allow to override fqcn in Log4jEventBuilder

log4j-core-test/src/main/resources/log4j2-calling-class.xml

@@ -23,6 +23,9 @@
     <List name="Method">
       <PatternLayout pattern="%method"/>
     </List>
+    <List name="Fqcn">
+      <PatternLayout pattern="%fqcn"/>
+    </List>
   </Appenders>
   <Loggers>
     <Logger name="ClassLogger" level="info">
@@ -31,6 +34,9 @@
     <Logger name="MethodLogger" level="info">
       <AppenderRef ref="Method"/>
     </Logger>
+    <Logger name="FqcnLogger" level="info">
+      <AppenderRef ref="Fqcn"/>
+    </Logger>
     <Root level="off"/>
   </Loggers>
 </Configuration>

log4j-slf4j2-impl/src/main/java/org/apache/logging/slf4j/Log4jEventBuilder.java

@@ -29,9 +29,10 @@
 import org.apache.logging.log4j.LogBuilder;
 import org.apache.logging.log4j.Logger;
 import org.slf4j.Marker;
+import org.slf4j.spi.CallerBoundaryAware;
 import org.slf4j.spi.LoggingEventBuilder;
 
-public class Log4jEventBuilder implements LoggingEventBuilder {
+public class Log4jEventBuilder implements LoggingEventBuilder, CallerBoundaryAware {
 
     private static final String FQCN = Log4jEventBuilder.class.getName();
 
@@ -43,6 +44,7 @@ public class Log4jEventBuilder implements LoggingEventBuilder {
     private Throwable throwable = null;
     private Map<String, String> keyValuePairs = null;
     private final Level level;
+    private String fqcn = FQCN;
 
     public Log4jEventBuilder(final Log4jMarkerFactory markerFactory, final Logger logger, final Level level) {
         this.markerFactory = markerFactory;
@@ -110,7 +112,7 @@ public void log() {
                 .withMarker(marker)
                 .withThrowable(throwable);
         if (logBuilder instanceof BridgeAware) {
-            ((BridgeAware) logBuilder).setEntryPoint(FQCN);
+            ((BridgeAware) logBuilder).setEntryPoint(fqcn);
         }
         if (keyValuePairs == null || keyValuePairs.isEmpty()) {
             logBuilder.log(message, arguments.toArray());
@@ -157,4 +159,8 @@ public void log(final Supplier<String> messageSupplier) {
         log();
     }
 
+    @Override
+    public void setCallerBoundary(String fqcn) {
+        this.fqcn = fqcn;
+    }
 }

log4j-slf4j2-impl/src/test/java/org/apache/logging/slf4j/CallerInformationTest.java

@@ -24,6 +24,8 @@
 import org.junit.Test;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+import org.slf4j.spi.CallerBoundaryAware;
+import org.slf4j.spi.LoggingEventBuilder;
 
 import static org.junit.Assert.assertEquals;
 
@@ -72,4 +74,18 @@ public void testMethodLogger() throws Exception {
             assertEquals("Incorrect caller method name.", "testMethodLogger", message);
         }
     }
+
+    @Test
+    public void testFqcnLogger() throws Exception {
+        final ListAppender app = ctx.getListAppender("Fqcn").clear();
+        final Logger logger = LoggerFactory.getLogger("FqcnLogger");
+        LoggingEventBuilder loggingEventBuilder = logger.atInfo();
+        ((CallerBoundaryAware)loggingEventBuilder).setCallerBoundary("MyFqcn");
+        loggingEventBuilder.log("A message");
+        final List<String> messages = app.getMessages();
+        assertEquals("Incorrect number of messages.", 1, messages.size());
+        for (final String message : messages) {
+            assertEquals("Incorrect fqcn.", "MyFqcn", message);
+        }
+    }
 }

src/changelog/.2.x.x/1533_set_fqcn_eventbuilder.xml

@@ -0,0 +1,29 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Licensed to the Apache Software Foundation (ASF) under one or more
+  ~ contributor license agreements.  See the NOTICE file distributed with
+  ~ this work for additional information regarding copyright ownership.
+  ~ The ASF licenses this file to you under 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 KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  -->
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="http://logging.apache.org/log4j/changelog"
+       xsi:schemaLocation="http://logging.apache.org/log4j/changelog https://logging.apache.org/log4j/changelog-0.1.1.xsd"
+       type="fixed">
+  <issue id="1533" link="https://github.com/apache/logging-log4j2/pull/1533"/>
+  <author id="github:oshai" name="Ohad Shai"/>
+  <!-- Committer -->
+  <author name="github:pkarwasz"/>
+  <description format="asciidoc">
+    Allow to override fqcn in `Log4jEventBuilder` by implementing `CallerBoundaryAware`.
+  </description>
+</entry>