Add a OTLP JSON span exporter to logs.

exporters/logging-otlp/README.md

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+# OpenTelemetry - OTLP JSON Logging Exporter
+
+[![Javadocs][javadoc-image]][javadoc-url]
+
+Exporters for writing data to logs using OTLP JSON format. They are appropriate for writing spans or
+metrics to logs in a way that is both human-readable and structured for machine parsing.
+
+[javadoc-image]: https://www.javadoc.io/badge/io.opentelemetry/opentelemetry-exporters-otlpjson.svg
+[javadoc-url]: https://www.javadoc.io/doc/io.opentelemetry/opentelemetry-exporters-otlpjson

exporters/logging-otlp/build.gradle

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+plugins {
+    id "java-library"
+    id "maven-publish"
+
+    id "ru.vyarus.animalsniffer"
+}
+
+description = 'OpenTelemetry Protocol JSON Logging Exporters'
+ext.moduleName = "io.opentelemetry.exporter.logging.otlp"
+
+dependencies {
+    compileOnly project(':sdk:trace')
+    compileOnly project(':sdk:metrics')
+
+    implementation project(':sdk-extensions:otproto'),
+            'org.curioswitch.curiostack:protobuf-jackson:1.1.0'
+
+    testImplementation project(':sdk:testing'),
+            'org.skyscreamer:jsonassert:1.5.0'
+
+    signature libraries.android_signature
+}

exporters/logging-otlp/src/main/java/io/opentelemetry/exporter/logging/otlp/HexEncodingStringJsonGenerator.java

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+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.logging.otlp;
+
+import com.fasterxml.jackson.core.Base64Variant;
+import com.fasterxml.jackson.core.JsonFactory;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.core.io.SegmentedStringWriter;
+import com.fasterxml.jackson.core.util.JsonGeneratorDelegate;
+import java.io.IOException;
+
+final class HexEncodingStringJsonGenerator extends JsonGeneratorDelegate {
+
+  static final JsonFactory JSON_FACTORY = new JsonFactory();
+
+  static JsonGenerator create(SegmentedStringWriter stringWriter) {
+    final JsonGenerator delegate;
+    try {
+      delegate = JSON_FACTORY.createGenerator(stringWriter);
+    } catch (IOException e) {
+      throw new IllegalStateException("Unable to create in-memory JsonGenerator, can't happen.", e);
+    }
+    return new HexEncodingStringJsonGenerator(delegate);
+  }
+
+  private HexEncodingStringJsonGenerator(JsonGenerator delegate) {
+    super(delegate);
+  }
+
+  @Override
+  public void writeBinary(Base64Variant b64variant, byte[] data, int offset, int len)
+      throws IOException {
+    writeString(bytesToHex(data, offset, len));
+  }
+
+  private static final char[] HEX_ARRAY = "0123456789abcdef".toCharArray();
+
+  private static String bytesToHex(byte[] bytes, int offset, int len) {
+    char[] hexChars = new char[len * 2];
+    for (int i = 0; i < len; i++) {
+      int v = bytes[offset + i] & 0xFF;
+      hexChars[i * 2] = HEX_ARRAY[v >>> 4];
+      hexChars[i * 2 + 1] = HEX_ARRAY[v & 0x0F];
+    }
+    return new String(hexChars);
+  }
+}

exporters/logging-otlp/src/main/java/io/opentelemetry/exporter/logging/otlp/OtlpJsonLoggingMetricExporter.java

