Add Kafka ItemWriter

This commit adds an ItemWriter implementation for Apache Kafka using
a KafkaTemplate with default topic set. Extending KeyValueItemWriter,
the writer requires a Converter to map the Kafka ProducerRecord's key
from the item.

Resolves BATCH-2765

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/kafka/KafkaItemWriter.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2018 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.batch.item.kafka;
+
+import org.springframework.batch.item.ItemWriter;
+import org.springframework.batch.item.KeyValueItemWriter;
+import org.springframework.kafka.core.KafkaTemplate;
+import org.springframework.util.Assert;
+
+/**
+ * <p>
+ * An {@link ItemWriter} implementation for Apache Kafka using a
+ * {@link KafkaTemplate} with default topic configured.
+ * </p>
+ *
+ * @author Mathieu Ouellet
+ * @since 4.2
+ *
+ */
+public class KafkaItemWriter<K, T> extends KeyValueItemWriter<K, T> {
+
+	private KafkaTemplate<K, T> kafkaTemplate;
+
+	@Override
+	protected void writeKeyValue(K key, T value) {
+		if (this.delete) {
+			this.kafkaTemplate.sendDefault(key, null);
+		}
+		else {
+			this.kafkaTemplate.sendDefault(key, value);
+		}
+	}
+
+	@Override
+	protected void init() {
+		Assert.notNull(this.kafkaTemplate, "KafkaTemplate must not be null.");
+		Assert.notNull(this.kafkaTemplate.getDefaultTopic(), "KafkaTemplate must have the default topic set.");
+	}
+
+	public void setKafkaTemplate(KafkaTemplate<K, T> kafkaTemplate) {
+		this.kafkaTemplate = kafkaTemplate;
+	}
+}

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/kafka/builder/KafkaItemWriterBuilder.java

@@ -0,0 +1,91 @@
+/*
+ * Copyright 2018 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.batch.item.kafka.builder;
+
+import org.springframework.batch.item.kafka.KafkaItemWriter;
+import org.springframework.core.convert.converter.Converter;
+import org.springframework.kafka.core.KafkaTemplate;
+import org.springframework.util.Assert;
+
+/**
+ * A builder implementation for the {@link KafkaItemWriter}
+ *
+ * @author Mathieu Ouellet
+ * @since 4.2
+ */
+public class KafkaItemWriterBuilder<K, V> {
+
+	private KafkaTemplate<K, V> kafkaTemplate;
+
+	private Converter<V, K> itemKeyMapper;
+
+	private boolean delete;
+
+	/**
+	 * Establishes the KafkaTemplate to be used by the KafkaItemWriter.
+	 * @param kafkaTemplate the template to be used
+	 * @return this instance for method chaining
+	 * @see KafkaItemWriter#setKafkaTemplate(KafkaTemplate)
+	 */
+	public KafkaItemWriterBuilder<K, V> kafkaTemplate(KafkaTemplate<K, V> kafkaTemplate) {
+		this.kafkaTemplate = kafkaTemplate;
+		return this;
+	}
+
+	/**
+	 * Set the {@link Converter} to use to derive the key from the item.
+	 *
+	 * @param itemKeyMapper the Converter to use.
+	 * @return The current instance of the builder.
+	 * @see KafkaItemWriter#setItemKeyMapper(Converter)
+	 */
+	public KafkaItemWriterBuilder<K, V> itemKeyMapper(Converter<V, K> itemKeyMapper) {
+		this.itemKeyMapper = itemKeyMapper;
+		return this;
+	}
+
+	/**
+	 * Indicates if the items being passed to the writer are all to be send as delete events to the topic. A delete
+	 * event is made of a key with a null value. If set to false (default), the items will be send with provided value
+	 * and key converter by the itemKeyMapper. If set to true, the items will be send with the key converter from the
+	 * value by the itemKeyMapper and a null value.
+	 *
+	 * @param delete removal indicator.
+	 * @return The current instance of the builder.
+	 * @see KafkaItemWriter#setDelete(boolean)
+	 */
+	public KafkaItemWriterBuilder<K, V> delete(boolean delete) {
+		this.delete = delete;
+		return this;
+	}
+
+	/**
+	 * Validates and builds a {@link KafkaItemWriter}.
+	 * 
+	 * @return a {@link KafkaItemWriter}
+	 */
+	public KafkaItemWriter<K, V> build() {
+		Assert.notNull(this.kafkaTemplate, "kafkaTemplate is required.");
+		Assert.notNull(this.itemKeyMapper, "itemKeyMapper is required.");
+
+		KafkaItemWriter<K, V> writer = new KafkaItemWriter<>();
+		writer.setKafkaTemplate(this.kafkaTemplate);
+		writer.setItemKeyMapper(this.itemKeyMapper);
+		writer.setDelete(this.delete);
+		return writer;
+	}
+}

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/kafka/builder/package-info.java

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2018 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.
+ */
+
+/**
+ * Builders for Apache Kafka item reader and writer.
+ *
+ * @author Mathieu Ouellet
+ */
+@NonNullApi
+package org.springframework.batch.item.kafka.builder;
+
+import org.springframework.lang.NonNullApi;

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/kafka/package-info.java

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2018 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.
+ */
+
+/**
+ * Apache Kafka related readers and writers
+ *
+ * @author Mathieu Ouellet
+ */
+@NonNullApi
+package org.springframework.batch.item.kafka;
+
+import org.springframework.lang.NonNullApi;