quickstarts/pub_sub/java/http

Dapr pub/sub

In this quickstart, there is a publisher microservice checkout and a subscriber microservice order-processor to demonstrate how Dapr enables a publish-subscribe pattern. checkout generates messages and publishes to a specific orders topic, and order-processor subscribers listen for messages of topic orders.

Visit this link for more information about Dapr and Pub-Sub.

Note: This example leverages HTTPClient only. If you are looking for the example using the Dapr Client SDK (recommended) click here.

This quickstart includes one publisher:

• Java client message generator checkout

And one subscriber:

• Java subscriber order-processor

Pre-requisites

• Dapr and Dapr Cli.
• Java JDK 17 (or greater):
  • Microsoft JDK 17
  • Oracle JDK 17
  • OpenJDK 17
• Apache Maven version 3.x.

Run all apps with multi-app run template file:

This section shows how to run both applications at once using multi-app run template files with dapr run -f .. This enables to you test the interactions between multiple applications.

1. Install dependencies:

cd ./order-processor
mvn clean install
cd ..
cd ./checkout
mvn clean install
cd ..

2. Open a new terminal window and run the multi app run template:

dapr run -f .

The terminal console output should look similar to this:

== APP - order-processor-http == 2023-09-04 14:25:37.624  INFO 88784 --- [nio-8080-exec-1] c.s.c.OrderProcessingServiceController   : Subscriber received: 1
== APP - checkout-http == 1175 [main] INFO com.service.CheckoutServiceApplication - Published data: 2
== APP - order-processor-http == 2023-09-04 14:25:38.558  INFO 88784 --- [nio-8080-exec-2] c.s.c.OrderProcessingServiceController   : Subscriber received: 2
== APP - checkout-http == 2184 [main] INFO com.service.CheckoutServiceApplication - Published data: 3
== APP - order-processor-http == 2023-09-04 14:25:39.567  INFO 88784 --- [nio-8080-exec-3] c.s.c.OrderProcessingServiceController   : Subscriber received: 3
== APP - checkout-http == 3195 [main] INFO com.service.CheckoutServiceApplication - Published data: 4
== APP - order-processor-http == 2023-09-04 14:25:40.578  INFO 88784 --- [nio-8080-exec-4] c.s.c.OrderProcessingServiceController   : Subscriber received: 4
== APP - checkout-http == 4203 [main] INFO com.service.CheckoutServiceApplication - Published data: 5
== APP - order-processor-http == 2023-09-04 14:25:41.586  INFO 88784 --- [nio-8080-exec-5] c.s.c.OrderProcessingServiceController   : Subscriber received: 5
== APP - checkout-http == 5215 [main] INFO com.service.CheckoutServiceApplication - Published data: 6
== APP - order-processor-http == 2023-09-04 14:25:42.600  INFO 88784 --- [nio-8080-exec-6] c.s.c.OrderProcessingServiceController   : Subscriber received: 6
== APP - checkout-http == 6219 [main] INFO com.service.CheckoutServiceApplication - Published data: 7
== APP - order-processor-http == 2023-09-04 14:25:43.601  INFO 88784 --- [nio-8080-exec-7] c.s.c.OrderProcessingServiceController   : Subscriber received: 7
== APP - checkout-http == 7224 [main] INFO com.service.CheckoutServiceApplication - Published data: 8
== APP - order-processor-http == 2023-09-04 14:25:44.607  INFO 88784 --- [nio-8080-exec-8] c.s.c.OrderProcessingServiceController   : Subscriber received: 8
== APP - checkout-http == 8229 [main] INFO com.service.CheckoutServiceApplication - Published data: 9
== APP - order-processor-http == 2023-09-04 14:25:45.612  INFO 88784 --- [nio-8080-exec-9] c.s.c.OrderProcessingServiceController   : Subscriber received: 9
== APP - checkout-http == 9237 [main] INFO com.service.CheckoutServiceApplication - Published data: 10
== APP - order-processor-http == 2023-09-04 14:25:46.620  INFO 88784 --- [io-8080-exec-10] c.s.c.OrderProcessingServiceController   : Subscriber received: 10

3. Stop and clean up application processes

dapr stop -f .

Run a single app at a time with Dapr (Optional)

An alternative to running all or multiple applications at once is to run single apps one-at-a-time using multiple dapr run .. -- dotnet run commands. This next section covers how to do this.

Run Java message subscriber app with Dapr

1. Navigate to directory and install dependencies:

cd ./order-processor
mvn clean install

2. Run the Java subscriber app with Dapr:

cd ./order-processor
 dapr run --app-port 8080 --app-id order-processor-http --resources-path ../../../components -- java -jar target/OrderProcessingService-0.0.1-SNAPSHOT.jar

Run Java message publisher app with Dapr

1. Navigate to the directory and install dependencies:

cd ./checkout
mvn clean install

2. Run the Java publisher app with Dapr:

cd ./checkout
 dapr run --app-id checkout-http --resources-path ../../../components -- java -jar target/CheckoutService-0.0.1-SNAPSHOT.jar

dapr stop --app-id checkout-http
dapr stop --app-id order-processor-http