由于重连操作主要在后台进行，许多库都提供了事件监听器，以便在发生重连事件时通知你。对于发送大量消息的应用程序而言，此事件尤为重要。
{% tabs %} {% tab title="Go" %}
// Connection event handlers are invoked asynchronously
// and the state of the connection may have changed when
// the callback is invoked.
nc, err := nats.Connect("demo.nats.io",
nats.DisconnectErrHandler(func(nc *nats.Conn, err error) {
// handle disconnect error event
}),
nats.ReconnectHandler(func(nc *nats.Conn) {
// handle reconnect event
}))
if err != nil {
log.Fatal(err)
}
defer nc.Close()
// Do something with the connection{% endtab %}
{% tab title="Java" %}
class MyConnectionListener implements ConnectionListener {
public void connectionEvent(Connection conn, Events event) {
switch (event) {
case CONNECTED:
// The connection has successfully completed the handshake with the nats-server.
break;
case CLOSED:
// The connection is permanently closed, either by manual action or failed reconnects
break;
case DISCONNECTED:
// The connection lost its connection, but may try to reconnect if configured to
break;
case RECONNECTED:
// The connection was connected, lost its connection and successfully reconnected.
break;
case RESUBSCRIBED:
// The connection was reconnected and the server has been notified of all subscriptions.
break;
case DISCOVERED_SERVERS:
// The connection was made aware of new servers from the current server connection.
break;
case LAME_DUCK:
// connected server is coming down soon, might want to prepare for it
break;
}
}
}
MyConnectionListener listener = new MyConnectionListener();
Options options = new Options.Builder()
.server("nats://demo.nats.io:4222")
.connectionListener(listener)
.build();
Connection nc = Nats.connect(options);
// Do something with the connection
nc.close();{% endtab %}
{% tab title="JavaScript" %}
const nc = await connect({
maxReconnectAttempts: 10,
servers: ["demo.nats.io"],
});
(async () => {
for await (const s of nc.status()) {
switch (s.type) {
case Events.Reconnect:
t.log(`client reconnected - ${s.data}`);
break;
default:
}
}
})().then();
});{% endtab %}
{% tab title="Python" %}
nc = NATS()
async def disconnected_cb():
print("Got disconnected!")
async def reconnected_cb():
# See who we are connected to on reconnect.
print("Got reconnected to {url}".format(url=nc.connected_url.netloc))
await nc.connect(
servers=["nats://demo.nats.io:4222"],
reconnect_time_wait=10,
reconnected_cb=reconnected_cb,
disconnected_cb=disconnected_cb,
)
# Do something with the connection.{% endtab %}
{% tab title="C#" %}
// dotnet add package NATS.Net
using NATS.Net;
await using var client = new NatsClient();
client.Connection.ConnectionDisconnected += async (sender, args) =>
{
Console.WriteLine($"Disconnected: {args.Message}");
};
client.Connection.ConnectionOpened += async (sender, args) =>
{
Console.WriteLine($"Connected: {args.Message}");
};
client.Connection.ReconnectFailed += async (sender, args) =>
{
Console.WriteLine($"Reconnect Failed: {args.Message}");
};
await client.ConnectAsync();{% endtab %}
{% tab title="Ruby" %}
require 'nats/client'
NATS.start(servers: ["nats://127.0.0.1:1222", "nats://127.0.0.1:1223", "nats://127.0.0.1:1224"]) do |nc|
# Do something with the connection
nc.on_reconnect do
puts "Got reconnected to #{nc.connected_server}"
end
nc.on_disconnect do |reason|
puts "Got disconnected! #{reason}"
end
end{% endtab %}
{% tab title="C" %}
static void
disconnectedCB(natsConnection *conn, void *closure)
{
// Handle disconnect error event
}
static void
reconnectedCB(natsConnection *conn, void *closure)
{
// Handle reconnect event
}
(...)
natsConnection *conn = NULL;
natsOptions *opts = NULL;
natsStatus s = NATS_OK;
s = natsOptions_Create(&opts);
// Connection event handlers are invoked asynchronously
// and the state of the connection may have changed when
// the callback is invoked.
if (s == NATS_OK)
s = natsOptions_SetDisconnectedCB(opts, disconnectedCB, NULL);
if (s == NATS_OK)
s = natsOptions_SetReconnectedCB(opts, reconnectedCB, NULL);
if (s == NATS_OK)
s = natsConnection_Connect(&conn, opts);
(...)
// Destroy objects that were created
natsConnection_Destroy(conn);
natsOptions_Destroy(opts);{% endtab %} {% endtabs %}