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<title>37.&nbsp;Apache Kafka Binder</title><link rel="stylesheet" type="text/css" href="css/manual-multipage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="multi_spring-cloud.html" title="Spring Cloud"><link rel="up" href="multi__binder_implementations.html" title="Part&nbsp;V.&nbsp;Binder Implementations"><link rel="prev" href="multi__binder_implementations.html" title="Part&nbsp;V.&nbsp;Binder Implementations"><link rel="next" href="multi__rabbitmq_binder.html" title="38.&nbsp;RabbitMQ Binder"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">37.&nbsp;Apache Kafka Binder</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi__binder_implementations.html">Prev</a>&nbsp;</td><th width="60%" align="center">Part&nbsp;V.&nbsp;Binder Implementations</th><td width="20%" align="right">&nbsp;<a accesskey="n" href="multi__rabbitmq_binder.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a name="_apache_kafka_binder" href="#_apache_kafka_binder"></a>37.&nbsp;Apache Kafka Binder</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_usage" href="#_usage"></a>37.1&nbsp;Usage</h2></div></div></div><p>For using the Apache Kafka binder, you just need to add it to your Spring Cloud Stream application, using the following Maven coordinates:</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.springframework.cloud<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>spring-cloud-stream-binder-kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/dependency&gt;</span></pre><p>Alternatively, you can also use the Spring Cloud Stream Kafka Starter.</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.springframework.cloud<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>spring-cloud-starter-stream-kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/dependency&gt;</span></pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_apache_kafka_binder_overview" href="#_apache_kafka_binder_overview"></a>37.2&nbsp;Apache Kafka Binder Overview</h2></div></div></div><p>A simplified diagram of how the Apache Kafka binder operates can be seen below.</p><div class="figure"><a name="d0e9258" href="#d0e9258"></a><p class="title"><b>Figure&nbsp;37.1.&nbsp;Kafka Binder</b></p><div class="figure-contents"><div class="mediaobject"><img src="images/kafka-binder.png" alt="kafka binder"></div></div></div><br class="figure-break"><p>The Apache Kafka Binder implementation maps each destination to an Apache Kafka topic.
The consumer group maps directly to the same Apache Kafka concept.
Partitioning also maps directly to Apache Kafka partitions as well.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_configuration_options_2" href="#_configuration_options_2"></a>37.3&nbsp;Configuration Options</h2></div></div></div><p>This section contains the configuration options used by the Apache Kafka binder.</p><p>For common configuration options and properties pertaining to binder, refer to the <a class="link" href="multi__configuration_options.html#binding-properties" title="28.2&nbsp;Binding Properties">core documentation</a>.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_kafka_binder_properties" href="#_kafka_binder_properties"></a>37.3.1&nbsp;Kafka Binder Properties</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">spring.cloud.stream.kafka.binder.brokers</span></dt><dd><p class="simpara">A list of brokers to which the Kafka binder will connect.</p><p class="simpara">Default: <code class="literal">localhost</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.defaultBrokerPort</span></dt><dd><p class="simpara"> <code class="literal">brokers</code> allows hosts specified with or without port information (e.g., <code class="literal">host1,host2:port2</code>).
This sets the default port when no port is configured in the broker list.</p><p class="simpara">Default: <code class="literal">9092</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.zkNodes</span></dt><dd><p class="simpara">A list of ZooKeeper nodes to which the Kafka binder can connect.</p><p class="simpara">Default: <code class="literal">localhost</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.defaultZkPort</span></dt><dd><p class="simpara"> <code class="literal">zkNodes</code> allows hosts specified with or without port information (e.g., <code class="literal">host1,host2:port2</code>).
This sets the default port when no port is configured in the node list.</p><p class="simpara">Default: <code class="literal">2181</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.configuration</span></dt><dd><p class="simpara"> Key/Value map of client properties (both producers and consumer) passed to all clients created by the binder.
Due to the fact that these properties will be used by both producers and consumers, usage should be restricted to common properties, especially security settings.</p><p class="simpara">Default: Empty map.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.headers</span></dt><dd><p class="simpara">The list of custom headers that will be transported by the binder.</p><p class="simpara">Default: empty.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.healthTimeout</span></dt><dd><p class="simpara">The time to wait to get partition information in seconds; default 60.
Health will report as down if this timer expires.</p><p class="simpara">Default: 10.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.offsetUpdateTimeWindow</span></dt><dd><p class="simpara"> The frequency, in milliseconds, with which offsets are saved.
Ignored if <code class="literal">0</code>.</p><p class="simpara">Default: <code class="literal">10000</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.offsetUpdateCount</span></dt><dd><p class="simpara"> The frequency, in number of updates, which which consumed offsets are persisted.
Ignored if <code class="literal">0</code>.
