GitHub - restatedev/sdk-java: Restate SDK for JVM Languages

Restate is a system for easily building resilient applications using distributed durable async/await. This repository contains the Restate SDK for writing services using JVM languages.

This SDK features:

Implement Restate services using either:
- Java
- Kotlin coroutines
Deploy Restate services as:
- Non-blocking HTTP servers
- On AWS Lambda

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Using the SDK

Prerequisites

JDK >= 17

tl;dr Use project templates

To get started, follow the Java quickstart or the Kotlin quickstart.

Setup a project (Java)

Scaffold a project using the build tool of your choice. For example, with Gradle (Kotlin script):

gradle init --type java-application

Add the annotation processor dependency sdk-api-gen, and then, depending on whether you want to deploy using HTTP or Lambda, use the appropriate dependency:

annotationProcessor("dev.restate:sdk-api-gen:2.7.0")

// For HTTP services
implementation("dev.restate:sdk-java-http:2.7.0")
// For Lambda services
// implementation("dev.restate:sdk-java-lambda:2.7.0")

Setup a project (Kotlin)

Scaffold a project using the build tool of your choice. For example, with Gradle (Kotlin script):

gradle init --type kotlin-application

Add the Kotlin symbol processing plugin:

plugins {
    id("com.google.devtools.ksp") version "2.2.10-2.0.2"
}

Add the ksp dependency sdk-api-gen, and then, depending on whether you want to deploy using HTTP or Lambda, use the appropriate dependency:

ksp("dev.restate:sdk-api-kotlin-gen:2.7.0")

// For HTTP services
implementation("dev.restate:sdk-kotlin-http:2.7.0")
// For Lambda services
// implementation("dev.restate:sdk-kotlin-lambda:2.7.0")

Implement your first Restate component (Java)

Implement your first virtual object in a new class, for example:

import dev.restate.sdk.ObjectContext;
import dev.restate.sdk.annotation.Handler;
import dev.restate.sdk.annotation.VirtualObject;
import dev.restate.sdk.common.StateKey;

@VirtualObject
public class Greeter {

  private static final StateKey<Long> COUNT = StateKey.of("total", Long.class);

  @Handler
  public String greet(ObjectContext ctx, String name) {
    long count = ctx.get(COUNT).orElse(0L);
    ctx.set(COUNT, count + 1);

    return String.format("Hello %s for the %d time!", name, count);
  }
}

By default, Jackson Databind will be used for serialization/deserialization. You can override this configuration by customizing the SerdeFactory, check out the javadocs for more details.

Implement your first Restate component (Kotlin)

Implement your first virtual object in a new class, for example:

import dev.restate.sdk.annotation.*
import dev.restate.sdk.kotlin.*

@VirtualObject
class Greeter {
  companion object {
    private val COUNT = stateKey("total")
  }

  @Handler
  suspend fun greet(context: ObjectContext, name: String): String {
    val count = context.get(COUNT) ?: 0L
    context.set(COUNT, count + 1)
    return "Hello $name for the $count time!"
  }
}

By default kotlinx.serialization will be used for serialization/deserialization. You can override this configuration by customizing the SerdeFactory, check out the javadocs for more details.

Deploy the service (HTTP Server)

To deploy the Restate service as HTTP server, add the following code to the main. For example in Java:

public static void main(String[] args) {
  RestateHttpServer.listen(
    Endpoint.bind(new Greeter())
  );
}

In Kotlin:

fun main() {
  RestateHttpServer.listen(
    endpoint {
      bind(Greeter())
    }
  )
}

Execute the project. For example, using Gradle:

Deploy the service (AWS Lambda)

To deploy the Restate service as Lambda, configure the build tool to generate Fat-JARs, which are required by AWS Lambda to correctly load the JAR. For example, using Gradle:

plugins {
  // ...
  // The shadow plugin generates a shadow JAR ready for AWS Lambda
  id("com.github.johnrengelman.shadow").version("7.1.2")
  // ...
}

Now create the Lambda handler invoking the service. For example, in Java:

public class MyLambdaHandler extends BaseRestateLambdaHandler {
  @Override
  public void register(Endpoint.Builder builder) {
    builder.bind(new Greeter());
  }
}

In Kotlin:

class MyLambdaHandler : BaseRestateLambdaHandler {
  override fun register(builder: Endpoint.Builder) {
    builder.bind(Greeter())
  }
}

Now build the Fat-JAR. For example, using Gradle:

You can now upload the generated Jar in AWS Lambda, and configure MyLambdaHandler as the Lambda class in the AWS UI.

