org.apache.kafka.streams

Class KafkaStreams

java.lang.Object

org.apache.kafka.streams.KafkaStreams

All Implemented Interfaces:

AutoCloseable

public class KafkaStreams
extends Object
implements AutoCloseable

A Kafka client that allows for performing continuous computation on input coming from one or more input topics and sends output to zero, one, or more output topics.

The computational logic can be specified either by using the Topology to define a DAG topology of Processors or by using the StreamsBuilder which provides the high-level DSL to define transformations.

One KafkaStreams instance can contain one or more threads specified in the configs for the processing work.

A KafkaStreams instance can co-ordinate with any other instances with the same application ID (whether in the same process, on other processes on this machine, or on remote machines) as a single (possibly distributed) stream processing application. These instances will divide up the work based on the assignment of the input topic partitions so that all partitions are being consumed. If instances are added or fail, all (remaining) instances will rebalance the partition assignment among themselves to balance processing load and ensure that all input topic partitions are processed.

Internally a KafkaStreams instance contains a normal KafkaProducer and KafkaConsumer instance that is used for reading input and writing output.

A simple example might look like this:

 Properties props = new Properties();
 props.put(StreamsConfig.APPLICATION_ID_CONFIG, "my-stream-processing-application");
 props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
 props.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
 props.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass());

 StreamsBuilder builder = new StreamsBuilder();
 builder.<String, String>stream("my-input-topic").mapValues(value -> String.valueOf(value.length())).to("my-output-topic");

 KafkaStreams streams = new KafkaStreams(builder.build(), props);
 streams.start();
 

See Also:

StreamsBuilder, Topology

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	KafkaStreams.State Kafka Streams states are the possible state that a Kafka Streams instance can be in.
static interface	KafkaStreams.StateListener Listen to KafkaStreams.State change events.

Field Summary

Fields

Modifier and Type	Field and Description
protected KafkaStreams.State	state
protected org.apache.kafka.streams.processor.internals.StateDirectory	stateDirectory
protected List<org.apache.kafka.streams.processor.internals.StreamThread>	threads
protected org.apache.kafka.streams.processor.internals.TopologyMetadata	topologyMetadata

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	KafkaStreams(org.apache.kafka.streams.processor.internals.TopologyMetadata topologyMetadata, StreamsConfig config, KafkaClientSupplier clientSupplier)
	KafkaStreams(Topology topology, Properties props) Create a KafkaStreams instance.
	KafkaStreams(Topology topology, Properties props, KafkaClientSupplier clientSupplier) Create a KafkaStreams instance.
	KafkaStreams(Topology topology, Properties props, KafkaClientSupplier clientSupplier, org.apache.kafka.common.utils.Time time) Create a KafkaStreams instance.
	KafkaStreams(Topology topology, Properties props, org.apache.kafka.common.utils.Time time) Create a KafkaStreams instance.
	KafkaStreams(Topology topology, StreamsConfig config) Create a KafkaStreams instance.
	KafkaStreams(Topology topology, StreamsConfig config, KafkaClientSupplier clientSupplier) Create a KafkaStreams instance.
	KafkaStreams(Topology topology, StreamsConfig config, org.apache.kafka.common.utils.Time time) Create a KafkaStreams instance.

