co.cask.tephra.persist.HDFSTransactionLogReaderSupplier.java Source code

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Here is the source code for co.cask.tephra.persist.HDFSTransactionLogReaderSupplier.java

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/*
 * Copyright  2015 Cask Data, 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 co.cask.tephra.persist;

import co.cask.tephra.TxConstants;
import com.google.common.base.Supplier;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Text;

/**
 * Provides the correct version of {@link TransactionLogReader}, based on the log's version metadata,
 * to read HDFS Transaction Logs.
 */
public class HDFSTransactionLogReaderSupplier implements Supplier<TransactionLogReader> {
    private final SequenceFile.Reader reader;
    private final byte version;
    private TransactionLogReader logReader;

    public HDFSTransactionLogReaderSupplier(SequenceFile.Reader reader) {
        this.reader = reader;
        Text versionInfo = reader.getMetadata().get(new Text(TxConstants.TransactionLog.VERSION_KEY));
        this.version = versionInfo == null ? 1 : Byte.parseByte(versionInfo.toString());
    }

    @Override
    public TransactionLogReader get() {
        if (logReader != null) {
            return logReader;
        }

        switch (version) {
        case 2:
            logReader = new HDFSTransactionLogReaderV2(reader);
            return logReader;
        case 1:
            logReader = new HDFSTransactionLogReaderV1(reader);
            return logReader;
        default:
            throw new IllegalArgumentException(
                    String.format("Invalid version %s found in the Transaction Log", version));
        }
    }
}