Add missing Javadocs.

Change-Id: I63f0086ed99a259391ef6094a5218744d4b2fc60

8 files changed, 396 insertions, 8 deletions

diff --git a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Formatter.java b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Formatter.java
index c8bb310..066f709 100644
--- a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Formatter.java
+++ b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Formatter.java
@@ -32,6 +32,12 @@ public class Formatter extends ExtFormatter {
   private final List<StructuredParameterProvider> parameterProviders;
   private final List<LabelProvider> labelProviders;
 
+  /**
+   * Constructs a {@link Formatter}.
+   *
+   * @param parameterProviders the {@link StructuredParameterProvider}s to apply to each log entry.
+   * @param labelProviders the {@link LabelProvider}s to apply to each log entry.
+   */
   public Formatter(
       Collection<StructuredParameterProvider> parameterProviders,
       Collection<LabelProvider> labelProviders) {
diff --git a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/GoogleCloudJsonLoggingRecorder.java b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/GoogleCloudJsonLoggingRecorder.java
index a26f4da..7234a71 100644
--- a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/GoogleCloudJsonLoggingRecorder.java
+++ b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/GoogleCloudJsonLoggingRecorder.java
@@ -3,12 +3,22 @@ package eu.mulk.quarkus.googlecloud.jsonlogging;
 import io.quarkus.arc.Arc;
 import io.quarkus.runtime.RuntimeValue;
 import io.quarkus.runtime.annotations.Recorder;
+import java.util.Collection;
 import java.util.Optional;
 import java.util.stream.Collectors;
 
 /** A Quarkus recorder that registers {@link Formatter} as a log formatter for the application. */
 @Recorder
 public class GoogleCloudJsonLoggingRecorder {
+
+  /**
+   * Registers {@link Formatter} as a log formatter for the application.
+   *
+   * <p>Collects all discoverable {@link StructuredParameterProvider}s and {@link LabelProvider}s
+   * and passes them to {@link Formatter#Formatter(Collection, Collection)}.
+   *
+   * @return the registered {@link Formatter}.
+   */
   public RuntimeValue<Optional<java.util.logging.Formatter>> initialize() {
 
     var parameterProviders =
diff --git a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/KeyValueParameter.java b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/KeyValueParameter.java
index 173d9e2..a5924b4 100644
--- a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/KeyValueParameter.java
+++ b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/KeyValueParameter.java
@@ -8,18 +8,29 @@ import javax.json.JsonObjectBuilder;
 import javax.json.JsonValue;
 
 /**
- * A simple single key--value pair forming a {@link StructuredParameter}.
+ * A simple single key–value pair forming a {@link StructuredParameter}.
  *
- * <p>This class is suitable for the common case of logging a key—value pair as parameter to the
+ * <p>This class is suitable for the common case of logging a key–value pair as parameter to the
  * {@code *f} family of logging functions on {@link org.jboss.logging.Logger}. For advanced use
  * cases, provide your own implementation of {@link StructuredParameter}.
  *
- * <p>Example:
+ * <p><strong>Example:</strong>
  *
  * <pre>{@code
  * logger.infof("Application starting.", StructuredParameter.of("version", "1.0"));
  * }</pre>
  *
+ * Result:
+ *
+ * <pre>{@code
+ * {
+ *   "jsonPayload": {
+ *     "message": "Application starting.",
+ *     "version": "1.0"
+ *   }
+ * }
+ * }</pre>
+ *
  * @see Label
  * @see StructuredParameter
  */
@@ -33,30 +44,93 @@ public final class KeyValueParameter implements StructuredParameter {
     this.value = value;
   }
 
+  /**
+   * Creates a {@link KeyValueParameter} from a {@link String} value.
+   *
+   * <p>The resulting JSON value is of type {@code string}.
+   *
+   * @param key the key part of the key–value pair.
+   * @param value the value part of the key–value pair.
+   * @return the newly constructed parameter, ready to be passed to a logging function.
+   */
   public static KeyValueParameter of(String key, String value) {
     return new KeyValueParameter(key, Json.createValue(value));
   }
 
