Add SdkMeterProvider toString method (#4464)

* Add SdkMeterProvider toString method

* Fix build

* Ignore null values in InstrumentSelector / View #toString()

docs/apidiffs/current_vs_latest/opentelemetry-sdk-metrics.txt

@@ -1,2 +1,13 @@
 Comparing source compatibility of  against 
-No changes.
+***  MODIFIED CLASS: PUBLIC FINAL io.opentelemetry.sdk.metrics.export.PeriodicMetricReader  (not serializable)
+	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
+	+++  NEW METHOD: PUBLIC(+) java.lang.String toString()
+***  MODIFIED CLASS: PUBLIC ABSTRACT io.opentelemetry.sdk.metrics.InstrumentSelector  (not serializable)
+	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
+	+++  NEW METHOD: PUBLIC(+) FINAL(+) java.lang.String toString()
+***  MODIFIED CLASS: PUBLIC FINAL io.opentelemetry.sdk.metrics.SdkMeterProvider  (not serializable)
+	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
+	+++  NEW METHOD: PUBLIC(+) java.lang.String toString()
+***  MODIFIED CLASS: PUBLIC ABSTRACT io.opentelemetry.sdk.metrics.View  (not serializable)
+	===  CLASS FILE FORMAT VERSION: 52.0 <- 52.0
+	+++  NEW METHOD: PUBLIC(+) FINAL(+) java.lang.String toString()

exporters/prometheus/src/main/java/io/opentelemetry/exporter/prometheus/PrometheusHttpServer.java

@@ -147,6 +147,11 @@ public final class PrometheusHttpServer implements Closeable, MetricReader {
     shutdown().join(10, TimeUnit.SECONDS);
   }
 
+  @Override
+  public String toString() {
+    return "PrometheusHttpServer{address=" + server.getAddress() + "}";
+  }
+
   // Visible for testing.
   InetSocketAddress getAddress() {
     return server.getAddress();

exporters/prometheus/src/test/java/io/opentelemetry/exporter/prometheus/PrometheusHttpServerTest.java

@@ -163,6 +163,12 @@ class PrometheusHttpServerTest {
     assertThat(response.contentUtf8()).isEqualTo("Exporter is Healthy.");
   }
 
+  @Test
+  void stringRepresentation() {
+    assertThat(prometheusServer.toString())
+        .isEqualTo("PrometheusHttpServer{address=" + prometheusServer.getAddress() + "}");
+  }
+
   private static ImmutableList<MetricData> generateTestData() {
     return ImmutableList.of(
         ImmutableMetricData.createLongSum(

sdk/all/src/main/java/io/opentelemetry/sdk/OpenTelemetrySdk.java

@@ -76,8 +76,13 @@ public final class OpenTelemetrySdk implements OpenTelemetry {
 
   @Override
   public String toString() {
-    // TODO(anuraaga): Add metrics / logs / propagators
+    // TODO(anuraaga): Add logs / propagators
-    return "OpenTelemetrySdk{" + "tracerProvider=" + tracerProvider.unobfuscate() + '}';
+    return "OpenTelemetrySdk{"
+        + "tracerProvider="
+        + tracerProvider.unobfuscate()
+        + ", meterProvider="
+        + meterProvider.unobfuscate()
+        + "}";
   }
 
