通配符订阅

订阅时使用 通配符主题 无需特殊代码。通配符是主题名称的正常组成部分。不过，根据传入消息所携带的主题来确定如何处理该消息是一个常用的技巧。

例如，您可以使用 * 进行订阅，然后根据实际主题采取行动。

Go

nc, err := nats.Connect("demo.nats.io")
if err != nil {
    log.Fatal(err)
}
defer nc.Close()

// Use a WaitGroup to wait for 2 messages to arrive
wg := sync.WaitGroup{}
wg.Add(2)

// Subscribe
if _, err := nc.Subscribe("time.*.east", func(m *nats.Msg) {
    log.Printf("%s: %s", m.Subject, m.Data)
    wg.Done()
}); err != nil {
    log.Fatal(err)
}

// Wait for the 2 messages to come in
wg.Wait()

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or do something similar with >:

Go

nc, err := nats.Connect("demo.nats.io")
if err != nil {
    log.Fatal(err)
}
defer nc.Close()

// Use a WaitGroup to wait for 4 messages to arrive
wg := sync.WaitGroup{}
wg.Add(4)

// Subscribe
if _, err := nc.Subscribe("time.>", func(m *nats.Msg) {
    log.Printf("%s: %s", m.Subject, m.Data)
    wg.Done()
}); err != nil {
    log.Fatal(err)
}

// Wait for the 4 messages to come in
wg.Wait()

// Close the connection
nc.Close()

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The following example can be used to test these two subscribers. The * subscriber should receive at most 2 messages, while the > subscriber receives 4. More importantly the time.*.east subscriber won't receive on time.us.east.atlanta because that won't match.

Go

nc, err := nats.Connect("demo.nats.io")
if err != nil {
    log.Fatal(err)
}
defer nc.Close()

zoneID, err := time.LoadLocation("America/New_York")
if err != nil {
    log.Fatal(err)
}
now := time.Now()
zoneDateTime := now.In(zoneID)
formatted := zoneDateTime.String()

nc.Publish("time.us.east", []byte(formatted))
nc.Publish("time.us.east.atlanta", []byte(formatted))

zoneID, err = time.LoadLocation("Europe/Warsaw")
if err != nil {
    log.Fatal(err)
}
zoneDateTime = now.In(zoneID)
formatted = zoneDateTime.String()

nc.Publish("time.eu.east", []byte(formatted))
nc.Publish("time.eu.east.warsaw", []byte(formatted))

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