= Quarkus Google Cloud JSON Logging
Matthias Andreas Benkard
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:description: Quarkus Google Cloud JSON Logging Manual
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Structured logging to standard output according to the Google Cloud
Logging specification.


== Summary

This package contains a log formatter for JBoss Logging in the form of
a Quarkus plugin that implements the
https://cloud.google.com/logging/docs/structured-logging[Google Cloud
Logging JSON format] on standard output.

It is possible to log unstructured text, structured data, or a mixture
of both depending on the situation.


== Activation

Add the runtime POM to your dependency list. As long as the JAR is on
the classpath at both build time and runtime, the log formatter
automatically registers itself on startup.


=== Activation with Maven

[source,xml]
----
<project>
  ...

  <dependencies>
    ...

    <dependency>
      <groupId>eu.mulk.quarkus-googlecloud-jsonlogging</groupId>
      <artifactId>quarkus-googlecloud-jsonlogging</artifactId>
      <version>4.0.0</version>
    </dependency>

    ...
  </dependencies>

  ...
</project>
----


=== Activation with Gradle

[source,groovy]
----
dependencies {
  ...

  implementation("eu.mulk.quarkus-googlecloud-jsonlogging:quarkus-googlecloud-jsonlogging:4.0.0")

  ...
}
----


== Usage

Logging unstructured data requires no code changes. All logs are
automatically converted to Google-Cloud-Logging-compatible JSON.

Structured data can be logged in one of 3 different ways: by passing
https://javadocs.dev/eu.mulk.quarkus-googlecloud-jsonlogging/quarkus-googlecloud-jsonlogging/3.1.0/eu.mulk.quarkus.googlecloud.jsonlogging/eu/mulk/quarkus/googlecloud/jsonlogging/Label.html[Label]s
and
https://javadocs.dev/eu.mulk.quarkus-googlecloud-jsonlogging/quarkus-googlecloud-jsonlogging/3.1.0/eu.mulk.quarkus.googlecloud.jsonlogging/eu/mulk/quarkus/googlecloud/jsonlogging/StructuredParameter.html[StructuredParameter]s
as parameters to individual log entries, by supplying
https://javadocs.dev/eu.mulk.quarkus-googlecloud-jsonlogging/quarkus-googlecloud-jsonlogging/3.1.0/eu.mulk.quarkus.googlecloud.jsonlogging/eu/mulk/quarkus/googlecloud/jsonlogging/LabelProvider.html[LabelProvider]s
and
https://javadocs.dev/eu.mulk.quarkus-googlecloud-jsonlogging/quarkus-googlecloud-jsonlogging/3.1.0/eu.mulk.quarkus.googlecloud.jsonlogging/eu/mulk/quarkus/googlecloud/jsonlogging/StructuredParameterProvider.html[StructuredParameterProvider]s,
or by using the Mapped Diagnostic Context.


=== Using Label and StructuredParameter

Instances of
https://javadocs.dev/eu.mulk.quarkus-googlecloud-jsonlogging/quarkus-googlecloud-jsonlogging/3.1.0/eu.mulk.quarkus.googlecloud.jsonlogging/eu/mulk/quarkus/googlecloud/jsonlogging/Label.html[Label]
and
https://javadocs.dev/eu.mulk.quarkus-googlecloud-jsonlogging/quarkus-googlecloud-jsonlogging/3.1.0/eu.mulk.quarkus.googlecloud.jsonlogging/eu/mulk/quarkus/googlecloud/jsonlogging/StructuredParameter.html[StructuredParameter]
can be passed as log parameters to the `*f` family of logging
functions on JBoss Logging's
https://docs.jboss.org/jbosslogging/latest/org/jboss/logging/Logger.html[Logger].

Simple key–value pairs are represented by
https://javadocs.dev/eu.mulk.quarkus-googlecloud-jsonlogging/quarkus-googlecloud-jsonlogging/3.1.0/eu.mulk.quarkus.googlecloud.jsonlogging/eu/mulk/quarkus/googlecloud/jsonlogging/KeyValueParameter.html[KeyValueParameter].

**Example:**

[source,java]
----
logger.logf(
  "Request rejected: unauthorized.",
  Label.of("requestId", "123"),
  KeyValueParameter.of("resource", "/users/mulk"),
  KeyValueParameter.of("method", "PATCH"),
  KeyValueParameter.of("reason", "invalid token"));
----

Result:

[source,json]
----
{
  "jsonPayload": {
    "message": "Request rejected: unauthorized.",
    "resource": "/users/mulk",
    "method": "PATCH",
    "reason": "invalid token"
  },
  "labels": {
    "requestId": "123"
  }
}
----


=== Using LabelProvider and StructuredParameterProvider

Any CDI beans that implement
https://javadocs.dev/eu.mulk.quarkus-googlecloud-jsonlogging/quarkus-googlecloud-jsonlogging/3.1.0/eu.mulk.quarkus.googlecloud.jsonlogging/eu/mulk/quarkus/googlecloud/jsonlogging/LabelProvider.html[LabelProvider]
and
https://javadocs.dev/eu.mulk.quarkus-googlecloud-jsonlogging/quarkus-googlecloud-jsonlogging/3.1.0/eu.mulk.quarkus.googlecloud.jsonlogging/eu/mulk/quarkus/googlecloud/jsonlogging/StructuredParameterProvider.html[StructuredParameterProvider]
are discovered at build time and consulted to provide labels and
parameters for each message that is logged.  This can be used to
provide contextual information such as tracing and request IDs stored
in thread-local storage.

Alternatively, you can also register providers through the Java
https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/ServiceLoader.html[ServiceLoader]
mechanism.

**Example:**

[source,java]
----
@Singleton
@Unremovable
public final class TraceLogParameterProvider implements StructuredParameterProvider, LabelProvider {

  @Override
  public StructuredParameter getParameter() {
    var b = Json.createObjectBuilder();
    b.add("traceId", Span.current().getSpanContext().getTraceId());
    b.add("spanId", Span.current().getSpanContext().getSpanId());
    return () -> b;
  }

  @Override
  public Collection<Label> getLabels() {
    return List.of(Label.of("requestId", "123"));
  }
}
----

Result:

[source,json]
----
{
  "jsonPayload": {
    "message": "Request rejected: unauthorized.",
    "traceId": "39f9a49a9567a8bd7087b708f8932550",
    "spanId": "c7431b14630b633d"
  },
  "labels": {
    "requestId": "123"
  }
}
----


=== Using the Mapped Diagnostic Context

Any key–value pairs in JBoss Logging's thread-local
https://docs.jboss.org/jbosslogging/latest/org/jboss/logging/MDC.html[MDC]
are added to the resulting JSON.

**Example:**

[source,java]
----
MDC.put("resource", "/users/mulk");
MDC.put("method", "PATCH");
logger.logf("Request rejected: unauthorized.");
----

Result:

[source,json]
----
{
  "jsonPayload": {
    "message": "Request rejected: unauthorized.",
    "resource": "/users/mulk",
    "method": "PATCH"
  }
}
----