# 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](https://docs.dapr.io/developing-applications/building-blocks/pubsub/) 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](../sdk).

This quickstart includes one publisher:

- Java client message generator `checkout`

And one subscriber:

- Java subscriber `order-processor`

## Pre-requisites

* [Dapr and Dapr Cli](https://docs.dapr.io/getting-started/install-dapr-cli/).
* Java JDK 11 (or greater):
    * [Microsoft JDK 11](https://docs.microsoft.com/en-us/java/openjdk/download#openjdk-11)
    * [Oracle JDK 11](https://www.oracle.com/technetwork/java/javase/downloads/index.html#JDK11)
    * [OpenJDK 11](https://jdk.java.net/11/)
* [Apache Maven](https://maven.apache.org/install.html) version 3.x.

### Run Java message subscriber app with Dapr

1. Navigate to directory and install dependencies:
<!-- STEP
name: Install Java dependencies
-->

```bash
cd ./order-processor
mvn clean install
```
<!-- END_STEP -->

2. Run the Java subscriber app with Dapr:
<!-- STEP
name: Run Java publisher
expected_stdout_lines:
  - 'Subscriber received: 2'
  - "Exited App successfully"
expected_stderr_lines:
working_dir: ./order-processor
output_match_mode: substring
background: true
sleep: 10
-->
```bash
cd ./order-processor
 dapr run --app-port 8080 --app-id order-processor-http --components-path ../../../components -- java -jar target/OrderProcessingService-0.0.1-SNAPSHOT.jar
```
<!-- END_STEP -->
### Run Java message publisher app with Dapr

1. Navigate to the directory and install dependencies:

<!-- STEP
name: Install Java dependencies
-->

```bash
cd ./checkout
mvn clean install
```
<!-- END_STEP -->

2. Run the Java publisher app with Dapr:
<!-- STEP
name: Run Java publisher
expected_stdout_lines:
  - 'Published data: 1'
  - 'Published data: 2'
  - "Exited App successfully"
expected_stderr_lines:
working_dir: ./checkout
output_match_mode: substring
background: true
sleep: 10
-->

```bash
cd ./checkout
 dapr run --app-id checkout-http --components-path ../../../components -- java -jar target/CheckoutService-0.0.1-SNAPSHOT.jar
```
<!-- END_STEP -->

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