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本文主要研究一下flink的PrintSinkFunction
DataStream.print
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/datastream/DataStream.java
/**
* Writes a DataStream to the standard output stream (stdout).
*
* For each element of the DataStream the result of {@link Object#toString()} is written.
*
*
NOTE: This will print to stdout on the machine where the code is executed, i.e. the Flink
* worker.
*
* @return The closed DataStream.
*/
@PublicEvolving
public DataStreamSink print() {
PrintSinkFunction printFunction = new PrintSinkFunction<>();
return addSink(printFunction).name("Print to Std. Out");
}
/**
* Writes a DataStream to the standard output stream (stderr).
*
* For each element of the DataStream the result of {@link Object#toString()} is written.
*
*
NOTE: This will print to stderr on the machine where the code is executed, i.e. the Flink
* worker.
*
* @return The closed DataStream.
*/
@PublicEvolving
public DataStreamSink printToErr() {
PrintSinkFunction printFunction = new PrintSinkFunction<>(true);
return addSink(printFunction).name("Print to Std. Err");
}
/**
* Writes a DataStream to the standard output stream (stdout).
*
* For each element of the DataStream the result of {@link Object#toString()} is written.
*
*
NOTE: This will print to stdout on the machine where the code is executed, i.e. the Flink
* worker.
*
* @param sinkIdentifier The string to prefix the output with.
* @return The closed DataStream.
*/
@PublicEvolving
public DataStreamSink print(String sinkIdentifier) {
PrintSinkFunction printFunction = new PrintSinkFunction<>(sinkIdentifier, false);
return addSink(printFunction).name("Print to Std. Out");
}
/**
* Writes a DataStream to the standard output stream (stderr).
*
* For each element of the DataStream the result of {@link Object#toString()} is written.
*
*
NOTE: This will print to stderr on the machine where the code is executed, i.e. the Flink
* worker.
*
* @param sinkIdentifier The string to prefix the output with.
* @return The closed DataStream.
*/
@PublicEvolving
public DataStreamSink printToErr(String sinkIdentifier) {
PrintSinkFunction printFunction = new PrintSinkFunction<>(sinkIdentifier, true);
return addSink(printFunction).name("Print to Std. Err");
}
/**
* Adds the given sink to this DataStream. Only streams with sinks added
* will be executed once the {@link StreamExecutionEnvironment#execute()}
* method is called.
*
* @param sinkFunction
* The object containing the sink's invoke function.
* @return The closed DataStream.
*/
public DataStreamSink addSink(SinkFunction sinkFunction) {
// read the output type of the input Transform to coax out errors about MissingTypeInfo
transformation.getOutputType();
// configure the type if needed
if (sinkFunction instanceof InputTypeConfigurable) {
((InputTypeConfigurable) sinkFunction).setInputType(getType(), getExecutionConfig());
}
StreamSink sinkOperator = new StreamSink<>(clean(sinkFunction));
DataStreamSink sink = new DataStreamSink<>(this, sinkOperator);
getExecutionEnvironment().addOperator(sink.getTransformation());
return sink;
}
- DataStream提供了几个print开头的方法，内部是创建了PrintSinkFunction，通过调用addSink操作把该PrintSinkFunction添加进去
- addSink方法的注释表明带有sinks的streams，会在StreamExecutionEnvironment.execute()调用的时候被执行
- SinkFunction先是被StreamSink包装，然后被DataStreamSink包装，最后通过DataStreamSink.getTransformation作为operator添加到ExecutionEnvironment
SinkFunction
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/functions/sink/SinkFunction.java
/**
* Interface for implementing user defined sink functionality.
*
* @param Input type parameter.
*/
@Public
public interface SinkFunction extends Function, Serializable {
/**
* @deprecated Use {@link #invoke(Object, Context)}.
*/
@Deprecated
default void invoke(IN value) throws Exception {}
/**
* Writes the given value to the sink. This function is called for every record.
*
* You have to override this method when implementing a {@code SinkFunction}, this is a
* {@code default} method for backward compatibility with the old-style method only.
*
* @param value The input record.
* @param context Additional context about the input record.
*
* @throws Exception This method may throw exceptions. Throwing an exception will cause the operation
* to fail and may trigger recovery.
*/
default void invoke(IN value, Context context) throws Exception {
invoke(value);
}
/**
* Context that {@link SinkFunction SinkFunctions } can use for getting additional data about
* an input record.
*
*
The context is only valid for the duration of a
* {@link SinkFunction#invoke(Object, Context)} call. Do not store the context and use
* afterwards!
*
* @param The type of elements accepted by the sink.
*/
@Public // Interface might be extended in the future with additional methods.
interface Context {
/** Returns the current processing time. */
long currentProcessingTime();
/** Returns the current event-time watermark. */
long currentWatermark();
/**
* Returns the timestamp of the current input record or {@code null} if the element does not
* have an assigned timestamp.
*/
Long timestamp();
}
}
- SinkFunction接口定义了invoke方法，用来触发sink逻辑；invoke方法里头传递了一个Context，该接口定义了currentProcessingTime、currentWatermark、timestamp三个方法
RichSinkFunction
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/functions/sink/RichSinkFunction.java
/**
* A {@link org.apache.flink.api.common.functions.RichFunction} version of {@link SinkFunction}.