Mutually exclusive with <code class="literal">offsetUpdateTimeWindow</code>.</p><p class="simpara">Default: <code class="literal">0</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.requiredAcks</span></dt><dd><p class="simpara">The number of required acks on the broker.</p><p class="simpara">Default: <code class="literal">1</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.minPartitionCount</span></dt><dd><p class="simpara"> Effective only if <code class="literal">autoCreateTopics</code> or <code class="literal">autoAddPartitions</code> is set.
The global minimum number of partitions that the binder will configure on topics on which it produces/consumes data.
It can be superseded by the <code class="literal">partitionCount</code> setting of the producer or by the value of <code class="literal">instanceCount</code> * <code class="literal">concurrency</code> settings of the producer (if either is larger).</p><p class="simpara">Default: <code class="literal">1</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.replicationFactor</span></dt><dd><p class="simpara">The replication factor of auto-created topics if <code class="literal">autoCreateTopics</code> is active.</p><p class="simpara">Default: <code class="literal">1</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.autoCreateTopics</span></dt><dd><p class="simpara"> If set to <code class="literal">true</code>, the binder will create new topics automatically.
If set to <code class="literal">false</code>, the binder will rely on the topics being already configured.
In the latter case, if the topics do not exist, the binder will fail to start.
Of note, this setting is independent of the <code class="literal">auto.topic.create.enable</code> setting of the broker and it does not influence it: if the server is set to auto-create topics, they may be created as part of the metadata retrieval request, with default broker settings.</p><p class="simpara">Default: <code class="literal">true</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.autoAddPartitions</span></dt><dd><p class="simpara"> If set to <code class="literal">true</code>, the binder will create add new partitions if required.
If set to <code class="literal">false</code>, the binder will rely on the partition size of the topic being already configured.
If the partition count of the target topic is smaller than the expected value, the binder will fail to start.</p><p class="simpara">Default: <code class="literal">false</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.socketBufferSize</span></dt><dd><p class="simpara">Size (in bytes) of the socket buffer to be used by the Kafka consumers.</p><p class="simpara">Default: <code class="literal">2097152</code>.</p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_kafka_consumer_properties" href="#_kafka_consumer_properties"></a>37.3.2&nbsp;Kafka Consumer Properties</h3></div></div></div><p>The following properties are available for Kafka consumers only and
must be prefixed with <code class="literal">spring.cloud.stream.kafka.bindings.&lt;channelName&gt;.consumer.</code>.</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">autoRebalanceEnabled</span></dt><dd><p class="simpara">When <code class="literal">true</code>, topic partitions will be automatically rebalanced between the members of a consumer group.
When <code class="literal">false</code>, each consumer will be assigned a fixed set of partitions based on <code class="literal">spring.cloud.stream.instanceCount</code> and <code class="literal">spring.cloud.stream.instanceIndex</code>.
This requires both <code class="literal">spring.cloud.stream.instanceCount</code> and <code class="literal">spring.cloud.stream.instanceIndex</code> properties to be set appropriately on each launched instance.
The property <code class="literal">spring.cloud.stream.instanceCount</code> must typically be greater than 1 in this case.</p><p class="simpara">Default: <code class="literal">true</code>.</p></dd><dt><span class="term">autoCommitOffset</span></dt><dd><p class="simpara"> Whether to autocommit offsets when a message has been processed.
If set to <code class="literal">false</code>, a header with the key <code class="literal">kafka_acknowledgment</code> of the type <code class="literal">org.springframework.kafka.support.Acknowledgment</code> header will be present in the inbound message.
Applications may use this header for acknowledging messages.
See the examples section for details.
When this property is set to <code class="literal">false</code>, Kafka binder will set the ack mode to <code class="literal">org.springframework.kafka.listener.AbstractMessageListenerContainer.AckMode.MANUAL</code>.</p><p class="simpara">Default: <code class="literal">true</code>.</p></dd><dt><span class="term">autoCommitOnError</span></dt><dd><p class="simpara"> Effective only if <code class="literal">autoCommitOffset</code> is set to <code class="literal">true</code>.
If set to <code class="literal">false</code> it suppresses auto-commits for messages that result in errors, and will commit only for successful messages, allows a stream to automatically replay from the last successfully processed message, in case of persistent failures.
If set to <code class="literal">true</code>, it will always auto-commit (if auto-commit is enabled).
If not set (default), it effectively has the same value as <code class="literal">enableDlq</code>, auto-committing erroneous messages if they are sent to a DLQ, and not committing them otherwise.</p><p class="simpara">Default: not set.</p></dd><dt><span class="term">recoveryInterval</span></dt><dd><p class="simpara">The interval between connection recovery attempts, in milliseconds.</p><p class="simpara">Default: <code class="literal">5000</code>.</p></dd><dt><span class="term">startOffset</span></dt><dd><p class="simpara"> The starting offset for new groups.
