java8中Stream的使用以及分割list案例

List<List<String>> splitList = Stream.iterate(0,n->n+1).limit(limit).parallel().map(a->{

 List<String> sendList = list.stream().skip(a*MAX_SEND).limit(MAX_SEND).parallel().collect(Collectors.toList());

}).collect(Collectors.toList());

SplitStream<Integer> split = someDataStream.split(new OutputSelector<Integer>() {
  @Override
  public Iterable<String> select(Integer value) {
    List<String> output = new ArrayList<String>();
    if (value % 2 == 0) {
      output.add("even");
    }
    else {
      output.add("odd");
    }
    return output;
  }
});

@Public
public class DataStream<T> {
 
 //......
 
 public SplitStream<T> split(OutputSelector<T> outputSelector) {
 return new SplitStream<>(this, clean(outputSelector));
 }
 
 //......
}

@PublicEvolving
public interface OutputSelector<OUT> extends Serializable {
 
 Iterable<String> select(OUT value);
 
}

@PublicEvolving
public class SplitStream<OUT> extends DataStream<OUT> {
 
 protected SplitStream(DataStream<OUT> dataStream, OutputSelector<OUT> outputSelector) {
 super(dataStream.getExecutionEnvironment(), new SplitTransformation<OUT>(dataStream.getTransformation(), outputSelector));
 }
 
 public DataStream<OUT> select(String... outputNames) {
 return selectOutput(outputNames);
 }
 
 private DataStream<OUT> selectOutput(String[] outputNames) {
 for (String outName : outputNames) {
  if (outName == null) {
  throw new RuntimeException("Selected names must not be null");
  }
 }
 
 SelectTransformation<OUT> selectTransform = new SelectTransformation<OUT>(this.getTransformation(), Lists.newArrayList(outputNames));
 return new DataStream<OUT>(this.getExecutionEnvironment(), selectTransform);
 }
 
}

@Internal
public class StreamGraphGenerator {
 
 //......
 
 private Collection<Integer> transform(StreamTransformation<?> transform) {
 
 if (alreadyTransformed.containsKey(transform)) {
  return alreadyTransformed.get(transform);
 }
 
 LOG.debug("Transforming " + transform);
 
 if (transform.getMaxParallelism() <= 0) {
 
  // if the max parallelism hasn't been set, then first use the job wide max parallelism
  // from theExecutionConfig.
  int globalMaxParallelismFromConfig = env.getConfig().getMaxParallelism();
  if (globalMaxParallelismFromConfig > 0) {
  transform.setMaxParallelism(globalMaxParallelismFromConfig);
  }
 }
 
 // call at least once to trigger exceptions about MissingTypeInfo
 transform.getOutputType();
 
 Collection<Integer> transformedIds;
 if (transform instanceof OneInputTransformation<?, ?>) {
  transformedIds = transformOneInputTransform((OneInputTransformation<?, ?>) transform);
 } else if (transform instanceof TwoInputTransformation<?, ?, ?>) {
  transformedIds = transformTwoInputTransform((TwoInputTransformation<?, ?, ?>) transform);
 } else if (transform instanceof SourceTransformation<?>) {
  transformedIds = transformSource((SourceTransformation<?>) transform);
 } else if (transform instanceof SinkTransformation<?>) {
  transformedIds = transformSink((SinkTransformation<?>) transform);
 } else if (transform instanceof UnionTransformation<?>) {
  transformedIds = transformUnion((UnionTransformation<?>) transform);
 } else if (transform instanceof SplitTransformation<?>) {
  transformedIds = transformSplit((SplitTransformation<?>) transform);
 } else if (transform instanceof SelectTransformation<?>) {
  transformedIds = transformSelect((SelectTransformation<?>) transform);
 } else if (transform instanceof FeedbackTransformation<?>) {
  transformedIds = transformFeedback((FeedbackTransformation<?>) transform);
 } else if (transform instanceof CoFeedbackTransformation<?>) {
  transformedIds = transformCoFeedback((CoFeedbackTransformation<?>) transform);
 } else if (transform instanceof PartitionTransformation<?>) {
  transformedIds = transformPartition((PartitionTransformation<?>) transform);
 } else if (transform instanceof SideOutputTransformation<?>) {
  transformedIds = transformSideOutput((SideOutputTransformation<?>) transform);
 } else {
  throw new IllegalStateException("Unknown transformation: " + transform);
 }
 
 // need this check because the iterate transformation adds itself before
 // transforming the feedback edges
 if (!alreadyTransformed.containsKey(transform)) {
  alreadyTransformed.put(transform, transformedIds);
 }
 
 if (transform.getBufferTimeout() >= 0) {
  streamGraph.setBufferTimeout(transform.getId(), transform.getBufferTimeout());
 }
 if (transform.getUid() != null) {
  streamGraph.setTransformationUID(transform.getId(), transform.getUid());
 }
 if (transform.getUserProvidedNodeHash() != null) {
  streamGraph.setTransformationUserHash(transform.getId(), transform.getUserProvidedNodeHash());
 }
 
 if (transform.getMinResources() != null && transform.getPreferredResources() != null) {
  streamGraph.setResources(transform.getId(), transform.getMinResources(), transform.getPreferredResources());
 }
 
 return transformedIds;
 }
 
 private <T> Collection<Integer> transformSelect(SelectTransformation<T> select) {
 StreamTransformation<T> input = select.getInput();
 Collection<Integer> resultIds = transform(input);
 
 // the recursive transform might have already transformed this
 if (alreadyTransformed.containsKey(select)) {
  return alreadyTransformed.get(select);
 }
 
 List<Integer> virtualResultIds = new ArrayList<>();
 
 for (int inputId : resultIds) {
  int virtualId = StreamTransformation.getNewNodeId();
  streamGraph.addVirtualSelectNode(inputId, virtualId, select.getSelectedNames());
  virtualResultIds.add(virtualId);
 }
 return virtualResultIds;
 }
 
 private <T> Collection<Integer> transformSplit(SplitTransformation<T> split) {
 
 StreamTransformation<T> input = split.getInput();
 Collection<Integer> resultIds = transform(input);
 
 // the recursive transform call might have transformed this already
 if (alreadyTransformed.containsKey(split)) {
  return alreadyTransformed.get(split);
 }
 
 for (int inputId : resultIds) {
  streamGraph.addOutputSelector(inputId, split.getOutputSelector());
 }
 
 return resultIds;
 }
 
 //......
}