org.apache.beam.sdk.io.hadoop.WritableCoder.java Source code

Introduction

Here is the source code for org.apache.beam.sdk.io.hadoop.WritableCoder.java

Source

/*
 * 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.io.hadoop;

import com.google.auto.service.AutoService;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.reflect.InvocationTargetException;
import java.util.Collections;
import java.util.List;
import java.util.Objects;
import org.apache.beam.sdk.coders.CannotProvideCoderException;
import org.apache.beam.sdk.coders.Coder;
import org.apache.beam.sdk.coders.CoderException;
import org.apache.beam.sdk.coders.CoderProvider;
import org.apache.beam.sdk.coders.CoderProviderRegistrar;
import org.apache.beam.sdk.coders.CustomCoder;
import org.apache.beam.sdk.coders.DefaultCoder;
import org.apache.beam.sdk.values.TypeDescriptor;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Writable;

/**
 * A {@code WritableCoder} is a {@link Coder} for a Java class that implements {@link Writable}.
 *
 * <p>To use, specify the coder type on a PCollection:
 *
 * <pre>{@code
 * PCollection<MyRecord> records =
 *     foo.apply(...).setCoder(WritableCoder.of(MyRecord.class));
 * }</pre>
 *
 * @param <T> the type of elements handled by this coder.
 */
public class WritableCoder<T extends Writable> extends CustomCoder<T> {
    private static final long serialVersionUID = 0L;

    /**
     * Returns a {@code WritableCoder} instance for the provided element class.
     *
     * @param <T> the element type
     */
    public static <T extends Writable> WritableCoder<T> of(Class<T> clazz) {
        return new WritableCoder<>(clazz);
    }

    private final Class<T> type;

    @SuppressWarnings("WeakerAccess")
    public WritableCoder(Class<T> type) {
        this.type = type;
    }

    @Override
    public void encode(T value, OutputStream outStream) throws IOException {
        value.write(new DataOutputStream(outStream));
    }

    @SuppressWarnings("unchecked")
    @Override
    public T decode(InputStream inStream) throws IOException {
        try {
            if (type == NullWritable.class) {
                // NullWritable has no default constructor
                return (T) NullWritable.get();
            }
            T t = type.getDeclaredConstructor().newInstance();
            t.readFields(new DataInputStream(inStream));
            return t;
        } catch (InstantiationException | IllegalAccessException | NoSuchMethodException
                | InvocationTargetException e) {
            throw new CoderException("unable to deserialize record", e);
        }
    }

    @Override
    public List<Coder<?>> getCoderArguments() {
        return Collections.emptyList();
    }

    @Override
    public void verifyDeterministic() throws NonDeterministicException {
        throw new NonDeterministicException(this, "Hadoop Writable may be non-deterministic.");
    }

    @Override
    public boolean equals(Object other) {
        if (other == this) {
            return true;
        }
        if (!(other instanceof WritableCoder)) {
            return false;
        }
        WritableCoder<?> that = (WritableCoder<?>) other;
        return Objects.equals(this.type, that.type);
    }

    @Override
    public int hashCode() {
        return type.hashCode();
    }

    /**
     * Returns a {@link CoderProvider} which uses the {@link WritableCoder} for Hadoop {@link Writable
     * writable types}.
     *
     * <p>This method is invoked reflectively from {@link DefaultCoder}.
     */
    @SuppressWarnings("WeakerAccess")
    public static CoderProvider getCoderProvider() {
        return new WritableCoderProvider();
    }

    /**
     * A {@link CoderProviderRegistrar} which registers a {@link CoderProvider} which can handle
     * {@link Writable writable types}.
     */
    @AutoService(CoderProviderRegistrar.class)
    public static class WritableCoderProviderRegistrar implements CoderProviderRegistrar {

        @Override
        public List<CoderProvider> getCoderProviders() {
            return Collections.singletonList(getCoderProvider());
        }
    }

    /** A {@link CoderProvider} for Hadoop {@link Writable writable types}. */
    private static class WritableCoderProvider extends CoderProvider {
        private static final TypeDescriptor<Writable> WRITABLE_TYPE = new TypeDescriptor<Writable>() {
        };

        @Override
        public <T> Coder<T> coderFor(TypeDescriptor<T> typeDescriptor, List<? extends Coder<?>> componentCoders)
                throws CannotProvideCoderException {
            if (!typeDescriptor.isSubtypeOf(WRITABLE_TYPE)) {
                throw new CannotProvideCoderException(
                        String.format("Cannot provide %s because %s does not implement the interface %s",
                                WritableCoder.class.getSimpleName(), typeDescriptor, Writable.class.getName()));
            }

            try {
                @SuppressWarnings("unchecked")
                Coder<T> coder = WritableCoder.of((Class) typeDescriptor.getRawType());
                return coder;
            } catch (IllegalArgumentException e) {
                throw new CannotProvideCoderException(e);
            }
        }
    }
}