Allowed values: <code class="literal">earliest</code>, <code class="literal">latest</code>.
If the consumer group is set explicitly for the consumer 'binding' (via <code class="literal">spring.cloud.stream.bindings.&lt;channelName&gt;.group</code>), then 'startOffset' is set to <code class="literal">earliest</code>; otherwise it is set to <code class="literal">latest</code> for the <code class="literal">anonymous</code> consumer group.</p><p class="simpara">Default: null (equivalent to <code class="literal">earliest</code>).</p></dd><dt><span class="term">enableDlq</span></dt><dd><p class="simpara">When set to true, it will send enable DLQ behavior for the consumer.
By default, messages that result in errors will be forwarded to a topic named <code class="literal">error.&lt;destination&gt;.&lt;group&gt;</code>.
The DLQ topic name can be configurable via the property <code class="literal">dlqName</code>.
This provides an alternative option to the more common Kafka replay scenario for the case when the number of errors is relatively small and replaying the entire original topic may be too cumbersome.</p><p class="simpara">Default: <code class="literal">false</code>.</p></dd><dt><span class="term">configuration</span></dt><dd><p class="simpara">Map with a key/value pair containing generic Kafka consumer properties.</p><p class="simpara">Default: Empty map.</p></dd><dt><span class="term">dlqName</span></dt><dd><p class="simpara">The name of the DLQ topic to receive the error messages.</p><p class="simpara">Default: null (If not specified, messages that result in errors will be forwarded to a topic named <code class="literal">error.&lt;destination&gt;.&lt;group&gt;</code>).</p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_kafka_producer_properties" href="#_kafka_producer_properties"></a>37.3.3&nbsp;Kafka Producer Properties</h3></div></div></div><p>The following properties are available for Kafka producers only and
must be prefixed with <code class="literal">spring.cloud.stream.kafka.bindings.&lt;channelName&gt;.producer.</code>.</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">bufferSize</span></dt><dd><p class="simpara">Upper limit, in bytes, of how much data the Kafka producer will attempt to batch before sending.</p><p class="simpara">Default: <code class="literal">16384</code>.</p></dd><dt><span class="term">sync</span></dt><dd><p class="simpara">Whether the producer is synchronous.</p><p class="simpara">Default: <code class="literal">false</code>.</p></dd><dt><span class="term">batchTimeout</span></dt><dd><p class="simpara"> How long the producer will wait before sending in order to allow more messages to accumulate in the same batch.
(Normally the producer does not wait at all, and simply sends all the messages that accumulated while the previous send was in progress.) A non-zero value may increase throughput at the expense of latency.</p><p class="simpara">Default: <code class="literal">0</code>.</p></dd><dt><span class="term">messageKeyExpression</span></dt><dd><p class="simpara"> A SpEL expression evaluated against the outgoing message used to populate the key of the produced Kafka message.
For example <code class="literal">headers.key</code> or <code class="literal">payload.myKey</code>.</p><p class="simpara">Default: <code class="literal">none</code>.</p></dd><dt><span class="term">configuration</span></dt><dd><p class="simpara">Map with a key/value pair containing generic Kafka producer properties.</p><p class="simpara">Default: Empty map.</p></dd></dl></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>The Kafka binder will use the <code class="literal">partitionCount</code> setting of the producer as a hint to create a topic with the given partition count (in conjunction with the <code class="literal">minPartitionCount</code>, the maximum of the two being the value being used).
Exercise caution when configuring both <code class="literal">minPartitionCount</code> for a binder and <code class="literal">partitionCount</code> for an application, as the larger value will be used.
If a topic already exists with a smaller partition count and <code class="literal">autoAddPartitions</code> is disabled (the default), then the binder will fail to start.
If a topic already exists with a smaller partition count and <code class="literal">autoAddPartitions</code> is enabled, new partitions will be added.
If a topic already exists with a larger number of partitions than the maximum of (<code class="literal">minPartitionCount</code> and <code class="literal">partitionCount</code>), the existing partition count will be used.</p></td></tr></table></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_usage_examples" href="#_usage_examples"></a>37.3.4&nbsp;Usage examples</h3></div></div></div><p>In this section, we illustrate the use of the above properties for specific scenarios.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="_example_setting_literal_autocommitoffset_literal_false_and_relying_on_manual_acking" href="#_example_setting_literal_autocommitoffset_literal_false_and_relying_on_manual_acking"></a>Example: Setting <code class="literal">autoCommitOffset</code> false and relying on manual acking.</h4></div></div></div><p>This example illustrates how one may manually acknowledge offsets in a consumer application.</p><p>This example requires that <code class="literal">spring.cloud.stream.kafka.bindings.input.consumer.autoCommitOffset</code> is set to false.