*/
@Public
public abstract class RichSinkFunction extends AbstractRichFunction implements SinkFunction {
private static final long serialVersionUID = 1L;
} - RichSinkFunction抽象类继承了AbstractRichFunction类，同时也声明实现SinkFunction接口；大部分内置的sink function都继承了RichSinkFunction；AbstractRichFunction主要是提供了RuntimeContext属性，可以用来获取function运行时的上下文
PrintSinkFunction
flink-streaming-java_2.11-1.7.0-sources.jar!/org/apache/flink/streaming/api/functions/sink/PrintSinkFunction.java
/**
* Implementation of the SinkFunction writing every tuple to the standard
* output or standard error stream.
*
*
* Four possible format options:
* {@code sinkIdentifier}:taskId> output <- {@code sinkIdentifier} provided, parallelism > 1
* {@code sinkIdentifier}> output <- {@code sinkIdentifier} provided, parallelism == 1
* taskId> output <- no {@code sinkIdentifier} provided, parallelism > 1
* output <- no {@code sinkIdentifier} provided, parallelism == 1
*
*
* @param Input record type
*/
@PublicEvolving
public class PrintSinkFunction extends RichSinkFunction {
private static final long serialVersionUID = 1L;
private final PrintSinkOutputWriter writer;
/**
* Instantiates a print sink function that prints to standard out.
*/
public PrintSinkFunction() {
writer = new PrintSinkOutputWriter<>(false);
}
/**
* Instantiates a print sink function that prints to standard out.
*
* @param stdErr True, if the format should print to standard error instead of standard out.
*/
public PrintSinkFunction(final boolean stdErr) {
writer = new PrintSinkOutputWriter<>(stdErr);
}
/**
* Instantiates a print sink function that prints to standard out and gives a sink identifier.
*
* @param stdErr True, if the format should print to standard error instead of standard out.
* @param sinkIdentifier Message that identify sink and is prefixed to the output of the value
*/
public PrintSinkFunction(final String sinkIdentifier, final boolean stdErr) {
writer = new PrintSinkOutputWriter<>(sinkIdentifier, stdErr);
}
@Override
public void open(Configuration parameters) throws Exception {
super.open(parameters);
StreamingRuntimeContext context = (StreamingRuntimeContext) getRuntimeContext();
writer.open(context.getIndexOfThisSubtask(), context.getNumberOfParallelSubtasks());
}
@Override
public void invoke(IN record) {
writer.write(record);
}
@Override
public String toString() {
return writer.toString();
}
} - PrintSinkFunction继承了RichSinkFunction，它主要是使用了PrintSinkOutputWriter，在invoke的时候调用PrintSinkOutputWriter的write方法来执行输出
PrintSinkOutputWriter
flink-core-1.7.0-sources.jar!/org/apache/flink/api/common/functions/util/PrintSinkOutputWriter.java
/**
* Print sink output writer for DataStream and DataSet print API.
*/
@Internal
public class PrintSinkOutputWriter implements Serializable {
private static final long serialVersionUID = 1L;
private static final boolean STD_OUT = false;
private static final boolean STD_ERR = true;
private final boolean target;
private transient PrintStream stream;
private final String sinkIdentifier;
private transient String completedPrefix;
public PrintSinkOutputWriter() {
this("", STD_OUT);
}
public PrintSinkOutputWriter(final boolean stdErr) {
this("", stdErr);
}
public PrintSinkOutputWriter(final String sinkIdentifier, final boolean stdErr) {
this.target = stdErr;
this.sinkIdentifier = (sinkIdentifier == null ? "" : sinkIdentifier);
}
public void open(int subtaskIndex, int numParallelSubtasks) {
// get the target stream
stream = target == STD_OUT ? System.out : System.err;
completedPrefix = sinkIdentifier;
if (numParallelSubtasks > 1) {
if (!completedPrefix.isEmpty()) {
completedPrefix += ":";
}
completedPrefix += (subtaskIndex + 1);
}
if (!completedPrefix.isEmpty()) {
completedPrefix += "> ";
}
}
public void write(IN record) {
stream.println(completedPrefix + record.toString());
}
@Override
public String toString() {
return "Print to " + (target == STD_OUT ? "System.out" : "System.err");
}
} - PrintSinkOutputWriter的构造器最多可以接收两个参数，分别是sinkIdentifier以及stdErr；sinkIdentifier即为输出的前缀，stdErr用于表示是否输出到System.err
- open方法主要用于做一些准备工作，它在PrintSinkFunction的open方法里头会被调用，PrintSinkFunction的open方法会从AbstractRichFunction定义的RuntimeContext里头获取subtaskIndex及numParallelSubtasks传递过来；这里的open方法根据sinkIdentifier以及subtaskIndex、numParallelSubtasks信息构建completedPrefix
- write方法就是调用System.out或者System.err的println方法，带上completedPrefix及record的信息
小结
- DataStream的几个print开头的方法内部创建的是PrintSinkFunction，然后调用addSink方法添加到ExecutionEnvironment中(
先是被StreamSink包装，然后被DataStreamSink包装，最后通过DataStreamSink.getTransformation作为operator添加到ExecutionEnvironment) - SinkFunction是sink function的基础接口，它主要定义了invoke方法，该方法里头传递了一个Context；而内置的一些sink function大多是继承的RichSinkFunction，RichSinkFunction主要是继承了AbstractRichFunction，可以提供funtion运行时的RuntimeContext信息
- PrintSinkFunction继承了RichSinkFunction，它主要是使用了PrintSinkOutputWriter，在invoke的时候调用PrintSinkOutputWriter的write方法来执行输出
doc
- PrintSinkFunction