RecordReader.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.nifi.serialization;

import java.io.Closeable;
import java.io.IOException;

import org.apache.nifi.serialization.record.Record;
import org.apache.nifi.serialization.record.RecordSchema;
import org.apache.nifi.serialization.record.RecordSet;

/**
 * <p>
 * A RowRecordReader is responsible for parsing data and returning a record at a time
 * in order to allow the caller to iterate over the records individually.
 * </p>
 *
 * <p>
 * PLEASE NOTE: This interface is still considered 'unstable' and may change in a non-backward-compatible
 * manner between minor or incremental releases of NiFi.
 * </p>
 */
public interface RecordReader extends Closeable {

    /**
     * Returns the next record in the stream or <code>null</code> if no more records are available.
     *
     * @return the next record in the stream or <code>null</code> if no more records are available.
     *
     * @throws IOException if unable to read from the underlying data
     * @throws MalformedRecordException if an unrecoverable failure occurs when trying to parse a record
     */
    Record nextRecord() throws IOException, MalformedRecordException;

    /**
     * @return a RecordSchema that is appropriate for the records in the stream
     * @throws MalformedRecordException if an unrecoverable failure occurs when trying to parse the underlying data
     */
    RecordSchema getSchema() throws MalformedRecordException;

    /**
     * @return a RecordSet that returns the records in this Record Reader in a streaming fashion
     */
    default RecordSet createRecordSet() {
        return new RecordSet() {
            @Override
            public RecordSchema getSchema() throws IOException {
                try {
                    return RecordReader.this.getSchema();
                } catch (final MalformedRecordException mre) {
                    throw new IOException(mre);
                }
            }

            @Override
            public Record next() throws IOException {
                try {
                    return RecordReader.this.nextRecord();
                } catch (final MalformedRecordException mre) {
                    throw new IOException(mre);
                }
            }
        };
    }
}