+  /**
+   * Creates a {@link KeyValueParameter} from an {@code int} value.
+   *
+   * <p>The resulting JSON value is of type {@code number}.
+   *
+   * @param key the key part of the key–value pair.
+   * @param value the value part of the key–value pair.
+   * @return the newly constructed parameter, ready to be passed to a logging function.
+   */
   public static KeyValueParameter of(String key, int value) {
     return new KeyValueParameter(key, Json.createValue(value));
   }
 
+  /**
+   * Creates a {@link KeyValueParameter} from a {@code long} value.
+   *
+   * <p>The resulting JSON value is of type {@code number}.
+   *
+   * @param key the key part of the key–value pair.
+   * @param value the value part of the key–value pair.
+   * @return the newly constructed parameter, ready to be passed to a logging function.
+   */
   public static KeyValueParameter of(String key, long value) {
     return new KeyValueParameter(key, Json.createValue(value));
   }
 
+  /**
+   * Creates a {@link KeyValueParameter} from a {@code double} value.
+   *
+   * <p>The resulting JSON value is of type {@code number}.
+   *
+   * @param key the key part of the key–value pair.
+   * @param value the value part of the key–value pair.
+   * @return the newly constructed parameter, ready to be passed to a logging function.
+   */
   public static KeyValueParameter of(String key, double value) {
     return new KeyValueParameter(key, Json.createValue(value));
   }
 
+  /**
+   * Creates a {@link KeyValueParameter} from a {@link BigDecimal} value.
+   *
+   * <p>The resulting JSON value is of type {@code number}.
+   *
+   * @param key the key part of the key–value pair.
+   * @param value the value part of the key–value pair.
+   * @return the newly constructed parameter, ready to be passed to a logging function.
+   */
   public static KeyValueParameter of(String key, BigDecimal value) {
     return new KeyValueParameter(key, Json.createValue(value));
   }
 
+  /**
+   * Creates a {@link KeyValueParameter} from a {@link BigInteger} value.
+   *
+   * <p>The resulting JSON value is of type {@code number}.
+   *
+   * @param key the key part of the key–value pair.
+   * @param value the value part of the key–value pair.
+   * @return the newly constructed parameter, ready to be passed to a logging function.
+   */
   public static KeyValueParameter of(String key, BigInteger value) {
     return new KeyValueParameter(key, Json.createValue(value));
   }
 
+  /**
+   * Creates a {@link KeyValueParameter} from a {@code boolean} value.
+   *
+   * <p>The resulting JSON value is of type {@code boolean}.
+   *
+   * @param key the key part of the key–value pair.
+   * @param value the value part of the key–value pair.
+   * @return the newly constructed parameter, ready to be passed to a logging function.
+   */
   public static KeyValueParameter of(String key, boolean value) {
     return new KeyValueParameter(key, value ? JsonValue.TRUE : JsonValue.FALSE);
   }
@@ -66,10 +140,23 @@ public final class KeyValueParameter implements StructuredParameter {
     return Json.createObjectBuilder().add(key, value);
   }
 
+  /**
+   * The key part of the key–value pair.
+   *
+   * @return the key part of the key–value pair.
+   */
   public String key() {
     return key;
   }
 
+  /**
+   * The value part of the key–value pair.
+   *
+   * <p>Can be of any non-composite JSON type (i.e. {@code string}, {@code number}, or {@code
+   * boolean}).
+   *
+   * @return the value pairt of the key–value pair.
+   */
   public JsonValue value() {
     return value;
   }
diff --git a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Label.java b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Label.java
index 72929f1..33664dd 100644
--- a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Label.java
+++ b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/Label.java
@@ -8,12 +8,23 @@ import java.util.Objects;
  * <p>Instances of {@link Label} can be passed as log parameters to the {@code *f} family of logging
  * functions on {@link org.jboss.logging.Logger}.
  *
- * <p>Example:
+ * <p><strong>Example:</strong>
  *
  * <pre>{@code
  * logger.logf("Request rejected: unauthorized.", Label.of("requestId", "123"));
  * }</pre>
  *
+ * Result:
+ *
+ * <pre>{@code
+ * {
+ *   "textPayload": "Request rejected: unauthorized.",
+ *   "labels": {
+ *     "requestId": "123"
+ *   }
+ * }
+ * }</pre>
+ *
  * @see KeyValueParameter
  * @see StructuredParameter
  */
@@ -27,14 +38,37 @@ public final class Label {
     this.value = value;
   }
 
