Add Java8 support

build.gradle

@@ -85,9 +85,6 @@ subprojects {
 	group = "com.google.cloud.opentelemetry"
 	// Note: Version now comes from nebula plugin
 
-	sourceCompatibility = JavaVersion.VERSION_11
-	targetCompatibility = JavaVersion.VERSION_11
-
 	repositories {
 		mavenCentral()
 		mavenLocal()
@@ -103,6 +100,15 @@ subprojects {
 		archivesBaseName = "${project.name}"
 	}
 
+	// Support for some higher language versions can only be achieved using Toolchains.
+	// Compatibility matrix at https://docs.gradle.org/current/userguide/compatibility.html#java
+	// See https://docs.gradle.org/current/userguide/toolchains.html#toolchains
+	java {
+		toolchain {
+			languageVersion = JavaLanguageVersion.of(8)
+		}
+	}
+
 	// Include license check and auto-format support.
 	spotless {
 		java {
@@ -234,12 +240,6 @@ subprojects {
 		archives javadocJar, sourcesJar
 	}
 
-	javadoc {
-		if(JavaVersion.current().isJava9Compatible()) {
-			options.addBooleanOption('html5', true)
-		}
-	}
-
 	java {
 		withJavadocJar()
 		withSourcesJar()

detectors/resources-support/build.gradle

@@ -24,12 +24,6 @@ dependencies {
 	testRuntimeOnly(testLibraries.junit5_runtime)
 }
 
-afterEvaluate {
-	tasks.named("compileJava"){
-		options.release = 8
-	}
-}
-
 test {
 	// required for discovering JUnit 5 tests
 	useJUnitPlatform()

detectors/resources/build.gradle

@@ -15,12 +15,6 @@
  */
 description = 'Google Cloud resource provider for OpenTelemetry'
 
-afterEvaluate {
-	tasks.named("compileJava"){
-		options.release = 8
-	}
-}
-
 dependencies {
 	implementation(libraries.opentelemetry_api)
 	implementation(libraries.opentelemetry_sdk)

detectors/resources/src/test/java/com/google/cloud/opentelemetry/detectors/GCPResourceTest.java

@@ -19,6 +19,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import com.google.cloud.opentelemetry.detection.DetectedPlatform;
 import com.google.cloud.opentelemetry.detection.GCPPlatformDetector;
@@ -37,7 +38,7 @@ public class GCPResourceTest {
   private static final String DUMMY_PROJECT_ID = "google-pid";
   private final ConfigProperties mockConfigProps = Mockito.mock(ConfigProperties.class);
   private final Map<String, String> mockGKECommonAttributes =
-      new HashMap<>() {
+      new HashMap<String, String>() {
         {
           put(GKE_CLUSTER_NAME, "gke-cluster");
           put(GKE_HOST_ID, "host1");
@@ -47,7 +48,7 @@ public class GCPResourceTest {
   // Mock Platforms
   private DetectedPlatform generateMockGCEPlatform() {
     Map<String, String> mockAttributes =
-        new HashMap<>() {
+        new HashMap<String, String>() {
           {
             put(GCE_CLOUD_REGION, "australia-southeast1");
             put(GCE_AVAILABILITY_ZONE, "australia-southeast1-b");
@@ -92,7 +93,7 @@ private DetectedPlatform generateMockServerlessPlatform(
       throw new IllegalArgumentException();
     }
     Map<String, String> mockAttributes =
-        new HashMap<>() {
+        new HashMap<String, String>() {
           {
             put(SERVERLESS_COMPUTE_NAME, "serverless-app");
             put(SERVERLESS_COMPUTE_REVISION, "v2");
@@ -110,7 +111,7 @@ private DetectedPlatform generateMockServerlessPlatform(
 
   private DetectedPlatform generateMockGAEPlatform() {
     Map<String, String> mockAttributes =
-        new HashMap<>() {
+        new HashMap<String, String>() {
           {
             put(GAE_MODULE_NAME, "gae-app");
             put(GAE_APP_VERSION, "v1");
@@ -129,7 +130,7 @@ private DetectedPlatform generateMockGAEPlatform() {
 
