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Log4j2 extensions (#1344)
* Initial commit of ContextDataProvider for Log4j 2.x * add initial OpenTelemetryJsonLayout implementation * move and reformat * add javadoc * update formatting * fixes for errorprone warnings * integrate feedback for TraceContextDataProvider * integrate feedback for OpenTelemetryJsonLayout * test reformat * check span validity rather than isRecording
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‎extensions/logging/log4j2_extensions/README.md‎

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OpenTelemetry Extensions for Log4j 2.x
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======================================================
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[![Javadocs][javadoc-image]][javadoc-url]
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This module contains extensions that support adding trace correlation information to your
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Log4j logs. Several modules are included.
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# Context Data Provider
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An implementation of the Log4J `ContextDataProvider` class is included. This class is loaded
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automatically via the Java ServiceProvider interface, so it works as long as this library is in
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your runtime classpath. This class will add three fields to the [thread context](https://logging.apache.org/log4j/2.x/manual/thread-context.html)
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for each log entry that happens within an open span. These fields can be addressed from Log4j
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layouts. For example, this `PatternLayout` configuration will add request correlation fields to
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your logs:
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```xml
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<PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} traceid='%X{traceid}' spanid='%X{spanid}' traceflags='%X{traceflags}' - %msg%n"/>
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```
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Similarly request correlation flags can be added to the JsonLayout:
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```xml
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<JsonLayout complete="false" compact="true">
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<KeyValuePair key="traceid" value="$${ctx:traceid}"/>
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<KeyValuePair key="spanid" value="$${ctx:spanid}"/>
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<KeyValuePair key="traceflags" value="$${ctx:traceflags}"/>
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</JsonLayout>
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```
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# Open Telemetry JSON Layout
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This module also includes a layout component, though it's output format is
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provisional and subject to change. To enable it, you must add
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`io.opentelemetry.contrib.logging.log4j2` to the `packages` attribute of the
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`Configuration` element in your log4j configuration file. You can then use
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the `<OpenTelemetryJsonLayout/>` element as a layout. An example configuration
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to output to standard output would be:
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```xml
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<Configuration status="WARN" packages="io.opentelemetry.contrib.logging.log4j2">
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<Appenders>
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<Console name="stdout">
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<OpenTelemetryJsonLayout/>
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</Console>
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</Appenders>
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<Loggers>
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<Root level="info">
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<AppenderRef ref="stdout"/>
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</Root>
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</Loggers>
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</Configuration>
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```
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[javadoc-image]: https://www.javadoc.io/badge/io.opentelemetry/opentelemetry-contrib-logging-log4j2-extensions.svg
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[javadoc-url]: https://www.javadoc.io/doc/io.opentelemetry/opentelemetry-contrib-logging-log4j2-extensions

‎extensions/logging/log4j2_extensions/build.gradle‎

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plugins {
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id "java"
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id "maven-publish"
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id "ru.vyarus.animalsniffer"
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}
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description = 'OpenTelemetry Contrib Log4j 2.x Extensions'
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ext.moduleName = "io.opentelemetry.extensions.logging.log4j2"
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dependencies {
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api project(':opentelemetry-api')
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api group: 'org.apache.logging.log4j', name: 'log4j-api', version: '2.13.3'
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api group: 'org.apache.logging.log4j', name: 'log4j-core', version: '2.13.3'
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implementation group: 'com.fasterxml.jackson.core', name: 'jackson-databind', version: '2.10.4'
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testImplementation project(':opentelemetry-sdk')
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testImplementation group: 'org.apache.logging.log4j', name: 'log4j-core', version: '2.13.3', classifier: 'tests'
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testImplementation group: 'com.google.code.gson', name: 'gson', version: '2.8.6'
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// For log4j async
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testImplementation group: 'com.lmax', name: 'disruptor', version: '3.4.2'
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annotationProcessor libraries.auto_value
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signature "org.codehaus.mojo.signature:java17:1.0@signature"
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signature "net.sf.androidscents.signature:android-api-level-24:7.0_r2@signature"
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}