   /**

sdk/all/src/test/java/io/opentelemetry/sdk/OpenTelemetrySdkTest.java

@@ -14,13 +14,17 @@ import static org.mockito.Mockito.when;
 import io.opentelemetry.api.GlobalOpenTelemetry;
 import io.opentelemetry.api.OpenTelemetry;
 import io.opentelemetry.api.common.AttributeKey;
-import io.opentelemetry.api.common.Attributes;
-import io.opentelemetry.api.trace.TracerProvider;
 import io.opentelemetry.context.propagation.ContextPropagators;
 import io.opentelemetry.context.propagation.TextMapPropagator;
 import io.opentelemetry.sdk.common.Clock;
 import io.opentelemetry.sdk.logs.SdkLogEmitterProvider;
+import io.opentelemetry.sdk.metrics.Aggregation;
+import io.opentelemetry.sdk.metrics.InstrumentSelector;
+import io.opentelemetry.sdk.metrics.InstrumentType;
 import io.opentelemetry.sdk.metrics.SdkMeterProvider;
+import io.opentelemetry.sdk.metrics.View;
+import io.opentelemetry.sdk.metrics.export.MetricExporter;
+import io.opentelemetry.sdk.metrics.export.PeriodicMetricReader;
 import io.opentelemetry.sdk.resources.Resource;
 import io.opentelemetry.sdk.trace.IdGenerator;
 import io.opentelemetry.sdk.trace.SdkTracerProvider;
@@ -28,6 +32,7 @@ import io.opentelemetry.sdk.trace.SpanLimits;
 import io.opentelemetry.sdk.trace.export.SimpleSpanProcessor;
 import io.opentelemetry.sdk.trace.export.SpanExporter;
 import io.opentelemetry.sdk.trace.samplers.Sampler;
+import java.time.Duration;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
@@ -41,7 +46,6 @@ class OpenTelemetrySdkTest {
   @Mock private SdkMeterProvider meterProvider;
   @Mock private SdkLogEmitterProvider logEmitterProvider;
   @Mock private ContextPropagators propagators;
-  @Mock private Clock clock;
 
   @AfterEach
   void tearDown() {
@@ -49,7 +53,7 @@ class OpenTelemetrySdkTest {
   }
 
   @Test
-  void testRegisterGlobal() {
+  void buildAndRegisterGlobal() {
     OpenTelemetrySdk sdk =
         OpenTelemetrySdk.builder().setPropagators(propagators).buildAndRegisterGlobal();
     assertThat(GlobalOpenTelemetry.get()).extracting("delegate").isSameAs(sdk);
@@ -67,7 +71,7 @@ class OpenTelemetrySdkTest {
   }
 
   @Test
-  void castingGlobalToSdkFails() {
+  void buildAndRegisterGlobal_castingGlobalToSdkFails() {
     OpenTelemetrySdk.builder().buildAndRegisterGlobal();
 
     assertThatThrownBy(
@@ -79,40 +83,7 @@ class OpenTelemetrySdkTest {
   }
 
   @Test
-  void testShortcutVersions() {
+  void builderDefaults() {
-    assertThat(GlobalOpenTelemetry.getTracer("testTracer1"))
-        .isSameAs(GlobalOpenTelemetry.getTracerProvider().get("testTracer1"));
-    assertThat(GlobalOpenTelemetry.getTracer("testTracer2", "testVersion"))
-        .isSameAs(GlobalOpenTelemetry.getTracerProvider().get("testTracer2", "testVersion"));
-    assertThat(
-            GlobalOpenTelemetry.tracerBuilder("testTracer2")
-                .setInstrumentationVersion("testVersion")
-                .setSchemaUrl("https://example.invalid")
-                .build())
-        .isSameAs(
-            GlobalOpenTelemetry.getTracerProvider()
-                .tracerBuilder("testTracer2")
-                .setInstrumentationVersion("testVersion")
-                .setSchemaUrl("https://example.invalid")
-                .build());
-
-    assertThat(GlobalOpenTelemetry.getMeter("testMeter1"))
-        .isSameAs(GlobalOpenTelemetry.getMeterProvider().get("testMeter1"));
-    assertThat(
-            GlobalOpenTelemetry.meterBuilder("testMeter2")
-                .setInstrumentationVersion("testVersion")
-                .setSchemaUrl("https://example.invalid")
-                .build())
-        .isSameAs(
-            GlobalOpenTelemetry.getMeterProvider()
-                .meterBuilder("testMeter2")
-                .setInstrumentationVersion("testVersion")
-                .setSchemaUrl("https://example.invalid")
-                .build());
-  }
-
-  @Test
-  void testBuilderDefaults() {
     OpenTelemetrySdk openTelemetry = OpenTelemetrySdk.builder().build();
     assertThat(openTelemetry.getTracerProvider())
         .isInstanceOfSatisfying(
@@ -129,7 +100,7 @@ class OpenTelemetrySdkTest {
   }
 
   @Test
-  void building() {
+  void builder() {
     OpenTelemetrySdk openTelemetry =
         OpenTelemetrySdk.builder()
             .setTracerProvider(tracerProvider)
@@ -151,54 +122,40 @@ class OpenTelemetrySdkTest {
   }
 