Additional setup

Logging

The SDK uses log4j2 as logging facade, to configure it add the file resources/log4j2.properties:

# Set to debug or trace if log4j initialization is failing
status = warn

# Console appender configuration
appender.console.type = Console
appender.console.name = consoleLogger
appender.console.layout.type = PatternLayout
appender.console.layout.pattern = %d{yyyy-MM-dd HH:mm:ss} %-5p %notEmpty{[%X{restateInvocationTarget}]}%notEmpty{[%X{restateInvocationId}]} %c - %m%n

# Filter out logging during replay
appender.console.filter.replay.type = ContextMapFilter
appender.console.filter.replay.onMatch = DENY
appender.console.filter.replay.onMismatch = NEUTRAL
appender.console.filter.replay.0.type = KeyValuePair
appender.console.filter.replay.0.key = restateInvocationStatus
appender.console.filter.replay.0.value = REPLAYING

# Restate logs to debug level
logger.app.name = dev.restate
logger.app.level = info
logger.app.additivity = false
logger.app.appenderRef.console.ref = consoleLogger

# Root logger
rootLogger.level = info
rootLogger.appenderRef.stdout.ref = consoleLogger

The SDK injects the following additional metadata to the logging context that can be used for filtering as well:

restateInvocationTarget: invocation target, e.g. counter.Counter/Add.
restateInvocationId: Invocation identifier, to be used in Restate observability tools. See https://docs.restate.dev/operate/invocation#invocation-identifier.
restateInvocationStatus: Invocation status, can be WAITING_START, REPLAYING, PROCESSING, CLOSED.

The dependencies sdk-java-http, sdk-java-lambda, sdk-kotlin-http and sdk-kotlin-lambda bring in log4j-core by default, but you can easily exclude/override that if you need to.

When assembling fat-jars, make sure to enable merging META-INF/services files. For more info, see apache/logging-log4j2#2099.

Tracing with OpenTelemetry

The SDK automatically propagates the OpenTelemetry Context from the restate-server into your handler. You can use that to create custom spans.

To configure the OpenTelemetry that should be used by the SDK to publish traces, configure it in the Endpoint.Builder object.

For example, to set up tracing using environment variables, add the following modules to your dependencies:

implementation("io.opentelemetry:opentelemetry-sdk-extension-autoconfigure:1.38.0")
implementation("io.opentelemetry:opentelemetry-exporter-otlp:1.38.0")

And then configure it in the endpoint builder:

.withOpenTelemetry(AutoConfiguredOpenTelemetrySdk.initialize().getOpenTelemetrySdk())

By exporting the following environment variables the OpenTelemetry SDK will be automatically configured to push traces:

export OTEL_SERVICE_NAME=my-service
export OTEL_TRACES_SAMPLER=always_on
export OTEL_EXPORTER_OTLP_TRACES_ENDPOINT=http://localhost:14250

Please refer to the Opentelemetry manual instrumentation documentation and the autoconfigure documentation for more info.

See https://docs.restate.dev/operate/monitoring/tracing to configure Restate tracing.

Versions

This library follows Semantic Versioning.

The compatibility with Restate is described in the following table:

Restate Server\sdk-java	< 2.0	2.0 - 2.1	2.2 - 2.3	2.4 - 2.8
< 1.3	✅	❌	❌	❌
1.3	✅	✅	✅ ⁽¹⁾	✅ ⁽²⁾
1.4	✅	✅	✅	✅ ⁽²⁾
1.5 - 1.6	⚠ ⁽³⁾	✅	✅	✅

⁽¹⁾ Note The new service/handler configuration options inactivityTimeout, abortTimeout, idempotencyRetention, journalRetention, ingressPrivate, enableLazyState work only from Restate 1.4 onward.

⁽²⁾ Note The new service/handler configuration option invocationRetryPolicy works only from Restate 1.5 onward.

⁽³⁾ Warning SDK versions < 2.0 are deprecated, and cannot be registered anymore. Check the Restate 1.5 release notes for more info.

Contributing

We’re excited if you join the Restate community and start contributing! Whether it is feature requests, bug reports, ideas & feedback or PRs, we appreciate any and all contributions. We know that your time is precious and, therefore, deeply value any effort to contribute!

Building the SDK locally

Prerequisites:

JDK >= 17
Docker or Podman

To build the SDK:

To run the tests:

To publish local snapshots of the project:

./gradlew -DskipSigning publishToMavenLocal