/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.beam.sdk.values;
import java.util.Collections;
import java.util.Map;
import org.apache.beam.sdk.Pipeline;
import org.apache.beam.sdk.io.TextIO.Read;
import org.apache.beam.sdk.transforms.PTransform;
/**
* {@link PBegin} is the "input" to a root {@link PTransform}, such as {@link Read Read} or
* {@link org.apache.beam.sdk.transforms.Create}.
*
* <p>Typically elided by simply calling {@link Pipeline#apply(String, PTransform)} or {@link
* Pipeline#apply(PTransform)}, but one can be explicitly 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 extends POutput> OutputT apply(PTransform<? super PBegin, OutputT> t) {
return Pipeline.applyTransform(this, t);
}
/**
* Applies the given {@link PTransform} to this {@link PBegin}, using {@code name} to identify
* this specific application of the transform.
*
* <p>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 extends POutput> OutputT apply(
String name, PTransform<? super PBegin, OutputT> t) {
return Pipeline.applyTransform(name, this, t);
}
@Override
public Pipeline getPipeline() {
return pipeline;
}
@Override
public Map<TupleTag<?>, PValue> expand() {
// A PBegin contains no PValues.
return Collections.emptyMap();
}
/////////////////////////////////////////////////////////////////////////////
/**
* Constructs a {@link PBegin} in the given {@link Pipeline}.
*/
protected PBegin(Pipeline pipeline) {
this.pipeline = pipeline;
}
private final Pipeline pipeline;
}