The documentation you are viewing is for Dapr v1.13 which is an older version of Dapr. For up-to-date documentation, see the latest version.
指南：发布消息并订阅主题
了解如何使用一个服务向主题发送消息，并在另一个服务中订阅该主题
现在，你已了解 Dapr 发布/订阅 构建块提供的功能，请了解它如何在你的服务中工作。 下面的示例代码粗略地描述了一个使用两个服务处理订单的应用程序，每个服务都使用 Dapr sidecars：
- 使用 Dapr 订阅消息队列中主题的结帐服务。
- 使用 Dapr 向 RabbitMQ 发布消息的订单处理服务。
Dapr 将在符合 CloudEvents v1.0 的信封中自动包装用户有效负载，对 Content-Type 头值使用 datacontenttype 属性。 了解更多关于使用CloudEvents的消息。
下面的示例演示了您的应用程序如何发布和订阅名为orders的主题。
注意
如果你还没有，请尝试使用发布/订阅快速入门快速了解如何使用发布/订阅。设置 发布/订阅 组件
第一步是设置 发布/订阅 组件：
When you run dapr init, Dapr creates a default Redis pubsub.yaml and runs a Redis container on your local machine, located:
- 在Windows上，在
%UserProfile%\.dapr\components\pubsub.yaml - 在Linux/MacOS上，在
~/.dapr/components/pubsub.yaml
使用 pubsub.yaml 组件，您可以轻松更换底层组件而无需更改应用程序代码。 在此示例中，我们使用 RabbitMQ。
apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
name: order-pub-sub
spec:
type: pubsub.rabbitmq
version: v1
metadata:
- name: host
value: "amqp://localhost:5672"
- name: durable
value: "false"
- name: deletedWhenUnused
value: "false"
- name: autoAck
value: "false"
- name: reconnectWait
value: "0"
- name: concurrency
value: parallel
scopes:
- orderprocessing
- checkout
您可以通过创建一个包含该文件的组件目录（在此示例中为myComponents），并在使用dapr run命令行界面时使用--resources-path标志，来使用另一个pubsub component来覆盖此文件。
dapr run --app-id myapp --resources-path ./myComponents -- dotnet run
dapr run --app-id myapp --resources-path ./myComponents -- mvn spring-boot:run
dapr run --app-id myapp --resources-path ./myComponents -- python3 app.py
dapr run --app-id myapp --resources-path ./myComponents -- go run app.go
dapr run --app-id myapp --resources-path ./myComponents -- npm start
To deploy this into a Kubernetes cluster, fill in the metadata connection details of the pub/sub component in the YAML below, save as pubsub.yaml, and run kubectl apply -f pubsub.yaml.
apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
name: order-pub-sub
spec:
type: pubsub.rabbitmq
version: v1
metadata:
- name: connectionString
value: "amqp://localhost:5672"
- name: protocol
value: amqp
- name: hostname
value: localhost
- name: username
value: username
- name: password
value: password
- name: durable
value: "false"
- name: deletedWhenUnused
value: "false"
- name: autoAck
value: "false"
- name: reconnectWait
value: "0"
- name: concurrency
value: parallel
scopes:
- orderprocessing
- checkout
订阅主题
Dapr 允许您的应用程序有两种方法来订阅 topics：
- 声明，其中订阅是在外部文件中定义的。
- 编程式，订阅在用户代码中定义。
详细了解声明式和程序化订阅方法文档。 这个示例演示了一个声明式订阅。
创建一个名为subscription.yaml的文件，并粘贴以下内容：
apiVersion: dapr.io/v2alpha1
kind: Subscription
metadata:
name: order-pub-sub
spec:
topic: orders
routes:
default: /checkout
pubsubname: order-pub-sub
scopes:
- orderprocessing
- checkout
上面的示例显示了对主题 orders 的事件订阅，用于 pubsub 组件 order-pub-sub。
route字段告诉Dapr将所有主题消息发送到应用程序中的/checkout端点。scopes字段使得此订阅适用于具有orderprocessing和checkout的应用程序。
将 subscription.yaml 放在与你的 pubsub.yaml 组件相同的目录中。 当 Dapr 启动时，它将加载组件和订阅。
下面是利用 Dapr SDK 订阅你在 subscription.yaml 中定义的主题的代码示例。
//dependencies
using System.Collections.Generic;
using System.Threading.Tasks;
using System;
using Microsoft.AspNetCore.Mvc;
using Dapr;
using Dapr.Client;
//code
namespace CheckoutService.controller
{
[ApiController]
public class CheckoutServiceController : Controller
{
//Subscribe to a topic
[Topic("order-pub-sub", "orders")]
[HttpPost("checkout")]
public void getCheckout([FromBody] int orderId)
{
Console.WriteLine("Subscriber received : " + orderId);
}
}
}
导航到包含上述代码的目录，然后运行以下命令启动 Dapr sidecar 和订阅程序：
dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 --app-protocol https dotnet run
//dependencies
import io.dapr.Topic;
import io.dapr.client.domain.CloudEvent;
import org.springframework.web.bind.annotation.*;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import reactor.core.publisher.Mono;
//code
@RestController
public class CheckoutServiceController {
private static final Logger log = LoggerFactory.getLogger(CheckoutServiceController.class);
