Support arbitrary Kafka properties

Add support for arbitrary Kafka properties via
`spring.kafka.properties.*` and also a `spring.kafka.max.poll.records`
property.

See gh-7672

spring-boot-docs/src/main/java/org/springframework/boot/kafka/KafkaSpecialProducerConsumerConfigExample.java

@@ -0,0 +1,125 @@
+/*
+ * Copyright 2016-2016 the original author or authors.
+ *
+ * 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 org.springframework.boot.kafka;
+
+import java.util.List;
+import java.util.Map;
+
+import org.apache.kafka.clients.CommonClientConfigs;
+import org.apache.kafka.common.metrics.KafkaMetric;
+import org.apache.kafka.common.metrics.MetricsReporter;
+
+import org.springframework.boot.autoconfigure.kafka.KafkaProperties;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.kafka.core.ConsumerFactory;
+import org.springframework.kafka.core.DefaultKafkaConsumerFactory;
+import org.springframework.kafka.core.DefaultKafkaProducerFactory;
+import org.springframework.kafka.core.ProducerFactory;
+
+/**
+ * Example custom kafka configuration beans used when the user wants to
+ * apply different common properties to the producer and consumer.
+ *
+ * @author Gary Russell
+ * @since 1.5
+ *
+ */
+public class KafkaSpecialProducerConsumerConfigExample {
+
+	// tag::configuration[]
+	@Configuration
+	public static class CustomKafkaBeans {
+
+		/**
+		 * Customized ProducerFactory bean.
+		 * @param properties the kafka properties.
+		 * @return the bean.
+		 */
+		@Bean
+		public ProducerFactory<?, ?> kafkaProducerFactory(KafkaProperties properties) {
+			Map<String, Object> producerProperties = properties.buildProducerProperties();
+			producerProperties.put(CommonClientConfigs.METRIC_REPORTER_CLASSES_CONFIG,
+					MyProducerMetricsReporter.class);
+			return new DefaultKafkaProducerFactory<Object, Object>(producerProperties);
+		}
+
+		/**
+		 * Customized ConsumerFactory bean.
+		 * @param properties the kafka properties.
+		 * @return the bean.
+		 */
+		@Bean
+		public ConsumerFactory<?, ?> kafkaConsumerFactory(KafkaProperties properties) {
+			Map<String, Object> consumererProperties = properties.buildConsumerProperties();
+			consumererProperties.put(CommonClientConfigs.METRIC_REPORTER_CLASSES_CONFIG,
+					MyConsumerMetricsReporter.class);
+			return new DefaultKafkaConsumerFactory<Object, Object>(consumererProperties);
+		}
+
+	}
+	// end::configuration[]
+
+	public static class MyConsumerMetricsReporter implements MetricsReporter {
+
+		@Override
+		public void configure(Map<String, ?> configs) {
+		}
+
+		@Override
+		public void init(List<KafkaMetric> metrics) {
+		}
+
+		@Override
+		public void metricChange(KafkaMetric metric) {
+		}
+
+		@Override
+		public void metricRemoval(KafkaMetric metric) {
+		}
+
+		@Override
+		public void close() {
+		}
+
+	}
+
+	public static class MyProducerMetricsReporter implements MetricsReporter {
+
+		@Override
+		public void configure(Map<String, ?> configs) {
+		}
+
+		@Override
+		public void init(List<KafkaMetric> metrics) {
+		}
+
+		@Override
+		public void metricChange(KafkaMetric metric) {
+		}
+
+		@Override
+		public void metricRemoval(KafkaMetric metric) {
+		}
+
+		@Override
+		public void close() {
+		}
+
+	}
+
+}