public class WikipediaEditsSource extends RichSourceFunction<WikipediaEditEvent>
SourceFunction.SourceContext<T>
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 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. |
Modifier and Type | Method and Description |
---|---|
void |
cancel()
Cancels the source.
|
void |
close()
Tear-down method for the user code.
|
void |
open(Configuration parameters)
Initialization method for the function.
|
void |
run(SourceFunction.SourceContext ctx)
Starts the source.
|
getIterationRuntimeContext, getRuntimeContext, setRuntimeContext
public static final String DEFAULT_HOST
public static final int DEFAULT_PORT
public static final String DEFAULT_CHANNEL
public WikipediaEditsSource()
WikipediaEditEvent
instances from the
IRC channel #en.wikipedia
.
This creates a separate Thread for the IRC connection.
public WikipediaEditsSource(String host, int port, String channel)
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.
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.public void open(Configuration parameters) throws Exception
RichFunction
The configuration object passed to the function can be used for configuration and initialization. The configuration contains all parameters that were configured on the function in the program composition.
public class MyMapper extends FilterFunction<String> {
private String searchString;
public void open(Configuration parameters) {
this.searchString = parameters.getString("foo");
}
public boolean filter(String value) {
return value.equals(searchString);
}
}
By default, this method does nothing.
open
in interface RichFunction
open
in class AbstractRichFunction
parameters
- The configuration containing the parameters attached to the contract.Exception
- Implementations may forward exceptions, which are caught by the runtime. When the
runtime catches an exception, it aborts the task and lets the fail-over logic
decide whether to retry the task execution.Configuration
public void close() throws Exception
RichFunction
This method can be used for clean up work.
close
in interface RichFunction
close
in class AbstractRichFunction
Exception
- Implementations may forward exceptions, which are caught by the runtime. When the
runtime catches an exception, it aborts the task and lets the fail-over logic
decide whether to retry the task execution.public void run(SourceFunction.SourceContext ctx) throws Exception
SourceFunction
SourceFunction.SourceContext
emit
elements.
Sources that implement Checkpointed
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 ExampleSource<T> implements SourceFunction<T>, Checkpointed<Long> {
private long count = 0L;
private volatile boolean isRunning = true;
public void run(SourceContext<T> ctx) {
while (isRunning && count < 1000) {
synchronized (ctx.getCheckpointLock()) {
ctx.collect(count);
count++;
}
}
}
public void cancel() {
isRunning = false;
}
public Long snapshotState(long checkpointId, long checkpointTimestamp) { return count; }
public void restoreState(Long state) { this.count = state; }
}
ctx
- The context to emit elements to and for accessing locks.Exception
public void cancel()
SourceFunction
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.
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