Removed MDCSpanObserver and opentracing-contrib/java-api-extensions d…

…ependency

README.md

@@ -127,30 +127,6 @@ The following table describes the contract how a flow id is propagated in differ
 | e28a8414294acf36 | n/a                        | e28a8414294acf36            | n/a                          | e28a8414294acf36              |
 | e28a8414294acf36 | REcCvlqMSReeo7adheiYFA     | REcCvlqMSReeo7adheiYFA      | REcCvlqMSReeo7adheiYFA       | REcCvlqMSReeo7adheiYFA        |
 
-### Logging
-
-```xml
-<dependency>
-    <groupId>io.opentracing.contrib</groupId>
-    <artifactId>opentracing-api-extensions-tracer</artifactId>
-    <version>0.2.0</version>
-</dependency>
-```
-
-*Tracer* comes with a very useful `SpanObserver` by default, the `MDCSpanObserver`:
-
-```java
-Tracer delegate = ...; // your OpenTracing implementation of choice
-APIExtensionsTracer tracer = new APIExtensionsTracer(delegate);
-tracer.addTracerObserver(new MDCSpanObserver());
-```
-
-It allows you to add the `trace_id`, `span_id` and/or `flow_id` to every log line:
-
-```xml
-<PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} [%X{trace_id}] [%X{flow_id}] - %msg%n"/>
-```
-
 ## Servlet
 
 On the server side is a single filter that you must be register in your filter chain. Make sure it runs very early — otherwise you might miss some crucial information when debugging.
@@ -183,17 +159,15 @@ OkHttpClient client = new OkHttpClient.Builder()
 
 ## Spring Boot Auto Configuration
 
-*Tracer* comes with a convenient auto configuration for Spring Boot users that sets up aspect, servlet filter and MDC support automatically with sensible defaults:
+*Tracer* comes with a convenient auto configuration for Spring Boot users that sets up aspect and servlet filter automatically with sensible defaults:
 
 | Configuration                 | Description                               | Default                     |
 |-------------------------------|-------------------------------------------|-----------------------------|
 | `tracer.filter.enabled`       | Enables the [`FlowFilter`](#servlet)      | `true`                      |
-| `tracer.mdc.enabled`          | Enables the [`MDCSpanObserver`](#logging) | `true`                      |
 
 ```yaml
 tracer:
     filter.enabled: true
-    mdc.enabled: true
 ```
 
 ## Getting Help with Tracer

pom.xml

@@ -140,13 +140,6 @@
                 <version>${opentracing.version}</version>
                 <scope>test</scope>
             </dependency>
-            <dependency>
-                <groupId>io.opentracing.contrib</groupId>
-                <artifactId>opentracing-api-extensions-tracer</artifactId>
-                <version>0.6.0</version>
-                <!-- Needed for pushing trace/span/flow id to MDC-->
-                <optional>true</optional>
-            </dependency>
             <!-- javax -->
             <dependency>
                 <groupId>javax.servlet</groupId>

tracer-core/pom.xml

@@ -15,10 +15,6 @@
         <developerConnection>scm:git:git@github.com:zalando/tracer.git</developerConnection>
     </scm>
     <dependencies>
-        <dependency>
-            <groupId>io.opentracing.contrib</groupId>
-            <artifactId>opentracing-api-extensions-tracer</artifactId>
-        </dependency>
         <dependency>
             <groupId>org.apache.logging.log4j</groupId>
             <artifactId>log4j-api</artifactId>

tracer-core/src/main/java/org/zalando/tracer/CompositeExtractor.java

@@ -13,15 +13,15 @@
 @AllArgsConstructor
 final class CompositeExtractor implements Extractor {
 
-    private final Collection<Extractor> strategies;
+    private final Collection<Extractor> extractors;
 
-    CompositeExtractor(final Extractor... strategies) {
-        this(Arrays.asList(strategies));
+    CompositeExtractor(final Extractor... extractors) {
+        this(Arrays.asList(extractors));
     }
 