+  /**
+   * Constructs a {@link Label} from a key (i.e. name) and a value.
+   *
+   * <p>It is often useful for the key to be a {@link String} constant that is shared by multiple
+   * parts of the program.
+   *
+   * @param key the key (name) of the label.
+   * @param value the value of the label.
+   * @return the newly constructed {@link Label}, ready to be passed to a logging function.
+   */
   public static Label of(String key, String value) {
     return new Label(key, value);
   }
 
+  /**
+   * The name of the label.
+   *
+   * <p>It is often useful for this to be a {@link String} constant that is shared by multiple parts
+   * of the program.
+   *
+   * @return the name of the label.
+   */
   public String key() {
     return key;
   }
 
+  /**
+   * The value of the label.
+   *
+   * @return the value of the label.
+   */
   public String value() {
     return value;
   }
diff --git a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/LabelProvider.java b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/LabelProvider.java
index ef31bcc..dbd035c 100644
--- a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/LabelProvider.java
+++ b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/LabelProvider.java
@@ -7,10 +7,39 @@ import java.util.Collection;
  *
  * <p>Any CDI beans registered under this class are applied to each log entry that is logged.
  *
+ * <p><strong>Example:</strong>
+ *
+ * <pre>{@code
+ * @Singleton
+ * @Unremovable
+ * public final class RequestIdLabelProvider implements LabelProvider {
+ *
+ *   @Override
+ *   public Collection<Label> getLabels() {
+ *     return List.of(Label.of("requestId", RequestContext.current().getRequestId()));
+ *   }
+ * }
+ * }</pre>
+ *
+ * Result:
+ *
+ * <pre>{@code
+ * {
+ *   "textPayload": "Request rejected: unauthorized.",
+ *   "labels": {
+ *     "requestId": "123"
+ *   }
+ * }
+ * }</pre>
+ *
  * @see StructuredParameterProvider
  */
 public interface LabelProvider {
 
-  /** Provides a collection of {@link Label}s to add to each log entry that is logged. */
+  /**
+   * Provides a collection of {@link Label}s to add to each log entry that is logged.
+   *
+   * @return a collection of {@link Label}s to add to each log entry that is logged.
+   */
   Collection<Label> getLabels();
 }
diff --git a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/StructuredParameter.java b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/StructuredParameter.java
index fa326d5..c718080 100644
--- a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/StructuredParameter.java
+++ b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/StructuredParameter.java
@@ -23,10 +23,12 @@ import javax.json.JsonObjectBuilder;
 public interface StructuredParameter {
 
   /**
-   * The JSON to be embedded in the log entry.
+   * The JSON to be embedded in the payload of the log entry.
    *
    * <p>May contain multiple keys and values as well as nested objects. Each top-level entry of the
-   * returned object is embedded as a top-level entry in the log entry.
+   * returned object is embedded as a top-level entry in the payload of the log entry.
+   *
+   * @return A {@link JsonObjectBuilder} holding a set of key–value pairs.
    */
   JsonObjectBuilder json();
 }
diff --git a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/StructuredParameterProvider.java b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/StructuredParameterProvider.java
index d8ab39b..cacfea6 100644
--- a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/StructuredParameterProvider.java
+++ b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/StructuredParameterProvider.java
@@ -5,10 +5,47 @@ package eu.mulk.quarkus.googlecloud.jsonlogging;
  *
  * <p>Any CDI beans registered under this class are applied to each log entry that is logged.
  *
+ * <p><strong>Example:</strong>
+ *
+ * <pre>{@code
+ * @Singleton
+ * @Unremovable
+ * public final class TraceLogParameterProvider implements StructuredParameterProvider {
+ *
+ *   @Override
+ *   public StructuredParameter getParameter() {
+ *     var b = Json.createObjectBuilder();
+ *     b.add("traceId", Span.current().getSpanContext().getTraceId());
+ *     b.add("spanId", Span.current().getSpanContext().getSpanId());
+ *     return () -> b;
+ *   }
+ * }
+ * }</pre>
+ *
+ * Result:
+ *
+ * <pre>{@code
+ * {
+ *   "jsonPayload": {
+ *     "message": "Request rejected: unauthorized.",
+ *     "traceId": "39f9a49a9567a8bd7087b708f8932550",
+ *     "spanId": "c7431b14630b633d"
+ *   }
+ * }
+ * }</pre>
+ *
  * @see LabelProvider
  */
 public interface StructuredParameterProvider {
 
