add self reference to TaggedMetricInstrument

Signed-off-by: Johannes Schneider <johannes.schneider@bosch.io>

internal/utils/metrics/src/main/java/org/eclipse/ditto/internal/utils/metrics/instruments/TaggedMetricInstrument.java

@@ -23,6 +23,11 @@
  */
 public interface TaggedMetricInstrument<T extends MetricInstrument> extends MetricInstrument {
 
+    /**
+     * @return this instance.
+     */
+    T self();
+
     /**
      * Adds the given tag to the timer.
      * Already existing tags with the same key will be overridden.

internal/utils/metrics/src/main/java/org/eclipse/ditto/internal/utils/metrics/instruments/counter/Counter.java

@@ -20,6 +20,11 @@
  */
 public interface Counter extends ResettableMetricInstrument, TaggedMetricInstrument<Counter> {
 
+    @Override
+    default Counter self() {
+        return this;
+    }
+
     /**
      * Increments the value of the counter by one.
      *

internal/utils/metrics/src/main/java/org/eclipse/ditto/internal/utils/metrics/instruments/gauge/Gauge.java

@@ -20,6 +20,11 @@
  */
 public interface Gauge extends ResettableMetricInstrument, TaggedMetricInstrument<Gauge> {
 
+    @Override
+    default Gauge self() {
+        return this;
+    }
+
     /**
      * Increments the value of the gauge by one.
      *

internal/utils/metrics/src/main/java/org/eclipse/ditto/internal/utils/metrics/instruments/histogram/Histogram.java

@@ -20,6 +20,11 @@
  */
 public interface Histogram extends ResettableMetricInstrument, TaggedMetricInstrument<Histogram> {
 
+    @Override
+    default Histogram self() {
+        return this;
+    }
+
     /**
      * Records the specified value in the histogram.
      *

internal/utils/metrics/src/main/java/org/eclipse/ditto/internal/utils/metrics/instruments/timer/PreparedTimer.java

@@ -24,6 +24,11 @@
  */
 public interface PreparedTimer extends Timer, ResettableMetricInstrument, TaggedMetricInstrument<PreparedTimer> {
 
+    @Override
+    default PreparedTimer self() {
+        return this;
+    }
+
     /**
      * Starts the Timer. This method is package private so only {@link Timers} can start
      * this timer.

internal/utils/metrics/src/main/java/org/eclipse/ditto/internal/utils/metrics/instruments/timer/StartedTimer.java

@@ -15,7 +15,6 @@
 import java.time.Instant;
 import java.util.List;
 import java.util.Map;
-import java.util.function.Consumer;
 
 import org.eclipse.ditto.internal.utils.metrics.instruments.TaggedMetricInstrument;
 
@@ -24,6 +23,11 @@
  */
 public interface StartedTimer extends Timer, TaggedMetricInstrument<StartedTimer> {
 
+    @Override
+    default StartedTimer self() {
+        return this;
+    }
+
     /**
      * Stops the timer and all its segments.
      *

internal/utils/tracing/src/main/java/org/eclipse/ditto/internal/utils/tracing/instruments/trace/PreparedTrace.java

@@ -24,6 +24,11 @@
  */
 public interface PreparedTrace extends TaggedMetricInstrument<PreparedTrace>, TraceTags<PreparedTrace> {
 
+    @Override
+    default PreparedTrace self() {
+        return this;
+    }
+
     /**
      * Starts the trace at the current instant.
      *

internal/utils/tracing/src/main/java/org/eclipse/ditto/internal/utils/tracing/instruments/trace/StartedTrace.java

@@ -25,6 +25,11 @@
  */
 public interface StartedTrace extends TaggedMetricInstrument<StartedTrace>, TraceTags<StartedTrace> {
 
+    @Override
+    default StartedTrace self() {
+        return this;
+    }
+
     /**
      * Finishes the trace. Any method called after the trace is finished has no effect.
      */

internal/utils/tracing/src/main/java/org/eclipse/ditto/internal/utils/tracing/instruments/trace/TraceTags.java

@@ -12,6 +12,8 @@
  */
 package org.eclipse.ditto.internal.utils.tracing.instruments.trace;
 
+import javax.annotation.Nullable;
+
 import org.eclipse.ditto.internal.utils.metrics.instruments.TaggedMetricInstrument;
 import org.eclipse.ditto.internal.utils.tracing.TracingTags;
 
@@ -28,7 +30,10 @@ public interface TraceTags<T extends TaggedMetricInstrument<T>> extends TaggedMe
      * @param correlationId the correlation ID to add to the trace
      * @return the new TaggedMetricInstrument instance containing the tag
      */
-    default T correlationId(final CharSequence correlationId) {
+    default T correlationId(@Nullable final CharSequence correlationId) {
+        if (null == correlationId) {
+            return self();
+        }
         return tag(TracingTags.CORRELATION_ID, correlationId.toString());
     }
 
@@ -38,7 +43,10 @@ default T correlationId(final CharSequence correlationId) {
      * @param connectionId the connection ID to add to the trace
      * @return the new TaggedMetricInstrument instance containing the tag
      */
-    default T connectionId(final CharSequence connectionId) {
+    default T connectionId(@Nullable final CharSequence connectionId) {
+        if (null == connectionId) {
+            return self();
+        }
         return tag(TracingTags.CONNECTION_ID, connectionId.toString());
     }
 
@@ -48,7 +56,10 @@ default T connectionId(final CharSequence connectionId) {
      * @param connectionType the connection type to add to the trace
      * @return the new TaggedMetricInstrument instance containing the tag
      */
-    default T connectionType(final CharSequence connectionType) {
+    default T connectionType(@Nullable final CharSequence connectionType) {
+        if (null == connectionType) {
+            return self();
+        }
         return tag(TracingTags.CONNECTION_TYPE, connectionType.toString());
     }