Dapr SDK for Java

This is the Dapr SDK for Java, including the following features:

• PubSub
• Service Invocation
• Binding
• State Store
• Actors

Getting Started

Pre-Requisites

• Java IDE installed:
  • IntelliJ
  • Eclipse
  • Apache NetBeans
  • Visual Studio Code
  • Any other IDE for Java that you prefer.
• Install one of the following build tools for Java:
  • Maven 3.x
  • Gradle 6.x
• If needed, install the corresponding plugin for the build tool in your IDE, for example:
  • Maven in IntelliJ
  • Gradle in IntelliJ
  • Maven in Eclipse with m2e
  • Gradle in Eclipse with Buildship
• An existing Java Maven or Gradle project. You may also start a new project via one of the options below:
  • New Maven project in IntelliJ
  • Maven in 5 minutes

Importing Dapr's Java SDK

For a Maven project, add the following to your pom.xml file:

<project>
  ...
  <repositories>
    ...
    <!-- BEGIN: Dapr's repositories -->
    <repository>
      <id>oss-snapshots</id>
      <url>https://oss.sonatype.org/content/repositories/snapshots</url>
    </repository>
    <repository>
      <id>oss-release</id>
      <url>https://oss.sonatype.org/content/repositories/releases/</url>
    </repository>
    <!-- END: Dapr's repositories -->
    ...
  </repositories>
  ...
  <dependencyManagement>
      <dependencies>
        ...
         <!-- Dapr's core SDK with all features, except Actors. -->
        <dependency>
          <groupId>io.dapr</groupId>
          <artifactId>dapr-sdk</artifactId>
          <version>0.10.0</version>
        </dependency>
        <!-- Dapr's SDK for Actors (optional). -->
        <dependency>
          <groupId>io.dapr</groupId>
          <artifactId>dapr-sdk-actors</artifactId>
          <version>0.10.0</version>
        </dependency>
        <!-- Dapr's SDK integration with SpringBoot (optional). -->
        <dependency>
          <groupId>io.dapr</groupId>
          <artifactId>dapr-sdk-springboot</artifactId>
          <version>0.10.0</version>
        </dependency>
        <!-- If needed, resolve version conflict of okhttp3. -->
        <dependency>
          <groupId>com.squareup.okhttp3</groupId>
          <artifactId>okhttp</artifactId>
          <version>4.2.2</version> <!-- version required by Dapr's sdk -->
        </dependency>
        ...
      </dependencies>
  </dependencyManagement>
</project>

For a Gradle project, add the following to your build.gradle file:

repositories {
    ...
    // Dapr repositories
    maven {
      url "https://oss.sonatype.org/content/repositories/snapshots"
	  mavenContent {
	    snapshotsOnly()
	  }
    }
    maven {
	  url "https://oss.sonatype.org/content/repositories/releases/"
    }
}
...
dependencies {
...
    // Dapr's core SDK with all features, except Actors.
    compile('io.dapr:dapr-sdk:0.10.0')
    // Dapr's SDK for Actors (optional).
    compile('io.dapr:dapr-sdk-actors:0.10.0')
    // Dapr's SDK integration with SpringBoot (optional).
    compile('io.dapr:dapr-sdk-springboot:0.10.0')

    // If needed, force conflict resolution for okhttp3.
    configurations.all {
        resolutionStrategy.force 'com.squareup.okhttp3:okhttp:4.2.2'
    }
}

Running the examples

Clone this repository including the submodules:

git clone https://github.com/dapr/java-sdk.git

Then head over to build the Maven (Apache Maven version 3.x) project:

# make sure you are in the `java-sdk` directory.
mvn clean install

Try the following examples to learn more about Dapr's Java SDK:

• Invoking a Http service
• Invoking a Grpc service
• State management
• PubSub with subscriber over Http
• Binding with input over Http
• Actors
• Secrets management
• Distributed tracing with OpenTelemetry SDK
• Exception handling

API Documentation

Please, refer to our Javadoc website.

Reactor API

The Java SDK for Dapr is built using Project Reactor. It provides an asynchronous API for Java. When consuming a result is consumed synchronously, as in the examples referenced above, the block() method is used.

The code below does not make any API call, it simply returns the Mono publisher object. Nothing happens until the application subscribes or blocks on the result:

Mono<Void> result = daprClient.publishEvent("mytopic", "my message");

To start execution and receive the result object synchronously(void or Void becomes an empty result), use block(). The code below shows how to execute the call and consume an empty response:

Mono<Void> result = daprClient.publishEvent("mytopic", "my message");
result.block();

How to use a custom serializer

This SDK provides a basic serialization for request/response objects but also for state objects. Applications should provide their own serialization for production scenarios.

1. Implement the DaprObjectSerializer interface. See this class as example.
2. Use your serializer class in the following scenarios:
   • When building a new instance of DaprClient:

   DaprClient client = (new DaprClientBuilder())
       .withObjectSerializer(new MyObjectSerializer()) // for request/response objects.
       .withStateSerializer(new MyStateSerializer()) // for state objects.
       .build();

   • When registering an Actor Type:

   ActorRuntime.getInstance().registerActor(
     DemoActorImpl.class,
     new MyObjectSerializer(), // for request/response objects.
     new MyStateSerializer()); // for state objects.

   • When building a new instance of ActorProxy to invoke an Actor instance, use the same serializer as when registering the Actor Type:

   ActorProxy actor = (new ActorProxyBuilder("DemoActor"))
       .withObjectSerializer(new MyObjectSerializer()) // for request/response objects.
       .build();

Debug Java application or Dapr's Java SDK

In IntelliJ Community Edition, consider debugging in IntelliJ.

In Visual Studio Code, consider debugging in Visual Studio Code.

If you have a Java application or an issue on this SDK that needs to be debugged, run Dapr using a dummy command and start the application from your IDE (IntelliJ, for example). For Linux and MacOS:

dapr run --app-id testapp --app-port 3000 --dapr-http-port 3500 --dapr-grpc-port 5001 -- cat

For Windows:

dapr run --app-id testapp --app-port 3000 --dapr-http-port 3500 --dapr-grpc-port 5001 -- waitfor FOREVER

When running your Java application from IDE, make sure the following environment variables are set, so the Java SDK knows how to connect to Dapr's sidecar:

DAPR_HTTP_PORT=3500
DAPR_GRPC_PORT=5001

Now you can go to your IDE (like Eclipse, for example) and debug your Java application, using port 3500 to call Dapr while also listening to port 3000 to expose Dapr's callback endpoint.

Calls to Dapr's APIs on http://127.0.0.1:3500/* should work now and trigger breakpoints in your code.

Exception handling

All exceptions thrown from the SDK are instances of DaprException. DaprException extends from RuntimeException, making it compatible with Project Reactor. See example for more details.

Development

Update proto files

Change the properties below in pom.xml to point to the desired reference URL in Git. Avoid pointing to master branch since it can change over time and create unpredictable behavior in the build.

<project>
  ...
  <properties>
    ...
    <dapr.proto.url>https://raw.githubusercontent.com/dapr/dapr/v0.4.0/pkg/proto/dapr/dapr.proto</dapr.proto.url>
    <dapr.client.proto.url>https://raw.githubusercontent.com/dapr/dapr/v0.4.0/pkg/proto/daprclient/daprclient.proto</dapr.client.proto.url>
    ...
  </properties>
  ...
</project>