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+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.logging.otlp;
+
+import static io.opentelemetry.exporter.logging.otlp.HexEncodingStringJsonGenerator.JSON_FACTORY;
+
+import com.fasterxml.jackson.core.Base64Variant;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.core.io.SegmentedStringWriter;
+import com.fasterxml.jackson.core.util.JsonGeneratorDelegate;
+import io.opentelemetry.proto.metrics.v1.ResourceMetrics;
+import io.opentelemetry.sdk.common.CompletableResultCode;
+import io.opentelemetry.sdk.extension.otproto.MetricAdapter;
+import io.opentelemetry.sdk.metrics.data.MetricData;
+import io.opentelemetry.sdk.metrics.export.MetricExporter;
+import java.io.IOException;
+import java.util.Collection;
+import java.util.List;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import org.curioswitch.common.protobuf.json.MessageMarshaller;
+
+/**
+ * A {@link MetricExporter} which writes {@linkplain MetricData spans} to a {@link Logger} in OTLP
+ * JSON format. Each log line will include a single {@link ResourceMetrics}.
+ */
+public class OtlpJsonLoggingMetricExporter implements MetricExporter {
+
+  private static final MessageMarshaller marshaller =
+      MessageMarshaller.builder()
+          .register(ResourceMetrics.class)
+          .omittingInsignificantWhitespace(true)
+          .build();
+
+  // Visible for testing
+  static final Logger logger = Logger.getLogger(OtlpJsonLoggingMetricExporter.class.getName());
+
+  /** Returns a new {@link OtlpJsonLoggingMetricExporter}. */
+  public static MetricExporter create() {
+    return new OtlpJsonLoggingMetricExporter();
+  }
+
+  private OtlpJsonLoggingMetricExporter() {}
+
+  @Override
+  public CompletableResultCode export(Collection<MetricData> metrics) {
+    List<ResourceMetrics> allResourceMetrics = MetricAdapter.toProtoResourceMetrics(metrics);
+    for (ResourceMetrics resourceMetrics : allResourceMetrics) {
+      SegmentedStringWriter sw = new SegmentedStringWriter(JSON_FACTORY._getBufferRecycler());
+      try (JsonGenerator gen = HexEncodingStringJsonGenerator.create(sw)) {
+        marshaller.writeValue(resourceMetrics, gen);
+      } catch (IOException e) {
+        // Shouldn't happen in practice, just skip it.
+        continue;
+      }
+      logger.log(Level.INFO, sw.getAndClear());
+    }
+    return CompletableResultCode.ofSuccess();
+  }
+
+  @Override
+  public CompletableResultCode flush() {
+    return CompletableResultCode.ofSuccess();
+  }
+
+  @Override
+  public CompletableResultCode shutdown() {
+    return CompletableResultCode.ofSuccess();
+  }
+
+  private static final class HexEncodingStringJsonGenerator extends JsonGeneratorDelegate {
+
+    static JsonGenerator create(SegmentedStringWriter stringWriter) {
+      final JsonGenerator delegate;
+      try {
+        delegate = JSON_FACTORY.createGenerator(stringWriter);
+      } catch (IOException e) {
+        throw new IllegalStateException(
+            "Unable to create in-memory JsonGenerator, can't happen.", e);
+      }
+      return new HexEncodingStringJsonGenerator(delegate);
+    }
+
+    private HexEncodingStringJsonGenerator(JsonGenerator delegate) {
+      super(delegate);
+    }
+
+    @Override
+    public void writeBinary(Base64Variant b64variant, byte[] data, int offset, int len)
+        throws IOException {
+      writeString(bytesToHex(data, offset, len));
+    }
+
+    private static final char[] HEX_ARRAY = "0123456789abcdef".toCharArray();
+
+    private static String bytesToHex(byte[] bytes, int offset, int len) {
+      char[] hexChars = new char[len * 2];
+      for (int i = 0; i < len; i++) {
+        int v = bytes[offset + i] & 0xFF;
+        hexChars[i * 2] = HEX_ARRAY[v >>> 4];
+        hexChars[i * 2 + 1] = HEX_ARRAY[v & 0x0F];
+      }
+      return new String(hexChars);
+    }
+  }
+}

exporters/logging-otlp/src/main/java/io/opentelemetry/exporter/logging/otlp/OtlpJsonLoggingSpanExporter.java

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+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.exporter.logging.otlp;
+
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.core.io.SegmentedStringWriter;
+import io.opentelemetry.proto.trace.v1.ResourceSpans;
+import io.opentelemetry.sdk.common.CompletableResultCode;
+import io.opentelemetry.sdk.extension.otproto.SpanAdapter;
+import io.opentelemetry.sdk.trace.data.SpanData;
+import io.opentelemetry.sdk.trace.export.SpanExporter;
+import java.io.IOException;
+import java.util.Collection;
+import java.util.List;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import org.curioswitch.common.protobuf.json.MessageMarshaller;
+
+/**
+ * A {@link SpanExporter} which writes {@linkplain SpanData spans} to a {@link Logger} in OTLP JSON
+ * format. Each log line will include a single {@link ResourceSpans}.
+ */
+public class OtlpJsonLoggingSpanExporter implements SpanExporter {
+
+  private static final MessageMarshaller marshaller =
+      MessageMarshaller.builder()
+          .register(ResourceSpans.class)
+          .omittingInsignificantWhitespace(true)
+          .build();
+
+  // Visible for testing
+  static final Logger logger = Logger.getLogger(OtlpJsonLoggingSpanExporter.class.getName());
+
+  /** Returns a new {@link OtlpJsonLoggingSpanExporter}. */
+  public static SpanExporter create() {
+    return new OtlpJsonLoggingSpanExporter();
+  }
+
+  private OtlpJsonLoggingSpanExporter() {}
+
+  @Override
+  public CompletableResultCode export(Collection<SpanData> spans) {
+    List<ResourceSpans> allResourceSpans = SpanAdapter.toProtoResourceSpans(spans);
+    for (ResourceSpans resourceSpans : allResourceSpans) {
+      SegmentedStringWriter sw =
+          new SegmentedStringWriter(
+              HexEncodingStringJsonGenerator.JSON_FACTORY._getBufferRecycler());
+      try (JsonGenerator gen = HexEncodingStringJsonGenerator.create(sw)) {
+        marshaller.writeValue(resourceSpans, gen);
+      } catch (IOException e) {
+        // Shouldn't happen in practice, just skip it.
+        continue;
+      }
+      logger.log(Level.INFO, sw.getAndClear());
+    }
+    return CompletableResultCode.ofSuccess();
+  }
+
+  @Override
+  public CompletableResultCode flush() {
+    return CompletableResultCode.ofSuccess();
+  }
+
+  @Override
+  public CompletableResultCode shutdown() {
+    return CompletableResultCode.ofSuccess();
+  }
+}

exporters/logging-otlp/src/main/java/io/opentelemetry/exporter/logging/otlp/package-info.java

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+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/** OpenTelemetry exporters which writes spans or metrics to log using OTLP JSON format. */
+@ParametersAreNonnullByDefault
+package io.opentelemetry.exporter.logging.otlp;
+
+import javax.annotation.ParametersAreNonnullByDefault;