java-sdk/daprdocs/content/en/java-sdk-docs/_index.md

type	title	linkTitle	weight	description
docs	Dapr Java SDK	Java	1000	Java SDK packages for developing Dapr applications

Pre-requisites

• [Dapr CLI]({{< ref install-dapr-cli.md >}}) installed
• Initialized [Dapr environment]({{< ref install-dapr-selfhost.md >}})
• JDK 11 or above - the published jars are compatible with Java 8:
  • AdoptOpenJDK 11 - LTS
  • Oracle's JDK 15
  • Oracle's JDK 11 - LTS
  • OpenJDK
• Install one of the following build tools for Java:
  • Maven 3.x
  • Gradle 6.x

Importing Dapr's Java SDK

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

<project>
  ...
  <dependencies>
    ...
     // Dapr's core SDK with all features, except Actors. 
    <dependency>
      <groupId>io.dapr</groupId>
      <artifactId>dapr-sdk</artifacetId>
      <version>1.1.0</version>
    </dependency>
    // Dapr's SDK for Actors (optional).
    <dependency>
      <groupId>io.dapr</groupId>
      <artifactId>dapr-sdk-actors</artifactId>
      <version>1.1.0</version>>
    </dependency>
    // Dapr's SDK integration with SpringBoot (optional).
    <dependency>
      <groupId>io.dapr</groupId>
      <artifactId>dapr-sdk-springboot</artifactId>
      <version>1.1.0</version>>
    </dependency>
    ...
  </dependencies>
  ...
</project>

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

dependencies {
...
    // Dapr's core SDK with all features, except Actors.
    compile('io.dapr:dapr-sdk:1.1.0'))
    // Dapr's SDK for Actors (optional).
    compile('io.dapr:dapr-sdk-actors:1.1.0')
    // Dapr's SDK integration with SpringBoot (optional).
    compile('io.dapr:dapr-sdk-springboot:1.1.0')
}

Building blocks

The Java SDK allows you to interface with all of the [Dapr building blocks]({{< ref building-blocks >}}).

Invoke a service

import io.dapr.client.DaprClient;
import io.dapr.client.DaprClientBuilder;

try (DaprClient client = (new DaprClientBuilder()).build()) {
  // invoke a 'GET' method (HTTP) skipping serialization: \say with a Mono<byte[]> return type
  // for gRPC set HttpExtension.NONE parameters below
  response = client.invokeMethod(SERVICE_TO_INVOKE, METHOD_TO_INVOKE, "{\"name\":\"World!\"}", HttpExtension.GET, byte[].class).block();

  // invoke a 'POST' method (HTTP) skipping serialization: to \say with a Mono<byte[]> return type     
  response = client.invokeMethod(SERVICE_TO_INVOKE, METHOD_TO_INVOKE, "{\"id\":\"100\", \"FirstName\":\"Value\", \"LastName\":\"Value\"}", HttpExtension.POST, byte[].class).block();

  System.out.println(new String(response));

  // invoke a 'POST' method (HTTP) with serialization: \employees with a Mono<Employee> return type      
  Employee newEmployee = new Employee("Nigel", "Guitarist");
  Employee employeeResponse = client.invokeMethod(SERVICE_TO_INVOKE, "employees", newEmployee, HttpExtension.POST, Employee.class).block();
}

• For a full guide on service invocation visit [How-To: Invoke a service]({{< ref howto-invoke-discover-services.md >}}).
• Visit Java SDK examples for code samples and instructions to try out service invocation

Save & get application state

import io.dapr.client.DaprClient;
import io.dapr.client.DaprClientBuilder;
import io.dapr.client.domain.State;
import reactor.core.publisher.Mono;

try (DaprClient client = (new DaprClientBuilder()).build()) {
  // Save state
  client.saveState(STATE_STORE_NAME, FIRST_KEY_NAME, myClass).block();

  // Get state
  State<MyClass> retrievedMessage = client.getState(STATE_STORE_NAME, FIRST_KEY_NAME, MyClass.class).block();