Method Summary

Modifier and Type	Method and Description
Optional<String>	addStreamThread() Adds and starts a stream thread in addition to the stream threads that are already running in this Kafka Streams client.
Map<String,Map<Integer,LagInfo>>	allLocalStorePartitionLags() Returns LagInfo, for all store partitions (active or standby) local to this Streams instance.
Collection<StreamsMetadata>	allMetadata() Deprecated. since 3.0.0 use metadataForAllStreamsClients()
Collection<StreamsMetadata>	allMetadataForStore(String storeName) Deprecated. since 3.0.0 use streamsMetadataForStore(java.lang.String) instead
void	cleanUp() Do a clean up of the local StateStore directory (StreamsConfig.STATE_DIR_CONFIG) by deleting all data with regard to the application ID.
void	close() Shutdown this KafkaStreams instance by signaling all the threads to stop, and then wait for them to join.
boolean	close(Duration timeout) Shutdown this KafkaStreams by signaling all the threads to stop, and then wait up to the timeout for the threads to join.
protected boolean	hasStartedOrFinishedShuttingDown()
protected boolean	isRunningOrRebalancing()
Set<ThreadMetadata>	localThreadsMetadata() Deprecated. since 3.0 use metadataForLocalThreads()
Collection<StreamsMetadata>	metadataForAllStreamsClients() Find all currently running KafkaStreams instances (potentially remotely) that use the same application ID as this instance (i.e., all instances that belong to the same Kafka Streams application) and return StreamsMetadata for each discovered instance.
Set<ThreadMetadata>	metadataForLocalThreads() Returns runtime information about the local threads of this KafkaStreams instance.
Map<org.apache.kafka.common.MetricName,? extends org.apache.kafka.common.Metric>	metrics() Get read-only handle on global metrics registry, including streams client's own metrics plus its embedded producer, consumer and admin clients' metrics.
protected void	processStreamThread(Consumer<org.apache.kafka.streams.processor.internals.StreamThread> consumer) handle each stream thread in a snapshot of threads.
<K> KeyQueryMetadata	queryMetadataForKey(String storeName, K key, org.apache.kafka.common.serialization.Serializer<K> keySerializer) Finds the metadata containing the active hosts and standby hosts where the key being queried would reside.
<K> KeyQueryMetadata	queryMetadataForKey(String storeName, K key, StreamPartitioner<? super K,?> partitioner) Finds the metadata containing the active hosts and standby hosts where the key being queried would reside.
Optional<String>	removeStreamThread() Removes one stream thread out of the running stream threads from this Kafka Streams client.
Optional<String>	removeStreamThread(Duration timeout) Removes one stream thread out of the running stream threads from this Kafka Streams client.
void	setGlobalStateRestoreListener(StateRestoreListener globalStateRestoreListener) Set the listener which is triggered whenever a StateStore is being restored in order to resume processing.
void	setStateListener(KafkaStreams.StateListener listener) An app can set a single KafkaStreams.StateListener so that the app is notified when state changes.
void	setUncaughtExceptionHandler(StreamsUncaughtExceptionHandler streamsUncaughtExceptionHandler) Set the handler invoked when an internal stream thread throws an unexpected exception.
void	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler uncaughtExceptionHandler) Deprecated. Since 2.8.0. Use setUncaughtExceptionHandler(StreamsUncaughtExceptionHandler) instead.
void	start() Start the KafkaStreams instance by starting all its threads.
KafkaStreams.State	state() Return the current KafkaStreams.State of this KafkaStreams instance.
<T> T	store(StoreQueryParameters<T> storeQueryParameters) Get a facade wrapping the local StateStore instances with the provided StoreQueryParameters.
Collection<StreamsMetadata>	streamsMetadataForStore(String storeName) Find all currently running KafkaStreams instances (potentially remotely) that use the same application ID as this instance (i.e., all instances that belong to the same Kafka Streams application) and that contain a StateStore with the given storeName and return StreamsMetadata for each discovered instance.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

threads

protected final List<org.apache.kafka.streams.processor.internals.StreamThread> threads

stateDirectory

protected final org.apache.kafka.streams.processor.internals.StateDirectory stateDirectory

topologyMetadata

protected final org.apache.kafka.streams.processor.internals.TopologyMetadata topologyMetadata

state

protected volatile KafkaStreams.State state

Constructor Detail

KafkaStreams

public KafkaStreams(Topology topology,
                    Properties props)

Create a KafkaStreams instance.

Note: even if you never call start() on a KafkaStreams instance, you still must close() it to avoid resource leaks.

Parameters:

topology - the topology specifying the computational logic

props - properties for StreamsConfig

Throws:

StreamsException - if any fatal error occurs

KafkaStreams

public KafkaStreams(Topology topology,
                    Properties props,
                    KafkaClientSupplier clientSupplier)

Create a KafkaStreams instance.

Note: even if you never call start() on a KafkaStreams instance, you still must close() it to avoid resource leaks.

Parameters:

topology - the topology specifying the computational logic

props - properties for StreamsConfig

clientSupplier - the Kafka clients supplier which provides underlying producer and consumer clients for the new KafkaStreams instance

Throws:

StreamsException - if any fatal error occurs

KafkaStreams

public KafkaStreams(Topology topology,
                    Properties props,
                    org.apache.kafka.common.utils.Time time)

Create a KafkaStreams instance.

Note: even if you never call start() on a KafkaStreams instance, you still must close() it to avoid resource leaks.

Parameters:

topology - the topology specifying the computational logic

props - properties for StreamsConfig

time - Time implementation; cannot be null

Throws:

StreamsException - if any fatal error occurs

KafkaStreams

public KafkaStreams(Topology topology,
                    Properties props,
                    KafkaClientSupplier clientSupplier,
                    org.apache.kafka.common.utils.Time time)

Create a KafkaStreams instance.

Note: even if you never call start() on a KafkaStreams instance, you still must close() it to avoid resource leaks.

