Add Log4j API to SLF4J bridge

log4j-api-to-slf4j/pom.xml

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+<?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.
+  -->
+<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/maven-v4_0_0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>org.apache.logging.log4j</groupId>
+    <artifactId>log4j-slf4j-parent</artifactId>
+    <version>${revision}</version>
+    <relativePath>../parent</relativePath>
+  </parent>
+
+  <artifactId>log4j-api-to-slf4j</artifactId>
+
+  <name>Log4j API to SLF4J logging bridge</name>
+
+  <description>Forwards the Log4j API calls to SLF4J.
+    (Refer to the `log4j-slf4j[2]-impl` artifacts for forwarding SLF4J to the Log4j API.)</description>
+
+  <properties>
+    <!-- Dependency versions -->
+    <logback.version>1.5.12</logback.version>
+    <osgi.framework.version>1.8.0</osgi.framework.version>
+
+    <!--
+      ~ OSGi and JPMS options
+      -->
+    <slf4j.support.range>[1.7,3)</slf4j.support.range>
+    <bnd-extra-package-options>
+      <!-- This bridge also support SLF4J 2.x -->
+      org.slf4j.*;version="${slf4j.support.range}"
+    </bnd-extra-package-options>
+  </properties>
+
+  <dependencies>
+
+    <dependency>
+      <groupId>org.osgi</groupId>
+      <artifactId>org.osgi.framework</artifactId>
+      <version>${osgi.framework.version}</version>
+      <scope>provided</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-api</artifactId>
+    </dependency>
+
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-api</artifactId>
+    </dependency>
+
+    <dependency>
+      <groupId>org.assertj</groupId>
+      <artifactId>assertj-core</artifactId>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-api</artifactId>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-params</artifactId>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>ch.qos.logback</groupId>
+      <artifactId>logback-classic</artifactId>
+      <version>${logback.version}</version>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>ch.qos.logback</groupId>
+      <artifactId>logback-core</artifactId>
+      <version>${logback.version}</version>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>ch.qos.logback</groupId>
+      <artifactId>logback-core</artifactId>
+      <version>${logback.version}</version>
+      <type>test-jar</type>
+      <scope>test</scope>
+    </dependency>
+
+    <!-- For the JUnit extensions -->
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-api-test</artifactId>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-core</artifactId>
+      <scope>test</scope>
+    </dependency>
+
+  </dependencies>
+
+  <build>
+    <plugins>
+
+      <!-- TODO: Fix parallel testing -->
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <configuration>
+          <reuseForks>false</reuseForks>
+        </configuration>
+      </plugin>
+
+    </plugins>
+  </build>
+</project>

log4j-api-to-slf4j/src/main/java/org/apache/logging/slf4j/Activator.java

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+/*
+ * 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.
+ */
+package org.apache.logging.slf4j;
+
+import org.apache.logging.log4j.util.ProviderActivator;
+import org.osgi.annotation.bundle.Header;
+
+@Header(name = org.osgi.framework.Constants.BUNDLE_ACTIVATOR, value = "${@class}")
+@Header(
+        name = org.osgi.framework.Constants.BUNDLE_ACTIVATIONPOLICY,
+        value = org.osgi.framework.Constants.ACTIVATION_LAZY)
+public class Activator extends ProviderActivator {
+
+    public Activator() {
+        super(new SLF4JProvider());
+    }
+}

log4j-api-to-slf4j/src/main/java/org/apache/logging/slf4j/MDCContextMap.java

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+/*
+ * 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.
+ */
+package org.apache.logging.slf4j;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Map.Entry;
+import org.apache.logging.log4j.spi.CleanableThreadContextMap;
+import org.apache.logging.log4j.util.SortedArrayStringMap;
+import org.apache.logging.log4j.util.StringMap;
+import org.slf4j.MDC;
+
+/**
+ * Bind the ThreadContextMap to the SLF4J MDC.
+ */
+public class MDCContextMap implements CleanableThreadContextMap {
+
+    private static final StringMap EMPTY_CONTEXT_DATA = new SortedArrayStringMap(1);
+
+    static {
+        EMPTY_CONTEXT_DATA.freeze();
+    }
+
+    @Override
+    public void put(final String key, final String value) {
+        MDC.put(key, value);
+    }
+
+    @Override
+    public void putAll(final Map<String, String> m) {
+        for (final Entry<String, String> entry : m.entrySet()) {
+            MDC.put(entry.getKey(), entry.getValue());
+        }
+    }
+
+    @Override
+    public String get(final String key) {
+        return MDC.get(key);
+    }
+
+    @Override
+    public void remove(final String key) {
+        MDC.remove(key);
+    }
+
+    @Override
+    public void removeAll(final Iterable<String> keys) {
+        for (final String key : keys) {
+            MDC.remove(key);
+        }
+    }
+
+    @Override
+    public void clear() {
+        MDC.clear();
+    }
+
+    @Override
+    public boolean containsKey(final String key) {
+        final Map<String, String> map = MDC.getCopyOfContextMap();
+        return map != null && map.containsKey(key);
+    }
+
+    @Override
+    public Map<String, String> getCopy() {
+        final Map<String, String> contextMap = MDC.getCopyOfContextMap();
+        return contextMap != null ? contextMap : new HashMap<>();
+    }
+
+    @Override
+    public Map<String, String> getImmutableMapOrNull() {
+        return MDC.getCopyOfContextMap();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        final Map<String, String> map = MDC.getCopyOfContextMap();
+        return map == null || map.isEmpty();
+    }
+
+    @Override
+    public StringMap getReadOnlyContextData() {
+        final Map<String, String> copy = getCopy();
+        if (copy.isEmpty()) {
+            return EMPTY_CONTEXT_DATA;
+        }
+        final StringMap result = new SortedArrayStringMap();
+        for (final Entry<String, String> entry : copy.entrySet()) {
+            result.putValue(entry.getKey(), entry.getValue());
+        }
+        return result;
+    }
+}