   @Test
-  void testConfiguration_tracerSettings() {
+  void getTracer() {
-    Resource resource = Resource.create(Attributes.builder().put("cat", "meow").build());
+    assertThat(GlobalOpenTelemetry.getTracer("testTracer1"))
-    IdGenerator idGenerator = mock(IdGenerator.class);
+        .isSameAs(GlobalOpenTelemetry.getTracerProvider().get("testTracer1"));
-    SpanLimits spanLimits = SpanLimits.getDefault();
+    assertThat(GlobalOpenTelemetry.getTracer("testTracer2", "testVersion"))
-    OpenTelemetrySdk openTelemetry =
+        .isSameAs(GlobalOpenTelemetry.getTracerProvider().get("testTracer2", "testVersion"));
-        OpenTelemetrySdk.builder()
+    assertThat(
-            .setTracerProvider(
+            GlobalOpenTelemetry.tracerBuilder("testTracer2")
-                SdkTracerProvider.builder()
+                .setInstrumentationVersion("testVersion")
-                    .setClock(clock)
+                .setSchemaUrl("https://example.invalid")
-                    .setResource(resource)
-                    .setIdGenerator(idGenerator)
-                    .setSpanLimits(spanLimits)
                 .build())
-            .build();
+        .isSameAs(
-    TracerProvider unobfuscatedTracerProvider =
+            GlobalOpenTelemetry.getTracerProvider()
-        ((OpenTelemetrySdk.ObfuscatedTracerProvider) openTelemetry.getTracerProvider())
+                .tracerBuilder("testTracer2")
-            .unobfuscate();
+                .setInstrumentationVersion("testVersion")
-
+                .setSchemaUrl("https://example.invalid")
-    assertThat(unobfuscatedTracerProvider)
+                .build());
-        .isInstanceOfSatisfying(
-            SdkTracerProvider.class,
-            sdkTracerProvider ->
-                assertThat(sdkTracerProvider.getSpanLimits()).isEqualTo(spanLimits));
-    // Since TracerProvider is in a different package, the only alternative to this reflective
-    // approach would be to make the fields public for testing which is worse than this.
-    assertThat(unobfuscatedTracerProvider)
-        .extracting("sharedState")
-        .hasFieldOrPropertyWithValue("clock", clock)
-        .hasFieldOrPropertyWithValue("resource", resource)
-        .hasFieldOrPropertyWithValue("idGenerator", idGenerator);
   }
 
   @Test
-  void testTracerBuilder() {
+  void tracerBuilder() {
     OpenTelemetrySdk openTelemetry = OpenTelemetrySdk.builder().build();
     assertThat(openTelemetry.tracerBuilder("instr"))
         .isNotSameAs(OpenTelemetry.noop().tracerBuilder("instr"));
   }
 
   @Test
-  void testTracerBuilderViaProvider() {
+  void tracerBuilder_ViaProvider() {
     OpenTelemetrySdk openTelemetry = OpenTelemetrySdk.builder().build();
     assertThat(openTelemetry.getTracerProvider().tracerBuilder("instr"))
         .isNotSameAs(OpenTelemetry.noop().tracerBuilder("instr"));
   }
 
   @Test
-  void testTracerProviderAccess() {
+  void getTracerProvider() {
     OpenTelemetrySdk openTelemetry =
         OpenTelemetrySdk.builder().setTracerProvider(tracerProvider).build();
     assertThat(openTelemetry.getTracerProvider())
@@ -210,7 +167,50 @@ class OpenTelemetrySdkTest {
   }
 
