Add JUL to Log4j API bridge

jul-to-log4j-api/pom.xml

@@ -0,0 +1,154 @@
+<?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/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>org.apache.logging.log4j</groupId>
+    <artifactId>log4j-jdk-parent</artifactId>
+    <version>${revision}</version>
+    <relativePath>../parent</relativePath>
+  </parent>
+
+  <artifactId>jul-to-log4j-api</artifactId>
+  <name>JUL to Log4j API logging bridge</name>
+  <description>A `java.util.logging` LogManager that forwards events to the Log4j API.</description>
+
+  <properties>
+    <!-- Skips BND Baseline until the first release -->
+    <bnd.baseline.fail.on.missing>false</bnd.baseline.fail.on.missing>
+
+    <!-- TODO: Adapt to Java 9 -->
+    <maven.compiler.release>17</maven.compiler.release>
+    <maven.compiler.source>${maven.compiler.release}</maven.compiler.source>
+    <maven.compiler.target>${maven.compiler.release}</maven.compiler.target>
+    <!--
+      ~ OSGi and JPMS options
+      -->
+    <bnd-extra-package-options>
+      <!-- Optional annotations -->
+      org.jspecify.*;resolution:=optional
+    </bnd-extra-package-options>
+    <bnd-extra-module-options>
+      <!-- Optional modules can not be `transitive` -->
+      org.jspecify;transitive=false
+    </bnd-extra-module-options>
+
+    <!-- Dependency versions -->
+    <log4j.version>3.0.0-SNAPSHOT</log4j.version>
+  </properties>
+
+  <dependencies>
+
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-api</artifactId>
+    </dependency>
+
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-kit</artifactId>
+    </dependency>
+
+    <dependency>
+      <groupId>org.assertj</groupId>
+      <artifactId>assertj-core</artifactId>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-async-logger</artifactId>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-core</artifactId>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-core-test</artifactId>
+      <scope>test</scope>
+    </dependency>
+
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>default-test</id>
+            <goals>
+              <goal>test</goal>
+            </goals>
+            <phase>test</phase>
+            <configuration>
+              <excludes>
+                <exclude>**/AsyncLoggerThreadsTest.class</exclude>
+                <exclude>**/CustomLoggerAdapterTest.class</exclude>
+              </excludes>
+              <!-- Use custom `j.u.l.LogManager` -->
+              <systemPropertyVariables>
+                <java.util.logging.manager>org.apache.logging.jul.tolog4j.LogManager</java.util.logging.manager>
+              </systemPropertyVariables>
+            </configuration>
+          </execution>
+          <execution>
+            <id>async-logger-test</id>
+            <goals>
+              <goal>test</goal>
+            </goals>
+            <phase>test</phase>
+            <configuration>
+              <includes>
+                <include>**/AsyncLoggerThreadsTest.class</include>
+              </includes>
+              <!-- Use custom `j.u.l.LogManager` and an asynchronous selector -->
+              <systemPropertyVariables>
+                <java.util.logging.manager>org.apache.logging.jul.tolog4j.LogManager</java.util.logging.manager>
+                <log4j.loggerContext.selector>org.apache.logging.log4j.async.logger.AsyncLoggerContextSelector</log4j.loggerContext.selector>
+              </systemPropertyVariables>
+            </configuration>
+          </execution>
+          <execution>
+            <id>custom-logger-adapter-test</id>
+            <goals>
+              <goal>test</goal>
+            </goals>
+            <phase>test</phase>
+            <configuration>
+              <includes>
+                <include>**/CustomLoggerAdapterTest.class</include>
+              </includes>
+              <!-- Use custom `j.u.l.LogManager` and a custom adapter -->
+              <systemPropertyVariables>
+                <java.util.logging.manager>org.apache.logging.jul.tolog4j.LogManager</java.util.logging.manager>
+                <log4j.jul.loggerAdapter>org.apache.logging.jul.tolog4j.test.support.CustomLoggerAdapterTest$CustomLoggerAdapter</log4j.jul.loggerAdapter>
+              </systemPropertyVariables>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

jul-to-log4j-api/src/main/java/org/apache/logging/jul/tolog4j/LevelTranslator.java