Use the corresponding input channel name for your example.</p><pre class="screen">@SpringBootApplication
@EnableBinding(Sink.class)
public class ManuallyAcknowdledgingConsumer {
public static void main(String[] args) {
SpringApplication.run(ManuallyAcknowdledgingConsumer.class, args);
}
@StreamListener(Sink.INPUT)
public void process(Message&lt;?&gt; message) {
Acknowledgment acknowledgment = message.getHeaders().get(KafkaHeaders.ACKNOWLEDGMENT, Acknowledgment.class);
if (acknowledgment != null) {
System.out.println("Acknowledgment provided");
acknowledgment.acknowledge();
}
}
}</pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="_example_security_configuration" href="#_example_security_configuration"></a>Example: security configuration</h4></div></div></div><p>Apache Kafka 0.9 supports secure connections between client and brokers.
To take advantage of this feature, follow the guidelines in the <a class="link" href="http://kafka.apache.org/090/documentation.html#security_configclients" target="_top">Apache Kafka Documentation</a> as well as the Kafka 0.9 <a class="link" href="http://docs.confluent.io/2.0.0/kafka/security.html" target="_top">security guidelines from the Confluent documentation</a>.
Use the <code class="literal">spring.cloud.stream.kafka.binder.configuration</code> option to set security properties for all clients created by the binder.</p><p>For example, for setting <code class="literal">security.protocol</code> to <code class="literal">SASL_SSL</code>, set:</p><pre class="screen">spring.cloud.stream.kafka.binder.configuration.security.protocol=SASL_SSL</pre><p>All the other security properties can be set in a similar manner.</p><p>When using Kerberos, follow the instructions in the <a class="link" href="http://kafka.apache.org/090/documentation.html#security_sasl_clientconfig" target="_top">reference documentation</a> for creating and referencing the JAAS configuration.</p><p>Spring Cloud Stream supports passing JAAS configuration information to the application using a JAAS configuration file and using Spring Boot properties.</p><div class="section"><div class="titlepage"><div><div><h5 class="title"><a name="_using_jaas_configuration_files" href="#_using_jaas_configuration_files"></a>Using JAAS configuration files</h5></div></div></div><p>The JAAS, and (optionally) krb5 file locations can be set for Spring Cloud Stream applications by using system properties.
Here is an example of launching a Spring Cloud Stream application with SASL and Kerberos using a JAAS configuration file:</p><pre class="screen"> java -Djava.security.auth.login.config=/path.to/kafka_client_jaas.conf -jar log.jar \
--spring.cloud.stream.kafka.binder.brokers=secure.server:9092 \
--spring.cloud.stream.kafka.binder.zkNodes=secure.zookeeper:2181 \
--spring.cloud.stream.bindings.input.destination=stream.ticktock \
--spring.cloud.stream.kafka.binder.configuration.security.protocol=SASL_PLAINTEXT</pre></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a name="_using_spring_boot_properties" href="#_using_spring_boot_properties"></a>Using Spring Boot properties</h5></div></div></div><p>As an alternative to having a JAAS configuration file, Spring Cloud Stream provides a mechanism for setting up the JAAS configuration for Spring Cloud Stream applications using Spring Boot properties.</p><p>The following properties can be used for configuring the login context of the Kafka client.</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">spring.cloud.stream.kafka.binder.jaas.loginModule</span></dt><dd><p class="simpara">The login module name. Not necessary to be set in normal cases.</p><p class="simpara">Default: <code class="literal">com.sun.security.auth.module.Krb5LoginModule</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.jaas.controlFlag</span></dt><dd><p class="simpara">The control flag of the login module.</p><p class="simpara">Default: <code class="literal">required</code>.</p></dd><dt><span class="term">spring.cloud.stream.kafka.binder.jaas.options</span></dt><dd><p class="simpara">Map with a key/value pair containing the login module options.</p><p class="simpara">Default: Empty map.</p></dd></dl></div><p>Here is an example of launching a Spring Cloud Stream application with SASL and Kerberos using Spring Boot configuration properties:</p><pre class="screen"> java --spring.cloud.stream.kafka.binder.brokers=secure.server:9092 \
--spring.cloud.stream.kafka.binder.zkNodes=secure.zookeeper:2181 \
--spring.cloud.stream.bindings.input.destination=stream.ticktock \
--spring.cloud.stream.kafka.binder.autoCreateTopics=false \
--spring.cloud.stream.kafka.binder.configuration.security.protocol=SASL_PLAINTEXT \
--spring.cloud.stream.kafka.binder.jaas.options.useKeyTab=true \
--spring.cloud.stream.kafka.binder.jaas.options.storeKey=true \
--spring.cloud.stream.kafka.binder.jaas.options.keyTab=/etc/security/keytabs/kafka_client.keytab \
--spring.cloud.stream.kafka.binder.jaas.options.principal=kafka-client-1@EXAMPLE.COM</pre><p>This represents the equivalent of the following JAAS file:</p><pre class="screen">KafkaClient {
com.sun.security.auth.module.Krb5LoginModule required
useKeyTab=true
storeKey=true
keyTab="/etc/security/keytabs/kafka_client.keytab"
principal="kafka-client-1@EXAMPLE.COM";
};</pre><p>If the topics required already exist on the broker, or will be created by an administrator, autocreation can be turned off and only client JAAS properties need to be sent. As an alternative to setting <code class="literal">spring.cloud.stream.kafka.binder.autoCreateTopics</code> you can simply remove the broker dependency from the application. See <a class="xref" href="multi__apache_kafka_binder.html#exclude-admin-utils" title="Excluding Kafka broker jar from the classpath of the binder based application">the section called &#8220;Excluding Kafka broker jar from the classpath of the binder based application&#8221;</a> for details.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>Do not mix JAAS configuration files and Spring Boot properties in the same application.
