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Receiving Structured Data
Client libraries may provide tools to help receive structured data, like JSON. The core traffic to the NATS server will always be opaque byte arrays. The server does not process message payloads in any form. For libraries that don't provide helpers, you can always encode and decode data before sending the associated bytes to the NATS client.
For example, to receive JSON you could do:
nc, err := nats.Connect("demo.nats.io")
if err != nil {
log.Fatal(err)
}
defer nc.Close()
ec, err := nats.NewEncodedConn(nc, nats.JSON_ENCODER)
if err != nil {
log.Fatal(err)
}
defer ec.Close()
// Define the object
type stock struct {
Symbol string
Price int
}
wg := sync.WaitGroup{}
wg.Add(1)
// Subscribe
if _, err := ec.Subscribe("updates", func(s *stock) {
log.Printf("Stock: %s - Price: %v", s.Symbol, s.Price)
wg.Done()
}); err != nil {
log.Fatal(err)
}
// Wait for a message to come in
wg.Wait()
class StockForJsonSub {
public String symbol;
public float price;
public String toString() {
return symbol + " is at " + price;
}
}
public class SubscribeJSON {
public static void main(String[] args) {
try {
Connection nc = Nats.connect("nats://demo.nats.io:4222");
// Use a latch to wait for 10 messages to arrive
CountDownLatch latch = new CountDownLatch(10);
// Create a dispatcher and inline message handler
Dispatcher d = nc.createDispatcher((msg) -> {
Gson gson = new Gson();
String json = new String(msg.getData(), StandardCharsets.UTF_8);
StockForJsonSub stk = gson.fromJson(json, StockForJsonSub.class);
// Use the object
System.out.println(stk);
latch.countDown();
});
// Subscribe
d.subscribe("updates");
// Wait for a message to come in
latch.await();
// Close the connection
nc.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
let nc = NATS.connect({
url: "nats://demo.nats.io:4222",
json: true
});
nc.subscribe('updates', (msg) => {
if(msg && msg.ticker === 'TSLA') {
t.log('got message:', msg);
}
});
import asyncio
import json
from nats.aio.client import Client as NATS
from nats.aio.errors import ErrTimeout
async def run(loop):
nc = NATS()
await nc.connect(servers=["nats://127.0.0.1:4222"], loop=loop)
async def message_handler(msg):
data = json.loads(msg.data.decode())
print(data)
sid = await nc.subscribe("updates", cb=message_handler)
await nc.flush()
await nc.auto_unsubscribe(sid, 2)
await nc.publish("updates", json.dumps({"symbol": "GOOG", "price": 1200 }).encode())
await asyncio.sleep(1, loop=loop)
await nc.close()