/*
* 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.transforms;
import com.google.common.base.Joiner;
import org.apache.beam.sdk.values.KV;
import org.apache.beam.sdk.values.PCollection;
/**
* {@link PTransform PTransforms} for converting a {@link PCollection PCollection<?>},
* {@link PCollection PCollection<KV<?,?>>}, or
* {@link PCollection PCollection<Iterable<?>>}
* to a {@link PCollection PCollection<String>}.
*
* <p><b>Note</b>: For any custom string conversion and formatting, we recommend applying your own
* {@link SerializableFunction} using {@link MapElements#via(SerializableFunction)}
*/
public final class ToString {
private ToString() {
// do not instantiate
}
/**
* Transforms each element of the input {@link PCollection} to a {@link String} using the {@link
* Object#toString} method.
*/
public static PTransform<PCollection<?>, PCollection<String>> elements() {
return new Elements();
}
/**
* Transforms each element of the input {@link PCollection} to a {@link String} by using the
* {@link Object#toString} on the key followed by a "," followed by the {@link Object#toString}
* of the value.
*/
public static PTransform<PCollection<? extends KV<?, ?>>, PCollection<String>> kvs() {
return kvs(",");
}
/**
* Transforms each element of the input {@link PCollection} to a {@link String} by using the
* {@link Object#toString} on the key followed by the specified delimiter followed by the {@link
* Object#toString} of the value.
*
* @param delimiter The delimiter to put between the key and value
*/
public static PTransform<PCollection<? extends KV<?, ?>>, PCollection<String>> kvs(
String delimiter) {
return new KVs(delimiter);
}
/**
* Transforms each item in the iterable of the input {@link PCollection} to a {@link String}
* using the {@link Object#toString} method followed by a "," until
* the last element in the iterable. There is no trailing delimiter.
*/
public static PTransform<PCollection<? extends Iterable<?>>, PCollection<String>> iterables() {
return iterables(",");
}
/**
* Transforms each item in the iterable of the input {@link PCollection} to a {@link String} using
* the {@link Object#toString} method followed by the specified delimiter until the last element
* in the iterable. There is no trailing delimiter.
*
* @param delimiter The delimiter to put between the items in the iterable.
*/
public static PTransform<PCollection<? extends Iterable<?>>, PCollection<String>> iterables(
String delimiter) {
return new Iterables(delimiter);
}
/**
* A {@link PTransform} that converts a {@code PCollection} to a {@code PCollection<String>} using
* the {@link Object#toString} method.
*
* <p>Example of use:
*
* <pre>{@code
* PCollection<Long> longs = ...;
* PCollection<String> strings = longs.apply(ToString.elements());
* }</pre>
*
* <p><b>Note</b>: For any custom string conversion and formatting, we recommend applying your own
* {@link SerializableFunction} using {@link MapElements#via(SerializableFunction)}
*/
private static final class Elements extends PTransform<PCollection<?>, PCollection<String>> {
@Override
public PCollection<String> expand(PCollection<?> input) {
return input.apply(MapElements.via(new SimpleFunction<Object, String>() {
@Override
public String apply(Object input) {
return input.toString();
}
}));
}
}
/**
* A {@link PTransform} that converts a {@code PCollection} of {@code KV} to a {@code
* PCollection<String>} using the {@link Object#toString} method for the key and value and an
* optional delimiter.
*
* <p>Example of use:
*
* <pre>{@code
* PCollection<KV<String, Long>> nameToLong = ...;
* PCollection<String> strings = nameToLong.apply(ToString.kv());
* }</pre>
*
* <p><b>Note</b>: For any custom string conversion and formatting, we recommend applying your own
* {@link SerializableFunction} using {@link MapElements#via(SerializableFunction)}
*/
private static final class KVs
extends PTransform<PCollection<? extends KV<?, ?>>, PCollection<String>> {
private final String delimiter;
public KVs(String delimiter) {
this.delimiter = delimiter;
}
@Override
public PCollection<String> expand(PCollection<? extends KV<?, ?>> input) {
return input.apply(MapElements.via(new SimpleFunction<KV<?, ?>, String>() {
@Override
public String apply(KV<?, ?> input) {
return input.getKey().toString() + delimiter + input.getValue().toString();
}
}));
}
}
/**
* A {@link PTransform} that converts a {@code PCollection} of {@link Iterable} to a {@code
* PCollection<String>} using the {@link Object#toString} method and an optional delimiter.
*
* <p>Example of use:
*
* <pre>{@code
* PCollection<Iterable<Long>> longs = ...;
* PCollection<String> strings = nameToLong.apply(ToString.iterable());
* }</pre>
*
* <p><b>Note</b>: For any custom string conversion and formatting, we recommend applying your own
* {@link SerializableFunction} using {@link MapElements#via(SerializableFunction)}
*/
private static final class Iterables
extends PTransform<PCollection<? extends Iterable<?>>, PCollection<String>> {
private final String delimiter;
public Iterables(String delimiter) {
this.delimiter = delimiter;
}
@Override
public PCollection<String> expand(PCollection<? extends Iterable<?>> input) {
return input.apply(MapElements.via(new SimpleFunction<Iterable<?>, String>() {
@Override
public String apply(Iterable<?> input) {
return Joiner.on(delimiter).join(input);
}
}));
}
}
}