Java Client "Missing required service schema" error

[djordjijeK]

Hi,

I have the following setup:

Gradle smithy module:

// src/main/smithy
$version: "2"

namespace krivokapic.djordjije.smithy.metrics.model

use aws.protocols#restJson1

@documentation("This service models a simple RESTful API for metric ingestion and retrieval.")
@restJson1
service MetricsService {
    version: "2025-04-20"
    operations: [
        PutMetric
    ]
}

@documentation("Write a new metric.")
@http(method: "POST", uri: "/metric")
operation PutMetric {
    input: PutMetricInput
    output: PutMetricOutput
    errors: [
        ValidationError
    ]
}

@documentation("Input for PutMetric operation.")
structure PutMetricInput {
    @required
    source: String

    @required
    metric: Metric
}

@documentation("Output for PutMetric operation.")
structure PutMetricOutput {
    @required
    metric: Metric

    @required
    timestamp: Timestamp
}

@documentation("Structure representing a metric.")
structure Metric {
    @required
    metricName: String

    instanceId: String

    @required
    value: MetricValue

    @required
    unit: MetricUnit
}

union MetricValue {
    intValue: Integer
    doubleValue: Double
    stringValue: String
}

enum MetricUnit {
    NONE
    BYTES
    COUNT
    PERCENT
    MILLISECONDS
}

// smithy-build.json
{
    "version": "1.0",
    "outputDirectory": "build/smithy"
}

// build.gradle.kts
plugins {
    id("java-library")
    id("software.amazon.smithy.gradle.smithy-jar").version("1.2.0")
}


repositories {
    mavenCentral()
}


dependencies {
    implementation("software.amazon.smithy:smithy-model:1.56.0")
    implementation("software.amazon.smithy:smithy-aws-traits:1.56.0")
}


tasks.named("compileJava") {
    dependsOn("smithyBuild")
}

I am trying to generate a Java client with the following configuration (second Gradle module):

// smithy-build.json
{
    "version": "1.0",
    "outputDirectory": "build/smithy",
    "plugins": {
        "java-client-codegen": {
            "service": "krivokapic.djordjije.smithy.metrics.model#MetricsService",
            "namespace": "krivokapic.djordjije.smithy.metrics.client",
            "protocol": "aws.protocols#restJson1"
        }
    }
}

plugins {
    id("application")
    id("software.amazon.smithy.gradle.smithy-jar").version("1.2.0")
}


repositories {
    mavenCentral()
}


dependencies {
    smithyBuild("software.amazon.smithy.java:plugins:0.0.2")

    implementation(project(":smithy"))
    implementation("software.amazon.smithy.java:client-core:0.0.2")
    implementation("software.amazon.smithy.java:aws-client-restjson:0.0.2")
}


afterEvaluate {
    val clientPath = smithy.getPluginProjectionPath(smithy.sourceProjection.get(), "java-client-codegen")

    sourceSets {
        main {
            java {
                srcDir(clientPath)
            }
        }
    }
}


tasks.named("compileJava") {
    dependsOn("smithyBuild")
}

I get the generated code and this is what I am trying to execute:

        MetricsServiceClient metricsServiceClient = MetricsServiceClient.builder()
            .endpointResolver(EndpointResolver.staticHost("http://localhost:8080"))
            .build();

        PutMetricOutput metric = metricsServiceClient.putMetric(PutMetricInput.builder()
            .source("SOURCE")
            .metric(Metric.builder()
                .metricName("NAME")
                .instanceId("INSTANCE")
                .value(MetricValue.builder().intValue(10).build())
                .unit(MetricUnit.COUNT)
                .build())
            .build());

I am getting the following error:

Exception in thread "main" java.lang.NullPointerException: Missing required service schema
	at java.base/java.util.Objects.requireNonNull(Objects.java:259)
	at software.amazon.smithy.java.client.core.ClientConfig.<init>(ClientConfig.java:91)
	at software.amazon.smithy.java.client.core.ClientConfig$Builder.build(ClientConfig.java:569)
	at software.amazon.smithy.java.client.core.Client.<init>(Client.java:49)
	at krivokapic.djordjije.smithy.metrics.client.client.MetricsServiceClientImpl.<init>(MetricsServiceClientImpl.java:33)
	at krivokapic.djordjije.smithy.metrics.client.client.MetricsServiceClient$Builder.build(MetricsServiceClient.java:78)
	at krivokapic.djordjije.MetricsClientMain.main(MetricsClientMain.java:17)

Looking at the generated code I have the following:

package krivokapic.djordjije.smithy.metrics.client.model;

import software.amazon.smithy.java.core.schema.ApiService;
import software.amazon.smithy.java.core.schema.Schema;
import software.amazon.smithy.model.shapes.ShapeId;
import software.amazon.smithy.utils.SmithyGenerated;

/**
 * Service API schema
 */
@SmithyGenerated
public final class MetricsServiceApiService implements ApiService {
    private static final MetricsServiceApiService $INSTANCE = new MetricsServiceApiService();
    private static final Schema $SCHEMA = Schema.createService(ShapeId.from("krivokapic.djordjije.smithy.metrics.model#MetricsService"));

    /**
     * Get an instance of this {@code ApiService}.
     *
     * @return An instance of this class.
     */
    public static MetricsServiceApiService instance() {
        return $INSTANCE;
    }

    private MetricsServiceApiService() {}

    @Override
    public Schema schema() {
        return $SCHEMA;
    }
}

But this ApiService is never populated in the Config object. As a sanity check, I generated from the CLI examples from your repository e.g. https://github.com/smithy-lang/smithy-java/blob/main/examples/end-to-end/README.md and I get the exact same problem.

[adwsingh]

This is fixed by #638 , pending release.

[djordjijeK]

Thanks. Will wait for release. Is there any workaround (I tried using ClientConfig but feels clunky)?