‎extensions/logging/log4j2_extensions/src/main/java/io/opentelemetry/contrib/logging/log4j2/OpenTelemetryJsonLayout.java‎

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/*
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* Copyright 2020, OpenTelemetry Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package io.opentelemetry.contrib.logging.log4j2;
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import com.fasterxml.jackson.core.JsonFactory;
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import com.fasterxml.jackson.core.JsonGenerator;
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import java.io.IOException;
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import java.nio.charset.StandardCharsets;
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import org.apache.logging.log4j.Level;
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import org.apache.logging.log4j.core.LogEvent;
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import org.apache.logging.log4j.core.config.plugins.Plugin;
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import org.apache.logging.log4j.core.config.plugins.PluginFactory;
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import org.apache.logging.log4j.core.layout.AbstractStringLayout;
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import org.apache.logging.log4j.core.time.Instant;
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import org.apache.logging.log4j.core.util.StringBuilderWriter;
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import org.apache.logging.log4j.spi.StandardLevel;
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import org.apache.logging.log4j.util.ReadOnlyStringMap;
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import org.apache.logging.log4j.util.Strings;
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/**
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* This class implements a JSON layout for Log4j 2.x that will include request correlation
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* information in the form of traceid, spanid, and traceflags fields. The format is provisional, but
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* is designed to mirror the <a
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* href="https://github.com/open-telemetry/oteps/blob/master/text/logs/0097-log-data-model.md">Log
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* Data Model</a>
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*/
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@Plugin(name = "OpenTelemetryJsonLayout", category = "Core", elementType = "layout")
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public class OpenTelemetryJsonLayout extends AbstractStringLayout {
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JsonFactory factory = new JsonFactory();
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protected OpenTelemetryJsonLayout() {
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super(StandardCharsets.UTF_8);
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}
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@Override
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public String toSerializable(LogEvent event) {
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StringBuilderWriter writer = new StringBuilderWriter();
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try {
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ReadOnlyStringMap contextData = event.getContextData();
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JsonGenerator generator = factory.createGenerator(writer);
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generator.writeStartObject();
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writeTimestamp(generator, event.getInstant());
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generator.writeFieldName("name");
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generator.writeString(event.getLoggerName());
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generator.writeFieldName("body");
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generator.writeString(event.getMessage().getFormattedMessage());
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generator.writeFieldName("severitytext");
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generator.writeString(event.getLevel().name());
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generator.writeFieldName("severitynumber");
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generator.writeNumber(decodeSeverity(event.getLevel()));
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if (contextData.containsKey("traceid")) {
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writeRequestCorrelation(generator, contextData);
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}
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generator.writeEndObject();
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generator.close();
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return writer.toString();
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} catch (IOException e) {
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LOGGER.error(e);
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return Strings.EMPTY;
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}
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}
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private static int decodeSeverity(Level level) {
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int intLevel = level.intLevel();
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if (intLevel <= StandardLevel.FATAL.intLevel() && intLevel > 0) {
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return OpenTelemetryLogLevels.FATAL.asInt();
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} else if (intLevel <= StandardLevel.ERROR.intLevel()) {
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return OpenTelemetryLogLevels.ERROR.asInt();
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} else if (intLevel <= StandardLevel.WARN.intLevel()) {
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return OpenTelemetryLogLevels.WARN.asInt();
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} else if (intLevel <= StandardLevel.INFO.intLevel()) {
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return OpenTelemetryLogLevels.INFO.asInt();
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} else if (intLevel <= StandardLevel.DEBUG.intLevel()) {
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return OpenTelemetryLogLevels.DEBUG.asInt();
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} else if (intLevel <= StandardLevel.TRACE.intLevel()) {
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return OpenTelemetryLogLevels.TRACE.asInt();
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} else {
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return OpenTelemetryLogLevels.UNSET.asInt();
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}
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}
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private static void writeRequestCorrelation(
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JsonGenerator generator, ReadOnlyStringMap contextData) throws IOException {
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generator.writeFieldName("traceid");
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generator.writeString(contextData.getValue("traceid").toString());
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generator.writeFieldName("spanid");
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generator.writeString(contextData.getValue("spanid").toString());
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generator.writeFieldName("traceflags");
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generator.writeNumber(contextData.getValue("traceflags").toString());
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}
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private static void writeTimestamp(JsonGenerator generator, Instant instant) throws IOException {
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generator.writeFieldName("timestamp");
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generator.writeStartObject();
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generator.writeFieldName("millis");
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generator.writeNumber(instant.getEpochMillisecond());
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int nanos = instant.getNanoOfMillisecond();
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if (nanos > 0) {
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generator.writeFieldName("nanos");
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generator.writeNumber(instant.getNanoOfMillisecond());
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}
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generator.writeEndObject();
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}
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@PluginFactory
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public static OpenTelemetryJsonLayout build() {
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return new OpenTelemetryJsonLayout();
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}
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}

