org.apache.flink.streaming.connectors.wikiedits

Class WikipediaEditsSource

java.lang.Object

org.apache.flink.api.common.functions.AbstractRichFunction

org.apache.flink.streaming.api.functions.source.RichSourceFunction<WikipediaEditEvent>

org.apache.flink.streaming.connectors.wikiedits.WikipediaEditsSource

All Implemented Interfaces:

Serializable, Function, RichFunction, SourceFunction<WikipediaEditEvent>

public class WikipediaEditsSource
extends RichSourceFunction<WikipediaEditEvent>

This class is a SourceFunction that reads WikipediaEditEvent instances from the IRC channel #en.wikipedia.

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.flink.streaming.api.functions.source.SourceFunction

SourceFunction.SourceContext<T>

Field Summary

Fields

Modifier and Type	Field and Description
static String	DEFAULT_CHANNEL IRC channel to join.
static String	DEFAULT_HOST Hostname of the server to connect to.
static int	DEFAULT_PORT Port of the server to connect to.

Constructor Summary

Constructors

Constructor and Description
WikipediaEditsSource() Creates a source reading WikipediaEditEvent instances from the IRC channel #en.wikipedia.
WikipediaEditsSource(String host, int port, String channel) Creates a source reading WikipediaEditEvent instances from the specified IRC channel.

Method Summary

Modifier and Type	Method and Description
void	cancel() Cancels the source.
void	run(SourceFunction.SourceContext<WikipediaEditEvent> ctx) Starts the source.

Methods inherited from class org.apache.flink.api.common.functions.AbstractRichFunction

close, getIterationRuntimeContext, getRuntimeContext, open, setRuntimeContext

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_HOST

public static final String DEFAULT_HOST

Hostname of the server to connect to.

See Also:

Constant Field Values

DEFAULT_PORT

public static final int DEFAULT_PORT

Port of the server to connect to.

See Also:

Constant Field Values

DEFAULT_CHANNEL

public static final String DEFAULT_CHANNEL

IRC channel to join.

See Also:

Constant Field Values

Constructor Detail

WikipediaEditsSource

public WikipediaEditsSource()

Creates a source reading WikipediaEditEvent instances from the IRC channel #en.wikipedia.

This creates a separate Thread for the IRC connection.

WikipediaEditsSource

public WikipediaEditsSource(String host,
                            int port,
                            String channel)

Creates a source reading WikipediaEditEvent instances from the specified IRC channel.

In most cases, you want to use the default WikipediaEditsSource(java.lang.String, int, java.lang.String) constructor. This constructor is meant to be used only if there is a problem with the default constructor.

Parameters:

host - The IRC server to connect to.

port - The port of the IRC server to connect to.

channel - The channel to join. Messages not matching the expected format will be ignored.

Method Detail

run

public void run(SourceFunction.SourceContext<WikipediaEditEvent> ctx)
         throws Exception

Description copied from interface: SourceFunction

Starts the source. Implementations can use the SourceFunction.SourceContext emit elements.

Sources that implement CheckpointedFunction must lock on the checkpoint lock (using a synchronized block) before updating internal state and emitting elements, to make both an atomic operation:

  public class ExampleCountSource implements SourceFunction<Long>, CheckpointedFunction {
      private long count = 0L;
      private volatile boolean isRunning = true;

      private transient ListState<Long> checkpointedCount;

      public void run(SourceContext<T> ctx) {
          while (isRunning && count < 1000) {
              // this synchronized block ensures that state checkpointing,
              // internal state updates and emission of elements are an atomic operation
              synchronized (ctx.getCheckpointLock()) {
                  ctx.collect(count);
                  count++;
              }
          }
      }

      public void cancel() {
          isRunning = false;
      }

      public void initializeState(FunctionInitializationContext context) {
          this.checkpointedCount = context
              .getOperatorStateStore()
              .getListState(new ListStateDescriptor<>("count", Long.class));

          if (context.isRestored()) {
              for (Long count : this.checkpointedCount.get()) {
                  this.count = count;
              }
          }
      }

      public void snapshotState(FunctionSnapshotContext context) {
          this.checkpointedCount.clear();
          this.checkpointedCount.add(count);
      }
 }
 

Parameters:

ctx - The context to emit elements to and for accessing locks.

Throws:

Exception

cancel

public void cancel()

Description copied from interface: SourceFunction

Cancels the source. Most sources will have a while loop inside the SourceFunction.run(SourceContext) method. The implementation needs to ensure that the source will break out of that loop after this method is called.

A typical pattern is to have an "volatile boolean isRunning" flag that is set to false in this method. That flag is checked in the loop condition.

When a source is canceled, the executing thread will also be interrupted (via Thread.interrupt()). The interruption happens strictly after this method has been called, so any interruption handler can rely on the fact that this method has completed. It is good practice to make any flags altered by this method "volatile", in order to guarantee the visibility of the effects of this method to any interruption handler.