Parameters:

topology - the topology specifying the computational logic

props - properties for StreamsConfig

clientSupplier - the Kafka clients supplier which provides underlying producer and consumer clients for the new KafkaStreams instance

time - Time implementation; cannot be null

Throws:

StreamsException - if any fatal error occurs

KafkaStreams

public KafkaStreams(Topology topology,
                    StreamsConfig config)

Create a KafkaStreams instance.

Note: even if you never call start() on a KafkaStreams instance, you still must close() it to avoid resource leaks.

Parameters:

topology - the topology specifying the computational logic

config - configs for Kafka Streams

Throws:

StreamsException - if any fatal error occurs

KafkaStreams

public KafkaStreams(Topology topology,
                    StreamsConfig config,
                    KafkaClientSupplier clientSupplier)

Create a KafkaStreams instance.

Note: even if you never call start() on a KafkaStreams instance, you still must close() it to avoid resource leaks.

Parameters:

topology - the topology specifying the computational logic

config - configs for Kafka Streams

clientSupplier - the Kafka clients supplier which provides underlying producer and consumer clients for the new KafkaStreams instance

Throws:

StreamsException - if any fatal error occurs

KafkaStreams

public KafkaStreams(Topology topology,
                    StreamsConfig config,
                    org.apache.kafka.common.utils.Time time)

Create a KafkaStreams instance.

Note: even if you never call start() on a KafkaStreams instance, you still must close() it to avoid resource leaks.

Parameters:

topology - the topology specifying the computational logic

config - configs for Kafka Streams

time - Time implementation; cannot be null

Throws:

StreamsException - if any fatal error occurs

KafkaStreams

protected KafkaStreams(org.apache.kafka.streams.processor.internals.TopologyMetadata topologyMetadata,
                       StreamsConfig config,
                       KafkaClientSupplier clientSupplier)
                throws StreamsException

Throws:

StreamsException

Method Detail

state

public KafkaStreams.State state()

Return the current KafkaStreams.State of this KafkaStreams instance.

Returns:

the current state of this Kafka Streams instance

isRunningOrRebalancing

protected boolean isRunningOrRebalancing()

hasStartedOrFinishedShuttingDown

protected boolean hasStartedOrFinishedShuttingDown()

setStateListener

public void setStateListener(KafkaStreams.StateListener listener)

An app can set a single KafkaStreams.StateListener so that the app is notified when state changes.

Parameters:

listener - a new state listener

Throws:

IllegalStateException - if this KafkaStreams instance has already been started.

setUncaughtExceptionHandler

@Deprecated
public void setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler uncaughtExceptionHandler)

Deprecated. Since 2.8.0. Use setUncaughtExceptionHandler(StreamsUncaughtExceptionHandler) instead.

Set the handler invoked when an internal stream thread abruptly terminates due to an uncaught exception.

Parameters:

uncaughtExceptionHandler - the uncaught exception handler for all internal threads; null deletes the current handler

Throws:

IllegalStateException - if this KafkaStreams instance has already been started.

setUncaughtExceptionHandler

public void setUncaughtExceptionHandler(StreamsUncaughtExceptionHandler streamsUncaughtExceptionHandler)

Set the handler invoked when an internal stream thread throws an unexpected exception. These might be exceptions indicating rare bugs in Kafka Streams, or they might be exceptions thrown by your code, for example a NullPointerException thrown from your processor logic. The handler will execute on the thread that produced the exception. In order to get the thread that threw the exception, use Thread.currentThread().

Note, this handler must be threadsafe, since it will be shared among all threads, and invoked from any thread that encounters such an exception.

Parameters:

streamsUncaughtExceptionHandler - the uncaught exception handler of type StreamsUncaughtExceptionHandler for all internal threads

Throws:

IllegalStateException - if this KafkaStreams instance has already been started.

NullPointerException - if streamsUncaughtExceptionHandler is null.

setGlobalStateRestoreListener

public void setGlobalStateRestoreListener(StateRestoreListener globalStateRestoreListener)

Set the listener which is triggered whenever a StateStore is being restored in order to resume processing.

Parameters:

globalStateRestoreListener - The listener triggered when StateStore is being restored.

Throws:

IllegalStateException - if this KafkaStreams instance has already been started.

metrics

public Map<org.apache.kafka.common.MetricName,? extends org.apache.kafka.common.Metric> metrics()

Get read-only handle on global metrics registry, including streams client's own metrics plus its embedded producer, consumer and admin clients' metrics.

Returns:

Map of all metrics.

addStreamThread

public Optional<String> addStreamThread()

Adds and starts a stream thread in addition to the stream threads that are already running in this Kafka Streams client.

