Adapt to ContextAccessor change: new readValue method (#3124)

reactor-core/src/main/java/reactor/util/context/ReactorContextAccessor.java

@@ -21,6 +21,8 @@
 
 import io.micrometer.context.ContextAccessor;
 
+import reactor.util.annotation.Nullable;
+
 /**
  * A {@code ContextAccessor} to enable reading values from a Reactor
  * {@link ContextView} and writing values to {@link Context}.
@@ -48,6 +50,12 @@ public void readValues(ContextView source, Predicate<Object> keyPredicate, Map<O
 		});
 	}
 
+	@Override
+	@Nullable
+	public <T> T readValue(ContextView sourceContext, Object key) {
+		return sourceContext.getOrDefault(key, null);
+	}
+
 	@Override
 	public boolean canWriteTo(Class<?> contextType) {
 		return Context.class.isAssignableFrom(contextType);

reactor-core/src/withMicrometerTest/java/reactor/util/context/ReactorContextAccessorTest.java

@@ -104,4 +104,23 @@ void writeValuesWithPutAllMap() {
 		Mockito.verify(target, never()).putAll((ContextView) any());
 		Mockito.verify(target, times(1)).putAllMap(anyMap());
 	}
+
+	@Test
+	void readValueWhenKeyPresent() {
+		ReactorContextAccessor test = new ReactorContextAccessor();
+		String expectedValue = "A";
+		ContextView source = Context.of(1, expectedValue, 2, "B");
+
+		String readValue = test.readValue(source, 1);
+		assertThat(readValue).isSameAs(expectedValue);
+	}
+
+	@Test
+	void readValueReturnsNullWhenKeyAbsent() {
+		ReactorContextAccessor test = new ReactorContextAccessor();
+		ContextView source = Context.of(1, "A");
+
+		String readValue = test.readValue(source, 2);
+		assertThat(readValue).isNull();
+	}
 }