-  /** Provides a {@link StructuredParameter} to add to each log entry that is logged. */
+  /**
+   * Provides a {@link StructuredParameter} to add to each log entry that is logged.
+   *
+   * <p>It is often useful to return a custom {@link StructuredParameter} rather than a {@link
+   * KeyValueParameter} from this method. This way multiple key–value pairs can be generated by a
+   * single invocation.
+   *
+   * @return a {@link StructuredParameter} to add to each log entry that is logged.
+   */
   StructuredParameter getParameter();
 }
diff --git a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/package-info.java b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/package-info.java
index cbb6e16..110ab73 100644
--- a/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/package-info.java
+++ b/runtime/src/main/java/eu/mulk/quarkus/googlecloud/jsonlogging/package-info.java
@@ -1,5 +1,188 @@
 /**
  * Provides structured logging to standard output according to the Google Cloud Logging
  * specification.
+ *
+ * <ul>
+ *   <li><a href="#sect-summary">Summary</a>
+ *   <li><a href="#sect-activation">Activation</a>
+ *   <li><a href="#sect-usage">Usage</a>
+ * </ul>
+ *
+ * <h2 id="sect-summary">Summary</h2>
+ *
+ * <p>This package contains a log formatter for JBoss Logging in the form of a Quarkus plugin that
+ * implements the <a href="https://cloud.google.com/logging/docs/structured-logging">Google Cloud
+ * Logging JSON format</a> on standard output.
+ *
+ * <p>It is possible to log unstructured text, structured data, or a mixture of both depending on
+ * the situation.
+ *
+ * <h2 id="sect-activation">Activation</h2>
+ *
+ * <ul>
+ *   <li><a href="#sect-activation-maven">Activation with Maven</a>
+ *   <li><a href="#sect-activation-gradle">Activation with Gradle</a>
+ * </ul>
+ *
+ * <p>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.
+ *
+ * <h3 id="sect-activation-maven">Activation with Maven</h3>
+ *
+ * <pre>{@code
+ * <project>
+ *   ...
+ *
+ *   <dependencies>
+ *     ...
+ *
+ *     <dependency>
+ *       <groupId>eu.mulk.quarkus-googlecloud-jsonlogging</groupId>
+ *       <artifactId>quarkus-googlecloud-jsonlogging</artifactId>
+ *       <version>3.1.0</version>
+ *     </dependency>
+ *
+ *     ...
+ *   </dependencies>
+ *
+ *   ...
+ * </project>
+ * }</pre>
+ *
+ * <h3 id="sect-activation-gradle">Activation with Gradle</h3>
+ *
+ * <pre>{@code
+ * dependencies {
+ *   ...
+ *
+ *   implementation("eu.mulk.quarkus-googlecloud-jsonlogging:quarkus-googlecloud-jsonlogging:3.1.0")
+ *
+ *   ...
+ * }
+ * }</pre>
+ *
+ * <h2 id="sect-usage">Usage</h2>
+ *
+ * <ul>
+ *   <li><a href="#sect-usage-parameter">Using Label and StructuredParameter</a>
+ *   <li><a href="#sect-usage-provider">Using LabelProvider and StructuredParameterProvider</a>
+ *   <li><a href="#sect-usage-mdc">Using the Mapped Diagnostic Context</a>
+ * </ul>
+ *
+ * <p>Logging unstructured data requires no code changes. All logs are automatically converted to
+ * Google-Cloud-Logging-compatible JSON.