   private DetectedPlatform generateMockUnknownPlatform() {
     Map<String, String> mockAttributes =
-        new HashMap<>() {
+        new HashMap<String, String>() {
           {
             put(GCE_INSTANCE_ID, "instance-id");
             put(GCE_CLOUD_REGION, "australia-southeast1");
@@ -385,8 +386,12 @@ public void testUnknownPlatformResourceAttributesMapping() {
   public void findsWithServiceLoader() {
     ServiceLoader<ResourceProvider> services =
         ServiceLoader.load(ResourceProvider.class, getClass().getClassLoader());
-    assertTrue(
-        services.stream().anyMatch(provider -> provider.type().equals(GCPResource.class)),
-        "Could not load GCP Resource detector using serviceloader, found: " + services);
+    while (services.iterator().hasNext()) {
+      ResourceProvider provider = services.iterator().next();
+      if (provider instanceof GCPResource) {
+        return;
+      }
+    }
+    fail("Could not load GCP Resource detector using serviceloader");
   }
 }

e2e-test-server/build.gradle

@@ -23,6 +23,11 @@ application {
 	mainClass.set('com.google.cloud.opentelemetry.endtoend.Server')
 }
 
+java {
+	toolchain {
+		languageVersion = JavaLanguageVersion.of(11)
+	}
+}
 description = 'End-To-End integration testing server'
 
 shadowJar {

examples/otlp-spring/build.gradle

@@ -27,6 +27,12 @@ repositories {
 	mavenCentral()
 }
 
+java {
+	toolchain {
+		languageVersion = JavaLanguageVersion.of(11)
+	}
+}
+
 dependencies {
 	implementation(libraries.opentelemetry_api)
 	implementation(libraries.opentelemetry_sdk)

exporters/metrics/src/main/java/com/google/cloud/opentelemetry/metric/AggregateByLabelMetricTimeSeriesBuilder.java

@@ -39,7 +39,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
 
@@ -167,7 +167,7 @@ private Attributes instrumentationLibraryLabels(
             instrumentationScopeInfo.getName())
         .put(
             AttributeKey.stringKey(LABEL_INSTRUMENTATION_VERSION),
-            Objects.requireNonNullElse(instrumentationScopeInfo.getVersion(), ""))
+            Optional.ofNullable(instrumentationScopeInfo.getVersion()).orElse(""))
         .build();
   }
 

exporters/metrics/src/test/java/com/google/cloud/opentelemetry/metric/GoogleCloudMetricExporterTest.java

@@ -85,7 +85,9 @@
 import io.opentelemetry.sdk.metrics.internal.data.ImmutableSummaryData;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.Set;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
@@ -419,7 +421,8 @@ public void testExportWithNonSupportedMetricTypeReturnsFailure() {
   public void testExportWithMonitoredResourceMappingSucceeds() {
     MonitoredResourceDescription monitoredResourceDescription =
         new MonitoredResourceDescription(
-            "custom_mr_instance", Set.of("service_instance_id", "host_id", "location"));
+            "custom_mr_instance",
+            new HashSet<>(Arrays.asList("service_instance_id", "host_id", "location")));
 
     // controls which resource attributes end up in metric labels
     Predicate<AttributeKey<?>> customAttributesFilter =
@@ -618,7 +621,8 @@ public void testExportWithMonitoredResourceMappingSucceeds_NoMRLabels() {
   public void testExportWithMonitoredResourceMappingSucceeds_NoResourceLabels() {
     MonitoredResourceDescription monitoredResourceDescription =
         new MonitoredResourceDescription(
-            "custom_mr_instance", Set.of("service_instance_id", "host_id", "location"));
+            "custom_mr_instance",
+            new HashSet<>(Arrays.asList("service_instance_id", "host_id", "location")));
 
     // controls which resource attributes end up in metric labels
     Predicate<AttributeKey<?>> customAttributesFilter =

exporters/metrics/src/test/java/com/google/cloud/opentelemetry/metric/MetricConfigurationTest.java

@@ -29,8 +29,9 @@
 import com.google.cloud.opentelemetry.metric.MetricConfiguration.Builder;
 import io.opentelemetry.api.common.AttributeKey;
 import java.time.Duration;
+import java.util.Arrays;
 import java.util.Date;
-import java.util.Set;
+import java.util.HashSet;
 import java.util.function.Predicate;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -61,7 +62,8 @@ public void testDefaultConfigurationSucceeds() {
   public void testSetAllConfigurationFieldsSucceeds() {
     Predicate<AttributeKey<?>> allowAllPredicate = attributeKey -> true;
     MonitoredResourceDescription customMRMapping =
-        new MonitoredResourceDescription("custom_mr", Set.of("instance_id", "foo_bar", "host_id"));
+        new MonitoredResourceDescription(
+            "custom_mr", new HashSet<>(Arrays.asList("instance_id", "foo_bar", "host_id")));
 
