Introduce a pulsar log4j2 appender

pom.xml

@@ -99,6 +99,7 @@ flexible messaging model and an intuitive client API.</description>
     <module>all</module>
     <module>docker</module>
     <module>tests</module>
+    <module>pulsar-log4j2-appender</module>
   </modules>
 
   <issueManagement>

pulsar-log4j2-appender/pom.xml

@@ -0,0 +1,77 @@
+<!--
+
+    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.pulsar</groupId>
+		<artifactId>pulsar</artifactId>
+		<version>2.0.0-incubating-SNAPSHOT</version>
+		<relativePath>..</relativePath>
+	</parent>
+
+	<artifactId>pulsar-log4j2-appender</artifactId>
+	<name>Pulsar Log4j2 Appender</name>
+	<description>Pulsar Log4j2 Appender</description>
+
+	<dependencies>
+		<dependency>
+			<groupId>${project.groupId}</groupId>
+			<artifactId>pulsar-client</artifactId>
+			<version>${project.version}</version>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.logging.log4j</groupId>
+			<artifactId>log4j-api</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.logging.log4j</groupId>
+			<artifactId>log4j-core</artifactId>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.logging.log4j</groupId>
+			<artifactId>log4j-slf4j-impl</artifactId>
+		</dependency>
+
+		<dependency>
+			<groupId>org.apache.logging.log4j</groupId>
+			<artifactId>log4j-api</artifactId>
+			<type>test-jar</type>
+			<version>${log4j2.version}</version>
+            <scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.logging.log4j</groupId>
+			<artifactId>log4j-core</artifactId>
+			<type>test-jar</type>
+			<version>${log4j2.version}</version>
+			<scope>test</scope>
+		</dependency>
+		<!-- Required for AsyncLoggers -->
+		<dependency>
+			<groupId>com.lmax</groupId>
+			<artifactId>disruptor</artifactId>
+			<version>3.4.0</version>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+
+</project>

pulsar-log4j2-appender/src/main/java/org/apache/pulsar/log4j2/appender/PulsarAppender.java