@@ -0,0 +1,88 @@
+/*
+ * 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.jul.tolog4j;
+
+import org.apache.logging.jul.tolog4j.internal.DefaultLevelConverter;
+import org.apache.logging.jul.tolog4j.internal.JulProperties;
+import org.apache.logging.jul.tolog4j.spi.LevelConverter;
+import org.apache.logging.log4j.Level;
+import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.kit.env.PropertyEnvironment;
+import org.apache.logging.log4j.status.StatusLogger;
+import org.apache.logging.log4j.util.LoaderUtil;
+
+/**
+ * Utility class to convert between JDK Levels and Log4j 2 Levels.
+ *
+ * @since 2.1
+ */
+public final class LevelTranslator {
+
+    /**
+     * Custom Log4j level corresponding to the {@link java.util.logging.Level#FINEST} logging level. This maps to a
+     * level more specific than {@link org.apache.logging.log4j.Level#TRACE}.
+     */
+    public static final Level FINEST = Level.forName("FINEST", Level.TRACE.intLevel() + 100);
+
+    /**
+     * Custom Log4j level corresponding to the {@link java.util.logging.Level#CONFIG} logging level. This maps to a
+     * level in between {@link org.apache.logging.log4j.Level#INFO} and {@link org.apache.logging.log4j.Level#DEBUG}.
+     */
+    public static final Level CONFIG = Level.forName("CONFIG", Level.INFO.intLevel() + 50);
+
+    private static final Logger LOGGER = StatusLogger.getLogger();
+    private static final LevelConverter LEVEL_CONVERTER;
+
+    static {
+        final Class<? extends LevelConverter> levelConverterClass =
+                PropertyEnvironment.getGlobal().getProperty(JulProperties.class).levelConverter();
+        if (levelConverterClass != null) {
+            LevelConverter levelConverter;
+            try {
+                levelConverter = LoaderUtil.newInstanceOf(levelConverterClass);
+            } catch (final Exception e) {
+                LOGGER.error("Could not create custom LevelConverter [{}].", levelConverterClass.getName(), e);
+                levelConverter = new DefaultLevelConverter();
+            }
+            LEVEL_CONVERTER = levelConverter;
+        } else {
+            LEVEL_CONVERTER = new DefaultLevelConverter();
+        }
+    }
+
+    /**
+     * Converts a JDK logging Level to a Log4j logging Level.
+     *
+     * @param level JDK Level to convert, may be null per the JUL specification.
+     * @return converted Level or null
+     */
+    public static Level toLevel(final java.util.logging.Level level) {
+        return LEVEL_CONVERTER.toLevel(level);
+    }
+
+    /**
+     * Converts a Log4j logging Level to a JDK logging Level.
+     *
+     * @param level Log4j Level to convert.
+     * @return converted Level.
+     */
+    public static java.util.logging.Level toJavaLevel(final Level level) {
+        return LEVEL_CONVERTER.toJavaLevel(level);
+    }
+
+    private LevelTranslator() {}
+}

jul-to-log4j-api/src/main/java/org/apache/logging/jul/tolog4j/LogManager.java

@@ -0,0 +1,104 @@
+/*
+ * 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.jul.tolog4j;
+
+import java.util.Collections;
+import java.util.Enumeration;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.logging.Logger;
+import org.apache.logging.jul.tolog4j.internal.ApiLoggerAdapter;
+import org.apache.logging.jul.tolog4j.internal.JulProperties;
+import org.apache.logging.jul.tolog4j.internal.NoOpLogger;
+import org.apache.logging.jul.tolog4j.spi.AbstractLoggerAdapter;
+import org.apache.logging.log4j.kit.env.PropertyEnvironment;
+import org.apache.logging.log4j.status.StatusLogger;
+import org.apache.logging.log4j.util.LoaderUtil;
+
+/**
+ * Log4j implementation of {@link java.util.logging.LogManager}.
+ * <p>
+ *      Note that the system property {@code java.util.logging.manager} must be set to
+ *      {@code org.apache.logging.jul.tolog4j.LogManager} in order to use this adaptor.
+ *      This LogManager requires the {@code log4j-api} library to be available.
+ * </p>
+ * <p>
+ *     To override the default {@link AbstractLoggerAdapter} that is used, specify the Log4j property
+ *     {@code log4j.jul.LoggerAdapter} and set it to the fully qualified class name of a custom
+ *     implementation.
+ *     All implementations must have a default constructor.
+ * </p>
+ *
+ * @since 2.1
+ */
+public class LogManager extends java.util.logging.LogManager {
+
+    private static final org.apache.logging.log4j.Logger LOGGER = StatusLogger.getLogger();
+    private final AbstractLoggerAdapter loggerAdapter;
+    // Contains the set of logger names that are actively being requested using getLogger.
+    private final ThreadLocal<Set<String>> recursive = ThreadLocal.withInitial(HashSet::new);
+
+    public LogManager() {
+        AbstractLoggerAdapter adapter = null;
+        final Class<? extends AbstractLoggerAdapter> adapterClass =
+                PropertyEnvironment.getGlobal().getProperty(JulProperties.class).loggerAdapter();
+        if (adapterClass != null) {
+            try {
+                LOGGER.info("Trying to use LoggerAdapter [{}] specified by Log4j property.", adapterClass.getName());
+                adapter = LoaderUtil.newInstanceOf(adapterClass);
+            } catch (final Exception e) {
+                LOGGER.error(
+                        "Specified LoggerAdapter [{}] can not be created, using default.", adapterClass.getName(), e);
+            }
+        }
+        if (adapter == null) {
+            // Use API by default
+            // See https://github.com/apache/logging-log4j2/issues/2353
+            adapter = new ApiLoggerAdapter();
+        }
+        loggerAdapter = adapter;
+        LOGGER.info("Registered Log4j as the java.util.logging.LogManager.");
+    }
+
+    @Override
+    public boolean addLogger(final Logger logger) {
+        // in order to prevent non-bridged loggers from being registered, we always return false to indicate that
+        // the named logger should be obtained through getLogger(name)
+        return false;
+    }
+
+    @Override
+    public Logger getLogger(final String name) {
+        LOGGER.trace("Call to LogManager.getLogger({})", name);
+        final Set<String> activeRequests = recursive.get();
+        if (activeRequests.add(name)) {
+            try {
+                return loggerAdapter.getLogger(name);
+            } finally {
+                activeRequests.remove(name);
+            }
+        }
+        LOGGER.warn("Recursive call to getLogger for {} ignored.", name);
+        return new NoOpLogger(name);
+    }
+
+    @Override
+    public Enumeration<String> getLoggerNames() {
+        return Collections.enumeration(
+                loggerAdapter.getLoggersInContext(loggerAdapter.getContext()).keySet());
+    }
+}