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/*
* Copyright (C) 2015 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.cloud.dataflow.sdk.values;
import com.google.cloud.dataflow.sdk.Pipeline;
import com.google.cloud.dataflow.sdk.io.TextIO.Read;
import com.google.cloud.dataflow.sdk.transforms.Create;
import com.google.cloud.dataflow.sdk.transforms.PTransform;
import java.util.Collection;
import java.util.Collections;
/**
* {@link PBegin} is the "input" to a root {@link PTransform}, such as {@link Read Read} or
* {@link Create}.
*
* Typically created by calling {@link Pipeline#begin} on a Pipeline.
*/
public class PBegin implements PInput {
/**
* Returns a {@link PBegin} in the given {@link Pipeline}.
*/
public static PBegin in(Pipeline pipeline) {
return new PBegin(pipeline);
}
/**
* Like {@link #apply(String, PTransform)} but defaulting to the name
* of the {@link PTransform}.
*/
public OutputT apply(
PTransform t) {
return Pipeline.applyTransform(this, t);
}
/**
* Applies the given {@link PTransform} to this input {@link PBegin},
* using {@code name} to identify this specific application of the transform.
* This name is used in various places, including the monitoring UI, logging,
* and to stably identify this application node in the job graph.
*/
public OutputT apply(
String name, PTransform t) {
return Pipeline.applyTransform(name, this, t);
}
@Override
public Pipeline getPipeline() {
return pipeline;
}
@Override
public Collection expand() {
// A PBegin contains no PValues.
return Collections.emptyList();
}
@Override
public void finishSpecifying() {
// Nothing more to be done.
}
/////////////////////////////////////////////////////////////////////////////
/**
* Constructs a {@link PBegin} in the given {@link Pipeline}.
*/
protected PBegin(Pipeline pipeline) {
this.pipeline = pipeline;
}
private final Pipeline pipeline;
}