聊聊flink的ProcessFunction
序
本文主要研究一下flink的ProcessFunction
实例
import org.apache.flink.api.common.state.ValueState;
import org.apache.flink.api.common.state.ValueStateDescriptor;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.configuration.Configuration;
import org.apache.flink.streaming.api.functions.ProcessFunction;
import org.apache.flink.streaming.api.functions.ProcessFunction.Context;
import org.apache.flink.streaming.api.functions.ProcessFunction.OnTimerContext;
import org.apache.flink.util.Collector;
// the source data stream
DataStream<Tuple2<String, String>> stream = ...;
// apply the process function onto a keyed stream
DataStream<Tuple2<String, Long>> result = stream
.keyBy(0)
.process(new CountWithTimeoutFunction());
/**
* The data type stored in the state
*/
public class CountWithTimestamp {
public String key;
public long count;
public long lastModified;
}
/**
* The implementation of the ProcessFunction that maintains the count and timeouts
*/
public class CountWithTimeoutFunction extends ProcessFunction<Tuple2<String, String>, Tuple2<String, Long>> {
/** The state that is maintained by this process function */
private ValueState<CountWithTimestamp> state;
@Override
public void open(Configuration parameters) throws Exception {
state = getRuntimeContext().getState(new ValueStateDescriptor<>("myState", CountWithTimestamp.class));
}
@Override
public void processElement(Tuple2<String, String> value, Context ctx, Collector<Tuple2<String, Long>> out)
throws Exception {
// retrieve the current count
CountWithTimestamp current = state.value();
if (current == null) {
current = new CountWithTimestamp();
current.key = value.f0;
}
// update the state's count
current.count++;
// set the state's timestamp to the record's assigned event time timestamp
current.lastModified = ctx.timestamp();
// write the state back
state.update(current);
// schedule the next timer 60 seconds from the current event time
ctx.timerService().registerEventTimeTimer(current.lastModified + 60000);
}
@Override
public void onTimer(long timestamp, OnTimerContext ctx, Collector<Tuple2<String, Long>> out)
throws Exception {
// get the state for the key that scheduled the timer
CountWithTimestamp result = state.value();
// check if this is an outdated timer or the latest timer
if (timestamp == result.lastModified + 60000) {
// emit the state on timeout
out.collect(new Tuple2<String, Long>(result.key, result.count));
}
}
}
- 本实例展示了如何在ProcessFunction里头使用keyed state以及timer；process方法使用的ProcessFunction是CountWithTimeoutFunction
- CountWithTimeoutFunction的open方法创建了CountWithTimestamp类型的ValueState；processElement方法里头会更新该ValueState，用于记录每个key的element个数以及最后访问时间，然后注册一个EventTimeTimer，在当前eventTime时间的60秒后到达
- onTimer用于响应timer，它会判断如果该key在60秒内没有被update，则emit相关数据
ProcessFunction
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/functions/ProcessFunction.java
@PublicEvolving
public abstract class ProcessFunction<I, O> extends AbstractRichFunction {
private static final long serialVersionUID = 1L;
public abstract void processElement(I value, Context ctx, Collector<O> out) throws Exception;
public void onTimer(long timestamp, OnTimerContext ctx, Collector<O> out) throws Exception {}
public abstract class Context {
public abstract Long timestamp();
public abstract TimerService timerService();
public abstract <X> void output(OutputTag<X> outputTag, X value);
}
public abstract class OnTimerContext extends Context {
public abstract TimeDomain timeDomain();
}
}
可以通过RuntimeContext获取keyed state
小结
可以通过RuntimeContext获取keyed state
doc
- Process Function (Low-level Operations)
正文到此结束
热门推荐
相关文章
Loading...
![[HBLOG]公众号](https://www.liuhaihua.cn/img/qrcode_gzh.jpg)
