Simplify + Allow custom MDC lookup (#193)

jul-ecs-formatter/src/main/java/co/elastic/logging/jul/EcsFormatter.java

@@ -29,6 +29,7 @@
 
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 import java.util.logging.Formatter;
 import java.util.logging.LogManager;
 import java.util.logging.LogRecord;
@@ -69,7 +70,7 @@ public String format(final LogRecord record) {
         EcsJsonSerializer.serializeFormattedMessage(builder, super.formatMessage(record));
         EcsJsonSerializer.serializeEcsVersion(builder);
         EcsJsonSerializer.serializeAdditionalFields(builder, additionalFields);
-        EcsJsonSerializer.serializeMDC(builder, JulMdc.getEntries());
+        EcsJsonSerializer.serializeMDC(builder, getMdcEntries());
         EcsJsonSerializer.serializeServiceName(builder, serviceName);
         EcsJsonSerializer.serializeServiceVersion(builder, serviceVersion);
         EcsJsonSerializer.serializeServiceEnvironment(builder, serviceEnvironment);
@@ -92,6 +93,16 @@ public String format(final LogRecord record) {
         return builder.toString();
     }
 
+    /**
+     * Used by APM agent to provide MDC for JUL through instrumentation and to allow testing without an actual MDC
+     * implementation.
+     *
+     * @return MDC entries
+     */
+    protected Map<String, String> getMdcEntries() {
+        return Collections.emptyMap();
+    }
+
     public void setIncludeOrigin(final boolean includeOrigin) {
         this.includeOrigin = includeOrigin;
     }

jul-ecs-formatter/src/test/java/co/elastic/logging/jul/EcsFormatterTest.java

@@ -11,9 +11,9 @@
  * the Apache License, Version 2.0 (the "License"); you may
  * not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *   http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing,
  * software distributed under the License is distributed on an
  * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
@@ -24,12 +24,15 @@
  */
 package co.elastic.logging.jul;
 
+import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
 import java.time.Instant;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.logging.Level;
 import java.util.logging.LogRecord;
 
@@ -40,7 +43,7 @@ public class EcsFormatterTest {
     private final EcsFormatter formatter = new EcsFormatter();
 
     private final LogRecord record = new LogRecord(Level.INFO, "Example Message");
-    private final ObjectMapper objectMapper = new ObjectMapper();
+    private static final ObjectMapper objectMapper = new ObjectMapper();
 
     @BeforeEach
     void setUp() {
@@ -57,21 +60,21 @@ public void testFormatWithIncludeOriginFlag() throws Exception {
 
         final String result = formatter.format(record);
 
-        assertThat(objectMapper.readTree(result).at("/log/origin/file/name").textValue()).isEqualTo("ExampleClass.java");
-        assertThat(objectMapper.readTree(result).at("/log/origin/function").textValue()).isEqualTo("exampleMethod");
+        assertThat(parseJson(result).at("/log/origin/file/name").textValue()).isEqualTo("ExampleClass.java");
+        assertThat(parseJson(result).at("/log/origin/function").textValue()).isEqualTo("exampleMethod");
     }
 
     @Test
     public void testFormatWithoutIncludeOriginFlag() throws Exception {
-        final JsonNode result = objectMapper.readTree(formatter.format(record));
+        final JsonNode result = parseJson(formatter.format(record));
         assertThat(result.get("log.origin")).isNull();
     }
 
     @Test
     public void testFormatWithoutLoggerName() throws Exception {
         record.setLoggerName(null);
 
-        final JsonNode result = objectMapper.readTree(formatter.format(record));
+        final JsonNode result = parseJson(formatter.format(record));
 
         assertThat(result.get("log.logger")).isNull();
     }
@@ -80,7 +83,7 @@ public void testFormatWithoutLoggerName() throws Exception {
     public void testFormatWithEmptyLoggerName() throws Exception {
         record.setLoggerName("");
 
-        final JsonNode result = objectMapper.readTree(formatter.format(record));
+        final JsonNode result = parseJson(formatter.format(record));
 
         assertThat(result.get("log.logger").textValue()).isEmpty();
     }
@@ -90,7 +93,7 @@ public void testFormatWithInnerClassName() throws Exception {
         formatter.setIncludeOrigin(true);
         record.setSourceClassName("test.ExampleClass$InnerClass");
 
-        JsonNode result = objectMapper.readTree(formatter.format(record));
+        JsonNode result = parseJson(formatter.format(record));
         assertThat(result.at("/log/origin/file/name").textValue()).isEqualTo("ExampleClass.java");
         assertThat(result.at("/log/origin/function").textValue()).isEqualTo("exampleMethod");
     }
@@ -100,9 +103,39 @@ public void testFormatWithInvalidClassName() throws Exception {
         formatter.setIncludeOrigin(true);
         record.setSourceClassName("$test.ExampleClass");
 
-        JsonNode result = objectMapper.readTree(formatter.format(record));
+        JsonNode result = parseJson(formatter.format(record));
         assertThat(result.at("/log/origin/file/name").textValue()).isEqualTo("<Unknown>");
         assertThat(result.at("/log/origin/function").textValue()).isEqualTo("exampleMethod");
     }
 
+    @Test
+    void testMdcSerialization_singleEntry() {
+        Map<String,String> mdc = new HashMap<>();
+        TestMdcEcsFormatter mdcFormatter = new TestMdcEcsFormatter(mdc);
+        mdc.put("mdc.key", "value");
+        JsonNode result = parseJson(mdcFormatter.format(record));
+        assertThat(result.get("mdc.key").textValue()).isEqualTo("value");
+    }
+
+    private static JsonNode parseJson(String formatter) {
+        try {
+            return objectMapper.readTree(formatter);
+        } catch (JsonProcessingException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private static class TestMdcEcsFormatter extends EcsFormatter {
+        private final Map<String, String> mdc;
+
+        public TestMdcEcsFormatter(Map<String, String> mdc) {
+            this.mdc = mdc;
+        }
+
+        @Override
+        protected Map<String, String> getMdcEntries() {
+            return mdc;
+        }
+    }
+
 }

jul-ecs-formatter/src/test/java/co/elastic/logging/jul/JulLoggingTest.java

@@ -82,12 +82,6 @@ public void debug(String message) {
         logger.log(Level.FINE, message);
     }
 
-    @Override
-    public boolean putMdc(String key, String value) {
-        JulMdc.put(key, value);
-        return true;
-    }
-
     @Override
     public ParameterizedLogSupport getParameterizedLogSettings() {
         return ParameterizedLogSupport.NUMBER_AND_BRACKETS;