If the <code class="literal">-Djava.security.auth.login.config</code> system property is already present, Spring Cloud Stream will ignore the Spring Boot properties.</p></td></tr></table></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>Exercise caution when using the <code class="literal">autoCreateTopics</code> and <code class="literal">autoAddPartitions</code> if using Kerberos.
Usually applications may use principals that do not have administrative rights in Kafka and Zookeeper, and relying on Spring Cloud Stream to create/modify topics may fail.
In secure environments, we strongly recommend creating topics and managing ACLs administratively using Kafka tooling.</p></td></tr></table></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="_using_the_binder_with_apache_kafka_0_10" href="#_using_the_binder_with_apache_kafka_0_10"></a>Using the binder with Apache Kafka 0.10</h4></div></div></div><p>The default Kafka support in Spring Cloud Stream Kafka binder is for Kafka version 0.10.1.1. The binder also supports connecting to other 0.10 based versions and 0.9 clients.
In order to do this, when you create the project that contains your application, include <code class="literal">spring-cloud-starter-stream-kafka</code> as you normally would do for the default binder.
Then add these dependencies at the top of the <code class="literal">&lt;dependencies&gt;</code> section in the pom.xml file to override the dependencies.</p><p>Here is an example for downgrading your application to 0.10.0.1. Since it is still on the 0.10 line, the default <code class="literal">spring-kafka</code> and <code class="literal">spring-integration-kafka</code> versions can be retained.</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.apache.kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>kafka_2.11<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;version&gt;</span>0.10.0.1<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/version&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;exclusions&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;exclusion&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.slf4j<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>slf4j-log4j12<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/exclusion&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/exclusions&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.apache.kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>kafka-clients<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;version&gt;</span>0.10.0.1<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/version&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/dependency&gt;</span></pre><p>Here is another example of using 0.9.0.1 version.</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.springframework.kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>spring-kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;version&gt;</span>1.0.5.RELEASE<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/version&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.springframework.integration<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>spring-integration-kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;version&gt;</span>2.0.1.RELEASE<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/version&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.apache.kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>kafka_2.11<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;version&gt;</span>0.9.0.1<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/version&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;exclusions&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;exclusion&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.slf4j<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>slf4j-log4j12<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/exclusion&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/exclusions&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.apache.kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>kafka-clients<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;version&gt;</span>0.9.0.1<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/version&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/dependency&gt;</span></pre><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>The versions above are provided only for the sake of the example.
For best results, we recommend using the most recent 0.10-compatible versions of the projects.</p></td></tr></table></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="exclude-admin-utils" href="#exclude-admin-utils"></a>Excluding Kafka broker jar from the classpath of the binder based application</h4></div></div></div><p>The Apache Kafka Binder uses the administrative utilities which are part of the Apache Kafka server library to create and reconfigure topics.
If the inclusion of the Apache Kafka server library and its dependencies is not necessary at runtime because the application will rely on the topics being configured administratively, the Kafka binder allows for Apache Kafka server dependency to be excluded from the application.</p><p>If you use non default versions for Kafka dependencies as advised above, all you have to do is not to include the kafka broker dependency.
If you use the default Kafka version, then ensure that you exclude the kafka broker jar from the <code class="literal">spring-cloud-starter-stream-kafka</code> dependency as following.</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.springframework.cloud<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>spring-cloud-starter-stream-kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;exclusions&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;exclusion&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.apache.kafka<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>kafka_2.11<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/exclusion&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/exclusions&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/dependency&gt;</span></pre><p>If you exclude the Apache Kafka server dependency and the topic is not present on the server, then the Apache Kafka broker will create the topic if auto topic creation is enabled on the server.
Please keep in mind that if you are relying on this, then the Kafka server will use the default number of partitions and replication factors.