@@ -0,0 +1,211 @@
+/**
+ * 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.pulsar.log4j2.appender;
+
+import java.io.Serializable;
+import java.util.Objects;
+import java.util.concurrent.TimeUnit;
+import org.apache.logging.log4j.core.AbstractLifeCycle;
+import org.apache.logging.log4j.core.Appender;
+import org.apache.logging.log4j.core.Filter;
+import org.apache.logging.log4j.core.Layout;
+import org.apache.logging.log4j.core.LogEvent;
+import org.apache.logging.log4j.core.appender.AbstractAppender;
+import org.apache.logging.log4j.core.config.Node;
+import org.apache.logging.log4j.core.config.Property;
+import org.apache.logging.log4j.core.config.plugins.Plugin;
+import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
+import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
+import org.apache.logging.log4j.core.config.plugins.PluginElement;
+import org.apache.logging.log4j.core.layout.SerializedLayout;
+
+/**
+ * The PulsarAppender logs events to an Apache Pulsar topic.
+ *
+ * <p>Each log event is sent as a Pulsar record.
+ */
+@Plugin(
+    name = "Pulsar",
+    category = Node.CATEGORY,
+    elementType = Appender.ELEMENT_TYPE,
+    printObject = true)
+public final class PulsarAppender extends AbstractAppender {
+
+    /**
+     * Builds PulsarAppender instances.
+     * @param <B> The type to build
+     */
+    public static class Builder<B extends Builder<B>> extends AbstractAppender.Builder<B>
+            implements org.apache.logging.log4j.core.util.Builder<PulsarAppender> {
+
+        @PluginAttribute("key")
+        private String key;
+
+        @PluginAttribute("topic")
+        private String topic;
+
+        @PluginAttribute("serviceUrl")
+        private String serviceUrl;
+
+        @PluginAttribute(value = "avoidRecursive", defaultBoolean = true)
+        private boolean avoidRecursive;
+
+        @PluginAttribute(value = "syncSend", defaultBoolean = false)
+        private boolean syncSend;
+
+        @PluginElement("Properties")
+        private Property[] properties;
+
+        @SuppressWarnings("resource")
+        @Override
+        public PulsarAppender build() {
+            final Layout<? extends Serializable> layout = getLayout();
+            if (layout == null) {
+                AbstractLifeCycle.LOGGER.error("No layout provided for PulsarAppender");
+                return null;
+            }
+            PulsarManager manager = new PulsarManager(
+                getConfiguration().getLoggerContext(),
+                getName(),
+                serviceUrl,
+                topic,
+                syncSend,
+                properties,
+                key);
+            return new PulsarAppender(
+                getName(),
+                layout,
+                getFilter(),
+                isIgnoreExceptions(),
+                avoidRecursive,
+                manager);
+        }
+
+        public String getTopic() {
+            return topic;
+        }
+
+        public boolean isSyncSend() {
+            return syncSend;
+        }
+
+        public Property[] getProperties() {
+            return properties;
+        }
+
+        public B setTopic(final String topic) {
+            this.topic = topic;
+            return asBuilder();
+        }
+
+        public B setSyncSend(final boolean syncSend) {
+            this.syncSend = syncSend;
+            return asBuilder();
+        }
+
+        public B setProperties(final Property[] properties) {
+            this.properties = properties;
+            return asBuilder();
+        }
+    }
+
+    /**
+     * Creates a builder for a PulsarAppender.
+     * @return a builder for a PulsarAppender.
+     */
+    @PluginBuilderFactory
+    public static <B extends Builder<B>> B newBuilder() {
+        return new Builder<B>().asBuilder();
+    }
+
+    private final boolean avoidRecursive;
+    private final PulsarManager manager;
+
+    private PulsarAppender(
+            final String name,
+            final Layout<? extends Serializable> layout,
+            final Filter filter,
+            final boolean ignoreExceptions,
+            final boolean avoidRecursive,
+            final PulsarManager manager) {
+        super(name, filter, layout, ignoreExceptions);
+        this.avoidRecursive = avoidRecursive;
+        this.manager = Objects.requireNonNull(manager, "manager");
+    }
+
+    @Override
+    public void append(final LogEvent event) {
+        if (avoidRecursive
+            && event.getLoggerName() != null
+            && event.getLoggerName().startsWith("org.apache.pulsar")) {
+            LOGGER.warn("Recursive logging from [{}] for appender [{}].", event.getLoggerName(), getName());
+        } else {
+            try {
+                tryAppend(event);
+            } catch (final Exception e) {
+                error("Unable to write to Pulsar in appender [" + getName() + "]", event, e);
+            }
+        }
+    }
+
+    private void tryAppend(final LogEvent event) {
+        final Layout<? extends Serializable> layout = getLayout();
+        byte[] data;
+        if (layout instanceof SerializedLayout) {
+            final byte[] header = layout.getHeader();
+            final byte[] body = layout.toByteArray(event);
+            data = new byte[header.length + body.length];
+            System.arraycopy(header, 0, data, 0, header.length);
+            System.arraycopy(body, 0, data, header.length, body.length);
+        } else {
+            data = layout.toByteArray(event);
+        }
+        manager.send(data);
+    }
+
+    @Override
+    public void start() {
+        super.start();
+        try {
+            manager.startup();
+        } catch (Exception e) {
+            // fail to start the manager
+        }
+    }
+
+    @Override
+    public boolean stop(final long timeout, final TimeUnit timeUnit) {
+        setStopping();
+        boolean stopped = super.stop(timeout, timeUnit, false);
+        stopped &= manager.stop(timeout, timeUnit);
+        setStopped();
+        return stopped;
+    }
+
+    @Override
+    public String toString() {
+        return "PulsarAppender{" +
+            "name=" + getName() +
+            ", state=" + getState() +
+            ", serviceUrl=" + manager.getServiceUrl() +
+            ", topic=" + manager.getTopic() +
+            '}';
+    }
+
+}