   @Test
-  void testMeterProviderAccess() {
+  void getMeter() {
+    assertThat(GlobalOpenTelemetry.getMeter("testMeter1"))
+        .isSameAs(GlobalOpenTelemetry.getMeterProvider().get("testMeter1"));
+    assertThat(
+            GlobalOpenTelemetry.meterBuilder("testMeter2")
+                .setInstrumentationVersion("testVersion")
+                .setSchemaUrl("https://example.invalid")
+                .build())
+        .isSameAs(
+            GlobalOpenTelemetry.getMeterProvider()
+                .meterBuilder("testMeter2")
+                .setInstrumentationVersion("testVersion")
+                .setSchemaUrl("https://example.invalid")
+                .build());
+  }
+
+  @Test
+  void meterBuilder() {
+    OpenTelemetrySdk openTelemetry =
+        OpenTelemetrySdk.builder()
+            .setMeterProvider(
+                SdkMeterProvider.builder()
+                    .registerMetricReader(PeriodicMetricReader.create(mock(MetricExporter.class)))
+                    .build())
+            .build();
+    assertThat(openTelemetry.meterBuilder("instr"))
+        .isNotSameAs(OpenTelemetry.noop().meterBuilder("instr"));
+  }
+
+  @Test
+  void meterBuilder_ViaProvider() {
+    OpenTelemetrySdk openTelemetry =
+        OpenTelemetrySdk.builder()
+            .setMeterProvider(
+                SdkMeterProvider.builder()
+                    .registerMetricReader(PeriodicMetricReader.create(mock(MetricExporter.class)))
+                    .build())
+            .build();
+    assertThat(openTelemetry.getMeterProvider().meterBuilder("instr"))
+        .isNotSameAs(OpenTelemetry.noop().meterBuilder("instr"));
+  }
+
+  @Test
+  void getMeterProvider() {
     OpenTelemetrySdk openTelemetry =
         OpenTelemetrySdk.builder().setMeterProvider(meterProvider).build();
     assertThat(openTelemetry.getMeterProvider())
@@ -225,10 +225,23 @@ class OpenTelemetrySdkTest {
   // Demonstrates how clear or confusing is SDK configuration
   @Test
   void fullOpenTelemetrySdkConfigurationDemo() {
-    SpanLimits newConfig = SpanLimits.builder().setMaxNumberOfAttributes(512).build();
-
-    OpenTelemetrySdkBuilder sdkBuilder =
     OpenTelemetrySdk.builder()
+        .setMeterProvider(
+            SdkMeterProvider.builder()
+                .setResource(Resource.empty())
+                .setClock(mock(Clock.class))
+                .registerMetricReader(
+                    PeriodicMetricReader.builder(mock(MetricExporter.class))
+                        .setInterval(Duration.ofSeconds(10))
+                        .build())
+                .registerMetricReader(PeriodicMetricReader.create(mock(MetricExporter.class)))
+                .registerView(
+                    InstrumentSelector.builder().setName("name").build(),
+                    View.builder().setName("new-name").build())
+                .registerView(
+                    InstrumentSelector.builder().setType(InstrumentType.COUNTER).build(),
+                    View.builder().setAttributeFilter(key -> key.equals("foo")).build())
+                .build())
         .setTracerProvider(
             SdkTracerProvider.builder()
                 .setSampler(mock(Sampler.class))
@@ -237,10 +250,10 @@ class OpenTelemetrySdkTest {
                 .setClock(mock(Clock.class))
                 .setIdGenerator(mock(IdGenerator.class))
                 .setResource(Resource.empty())
-                    .setSpanLimits(newConfig)
+                .setSpanLimits(SpanLimits.builder().setMaxNumberOfAttributes(512).build())
-                    .build());
+                .build())
-
+        .setPropagators(ContextPropagators.create(mock(TextMapPropagator.class)))
-    sdkBuilder.build();
+        .build();
   }
 
   // This is just a demonstration of the bare minimal required configuration in order to get useful
@@ -249,6 +262,10 @@ class OpenTelemetrySdkTest {
   @Test
   void trivialOpenTelemetrySdkConfigurationDemo() {
     OpenTelemetrySdk.builder()
+        .setMeterProvider(
+            SdkMeterProvider.builder()
+                .registerMetricReader(PeriodicMetricReader.create(mock(MetricExporter.class)))
+                .build())
         .setTracerProvider(
             SdkTracerProvider.builder()
                 .addSpanProcessor(SimpleSpanProcessor.create(mock(SpanExporter.class)))
@@ -262,6 +279,10 @@ class OpenTelemetrySdkTest {
   @Test
   void minimalOpenTelemetrySdkConfigurationDemo() {
     OpenTelemetrySdk.builder()
+        .setMeterProvider(
+            SdkMeterProvider.builder()
+                .registerMetricReader(PeriodicMetricReader.create(mock(MetricExporter.class)))
+                .build())
         .setTracerProvider(
             SdkTracerProvider.builder()
                 .addSpanProcessor(SimpleSpanProcessor.create(mock(SpanExporter.class)))
@@ -271,6 +292,13 @@ class OpenTelemetrySdkTest {
         .build();
 
