src/java/org/apache/hcatalog/data/transfer/HCatWriter.java

/**
 * 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.hcatalog.data.transfer;

import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

import org.apache.hadoop.conf.Configuration;
import org.apache.hcatalog.common.HCatException;
import org.apache.hcatalog.data.HCatRecord;
import org.apache.hcatalog.data.transfer.state.StateProvider;

/**
 * This abstraction is internal to HCatalog. This is to facilitate writing to
 * HCatalog from external systems. Don't try to instantiate this directly.
 * Instead, use {@link DataTransferFactory}
 */

public abstract class HCatWriter {

    protected Configuration conf;
    protected WriteEntity we; // This will be null at slave nodes.
    protected WriterContext info;
    protected StateProvider sp;

    /**
     * External system should invoke this method exactly once from a master node.
     *
     * @return {@link WriterContext} This should be serialized and sent to slave
     *         nodes to construct HCatWriter there.
     * @throws HCatException
     */
    public abstract WriterContext prepareWrite() throws HCatException;

    /**
     * This method should be used at slave needs to perform writes.
     *
     * @param recordItr
     *          {@link Iterator} records to be written into HCatalog.
     * @throws {@link HCatException}
     */
    public abstract void write(final Iterator<HCatRecord> recordItr)
        throws HCatException;

    /**
     * This method should be called at master node. Primary purpose of this is to
     * do metadata commit.
     *
     * @throws {@link HCatException}
     */
    public abstract void commit(final WriterContext context) throws HCatException;

    /**
     * This method should be called at master node. Primary purpose of this is to
     * do cleanups in case of failures.
     *
     * @throws {@link HCatException} *
     */
    public abstract void abort(final WriterContext context) throws HCatException;

    /**
     * This constructor will be used at master node
     *
     * @param we
     *          WriteEntity defines where in storage records should be written to.
     * @param config
     *          Any configuration which external system wants to communicate to
     *          HCatalog for performing writes.
     */
    protected HCatWriter(final WriteEntity we, final Map<String, String> config) {
        this(config);
        this.we = we;
    }

    /**
     * This constructor will be used at slave nodes.
     *
     * @param config
     */
    protected HCatWriter(final Configuration config, final StateProvider sp) {
        this.conf = config;
        this.sp = sp;
    }

    private HCatWriter(final Map<String, String> config) {
        Configuration conf = new Configuration();
        if (config != null) {
            // user is providing config, so it could be null.
            for (Entry<String, String> kv : config.entrySet()) {
                conf.set(kv.getKey(), kv.getValue());
            }
        }

        this.conf = conf;
    }
}