com.google.cloud.dataflow.sdk.io.hdfs.WritableCoder.java Source code

Introduction

Here is the source code for com.google.cloud.dataflow.sdk.io.hdfs.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 com.google.cloud.dataflow.sdk.io.hdfs;

import com.google.cloud.dataflow.sdk.coders.Coder;
import com.google.cloud.dataflow.sdk.coders.CoderException;
import com.google.cloud.dataflow.sdk.coders.StandardCoder;
import com.google.cloud.dataflow.sdk.util.CloudObject;
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Writable;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.List;

/**
 * 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 StandardCoder<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);
    }

    @JsonCreator
    @SuppressWarnings("unchecked")
    public static WritableCoder<?> of(@JsonProperty("type") String classType) throws ClassNotFoundException {
        Class<?> clazz = Class.forName(classType);
        if (!Writable.class.isAssignableFrom(clazz)) {
            throw new ClassNotFoundException("Class " + classType + " does not implement Writable");
        }
        return of((Class<? extends Writable>) clazz);
    }

    private final Class<T> type;

    public WritableCoder(Class<T> type) {
        this.type = type;
    }

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

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

    @Override
    public List<Coder<?>> getCoderArguments() {
        return null;
    }

    @Override
    public CloudObject asCloudObject() {
        CloudObject result = super.asCloudObject();
        result.put("type", type.getName());
        return result;
    }

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

}