Since the number of stream threads increases, the sizes of the caches in the new stream thread and the existing stream threads are adapted so that the sum of the cache sizes over all stream threads does not exceed the total cache size specified in configuration StreamsConfig.CACHE_MAX_BYTES_BUFFERING_CONFIG.

Stream threads can only be added if this Kafka Streams client is in state RUNNING or REBALANCING.

Returns:

name of the added stream thread or empty if a new stream thread could not be added

removeStreamThread

public Optional<String> removeStreamThread()

Removes one stream thread out of the running stream threads from this Kafka Streams client.

The removed stream thread is gracefully shut down. This method does not specify which stream thread is shut down.

Since the number of stream threads decreases, the sizes of the caches in the remaining stream threads are adapted so that the sum of the cache sizes over all stream threads equals the total cache size specified in configuration StreamsConfig.CACHE_MAX_BYTES_BUFFERING_CONFIG.

Returns:

name of the removed stream thread or empty if a stream thread could not be removed because no stream threads are alive

removeStreamThread

public Optional<String> removeStreamThread(Duration timeout)

Removes one stream thread out of the running stream threads from this Kafka Streams client.

The removed stream thread is gracefully shut down. This method does not specify which stream thread is shut down.

Since the number of stream threads decreases, the sizes of the caches in the remaining stream threads are adapted so that the sum of the cache sizes over all stream threads equals the total cache size specified in configuration StreamsConfig.CACHE_MAX_BYTES_BUFFERING_CONFIG.

Parameters:

timeout - The length of time to wait for the thread to shutdown

Returns:

name of the removed stream thread or empty if a stream thread could not be removed because no stream threads are alive

Throws:

org.apache.kafka.common.errors.TimeoutException - if the thread does not stop in time

start

public void start()
           throws IllegalStateException,
                  StreamsException

Start the KafkaStreams instance by starting all its threads. This function is expected to be called only once during the life cycle of the client.

Because threads are started in the background, this method does not block. However, if you have global stores in your topology, this method blocks until all global stores are restored. As a consequence, any fatal exception that happens during processing is by default only logged. If you want to be notified about dying threads, you can register an uncaught exception handler before starting the KafkaStreams instance.

Note, for brokers with version 0.9.x or lower, the broker version cannot be checked. There will be no error and the client will hang and retry to verify the broker version until it times out.

Throws:

IllegalStateException - if process was already started

StreamsException - if the Kafka brokers have version 0.10.0.x or if exactly-once is enabled for pre 0.11.0.x brokers

close

public void close()

Shutdown this KafkaStreams instance by signaling all the threads to stop, and then wait for them to join. This will block until all threads have stopped.

Specified by:

close in interface AutoCloseable

close

public boolean close(Duration timeout)
              throws IllegalArgumentException

Shutdown this KafkaStreams by signaling all the threads to stop, and then wait up to the timeout for the threads to join. A timeout of Duration.ZERO (or any other zero duration) makes the close operation asynchronous. Negative-duration timeouts are rejected.

Parameters:

timeout - how long to wait for the threads to shutdown

Returns:

true if all threads were successfully stopped—false if the timeout was reached before all threads stopped Note that this method must not be called in the KafkaStreams.StateListener.onChange(KafkaStreams.State, KafkaStreams.State) callback of KafkaStreams.StateListener.

Throws:

IllegalArgumentException - if timeout can't be represented as long milliseconds

cleanUp

public void cleanUp()

Do a clean up of the local StateStore directory (StreamsConfig.STATE_DIR_CONFIG) by deleting all data with regard to the application ID.

May only be called either before this KafkaStreams instance is started or after the instance is closed.

Calling this method triggers a restore of local StateStores on the next application start.

Throws:

IllegalStateException - if this KafkaStreams instance has been started and hasn't fully shut down

StreamsException - if cleanup failed

allMetadata

@Deprecated
public Collection<StreamsMetadata> allMetadata()

Deprecated. since 3.0.0 use metadataForAllStreamsClients()

Find all currently running KafkaStreams instances (potentially remotely) that use the same application ID as this instance (i.e., all instances that belong to the same Kafka Streams application) and return StreamsMetadata for each discovered instance.

Note: this is a point in time view and it may change due to partition reassignment.

Returns:

StreamsMetadata for each KafkaStreams instances of this application

metadataForAllStreamsClients

public Collection<StreamsMetadata> metadataForAllStreamsClients()

Find all currently running KafkaStreams instances (potentially remotely) that use the same application ID as this instance (i.e., all instances that belong to the same Kafka Streams application) and return StreamsMetadata for each discovered instance.

Note: this is a point in time view and it may change due to partition reassignment.