+ *
+ * <p>Structured data can be logged in one of 3 different ways: by passing {@link
+ * eu.mulk.quarkus.googlecloud.jsonlogging.Label}s and {@link
+ * eu.mulk.quarkus.googlecloud.jsonlogging.StructuredParameter}s as parameters to individual log
+ * entries, by supplying {@link eu.mulk.quarkus.googlecloud.jsonlogging.LabelProvider}s and {@link
+ * eu.mulk.quarkus.googlecloud.jsonlogging.StructuredParameterProvider}s, or by using the Mapped
+ * Diagnostic Context.
+ *
+ * <h3 id="sect-usage-parameter">Using Label and StructuredParameter</h3>
+ *
+ * <p>Instances of {@link eu.mulk.quarkus.googlecloud.jsonlogging.Label} and {@link
+ * eu.mulk.quarkus.googlecloud.jsonlogging.StructuredParameter} can be passed as log parameters to
+ * the {@code *f} family of logging functions on JBoss Logging's {@link org.jboss.logging.Logger}.
+ *
+ * <p>Simple key–value pairs are represented by {@link
+ * eu.mulk.quarkus.googlecloud.jsonlogging.KeyValueParameter}.
+ *
+ * <p><strong>Example:</strong>
+ *
+ * <pre>{@code
+ * logger.logf(
+ *   "Request rejected: unauthorized.",
+ *   Label.of("requestId", "123"),
+ *   KeyValueParameter.of("resource", "/users/mulk"),
+ *   KeyValueParameter.of("method", "PATCH"),
+ *   KeyValueParameter.of("reason", "invalid token"));
+ * }</pre>
+ *
+ * Result:
+ *
+ * <pre>{@code
+ * {
+ *   "jsonPayload": {
+ *     "message": "Request rejected: unauthorized.",
+ *     "resource": "/users/mulk",
+ *     "method": "PATCH",
+ *     "reason": "invalid token"
+ *   },
+ *   "labels": {
+ *     "requestId": "123"
+ *   }
+ * }
+ * }</pre>
+ *
+ * <h3 id="sect-usage-provider">Using LabelProvider and StructuredParameterProvider</h3>
+ *
+ * <p>Any CDI beans that implement {@link eu.mulk.quarkus.googlecloud.jsonlogging.LabelProvider}s
+ * and {@link eu.mulk.quarkus.googlecloud.jsonlogging.StructuredParameterProvider}s 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.
+ *
+ * <p><strong>Example:</strong>
+ *
+ * <pre>{@code
+ * @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"));
+ *   }
+ * }
+ * }</pre>
+ *
+ * Result:
+ *
+ * <pre>{@code
+ * {
+ *   "jsonPayload": {
+ *     "message": "Request rejected: unauthorized.",
+ *     "traceId": "39f9a49a9567a8bd7087b708f8932550",
+ *     "spanId": "c7431b14630b633d"
+ *   },
+ *   "labels": {
+ *     "requestId": "123"
+ *   }
+ * }
+ * }</pre>
+ *
+ * <h3 id="sect-usage-mdc">Using the Mapped Diagnostic Context</h3>
+ *
+ * <p>Any key–value pairs in JBoss Logging's thread-local {@link org.jboss.logging.MDC} are added to
+ * the resulting JSON.
+ *
+ * <p><strong>Example:</strong>
+ *
+ * <pre>{@code
+ * MDC.put("resource", "/users/mulk");
+ * MDC.put("method", "PATCH");
+ * logger.logf("Request rejected: unauthorized.");
+ * }</pre>
+ *
+ * Result:
+ *
+ * <pre>{@code
+ * {
+ *   "jsonPayload": {
+ *     "message": "Request rejected: unauthorized.",
+ *     "resource": "/users/mulk",
+ *     "method": "PATCH"
+ *   }
+ * }
+ * }</pre>
  */
 package eu.mulk.quarkus.googlecloud.jsonlogging;