     OpenTelemetrySdk.builder()
+        .setMeterProvider(
+            SdkMeterProvider.builder()
+                .registerMetricReader(PeriodicMetricReader.create(mock(MetricExporter.class)))
+                .registerView(
+                    InstrumentSelector.builder().setType(InstrumentType.COUNTER).build(),
+                    View.builder().setAggregation(Aggregation.explicitBucketHistogram()).build())
+                .build())
         .setTracerProvider(
             SdkTracerProvider.builder()
                 .addSpanProcessor(SimpleSpanProcessor.create(mock(SpanExporter.class)))
@@ -283,8 +311,10 @@ class OpenTelemetrySdkTest {
 
   @Test
   void stringRepresentation() {
-    SpanExporter exporter = mock(SpanExporter.class);
+    SpanExporter spanExporter = mock(SpanExporter.class);
-    when(exporter.toString()).thenReturn("MockSpanExporter{}");
+    when(spanExporter.toString()).thenReturn("MockSpanExporter{}");
+    MetricExporter metricExporter = mock(MetricExporter.class);
+    when(metricExporter.toString()).thenReturn("MockMetricExporter{}");
     Resource resource =
         Resource.builder().put(AttributeKey.stringKey("service.name"), "otel-test").build();
     OpenTelemetrySdk sdk =
@@ -293,7 +323,16 @@ class OpenTelemetrySdkTest {
                 SdkTracerProvider.builder()
                     .setResource(resource)
                     .addSpanProcessor(
-                        SimpleSpanProcessor.create(SpanExporter.composite(exporter, exporter)))
+                        SimpleSpanProcessor.create(
+                            SpanExporter.composite(spanExporter, spanExporter)))
+                    .build())
+            .setMeterProvider(
+                SdkMeterProvider.builder()
+                    .setResource(resource)
+                    .registerMetricReader(PeriodicMetricReader.create(metricExporter))
+                    .registerView(
+                        InstrumentSelector.builder().setName("instrument").build(),
+                        View.builder().setName("new-instrument").build())
                     .build())
             .build();
 
@@ -306,6 +345,14 @@ class OpenTelemetrySdkTest {
                 + "resource=Resource{schemaUrl=null, attributes={service.name=\"otel-test\"}}, "
                 + "spanLimitsSupplier=SpanLimitsValue{maxNumberOfAttributes=128, maxNumberOfEvents=128, maxNumberOfLinks=128, maxNumberOfAttributesPerEvent=128, maxNumberOfAttributesPerLink=128, maxAttributeValueLength=2147483647}, "
                 + "sampler=ParentBased{root:AlwaysOnSampler,remoteParentSampled:AlwaysOnSampler,remoteParentNotSampled:AlwaysOffSampler,localParentSampled:AlwaysOnSampler,localParentNotSampled:AlwaysOffSampler}, "
-                + "spanProcessor=SimpleSpanProcessor{spanExporter=MultiSpanExporter{spanExporters=[MockSpanExporter{}, MockSpanExporter{}]}}}}");
+                + "spanProcessor=SimpleSpanProcessor{spanExporter=MultiSpanExporter{spanExporters=[MockSpanExporter{}, MockSpanExporter{}]}}"
+                + "}, "
+                + "meterProvider=SdkMeterProvider{"
+                + "clock=SystemClock{}, "
+                + "resource=Resource{schemaUrl=null, attributes={service.name=\"otel-test\"}}, "
+                + "metricReaders=[PeriodicMetricReader{exporter=MockMetricExporter{}, intervalNanos=60000000000}], "
+                + "views=[RegisteredView{instrumentSelector=InstrumentSelector{instrumentName=instrument}, view=View{name=new-instrument, aggregation=DefaultAggregation, attributesProcessor=NoopAttributesProcessor{}}}]"
+                + "}"
+                + "}");
   }
 }

