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We are in the process of rewritting the JVM clients for Kafka. As of 0.8.2 Kafka includes a newly rewritten Java producer. The next release will include an equivalent Java consumer. These new clients are meant to supplant the existing Scala clients, but for compatability they will co-exist for some time. These clients are available in a seperate jar with minimal dependencies, while the old Scala clients remain packaged with the server.
As of the 0.8.2 release we encourage all new development to use the new Java producer. This client is production tested and generally both faster and more fully featured than the previous Scala client. You can use this client by adding a dependency on the client jar using the following example maven co-ordinates (you can change the version numbers with new releases):
* Create a list of message streams of type T for each topic, using the default decoder.
*/
public Map<String, List<KafkaStream<byte[], byte[]>>> createMessageStreams(Map<String, Integer> topicCountMap);
/**
* Create a list of message streams for topics matching a wildcard.
*
* @param topicFilter a TopicFilter that specifies which topics to
* subscribe to (encapsulates a whitelist or a blacklist).
* @param numStreams the number of message streams to return.
* @param keyDecoder a decoder that decodes the message key
* @param valueDecoder a decoder that decodes the message itself
* @return a list of KafkaStream. Each stream supports an
* iterator over its MessageAndMetadata elements.
*/
public <K,V> List<KafkaStream<K,V>>
createMessageStreamsByFilter(TopicFilter topicFilter, int numStreams, Decoder<K> keyDecoder, Decoder<V> valueDecoder);
/**
* Create a list of message streams for topics matching a wildcard, using the default decoder.
*/
public List<KafkaStream<byte[], byte[]>> createMessageStreamsByFilter(TopicFilter topicFilter, int numStreams);
/**
* Create a list of message streams for topics matching a wildcard, using the default decoder, with one stream.
*/
public List<KafkaStream<byte[], byte[]>> createMessageStreamsByFilter(TopicFilter topicFilter);
/**
* Commit the offsets of all topic/partitions connected by this connector.
*/
public void commitOffsets();
/**
* Shut down the connector
*/
public void shutdown();
}
</pre>
You can follow
<ahref="https://cwiki.apache.org/confluence/display/KAFKA/Consumer+Group+Example"title="Kafka 0.8 consumer example">this example</a> to learn how to use the high level consumer api.
* @param request specifies the topic name, topic partition, starting byte offset, maximum bytes to be fetched.
* @return a set of fetched messages
*/
public FetchResponse fetch(kafka.javaapi.FetchRequest request);
/**
* Fetch metadata for a sequence of topics.
*
* @param request specifies the versionId, clientId, sequence of topics.
* @return metadata for each topic in the request.
*/
public kafka.javaapi.TopicMetadataResponse send(kafka.javaapi.TopicMetadataRequest request);
/**
* Get a list of valid offsets (up to maxSize) before the given time.
*
* @param request a [[kafka.javaapi.OffsetRequest]] object.
* @return a [[kafka.javaapi.OffsetResponse]] object.
*/
public kafka.javaapi.OffsetResponse getOffsetsBefore(OffsetRequest request);
/**
* Close the SimpleConsumer.
*/
public void close();
}
</pre>
For most applications, the high level consumer Api is good enough. Some applications want features not exposed to the high level consumer yet (e.g., set initial offset when restarting the consumer). They can instead use our low level SimpleConsumer Api. The logic will be a bit more complicated and you can follow the example in
As of the 0.9.0 release we have added a replacement for our existing simple and high-level consumers. This client is considered beta quality. You can use this client by adding a dependency on the client jar using the following example maven co-ordinates (you can change the version numbers with new releases):