//Subscribe to a topic
@Topic(name = "orders", pubsubName = "order-pub-sub")
@PostMapping(path = "/checkout")
public Mono<Void> getCheckout(@RequestBody(required = false) CloudEvent<String> cloudEvent) {
return Mono.fromRunnable(() -> {
try {
log.info("Subscriber received: " + cloudEvent.getData());
} catch (Exception e) {
throw new RuntimeException(e);
}
});
}
}
导航到包含上述代码的目录，然后运行以下命令启动 Dapr sidecar 和订阅程序：
dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 mvn spring-boot:run
#dependencies
from cloudevents.sdk.event import v1
from dapr.ext.grpc import App
import logging
import json
#code
app = App()
logging.basicConfig(level = logging.INFO)
#Subscribe to a topic
@app.subscribe(pubsub_name='order-pub-sub', topic='orders')
def mytopic(event: v1.Event) -> None:
data = json.loads(event.Data())
logging.info('Subscriber received: ' + str(data))
app.run(6002)
导航到包含上述代码的目录，然后运行以下命令启动 Dapr sidecar 和订阅程序：
dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --app-protocol grpc -- python3 CheckoutService.py
//dependencies
import (
"log"
"net/http"
"context"
"github.com/dapr/go-sdk/service/common"
daprd "github.com/dapr/go-sdk/service/http"
)
//code
var sub = &common.Subscription{
PubsubName: "order-pub-sub",
Topic: "orders",
Route: "/checkout",
}
func main() {
s := daprd.NewService(":6002")
//Subscribe to a topic
if err := s.AddTopicEventHandler(sub, eventHandler); err != nil {
log.Fatalf("error adding topic subscription: %v", err)
}
if err := s.Start(); err != nil && err != http.ErrServerClosed {
log.Fatalf("error listenning: %v", err)
}
}
func eventHandler(ctx context.Context, e *common.TopicEvent) (retry bool, err error) {
log.Printf("Subscriber received: %s", e.Data)
return false, nil
}
导航到包含上述代码的目录，然后运行以下命令启动 Dapr sidecar 和订阅程序：
dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 go run CheckoutService.go
//dependencies
import { DaprServer, CommunicationProtocolEnum } from '@dapr/dapr';
//code
const daprHost = "127.0.0.1";
const serverHost = "127.0.0.1";
const serverPort = "6002";
start().catch((e) => {
console.error(e);
process.exit(1);
});
async function start(orderId) {
const server = new DaprServer({
serverHost,
serverPort,
communicationProtocol: CommunicationProtocolEnum.HTTP,
clientOptions: {
daprHost,
daprPort: process.env.DAPR_HTTP_PORT,
},
});
//Subscribe to a topic
await server.pubsub.subscribe("order-pub-sub", "orders", async (orderId) => {
console.log(`Subscriber received: ${JSON.stringify(orderId)}`)
});
await server.start();
}
导航到包含上述代码的目录，然后运行以下命令启动 Dapr sidecar 和订阅程序：
dapr run --app-id checkout --app-port 6002 --dapr-http-port 3602 --dapr-grpc-port 60002 npm start
发布消息
用名为 orderprocessing 的 app-id 启动一个 Dapr 实例：
dapr run --app-id orderprocessing --dapr-http-port 3601
然后发布一条消息给 orders 主题:
dapr publish --publish-app-id orderprocessing --pubsub order-pub-sub --topic orders --data '{"orderId": "100"}'
curl -X POST http://localhost:3601/v1.0/publish/order-pub-sub/orders -H "Content-Type: application/json" -d '{"orderId": "100"}'
Invoke-RestMethod -Method Post -ContentType 'application/json' -Body '{"orderId": "100"}' -Uri 'http://localhost:3601/v1.0/publish/order-pub-sub/orders'
下面是利用 Dapr SDK 发布主题的代码示例。
//dependencies
using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;
using Dapr.Client;
using Microsoft.AspNetCore.Mvc;
using System.Threading;
//code
namespace EventService
{
class Program
{
static async Task Main(string[] args)
{
string PUBSUB_NAME = "order-pub-sub";
string TOPIC_NAME = "orders";
while(true) {
System.Threading.Thread.Sleep(5000);
Random random = new Random();
int orderId = random.Next(1,1000);
CancellationTokenSource source = new CancellationTokenSource();
CancellationToken cancellationToken = source.Token;
using var client = new DaprClientBuilder().Build();
//Using Dapr SDK to publish a topic
await client.PublishEventAsync(PUBSUB_NAME, TOPIC_NAME, orderId, cancellationToken);
Console.WriteLine("Published data: " + orderId);
}