On the other hand, if auto topic creation is disabled on the server, then care must be taken before running the application to create the topic with the desired number of partitions.</p><p>If you want to have full control over how partitions are allocated, then leave the default settings as they are, i.e. do not exclude the kafka broker jar and ensure that <code class="literal">spring.cloud.stream.kafka.binder.autoCreateTopics</code> is set to <code class="literal">true</code>, which is the default.</p></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_kafka_streams_binding_capabilities_of_spring_cloud_stream" href="#_kafka_streams_binding_capabilities_of_spring_cloud_stream"></a>37.4&nbsp;Kafka Streams Binding Capabilities of Spring Cloud Stream</h2></div></div></div><p>Spring Cloud Stream Kafka support also includes a binder specifically designed for Kafka Streams binding.
Using this binder, applications can be written that leverage the Kafka Streams API.
For more information on Kafka Streams, see <a class="link" href="https://kafka.apache.org/documentation/streams/developer-guide" target="_top">Kafka Streams API Developer Manual</a></p><p>Kafka Streams support in Spring Cloud Stream is based on the foundations provided by the Spring Kafka project. For details on that support, see <a class="link" href="http://docs.spring.io/spring-kafka/reference/html/_reference.html#kafka-streams" target="_top">Kafaka Streams Support in Spring Kafka</a>.</p><p>Here are the maven coordinates for the Spring Cloud Stream KStream binder artifact.</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;dependency&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;groupId&gt;</span>org.springframework.cloud<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/groupId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;artifactId&gt;</span>spring-cloud-stream-binder-kstream<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/artifactId&gt;</span>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-tag">&lt;/dependency&gt;</span></pre><p>In addition to leveraging the Spring Cloud Stream programming model which is based on Spring Boot, one of the main other benefits that the KStream binder provides is the fact that it avoids the boilerplate configuration that one needs to write when using the Kafka Streams API directly.
High level streams DSL provided through the Kafka Streams API can be used through Spring Cloud Stream in the current support.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_usage_example_of_high_level_streams_dsl" href="#_usage_example_of_high_level_streams_dsl"></a>37.4.1&nbsp;Usage example of high level streams DSL</h3></div></div></div><p>This application will listen from a Kafka topic and write the word count for each unique word that it sees in a 5 seconds time window.</p><pre class="screen">@SpringBootApplication
@EnableBinding(KStreamProcessor.class)
public class WordCountProcessorApplication {
@StreamListener("input")
@SendTo("output")
public KStream&lt;?, String&gt; process(KStream&lt;?, String&gt; input) {
return input
.flatMapValues(value -&gt; Arrays.asList(value.toLowerCase().split("\\W+")))
.map((key, word) -&gt; new KeyValue&lt;&gt;(word, word))
.groupByKey(Serdes.String(), Serdes.String())
.count(TimeWindows.of(5000), "store-name")
.toStream()
.map((w, c) -&gt; new KeyValue&lt;&gt;(null, "Count for " + w.key() + ": " + c));
}
public static void main(String[] args) {
SpringApplication.run(WordCountProcessorApplication.class, args);
}</pre><p>If you build it as Spring Boot runnable fat jar, you can run the above example in the following way:</p><pre class="screen">java -jar uber.jar --spring.cloud.stream.bindings.input.destination=words --spring.cloud.stream.bindings.output.destination=counts</pre><p>This means that the application will listen from the incoming Kafka topic words and write to the output topic counts.</p><p>Spring Cloud Stream will ensure that the messages from both the incoming and outgoing topics are bound as KStream objects.
As one may observe, the developer can exclusively focus on the business aspects of the code, i.e. writing the logic required in the processor rather than setting up the streams specific configuration required by the Kafka Streams infrastructure.
All those boilerplate is handled by Spring Cloud Stream behind the scenes.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_support_for_interactive_queries" href="#_support_for_interactive_queries"></a>37.4.2&nbsp;Support for interactive queries</h3></div></div></div><p>If access to the <code class="literal">KafkaStreams</code> is needed for interactive queries, the internal <code class="literal">KafkaStreams</code> instance can be accessed via <code class="literal">KStreamBuilderFactoryBean.getKafkaStreams()</code>.
You can autowire the <code class="literal">KStreamBuilderFactoryBean</code> instance provided by the KStream binder. Then you can get <code class="literal">KafkaStreams</code> instance from it and retrieve the underlying store, execute queries on it, etc.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_kafka_streams_properties" href="#_kafka_streams_properties"></a>37.4.3&nbsp;Kafka Streams properties</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">configuration</span></dt><dd><p class="simpara">Map with a key/value pair containing properties pertaining to Kafka Streams API.
