.array();
}
2. offsetMsgId
- Broker 服务端将消息追加到内存后会返回其物理偏移量,即在 commitlog 文件中的偏移量,然后会生成一个id,代码中虽然也叫 msgId,其实是 offsetMsgId
- 组成规则:Broker 服务器的 IP 与端口号、消息的物理偏移量
- ByteBuffer input: 用来存放 offsetMsgId 的字节缓存区
- ByteBuffer addr: Broker 服务器的 IP 地址与端口号,即通过解析 offsetMsgId 从而得到消息服务器的地址信息
- long offset:消息的物理偏移量
类:org.apache.rocketmq.common.message.MessageDecoder
public static String createMessageId(final ByteBuffer input, final ByteBuffer addr, final long offset) {
input.flip();
int msgIDLength = addr.limit() == 8 ? 16 : 28;
input.limit(msgIDLength);
input.put(addr);
input.putLong(offset);
return UtilAll.bytes2string(input.array());
}
二. 消息发送
其中包含了msgId、offsetMsgId
三. 消息消费
- 消费客户端返回的对象是 MessageClientExt ,继承自 MessageExt ,MessageExt继承自 Message
- 如果消息消费失败需要重试,RocketMQ 的做法是将消息重新发送到 Broker 服务器,此时 msgId 是不会发生变化的,但该消息的 offsetMsgId 会发生变化,因为其存储在 Broker 服务器中的位置发生了变化
- 在调用 MessageClientExt 中的 getMsgId() 方法时,先返回消息属性中的MsgId,不存在则返回消息的 offsetMsgId
public String getMsgId() {
String uniqID = MessageClientIDSetter.getUniqID(this);
if (uniqID == null) {
return this.getOffsetMsgId();
} else {
return uniqID;
}
}
- MessageExt 的toString 方法
public String toString() {
return "MessageExt [brokerName=" + brokerName + ", queueId=" + queueId + ", storeSize=" + storeSize + ", queueOffset=" + queueOffset
+ ", sysFlag=" + sysFlag + ", bornTimestamp=" + bornTimestamp + ", bornHost=" + bornHost
+ ", storeTimestamp=" + storeTimestamp + ", storeHost=" + storeHost + ", msgId=" + msgId
+ ", commitLogOffset=" + commitLogOffset + ", bodyCRC=" + bodyCRC + ", reconsumeTimes="
+ reconsumeTimes + ", preparedTransactionOffset=" + preparedTransactionOffset
+ ", toString()=" + super.toString() + "]";
}
- MessageClientExt类( 本类没有重写toString()方法,调用的是父类MessageExt的方法)
public class MessageClientExt extends MessageExt {
public String getOffsetMsgId() {
return super.getMsgId();
}
public void setOffsetMsgId(String offsetMsgId) {
super.setMsgId(offsetMsgId);
}
@Override
public String getMsgId() {
String uniqID = MessageClientIDSetter.getUniqID(this);
if (uniqID == null) {
return this.getOffsetMsgId();
} else {
return uniqID;
}
}
public void setMsgId(String msgId) {
//DO NOTHING
//MessageClientIDSetter.setUniqID(this);
}
}
四. Dashboard根据ID查询
- 界面显示的是 msgId,即uniqId
- RocketMQ会先调用queryMsgById方法,先通过msgId查询,查询无结果再通过 offsetMsgId 查询
- 界面新增显示 offsetMsgId 字段
MessageServiceImpl.viewMessage
String offsetMsgId = ((MessageClientExt) messageExt).getOffsetMsgId();
messageView.setOffsetMsgId(offsetMsgId);