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/InstrumentSelector.java

@@ -6,6 +6,7 @@
 package io.opentelemetry.sdk.metrics;
 
 import com.google.auto.value.AutoValue;
+import java.util.StringJoiner;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
@@ -75,4 +76,25 @@ public abstract class InstrumentSelector {
    */
   @Nullable
   public abstract String getMeterSchemaUrl();
+
+  @Override
+  public final String toString() {
+    StringJoiner joiner = new StringJoiner(", ", "InstrumentSelector{", "}");
+    if (getInstrumentType() != null) {
+      joiner.add("instrumentType=" + getInstrumentType());
+    }
+    if (getInstrumentName() != null) {
+      joiner.add("instrumentName=" + getInstrumentName());
+    }
+    if (getMeterName() != null) {
+      joiner.add("meterName=" + getMeterName());
+    }
+    if (getMeterVersion() != null) {
+      joiner.add("meterVersion=" + getMeterVersion());
+    }
+    if (getMeterSchemaUrl() != null) {
+      joiner.add("meterSchemaUrl=" + getMeterSchemaUrl());
+    }
+    return joiner.toString();
+  }
 }

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/SdkMeterProvider.java

@@ -39,6 +39,7 @@ public final class SdkMeterProvider implements MeterProvider, Closeable {
   private static final Logger LOGGER = Logger.getLogger(SdkMeterProvider.class.getName());
   static final String DEFAULT_METER_NAME = "unknown";
 
+  private final List<MetricReader> metricReaders;
   private final ComponentRegistry<SdkMeter> registry;
   private final MeterProviderSharedState sharedState;
   private final Map<CollectionHandle, CollectionInfo> collectionInfoMap;
@@ -62,6 +63,7 @@ public final class SdkMeterProvider implements MeterProvider, Closeable {
       ViewRegistry viewRegistry,
       ExemplarFilter exemplarFilter,
       long minimumCollectionIntervalNanos) {
+    this.metricReaders = metricReaders;
     this.sharedState =
         MeterProviderSharedState.create(clock, resource, viewRegistry, exemplarFilter);
     this.registry =
@@ -142,6 +144,20 @@ public final class SdkMeterProvider implements MeterProvider, Closeable {
     shutdown().join(10, TimeUnit.SECONDS);
   }
 
+  @Override
+  public String toString() {
+    return "SdkMeterProvider{"
+        + "clock="
+        + sharedState.getClock()
+        + ", resource="
+        + sharedState.getResource()
+        + ", metricReaders="
+        + metricReaders
+        + ", views="
+        + sharedState.getViewRegistry().getViews()
+        + "}";
+  }
+
   /** Helper class to expose registered metric exports. */
   private class LeasedMetricProducer implements MetricProducer {
     private final CollectionHandle handle;

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/View.java

@@ -7,6 +7,7 @@ package io.opentelemetry.sdk.metrics;
 
 import com.google.auto.value.AutoValue;
 import io.opentelemetry.sdk.metrics.internal.view.AttributesProcessor;
+import java.util.StringJoiner;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
@@ -47,4 +48,18 @@ public abstract class View {
 
   /** The attribute processor used for this view. */
   abstract AttributesProcessor getAttributesProcessor();
+
+  @Override
+  public final String toString() {
+    StringJoiner joiner = new StringJoiner(", ", "View{", "}");
+    if (getName() != null) {
+      joiner.add("name=" + getName());
+    }
+    if (getDescription() != null) {
+      joiner.add("description=" + getDescription());
+    }
+    joiner.add("aggregation=" + getAggregation());
+    joiner.add("attributesProcessor=" + getAttributesProcessor());
+    return joiner.toString();
+  }
 }

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/export/PeriodicMetricReader.java

@@ -106,6 +106,16 @@ public final class PeriodicMetricReader implements MetricReader {
     start();
   }
 
+  @Override
+  public String toString() {
+    return "PeriodicMetricReader{"
+        + "exporter="
+        + exporter
+        + ", intervalNanos="
+        + intervalNanos
+        + '}';
+  }
+
   void start() {
     synchronized (lock) {
       if (scheduledFuture != null) {

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/state/MeterProviderSharedState.java

@@ -33,10 +33,10 @@ public abstract class MeterProviderSharedState {
   public abstract Clock getClock();
 
   /** Returns the {@link Resource} to attach telemetry to. */
-  abstract Resource getResource();
+  public abstract Resource getResource();
 
   /** Returns the {@link ViewRegistry} for custom aggregation and metric definitions. */
-  abstract ViewRegistry getViewRegistry();
+  public abstract ViewRegistry getViewRegistry();
 
