README.md for contrib/kafka

Author: Raghu Angadi

contrib/kafka/README.md

@@ -0,0 +1,36 @@
+# KafkaIO : Dataflow Unbounded Source and Sink for Kafka Topics
+
+KafkaIO provides unbounded sources and sinks for [Kafka](https://www.firebase.com/)
+topics. Kafka version 0.9 and above are supported.
+
+## Basic Usage
+ * Read from a topic with 8 byte long keys and string values:
+   ```java
+     PCollection<KV<Long, String>> kafkaRecords =
+       pipeline
+         .applY(KafkaIO.read()
+           .withBootstrapServers("broker_1:9092,broker_2:9092")
+           .withTopics(ImmutableList.of("topic_a"))
+           .withKeyCoder(BigEndianLongCoder.of())
+           .withValueCoder(StringUtf8Coder.of())
+           .withoutMetadata()
+         );
+    ```
+ * Write the same PCollection to a Kafka topic:
+   ```java
+     kafkaRecords.apply(KafkaIO.write()
+       .withBootstrapServers("broker_1:9092,broker_2:9092")
+       .withTopic("results")
+       .withKeyCoder(BigEndianLongCoder.of())
+       .withValueCoder(StringUtf8Coder.of())
+   ```
+
+Please see JavaDoc for KafkaIO in
+[KafkaIO.java](https://github.com/GoogleCloudPlatform/DataflowJavaSDK/blob/master/contrib/kafka/src/main/java/com/google/cloud/dataflow/contrib/kafka/KafkaIO.java#L100)
+for complete documentation and a more descriptive usage example.
+
+## Release Notes
+  * **0.2.0** : Assign one split for each of the Kafka topic partitions. This makes Dataflow
+                [Update](https://cloud.google.com/dataflow/pipelines/updating-a-pipeline)
+                from previous version incompatible.
+  * **0.1.0** : KafkaIO with support for Unbounded Source and Sink.