Returns:

StreamsMetadata for each KafkaStreams instances of this application

allMetadataForStore

@Deprecated
public Collection<StreamsMetadata> allMetadataForStore(String storeName)

Deprecated. since 3.0.0 use streamsMetadataForStore(java.lang.String) instead

Find all currently running KafkaStreams instances (potentially remotely) that

• use the same application ID as this instance (i.e., all instances that belong to the same Kafka Streams application)
• and that contain a StateStore with the given storeName

and return StreamsMetadata for each discovered instance.

Note: this is a point in time view and it may change due to partition reassignment.

Parameters:

storeName - the storeName to find metadata for

Returns:

StreamsMetadata for each KafkaStreams instances with the provide storeName of this application

streamsMetadataForStore

public Collection<StreamsMetadata> streamsMetadataForStore(String storeName)

Find all currently running KafkaStreams instances (potentially remotely) that

• use the same application ID as this instance (i.e., all instances that belong to the same Kafka Streams application)
• and that contain a StateStore with the given storeName

and return StreamsMetadata for each discovered instance.

Note: this is a point in time view and it may change due to partition reassignment.

Parameters:

storeName - the storeName to find metadata for

Returns:

StreamsMetadata for each KafkaStreams instances with the provide storeName of this application

queryMetadataForKey

public <K> KeyQueryMetadata queryMetadataForKey(String storeName,
                                                K key,
                                                org.apache.kafka.common.serialization.Serializer<K> keySerializer)

Finds the metadata containing the active hosts and standby hosts where the key being queried would reside.

Type Parameters:

K - key type Returns KeyQueryMetadata containing all metadata about hosting the given key for the given store, or null if no matching metadata could be found.

Parameters:

storeName - the storeName to find metadata for

key - the key to find metadata for

keySerializer - serializer for the key

queryMetadataForKey

public <K> KeyQueryMetadata queryMetadataForKey(String storeName,
                                                K key,
                                                StreamPartitioner<? super K,?> partitioner)

Finds the metadata containing the active hosts and standby hosts where the key being queried would reside.

Type Parameters:

K - key type Returns KeyQueryMetadata containing all metadata about hosting the given key for the given store, using the the supplied partitioner, or null if no matching metadata could be found.

Parameters:

storeName - the storeName to find metadata for

key - the key to find metadata for

partitioner - the partitioner to be use to locate the host for the key

store

public <T> T store(StoreQueryParameters<T> storeQueryParameters)

Get a facade wrapping the local StateStore instances with the provided StoreQueryParameters. The returned object can be used to query the StateStore instances.

Parameters:

storeQueryParameters - the parameters used to fetch a queryable store

Returns:

A facade wrapping the local StateStore instances

Throws:

StreamsNotStartedException - If Streams has not yet been started. Just call start() and then retry this call.

UnknownStateStoreException - If the specified store name does not exist in the topology.

InvalidStateStorePartitionException - If the specified partition does not exist.

InvalidStateStoreException - If the Streams instance isn't in a queryable state. If the store's type does not match the QueryableStoreType, the Streams instance is not in a queryable state with respect to the parameters, or if the store is not available locally, then an InvalidStateStoreException is thrown upon store access.

processStreamThread

protected void processStreamThread(Consumer<org.apache.kafka.streams.processor.internals.StreamThread> consumer)

handle each stream thread in a snapshot of threads. noted: iteration over SynchronizedList is not thread safe so it must be manually synchronized. However, we may require other locks when looping threads and it could cause deadlock. Hence, we create a copy to avoid holding threads lock when looping threads.

Parameters:

consumer - handler

localThreadsMetadata

@Deprecated
public Set<ThreadMetadata> localThreadsMetadata()

Deprecated. since 3.0 use metadataForLocalThreads()

Returns runtime information about the local threads of this KafkaStreams instance.

Returns:

the set of ThreadMetadata.

metadataForLocalThreads

public Set<ThreadMetadata> metadataForLocalThreads()

Returns runtime information about the local threads of this KafkaStreams instance.

Returns:

the set of ThreadMetadata.

allLocalStorePartitionLags

public Map<String,Map<Integer,LagInfo>> allLocalStorePartitionLags()

Returns LagInfo, for all store partitions (active or standby) local to this Streams instance. Note that the values returned are just estimates and meant to be used for making soft decisions on whether the data in the store partition is fresh enough for querying. Note: Each invocation of this method issues a call to the Kafka brokers. Thus its advisable to limit the frequency of invocation to once every few seconds.

Returns:

map of store names to another map of partition to LagInfos

Throws:

StreamsException - if the admin client request throws exception