  // Delete state
  client.deleteState(STATE_STORE_NAME, FIRST_KEY_NAME).block();
}

• For a full list of state operations visit [How-To: Get & save state]({{< ref howto-get-save-state.md >}}).
• Visit Java SDK examples for code samples and instructions to try out state management

Publish & subscribe to messages

Publish messages

import io.dapr.client.DaprClient;
import io.dapr.client.DaprClientBuilder;
import io.dapr.client.domain.Metadata;
import static java.util.Collections.singletonMap;

try (DaprClient client = (new DaprClientBuilder()).build()) {
  client.publishEvent(PUBSUB_NAME, TOPIC_NAME, message, singletonMap(Metadata.TTL_IN_SECONDS, MESSAGE_TTL_IN_SECONDS)).block();
}

Subscribe to messages

import com.fasterxml.jackson.databind.ObjectMapper;
import io.dapr.Topic;
import io.dapr.client.domain.CloudEvent;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;
import reactor.core.publisher.Mono;

@RestController
public class SubscriberController {

  private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

  @Topic(name = "testingtopic", pubsubName = "${myAppProperty:messagebus}")
  @PostMapping(path = "/testingtopic")
  public Mono<Void> handleMessage(@RequestBody(required = false) CloudEvent cloudEvent) {
    return Mono.fromRunnable(() -> {
      try {
        System.out.println("Subscriber got: " + cloudEvent.getData());
        System.out.println("Subscriber got: " + OBJECT_MAPPER.writeValueAsString(cloudEvent));
      } catch (Exception e) {
        throw new RuntimeException(e);
      }
    });
  }

}

• For a full list of state operations visit [How-To: Publish & subscribe]({{< ref howto-publish-subscribe.md >}}).
• Visit Java SDK examples for code samples and instructions to try out pub/sub

Interact with output bindings

import io.dapr.client.DaprClient;
import io.dapr.client.DaprClientBuilder;

try (DaprClient client = (new DaprClientBuilder()).build()) {
  // sending a class with message; BINDING_OPERATION="create"
  client.invokeBinding(BINDING_NAME, BINDING_OPERATION, myClass).block();

  // sending a plain string
  client.invokeBinding(BINDING_NAME, BINDING_OPERATION, message).block();
}

• For a full guide on output bindings visit [How-To: Use bindings]({{< ref howto-bindings.md >}}).
• Visit Java SDK examples for code samples and instructions to try out output bindings

Retrieve secrets

import com.fasterxml.jackson.databind.ObjectMapper;
import io.dapr.client.DaprClient;
import io.dapr.client.DaprClientBuilder;
import java.util.Map;

try (DaprClient client = (new DaprClientBuilder()).build()) {
  Map<String, String> secret = client.getSecret(SECRET_STORE_NAME, secretKey).block();
  System.out.println(JSON_SERIALIZER.writeValueAsString(secret));
}

• For a full guide on secrets visit [How-To: Retrieve secrets]({{< ref howto-secrets.md >}}).
• Visit Java SDK examples for code samples and instructions to try out retrieving secrets

Actors

An actor is an isolated, independent unit of compute and state with single-threaded execution. Dapr provides an actor implementation based on the Virtual Actor pattern, which provides a single-threaded programming model and where actors are garbage collected when not in use. With Dapr's implementaiton, you write your Dapr actors according to the Actor model, and Dapr leverages the scalability and reliability that the underlying platform provides.

import io.dapr.actors.ActorMethod;
import io.dapr.actors.ActorType;
import reactor.core.publisher.Mono;

@ActorType(name = "DemoActor")
public interface DemoActor {

  void registerReminder();

  @ActorMethod(name = "echo_message")
  String say(String something);

  void clock(String message);

  @ActorMethod(returns = Integer.class)
  Mono<Integer> incrementAndGet(int delta);
}

• For a full guide on actors visit [How-To: Use virtual actors in Dapr]({{< ref howto-actors.md >}}).
• Visit Java SDK examples for code samples and instructions to try actors

Related links

• Java SDK examples