}
}
}
导航到包含上述代码的目录，然后运行以下命令启动 Dapr sidecar 和发布程序：
dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 --app-protocol https dotnet run
//dependencies
import io.dapr.client.DaprClient;
import io.dapr.client.DaprClientBuilder;
import io.dapr.client.domain.Metadata;
import static java.util.Collections.singletonMap;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.Random;
import java.util.concurrent.TimeUnit;
//code
@SpringBootApplication
public class OrderProcessingServiceApplication {
private static final Logger log = LoggerFactory.getLogger(OrderProcessingServiceApplication.class);
public static void main(String[] args) throws InterruptedException{
String MESSAGE_TTL_IN_SECONDS = "1000";
String TOPIC_NAME = "orders";
String PUBSUB_NAME = "order-pub-sub";
while(true) {
TimeUnit.MILLISECONDS.sleep(5000);
Random random = new Random();
int orderId = random.nextInt(1000-1) + 1;
DaprClient client = new DaprClientBuilder().build();
//Using Dapr SDK to publish a topic
client.publishEvent(
PUBSUB_NAME,
TOPIC_NAME,
orderId,
singletonMap(Metadata.TTL_IN_SECONDS, MESSAGE_TTL_IN_SECONDS)).block();
log.info("Published data:" + orderId);
}
}
}
导航到包含上述代码的目录，然后运行以下命令启动 Dapr sidecar 和发布程序：
dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 mvn spring-boot:run
#dependencies
import random
from time import sleep
import requests
import logging
import json
from dapr.clients import DaprClient
#code
logging.basicConfig(level = logging.INFO)
while True:
sleep(random.randrange(50, 5000) / 1000)
orderId = random.randint(1, 1000)
PUBSUB_NAME = 'order-pub-sub'
TOPIC_NAME = 'orders'
with DaprClient() as client:
#Using Dapr SDK to publish a topic
result = client.publish_event(
pubsub_name=PUBSUB_NAME,
topic_name=TOPIC_NAME,
data=json.dumps(orderId),
data_content_type='application/json',
)
logging.info('Published data: ' + str(orderId))
导航到包含上述代码的目录，然后运行以下命令启动 Dapr sidecar 和发布程序：
dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --app-protocol grpc python3 OrderProcessingService.py
//dependencies
import (
"context"
"log"
"math/rand"
"time"
"strconv"
dapr "github.com/dapr/go-sdk/client"
)
//code
var (
PUBSUB_NAME = "order-pub-sub"
TOPIC_NAME = "orders"
)
func main() {
for i := 0; i < 10; i++ {
time.Sleep(5000)
orderId := rand.Intn(1000-1) + 1
client, err := dapr.NewClient()
if err != nil {
panic(err)
}
defer client.Close()
ctx := context.Background()
//Using Dapr SDK to publish a topic
if err := client.PublishEvent(ctx, PUBSUB_NAME, TOPIC_NAME, []byte(strconv.Itoa(orderId)));
err != nil {
panic(err)
}
log.Println("Published data: " + strconv.Itoa(orderId))
}
}
导航到包含上述代码的目录，然后运行以下命令启动 Dapr sidecar 和发布程序：
dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 go run OrderProcessingService.go
//dependencies
import { DaprServer, DaprClient, CommunicationProtocolEnum } from '@dapr/dapr';
const daprHost = "127.0.0.1";
var main = function() {
for(var i=0;i<10;i++) {
sleep(5000);
var orderId = Math.floor(Math.random() * (1000 - 1) + 1);
start(orderId).catch((e) => {
console.error(e);
process.exit(1);
});
}
}
async function start(orderId) {
const PUBSUB_NAME = "order-pub-sub"
const TOPIC_NAME = "orders"
const client = new DaprClient({
daprHost,
daprPort: process.env.DAPR_HTTP_PORT,
communicationProtocol: CommunicationProtocolEnum.HTTP
});
console.log("Published data:" + orderId)
//Using Dapr SDK to publish a topic
await client.pubsub.publish(PUBSUB_NAME, TOPIC_NAME, orderId);
}
function sleep(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
main();
导航到包含上述代码的目录，然后运行以下命令启动 Dapr sidecar 和发布程序：
dapr run --app-id orderprocessing --app-port 6001 --dapr-http-port 3601 --dapr-grpc-port 60001 npm start
消息确认和重试
为了告诉Dapr消息处理成功，返回一个200 OK响应。 如果 Dapr 收到超过 200 的返回状态代码，或者你的应用崩溃，Dapr 将根据 At-Least-Once 语义尝试重新传递消息。
演示视频
观看此演示视频以了解使用Dapr进行发布/订阅消息传递的更多信息。
下一步
- 尝试一下pub/sub（发布/订阅）教程。
- 了解messaging with CloudEvents以及您可能想要在没有CloudEvents的情况下发送消息。
- 查看列表 发布/订阅组件。
- 阅读API参考。
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