This property must be prefixed with <code class="literal">spring.cloud.stream.kstream.binder.</code>.</p><pre class="literallayout">Following are some examples of using this property.</pre></dd></dl></div><pre class="screen">spring.cloud.stream.kstream.binder.configuration.key.serde=org.apache.kafka.common.serialization.Serdes$StringSerde
spring.cloud.stream.kstream.binder.configuration.value.serde=org.apache.kafka.common.serialization.Serdes$StringSerde
spring.cloud.stream.kstream.binder.configuration.commit.interval.ms=1000</pre><pre class="literallayout">For more information about all the properties that may go into streams configuration, see StreamsConfig JavaDocs.</pre><p>There can also be binding specific properties.</p><p>For instance, you can use a different Serde for your input or output destination.</p><pre class="screen">spring.cloud.stream.kstream.bindings.output.producer.keySerde=org.apache.kafka.common.serialization.Serdes$IntegerSerde
spring.cloud.stream.kstream.bindings.output.producer.valueSerde=org.apache.kafka.common.serialization.Serdes$LongSerde</pre><div class="variablelist"><dl class="variablelist"><dt><span class="term">timewindow.length</span></dt><dd><p class="simpara">Many streaming applications written using Kafka Streams involve windowning operations.
If you specify this property, there is a <code class="literal">org.apache.kafka.streams.kstream.TimeWindows</code> bean automatically provided that can be autowired in applications.
This property must be prefixed with <code class="literal">spring.cloud.stream.kstream.</code>.
A bean of type <code class="literal">org.apache.kafka.streams.kstream.TimeWindows</code> is created only if this property is provided.</p><pre class="literallayout">Following is an example of using this property.
Values are provided in milliseconds.</pre></dd></dl></div><pre class="screen">spring.cloud.stream.kstream.timeWindow.length=5000</pre><div class="variablelist"><dl class="variablelist"><dt><span class="term">timewindow.advanceBy</span></dt><dd><p class="simpara">This property goes hand in hand with <code class="literal">timewindow.length</code> and has no effect on its own.
If you provide this property, the generated <code class="literal">org.apache.kafka.streams.kstream.TimeWindows</code> bean will automatically conatin this information.
This property must be prefixed with <code class="literal">spring.cloud.stream.kstream.</code>.</p><pre class="literallayout">Following is an example of using this property.
Values are provided in milliseconds.</pre></dd></dl></div><pre class="screen">spring.cloud.stream.kstream.timeWindow.advanceBy=1000</pre></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="kafka-error-channels" href="#kafka-error-channels"></a>37.5&nbsp;Error Channels</h2></div></div></div><p>Starting with <span class="emphasis"><em>version 1.3</em></span>, the binder unconditionally sends exceptions to an error channel for each consumer destination, and can be configured to send async producer send failures to an error channel too.
See <a class="xref" href="multi__programming_model.html#binder-error-channels" title="Message Channel Binders and Error Channels">the section called &#8220;Message Channel Binders and Error Channels&#8221;</a> for more information.</p><p>The payload of the <code class="literal">ErrorMessage</code> for a send failure is a <code class="literal">KafkaSendFailureException</code> with properties:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="literal">failedMessage</code> - the spring-messaging <code class="literal">Message&lt;?&gt;</code> that failed to be sent.</li><li class="listitem"><code class="literal">record</code> - the raw <code class="literal">ProducerRecord</code> that was created from the <code class="literal">failedMessage</code></li></ul></div><p>There is no automatic handling of these exceptions (such as sending to a <a class="link" href="multi__apache_kafka_binder.html#kafka-dlq-processing" title="37.7&nbsp;Dead-Letter Topic Processing">Dead-Letter queue</a>); you can consume these exceptions with your own Spring Integration flow.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="kafka-metrics" href="#kafka-metrics"></a>37.6&nbsp;Kafka Metrics</h2></div></div></div><p>Kafka binder module exposes the following metrics:</p><p><code class="literal">spring.cloud.stream.binder.kafka.someGroup.someTopic.lag</code> - this metric indicates how many messages have not been yet consumed from given binder&#8217;s topic by given consumer group.
For example if the value of the metric <code class="literal">spring.cloud.stream.binder.kafka.myGroup.myTopic.lag</code> is <code class="literal">1000</code>, then consumer group <code class="literal">myGroup</code> has <code class="literal">1000</code> messages to waiting to be consumed from topic <code class="literal">myTopic</code>.
This metric is particularly useful to provide auto-scaling feedback to PaaS platform of your choice.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="kafka-dlq-processing" href="#kafka-dlq-processing"></a>37.7&nbsp;Dead-Letter Topic Processing</h2></div></div></div><p>Because it can&#8217;t be anticipated how users would want to dispose of dead-lettered messages, the framework does not provide any standard mechanism to handle them.
If the reason for the dead-lettering is transient, you may wish to route the messages back to the original topic.
However, if the problem is a permanent issue, that could cause an infinite loop.
The following <code class="literal">spring-boot</code> application is an example of how to route those messages back to the original topic, but moves them to a third "parking lot" topic after three attempts.