   /**
    * Returns the timestamp when this {@code MeterProvider} was started, in nanoseconds since Unix

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/view/AttributesProcessor.java

@@ -5,6 +5,8 @@
 
 package io.opentelemetry.sdk.metrics.internal.view;
 
+import static io.opentelemetry.sdk.metrics.internal.view.NoopAttributesProcessor.NOOP;
+
 import io.opentelemetry.api.baggage.Baggage;
 import io.opentelemetry.api.common.Attributes;
 import io.opentelemetry.api.common.AttributesBuilder;
@@ -27,7 +29,8 @@ import javax.annotation.concurrent.Immutable;
  */
 @Immutable
 public abstract class AttributesProcessor {
-  private AttributesProcessor() {}
+
+  AttributesProcessor() {}
 
   /**
    * Manipulates a set of attributes, returning the desired set.
@@ -142,8 +145,6 @@ public abstract class AttributesProcessor {
     };
   }
 
-  static final AttributesProcessor NOOP = simple(incoming -> incoming);
-
   /** A {@link AttributesProcessor} that runs a sequence of processors. */
   @Immutable
   static final class JoinedAttributesProcessor extends AttributesProcessor {

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/view/NoopAttributesProcessor.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.metrics.internal.view;
+
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.context.Context;
+
+class NoopAttributesProcessor extends AttributesProcessor {
+
+  static final NoopAttributesProcessor NOOP = new NoopAttributesProcessor();
+
+  private NoopAttributesProcessor() {}
+
+  @Override
+  public Attributes process(Attributes incoming, Context context) {
+    return incoming;
+  }
+
+  @Override
+  public boolean usesContext() {
+    return false;
+  }
+
+  @Override
+  public String toString() {
+    return "NoopAttributesProcessor{}";
+  }
+}

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/view/RegisteredView.java

@@ -42,4 +42,14 @@ public abstract class RegisteredView {
 
   /** The {@link SourceInfo} from where the view was registered. */
   public abstract SourceInfo getViewSourceInfo();
+
+  @Override
+  public final String toString() {
+    return "RegisteredView{"
+        + "instrumentSelector="
+        + getInstrumentSelector()
+        + ", view="
+        + getView()
+        + "}";
+  }
 }

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/view/ViewRegistry.java

@@ -5,6 +5,8 @@
 
 package io.opentelemetry.sdk.metrics.internal.view;
 
+import static io.opentelemetry.sdk.metrics.internal.view.NoopAttributesProcessor.NOOP;
+
 import io.opentelemetry.sdk.common.InstrumentationScopeInfo;
 import io.opentelemetry.sdk.metrics.InstrumentSelector;
 import io.opentelemetry.sdk.metrics.SdkMeterProviderBuilder;
@@ -36,7 +38,7 @@ public final class ViewRegistry {
       RegisteredView.create(
           InstrumentSelector.builder().setName("*").build(),
           DEFAULT_VIEW,
-          AttributesProcessor.NOOP,
+          NOOP,
           SourceInfo.noSourceInfo());
   private static final Logger logger = Logger.getLogger(ViewRegistry.class.getName());
 
@@ -51,6 +53,11 @@ public final class ViewRegistry {
     return new ViewRegistryBuilder();
   }
 
+  /** Return a list of all registered views. */
+  public List<RegisteredView> getViews() {
+    return new ArrayList<>(reverseRegistration);
+  }
+
   /**
    * Returns the metric {@link View} for a given instrument.
    *

sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/InstrumentSelectorTest.java

@@ -74,4 +74,27 @@ class InstrumentSelectorTest {
             .build();
     assertThat(selector.getMeterSchemaUrl()).isEqualTo("http://bar.com");
   }
+
+  @Test
+  void stringRepresentation() {
+    assertThat(InstrumentSelector.builder().setName("name").build().toString())
+        .isEqualTo("InstrumentSelector{instrumentName=name}");
+    assertThat(
+            InstrumentSelector.builder()
+                .setType(InstrumentType.COUNTER)
+                .setName("name")
+                .setMeterName("meter")
+                .setMeterVersion("version")
+                .setMeterSchemaUrl("http://url.com")
+                .build()
+                .toString())
+        .isEqualTo(
+            "InstrumentSelector{"
+                + "instrumentType=COUNTER, "
+                + "instrumentName=name, "
+                + "meterName=meter, "
+                + "meterVersion=version, "
+                + "meterSchemaUrl=http://url.com"
+                + "}");
+  }
 }

sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/ViewTest.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.metrics;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class ViewTest {
+
+  @Test
+  void stringRepresentation() {
+    assertThat(View.builder().build().toString())
+        .isEqualTo(
+            "View{aggregation=DefaultAggregation, attributesProcessor=NoopAttributesProcessor{}}");
+    assertThat(
+            View.builder()
+                .setName("name")
+                .setDescription("description")
+                .setAggregation(Aggregation.sum())
+                .build()
+                .toString())
+        .isEqualTo(
+            "View{"
+                + "name=name, "
+                + "description=description, "
+                + "aggregation=SumAggregation, "
+                + "attributesProcessor=NoopAttributesProcessor{}"
+                + "}");
+  }
+}

sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/export/PeriodicMetricReaderTest.java

@@ -208,6 +208,21 @@ class PeriodicMetricReaderTest {
         .hasMessage("executor");
   }
 
+  @Test
+  void stringRepresentation() {
+    when(metricExporter.toString()).thenReturn("MockMetricExporter{}");
+    assertThat(
+            PeriodicMetricReader.builder(metricExporter)
+                .setInterval(Duration.ofSeconds(1))
+                .build()
+                .toString())
+        .isEqualTo(
+            "PeriodicMetricReader{"
+                + "exporter=MockMetricExporter{}, "
+                + "intervalNanos=1000000000"
+                + "}");
+  }
+
   private static class WaitingMetricExporter implements MetricExporter {
 
     private final AtomicBoolean hasShutdown = new AtomicBoolean(false);

sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/internal/view/RegisteredViewTest.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.metrics.internal.view;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+
+import io.opentelemetry.sdk.metrics.Aggregation;
+import io.opentelemetry.sdk.metrics.InstrumentSelector;
+import io.opentelemetry.sdk.metrics.InstrumentType;
+import io.opentelemetry.sdk.metrics.View;
+import io.opentelemetry.sdk.metrics.internal.debug.SourceInfo;
+import org.junit.jupiter.api.Test;
+
+class RegisteredViewTest {
+
+  @Test
+  void stringRepresentation() {
+    assertThat(
+            RegisteredView.create(
+                    InstrumentSelector.builder()
+                        .setName("name")
+                        .setType(InstrumentType.COUNTER)
+                        .setMeterName("meter-name")
+                        .setMeterVersion("meter-version")
+                        .setMeterSchemaUrl("meter-schema-url")
+                        .build(),
+                    View.builder()
+                        .setName("name")
+                        .setDescription("description")
+                        .setAggregation(Aggregation.sum())
+                        .build(),
+                    AttributesProcessor.noop(),
+                    SourceInfo.fromCurrentStack())
+                .toString())
+        .isEqualTo(
+            "RegisteredView{"
+                + "instrumentSelector=InstrumentSelector{instrumentType=COUNTER, instrumentName=name, meterName=meter-name, meterVersion=meter-version, meterSchemaUrl=meter-schema-url}, "
+                + "view=View{name=name, description=description, aggregation=SumAggregation, attributesProcessor=NoopAttributesProcessor{}}"
+                + "}");
+  }
+}

sdk/testing/src/main/java/io/opentelemetry/sdk/testing/exporter/InMemoryMetricReader.java

@@ -90,4 +90,9 @@ public class InMemoryMetricReader implements MetricReader {
     isShutdown.set(true);
     return CompletableResultCode.ofSuccess();
   }
+
+  @Override
+  public String toString() {
+    return "InMemoryMetricReader{aggregationTemporality=" + aggregationTemporality + "}";
+  }
 }

sdk/testing/src/test/java/io/opentelemetry/sdk/testing/exporter/InMemoryMetricReaderTest.java

@@ -89,4 +89,10 @@ class InMemoryMetricReaderTest {
     assertThat(cumulativeReader.collectAllMetrics()).hasSize(0);
     assertThat(deltaReader.collectAllMetrics()).hasSize(0);
   }
+
+  @Test
+  void stringRepresentation() {
+    assertThat(deltaReader.toString())
+        .isEqualTo("InMemoryMetricReader{aggregationTemporality=DELTA}");
+  }
 }