     @Override
     public Optional<FlowId> extract(final Span span, final UnaryOperator<String> reader) {
-        return strategies.stream()
+        return extractors.stream()
                 .map(strategy -> strategy.extract(span, reader))
                 .filter(Optional::isPresent)
                 .findFirst()

tracer-core/src/main/java/org/zalando/tracer/TraceExtractor.java

@@ -11,6 +11,8 @@ final class TraceExtractor implements Extractor {
     @Override
     public Optional<FlowId> extract(final Span span, final UnaryOperator<String> reader) {
         return Optional.of(span.context().toTraceId())
+                // "An empty String will be returned if the tracer does not support this functionality"
+                .filter(s -> !s.isEmpty())
                 .map(id -> new SimpleFlowId(id, Source.TRACE));
     }
 

tracer-core/src/test/java/org/zalando/tracer/DefaultFlowNoopTracerTest.java

@@ -1,14 +1,12 @@
 package org.zalando.tracer;
 
-import io.opentracing.contrib.api.tracer.APIExtensionsTracer;
 import io.opentracing.noop.NoopTracerFactory;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 class DefaultFlowNoopTracerTest {
-    private final APIExtensionsTracer tracer = new APIExtensionsTracer(NoopTracerFactory.create());
-    private final Flow unit = Flow.create(tracer);
+    private final Flow unit = Flow.create(NoopTracerFactory.create());
 
     @Test
     void shouldThrowNoActiveSpanFoundException() {

tracer-spring-boot-autoconfigure/pom.xml

@@ -27,10 +27,6 @@
             <groupId>org.zalando</groupId>
             <artifactId>tracer-servlet</artifactId>
         </dependency>
-        <dependency>
-            <groupId>io.opentracing.contrib</groupId>
-            <artifactId>opentracing-api-extensions-tracer</artifactId>
-        </dependency>
         <dependency>
             <groupId>javax.servlet</groupId>
             <artifactId>javax.servlet-api</artifactId>
@@ -109,6 +105,10 @@
                     <groupId>junit</groupId>
                     <artifactId>junit</artifactId>
                 </exclusion>
+                <exclusion>
+                    <groupId>org.junit.vintage</groupId>
+                    <artifactId>junit-vintage-engine</artifactId>
+                </exclusion>
                 <exclusion>
                     <groupId>org.hamcrest</groupId>
                     <artifactId>hamcrest-core</artifactId>

tracer-spring-boot-autoconfigure/src/main/java/org/zalando/tracer/autoconfigure/TracerAutoConfiguration.java

@@ -1,7 +1,6 @@
 package org.zalando.tracer.autoconfigure;
 
 import io.opentracing.Tracer;
-import io.opentracing.contrib.api.tracer.APIExtensionsTracer;
 import org.apiguardian.api.API;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
@@ -12,10 +11,8 @@
 import org.springframework.boot.web.servlet.FilterRegistrationBean;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
-import org.springframework.context.annotation.Primary;
 import org.springframework.core.Ordered;
 import org.zalando.tracer.Flow;
-import org.zalando.tracer.MDCSpanObserver;
 import org.zalando.tracer.httpclient.FlowHttpRequestInterceptor;
 import org.zalando.tracer.servlet.FlowFilter;
 
@@ -48,16 +45,6 @@ public FlowHttpRequestInterceptor flowHttpRequestInterceptor(final Flow flow) {
         return new FlowHttpRequestInterceptor(flow);
     }
 
-    @API(status = INTERNAL)
-    @Bean
-    @Primary
-    @ConditionalOnProperty(name = "tracer.mdc.enabled", havingValue = "true", matchIfMissing = true)
-    public Tracer mdcTracer(final Tracer tracer) {
-        final APIExtensionsTracer extensionsTracer = new APIExtensionsTracer(tracer);
-        extensionsTracer.addTracerObserver(new MDCSpanObserver());
-        return extensionsTracer;
-    }
-
     @Configuration
     @ConditionalOnClass({Filter.class, FilterRegistrationBean.class})
     @ConditionalOnWebApplication