Add support for Log4j 2's ThreadContext

.mvn/javadoc/package-list

@@ -11,6 +11,7 @@ nl.talsmasoftware.context.metrics
 nl.talsmasoftware.context.locale
 nl.talsmasoftware.context.mdc
 nl.talsmasoftware.context.slf4j.mdc
+nl.talsmasoftware.context.log4j2.threadcontext
 nl.talsmasoftware.context.opentracing
 nl.talsmasoftware.context.servletrequest
 nl.talsmasoftware.context.springsecurity

context-propagation-bom/pom.xml

@@ -130,6 +130,24 @@
                 <classifier>sources</classifier>
             </dependency>
 
+            <dependency>
+                <groupId>${project.groupId}</groupId>
+                <artifactId>log4j2-propagation</artifactId>
+                <version>${project.version}</version>
+            </dependency>
+            <dependency>
+                <groupId>${project.groupId}</groupId>
+                <artifactId>log4j2-propagation</artifactId>
+                <version>${project.version}</version>
+                <classifier>javadoc</classifier>
+            </dependency>
+            <dependency>
+                <groupId>${project.groupId}</groupId>
+                <artifactId>log4j2-propagation</artifactId>
+                <version>${project.version}</version>
+                <classifier>sources</classifier>
+            </dependency>
+
             <dependency>
                 <groupId>${project.groupId}</groupId>
                 <artifactId>locale-context</artifactId>

log4j2-propagation/README.md

@@ -0,0 +1,41 @@
+[![Maven Version][maven-img]][maven] 
+
+# Log4j 2 Thread Context propagation library
+
+Adding the `log4j2-propagation` jar to your classpath
+is all that is needed to let the [Thread Context][thread-context] 
+from the [Log4j 2 library][log4j2] be automatically included into
+the `ContextSnapshot`.
+
+## How to use this library
+
+Add it to your classpath. 
+```xml
+<dependency>
+    <groupId>nl.talsmasoftware.context</groupId>
+    <artifactId>log4j2-propagation</artifactId>
+    <version>[see Maven badge above]</version>
+</dependency>
+```
+
+Done!
+
+Now the data of the Log4j 2 Thread Context is copied into each snapshot 
+from the `ContextManagers.createSnapshot()` method
+to be reactivated by the `Contextsnapshot.reactivate()` call.
+The `ContextAwareExecutorService` automatically propagates the full
+Thread Context data into all executed tasks this way.
+
+When Thread Context data is propagated, it is added on top of the existing
+data, if any: Thread Context stack values are pushed on top of the existing
+stack; map entries are added to the existing map, only replacing existing
+ones in case of a map key conflict.
+
+Calling `ContextManagers.clearActiveContexts()` will clear the Thread Context
+data of the current thread.
+
+  [maven-img]: https://img.shields.io/maven-central/v/nl.talsmasoftware.context/log4j2-propagation
+  [maven]: https://search.maven.org/artifact/nl.talsmasoftware.context/log4j2-propagation
+
+  [log4j2]: https://logging.apache.org/log4j/2.x/index.html
+  [thread-context]: https://logging.apache.org/log4j/2.x/manual/thread-context.html

log4j2-propagation/pom.xml

@@ -0,0 +1,54 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    Copyright 2016-2021 Talsma ICT
+
+    Licensed 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.
+
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>nl.talsmasoftware.context</groupId>
+        <artifactId>context-propagation-root</artifactId>
+        <version>1.0.9-SNAPSHOT</version>
+    </parent>
+
+    <!-- Artifact identification -->
+    <artifactId>log4j2-propagation</artifactId>
+    <name>Propagation of Log4j 2 ThreadContext</name>
+    <packaging>jar</packaging>
+
+    <properties>
+        <!-- Latest Log4j 2 versions require Java >= 8; however this project might also support older versions -->
+        <maven.compiler.source>1.5</maven.compiler.source>
+        <maven.compiler.target>1.5</maven.compiler.target>
+        <project.moduleName>${project.groupId}.log4j2</project.moduleName>
+        <root.basedir>${project.parent.basedir}</root.basedir>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>context-propagation</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.apache.logging.log4j</groupId>
+            <artifactId>log4j-api</artifactId>
+            <version>${log4j2.version}</version>
+        </dependency>
+    </dependencies>
+</project>

log4j2-propagation/src/main/java/nl/talsmasoftware/context/log4j2/threadcontext/Log4j2ThreadContextData.java

@@ -0,0 +1,104 @@
+/*
+ * Copyright 2016-2021 Talsma ICT
+ *
+ * Licensed 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.
+ */
+package nl.talsmasoftware.context.log4j2.threadcontext;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+
+import org.apache.logging.log4j.ThreadContext;
+
+/**
+ * Snapshot of the data from the Log4j 2 {@link ThreadContext} of a
+ * specific thread at a certain point in the past.
+ */
+public class Log4j2ThreadContextData {
+    private final Map<String, String> contextMap;
+    private final List<String> contextStack;
+
+    /**
+     * Applies the data to the current thread.
+     *
+     * @param data data to apply, may be {@code null}
+     * @param overwrite whether all existing data should overwritten
+     */
+    static void applyToCurrentThread(Log4j2ThreadContextData data, boolean overwrite) {
+        if (overwrite) {
+            ThreadContext.clearAll();
+        }
+        if (data != null) {
+            data.applyToCurrentThread();
+        }
+    }
+
+    /**
+     * Applies the data on top of the {@code ThreadContext} of the current thread.
+     * Conflicting entries are overwritten but all other existing data is kept.
+     */
+    void applyToCurrentThread() {
+        ThreadContext.putAll(contextMap);
+
+        // There is currently no method for pushing a collection, therefore have to
+        // push one by one
+        for (String element : contextStack) {
+            ThreadContext.push(element);
+        }
+    }
+
+    private Log4j2ThreadContextData(Map<String, String> contextMap, List<String> contextStack) {
+        this.contextMap = Collections.unmodifiableMap(contextMap);
+        this.contextStack = Collections.unmodifiableList(contextStack);
+    }
+
+    /**
+     * Captures the {@code ThreadContext} data of the current thread.
+     *
+     * @return data representing the {@code ThreadContext} of the current thread
+     */
+    static Log4j2ThreadContextData fromCurrentThreadContext() {
+        // Get a copy of context map and context stack
+        return new Log4j2ThreadContextData(ThreadContext.getContext(), ThreadContext.getImmutableStack().asList());
+    }
+
+    /**
+     * Returns an unmodifiable view of the {@code ThreadContext} map contained
+     * in this snapshot.
+     *
+     * @return {@code ThreadContext} map contained in this snapshot
+     */
+    public Map<String, String> getContextMap() {
+        return contextMap;
+    }
+
+    /**
+     * Returns an unmodifiable view of the {@code ThreadContext} stack contained
+     * in this snapshot. The elements are ordered from least recently added at
+     * the beginning of the list to most recently added at the end.
+     *
+     * @return {@code ThreadContext} stack contained in this snapshot
+     */
+    public List<String> getContextStack() {
+        return contextStack;
+    }
+
+    @Override
+    public String toString() {
+        return "Log4j2ThreadContextData{"
+            + "map=" + contextMap
+            + ",stack=" + contextStack
+            + '}';
+    }
+}