The application is simply another spring-cloud-stream application that reads from the dead-letter topic.
It terminates when no messages are received for 5 seconds.</p><p>The examples assume the original destination is <code class="literal">so8400out</code> and the consumer group is <code class="literal">so8400</code>.</p><p>There are several considerations.</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">Consider only running the rerouting when the main application is not running.
Otherwise, the retries for transient errors will be used up very quickly.</li><li class="listitem">Alternatively, use a two-stage approach - use this application to route to a third topic, and another to route from there back to the main topic.</li><li class="listitem">Since this technique uses a message header to keep track of retries, it won&#8217;t work with <code class="literal">headerMode=raw</code>.
In that case, consider adding some data to the payload (that can be ignored by the main application).</li><li class="listitem"><code class="literal">x-retries</code> has to be added to the <code class="literal">headers</code> property <code class="literal">spring.cloud.stream.kafka.binder.headers=x-retries</code> on both this, and the main application so that the header is transported between the applications.</li><li class="listitem">Since kafka is publish/subscribe, replayed messages will be sent to each consumer group, even those that successfully processed a message the first time around.</li></ul></div><p><b>application.properties.&nbsp;</b>
</p><pre class="screen">spring.cloud.stream.bindings.input.group=so8400replay
spring.cloud.stream.bindings.input.destination=error.so8400out.so8400
spring.cloud.stream.bindings.output.destination=so8400out
spring.cloud.stream.bindings.output.producer.partitioned=true
spring.cloud.stream.bindings.parkingLot.destination=so8400in.parkingLot
spring.cloud.stream.bindings.parkingLot.producer.partitioned=true
spring.cloud.stream.kafka.binder.configuration.auto.offset.reset=earliest
spring.cloud.stream.kafka.binder.headers=x-retries</pre><p>
</p><p><b>Application.&nbsp;</b>
</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@SpringBootApplication</span></em>
<em><span class="hl-annotation" style="color: gray">@EnableBinding(TwoOutputProcessor.class)</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span> ReRouteDlqKApplication <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">implements</span> CommandLineRunner {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">static</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">final</span> String X_RETRIES_HEADER = <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"x-retries"</span>;
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">static</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> main(String[] args) {
SpringApplication.run(ReRouteDlqKApplication.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>, args).close();
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">final</span> AtomicInteger processed = <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> AtomicInteger();
<em><span class="hl-annotation" style="color: gray">@Autowired</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">private</span> MessageChannel parkingLot;
<em><span class="hl-annotation" style="color: gray">@StreamListener(Processor.INPUT)</span></em>
<em><span class="hl-annotation" style="color: gray">@SendTo(Processor.OUTPUT)</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> Message&lt;?&gt; reRoute(Message&lt;?&gt; failed) {
processed.incrementAndGet();
Integer retries = failed.getHeaders().get(X_RETRIES_HEADER, Integer.<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">class</span>);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">if</span> (retries == null) {
System.out.println(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"First retry for "</span> + failed);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> MessageBuilder.fromMessage(failed)
.setHeader(X_RETRIES_HEADER, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> Integer(<span class="hl-number">1</span>))
.setHeader(BinderHeaders.PARTITION_OVERRIDE,
failed.getHeaders().get(KafkaHeaders.RECEIVED_PARTITION_ID))
.build();
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">else</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">if</span> (retries.intValue() &lt; <span class="hl-number">3</span>) {
System.out.println(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"Another retry for "</span> + failed);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> MessageBuilder.fromMessage(failed)
.setHeader(X_RETRIES_HEADER, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> Integer(retries.intValue() + <span class="hl-number">1</span>))
.setHeader(BinderHeaders.PARTITION_OVERRIDE,
failed.getHeaders().get(KafkaHeaders.RECEIVED_PARTITION_ID))
.build();
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">else</span> {
System.out.println(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"Retries exhausted for "</span> + failed);
parkingLot.send(MessageBuilder.fromMessage(failed)
.setHeader(BinderHeaders.PARTITION_OVERRIDE,
failed.getHeaders().get(KafkaHeaders.RECEIVED_PARTITION_ID))
.build());
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> null;
}
<em><span class="hl-annotation" style="color: gray">@Override</span></em>
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> run(String... args) <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">throws</span> Exception {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">while</span> (true) {
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">int</span> count = <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">this</span>.processed.get();
Thread.sleep(<span class="hl-number">5000</span>);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">if</span> (count == <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">this</span>.processed.get()) {
System.out.println(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"Idle, terminating"</span>);
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span>;
}
}
}
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">interface</span> TwoOutputProcessor <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">extends</span> Processor {
<em><span class="hl-annotation" style="color: gray">@Output("parkingLot")</span></em>
MessageChannel parkingLot();
}
}</pre><p>
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