‎extensions/logging/log4j2_extensions/src/main/java/io/opentelemetry/contrib/logging/log4j2/OpenTelemetryLogLevels.java‎

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/*
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* Copyright 2020, OpenTelemetry Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package io.opentelemetry.contrib.logging.log4j2;
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/**
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* This enumerates the log levels defined in the <a
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* href="https://github.com/open-telemetry/oteps/blob/master/text/logs/0097-log-data-model.md">log
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* data model</a>.
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*/
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public enum OpenTelemetryLogLevels {
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UNSET(0),
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TRACE(1),
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TRACE2(2),
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TRACE3(3),
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TRACE4(4),
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DEBUG(5),
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DEBUG2(6),
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DEBUG3(7),
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DEBUG4(8),
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INFO(9),
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INFO2(10),
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INFO3(11),
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INFO4(12),
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WARN(13),
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WARN2(14),
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WARN3(15),
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WARN4(16),
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ERROR(17),
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ERROR2(18),
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ERROR3(19),
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ERROR4(20),
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FATAL(21),
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FATAL2(22),
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FATAL3(23),
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FATAL4(24),
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;
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private final int intLevel;
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OpenTelemetryLogLevels(int intLevel) {
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this.intLevel = intLevel;
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}
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public int asInt() {
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return intLevel;
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}
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}

‎extensions/logging/log4j2_extensions/src/main/java/io/opentelemetry/contrib/logging/log4j2/TraceContextDataProvider.java‎

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/*
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* Copyright 2020, OpenTelemetry Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package io.opentelemetry.contrib.logging.log4j2;
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import io.opentelemetry.trace.Span;
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import io.opentelemetry.trace.SpanContext;
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import io.opentelemetry.trace.TracingContextUtils;
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import java.util.HashMap;
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import java.util.Map;
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import org.apache.logging.log4j.core.util.ContextDataProvider;
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/**
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* This ContextDataProvider is loaded via the ServiceProvider facility. {@link #supplyContextData()}
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* is called when a log entry is created.
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*/
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public class TraceContextDataProvider implements ContextDataProvider {
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/**
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* This method is called on the creation of a log event, and is called in the same thread as the
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* call to the logger. This allows us to pull out request correlation information and make it
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* available to a layout, even if the logger is using an {@link
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* org.apache.logging.log4j.core.appender.AsyncAppender}
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*
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* @return A map containing string versions of the traceid, spanid, and traceflags which can then
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* be accessed from layout components
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* @see OpenTelemetryJsonLayout
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*/
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@Override
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public Map<String, String> supplyContextData() {
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Span span = TracingContextUtils.getCurrentSpan();
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Map<String, String> map = new HashMap<>();
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if (span != null && span.getContext().isValid()) {
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SpanContext context = span.getContext();
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if (context != null && context.isValid()) {
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map.put("traceid", span.getContext().getTraceId().toLowerBase16());
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map.put("spanid", span.getContext().getSpanId().toLowerBase16());
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map.put("traceflags", span.getContext().getTraceFlags().toLowerBase16());
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}
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}
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return map;
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}
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}

‎extensions/logging/log4j2_extensions/src/main/resources/META-INF/services/org.apache.logging.log4j.core.util.ContextDataProvider‎

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io.opentelemetry.contrib.logging.log4j2.TraceContextDataProvider

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