org.apache.carbondata.core.reader.ThriftReader.java Source code

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Here is the source code for org.apache.carbondata.core.reader.ThriftReader.java

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/*
 * 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.carbondata.core.reader;

import java.io.DataInputStream;
import java.io.IOException;

import org.apache.carbondata.core.datastore.impl.FileFactory;
import org.apache.carbondata.core.util.CarbonUtil;

import org.apache.thrift.TBase;
import org.apache.thrift.TException;
import org.apache.thrift.protocol.TCompactProtocol;
import org.apache.thrift.protocol.TProtocol;
import org.apache.thrift.transport.TIOStreamTransport;

/**
 * A simple class for reading Thrift objects (of a single type) from a fileName.
 */
public class ThriftReader {
    /**
     * buffer size
     */
    private static final int bufferSize = 2048;
    /**
     * File containing the objects.
     */
    private String fileName;
    /**
     * Used to create empty objects that will be initialized with values from the fileName.
     */
    private TBaseCreator creator;
    /**
     * For reading the fileName.
     */
    private DataInputStream dataInputStream;
    /**
     * For reading the binary thrift objects.
     */
    private TProtocol binaryIn;

    /**
     * Constructor.
     */
    public ThriftReader(String fileName, TBaseCreator creator) {
        this.fileName = fileName;
        this.creator = creator;
    }

    /**
     * Constructor.
     */
    public ThriftReader(String fileName) {
        this.fileName = fileName;
    }

    /**
     * Opens the fileName for reading.
     */
    public void open() throws IOException {
        FileFactory.FileType fileType = FileFactory.getFileType(fileName);
        dataInputStream = FileFactory.getDataInputStream(fileName, fileType, bufferSize);
        binaryIn = new TCompactProtocol(new TIOStreamTransport(dataInputStream));
    }

    /**
     * This method will set the position of stream from where data has to be read
     */
    public void setReadOffset(long bytesToSkip) throws IOException {
        if (dataInputStream.skip(bytesToSkip) != bytesToSkip) {
            throw new IOException("It doesn't set the offset properly");
        }
    }

    /**
     * Checks if another objects is available by attempting to read another byte from the stream.
     */
    public boolean hasNext() throws IOException {
        dataInputStream.mark(1);
        int val = dataInputStream.read();
        dataInputStream.reset();
        return val != -1;
    }

    /**
     * Reads the next object from the fileName.
     */
    public TBase read() throws IOException {
        TBase t = creator.create();
        try {
            t.read(binaryIn);
        } catch (TException e) {
            throw new IOException(e);
        }
        return t;
    }

    /**
     * Reads the next object from the fileName.
     *
     * @param creator type of object which will be returned
     * @throws IOException any problem while reading
     */
    public TBase read(TBaseCreator creator) throws IOException {
        TBase t = creator.create();
        try {
            t.read(binaryIn);
        } catch (TException e) {
            throw new IOException(e);
        }
        return t;
    }

    /**
     * Close the fileName.
     */
    public void close() {
        CarbonUtil.closeStreams(dataInputStream);
    }

    /**
     * Thrift deserializes by taking an existing object and populating it. ThriftReader
     * needs a way of obtaining instances of the class to be populated and this interface
     * defines the mechanism by which a client provides these instances.
     */
    public interface TBaseCreator {
        TBase create();
    }
}