com.cloudera.cdk.data.filesystem.FileSystemDatasetReader.java Source code

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Here is the source code for com.cloudera.cdk.data.filesystem.FileSystemDatasetReader.java

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/**
 * Copyright 2013 Cloudera 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.cloudera.cdk.data.filesystem;

import com.cloudera.cdk.data.spi.ReaderWriterState;
import com.cloudera.cdk.data.DatasetReaderException;
import com.cloudera.cdk.data.spi.AbstractDatasetReader;
import com.google.common.base.Objects;
import com.google.common.base.Preconditions;
import org.apache.avro.Schema;
import org.apache.avro.file.DataFileReader;
import org.apache.avro.reflect.ReflectDatumReader;
import org.apache.hadoop.fs.AvroFSInput;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;

class FileSystemDatasetReader<E> extends AbstractDatasetReader<E> {

    private final FileSystem fileSystem;
    private final Path path;
    private final Schema schema;

    private ReaderWriterState state;
    private DataFileReader<E> reader;

    private static final Logger logger = LoggerFactory.getLogger(FileSystemDatasetReader.class);

    public FileSystemDatasetReader(FileSystem fileSystem, Path path, Schema schema) {
        Preconditions.checkArgument(fileSystem != null, "FileSystem cannot be null");
        Preconditions.checkArgument(path != null, "Path cannot be null");
        Preconditions.checkArgument(schema != null, "Schema cannot be null");

        this.fileSystem = fileSystem;
        this.path = path;
        this.schema = schema;

        this.state = ReaderWriterState.NEW;
    }

    @Override
    public void open() {
        Preconditions.checkState(state.equals(ReaderWriterState.NEW),
                "A reader may not be opened more than once - current state:%s", state);

        logger.debug("Opening reader on path:{}", path);

        try {
            reader = new DataFileReader<E>(
                    new AvroFSInput(fileSystem.open(path), fileSystem.getFileStatus(path).getLen()),
                    new ReflectDatumReader<E>(schema));
        } catch (IOException e) {
            throw new DatasetReaderException("Unable to create reader path:" + path, e);
        }

        state = ReaderWriterState.OPEN;
    }

    @Override
    public boolean hasNext() {
        Preconditions.checkState(state.equals(ReaderWriterState.OPEN), "Attempt to read from a file in state:%s",
                state);
        return reader.hasNext();
    }

    @Override
    public E next() {
        Preconditions.checkState(state.equals(ReaderWriterState.OPEN), "Attempt to read from a file in state:%s",
                state);

        return reader.next();
    }

    @Override
    public void close() {
        if (!state.equals(ReaderWriterState.OPEN)) {
            return;
        }

        logger.debug("Closing reader on path:{}", path);

        try {
            reader.close();
        } catch (IOException e) {
            throw new DatasetReaderException("Unable to close reader path:" + path, e);
        }

        state = ReaderWriterState.CLOSED;
    }

    @Override
    public boolean isOpen() {
        return state.equals(ReaderWriterState.OPEN);
    }

    @Override
    public String toString() {
        return Objects.toStringHelper(this).add("fileSystem", fileSystem).add("path", path).add("schema", schema)
                .add("state", state).add("reader", reader).toString();
    }

}