     MetricConfiguration configuration =
         MetricConfiguration.builder()

exporters/trace/src/main/java/com/google/cloud/opentelemetry/trace/InternalTraceExporter.java

@@ -16,6 +16,7 @@
 package com.google.cloud.opentelemetry.trace;
 
 import static com.google.api.client.util.Preconditions.checkNotNull;
+import static java.util.AbstractMap.SimpleEntry;
 
 import com.google.api.gax.core.FixedCredentialsProvider;
 import com.google.api.gax.core.NoCredentialsProvider;
@@ -40,6 +41,8 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 /**
  * This class encapsulates internal implementation details for exporting spans to Google Cloud
@@ -53,7 +56,10 @@ class InternalTraceExporter implements SpanExporter {
   private final TraceTranslator translator;
 
   private static final Map<String, String> HEADERS =
-      Map.of("User-Agent", "opentelemetry-operations-java/" + TraceVersions.EXPORTER_VERSION);
+      Stream.of(
+              new SimpleEntry<>(
+                  "User-Agent", "opentelemetry-operations-java/" + TraceVersions.EXPORTER_VERSION))
+          .collect(Collectors.toMap(SimpleEntry::getKey, SimpleEntry::getValue));
   private static final HeaderProvider HEADER_PROVIDER = () -> HEADERS;
 
   private static InternalTraceExporter createWithClient(

propagators/gcp/src/test/java/com/google/cloud/opentelemetry/propagators/AutoConfigureTest.java

@@ -20,8 +20,12 @@
 import io.opentelemetry.context.propagation.ContextPropagators;
 import io.opentelemetry.sdk.autoconfigure.AutoConfiguredOpenTelemetrySdk;
 import io.opentelemetry.sdk.autoconfigure.spi.ConfigurablePropagatorProvider;
-import java.util.Map;
+import java.util.AbstractMap.SimpleEntry;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.ServiceLoader;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -33,19 +37,20 @@ public class AutoConfigureTest {
   public void findsWithServiceLoader() {
     ServiceLoader<ConfigurablePropagatorProvider> services =
         ServiceLoader.load(ConfigurablePropagatorProvider.class, getClass().getClassLoader());
+
+    List<ConfigurablePropagatorProvider> servicesList = new ArrayList<>();
+    services.iterator().forEachRemaining(servicesList::add);
+
     assertTrue(
         "Could not load gcp_oneway propagator using serviceloader, found: " + services,
-        services.stream()
+        servicesList.stream()
             .anyMatch(
-                provider ->
-                    provider.type().equals(OneWayXCloudTraceConfigurablePropagatorProvider.class)));
+                provider -> (provider instanceof OneWayXCloudTraceConfigurablePropagatorProvider)));
 
     assertTrue(
         "Could not load gcp propagator using serviceloader, found: " + services,
-        services.stream()
-            .anyMatch(
-                provider ->
-                    provider.type().equals(XCloudTraceConfigurablePropagatorProvider.class)));
+        servicesList.stream()
+            .anyMatch(provider -> (provider instanceof XCloudTraceConfigurablePropagatorProvider)));
   }
 
   @Test
@@ -64,15 +69,12 @@ private static ContextPropagators findsWithAutoConfigure(String propagator) {
             .disableShutdownHook()
             .addPropertiesSupplier(
                 () ->
-                    Map.of(
-                        "otel.propagators",
-                        propagator,
-                        "otel.traces.exporter",
-                        "none",
-                        "otel.metrics.exporter",
-                        "none",
-                        "otel.logs.exporter",
-                        "none"))
+                    Stream.of(
+                            new SimpleEntry<>("otel.propagators", propagator),
+                            new SimpleEntry<>("otel.traces.exporter", "none"),
+                            new SimpleEntry<>("otel.metrics.exporter", "none"),
+                            new SimpleEntry<>("otel.logs.exporter", "none"))
+                        .collect(Collectors.toMap(SimpleEntry::getKey, SimpleEntry::getValue)))
             .build();
     return sdk.getOpenTelemetrySdk().getPropagators();
   }