001/**
002 *
003 * Licensed to the Apache Software Foundation (ASF) under one
004 * or more contributor license agreements.  See the NOTICE file
005 * distributed with this work for additional information
006 * regarding copyright ownership.  The ASF licenses this file
007 * to you under the Apache License, Version 2.0 (the
008 * "License"); you may not use this file except in compliance
009 * with the License.  You may obtain a copy of the License at
010 *
011 *     http://www.apache.org/licenses/LICENSE-2.0
012 *
013 * Unless required by applicable law or agreed to in writing, software
014 * distributed under the License is distributed on an "AS IS" BASIS,
015 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
016 * See the License for the specific language governing permissions and
017 * limitations under the License.
018 */
019package org.apache.hadoop.hbase.client;
020
021import java.io.Closeable;
022import java.io.IOException;
023import java.io.UncheckedIOException;
024import java.util.ArrayList;
025import java.util.Iterator;
026import java.util.List;
027
028import org.apache.yetus.audience.InterfaceAudience;
029import org.apache.hadoop.hbase.client.metrics.ScanMetrics;
030
031/**
032 * Interface for client-side scanning. Go to {@link Table} to obtain instances.
033 */
034@InterfaceAudience.Public
035public interface ResultScanner extends Closeable, Iterable<Result> {
036
037  @Override
038  default Iterator<Result> iterator() {
039    return new Iterator<Result>() {
040      // The next RowResult, possibly pre-read
041      Result next = null;
042
043      // return true if there is another item pending, false if there isn't.
044      // this method is where the actual advancing takes place, but you need
045      // to call next() to consume it. hasNext() will only advance if there
046      // isn't a pending next().
047      @Override
048      public boolean hasNext() {
049        if (next != null) {
050          return true;
051        }
052        try {
053          return (next = ResultScanner.this.next()) != null;
054        } catch (IOException e) {
055          throw new UncheckedIOException(e);
056        }
057      }
058
059      // get the pending next item and advance the iterator. returns null if
060      // there is no next item.
061      @Override
062      public Result next() {
063        // since hasNext() does the real advancing, we call this to determine
064        // if there is a next before proceeding.
065        if (!hasNext()) {
066          return null;
067        }
068
069        // if we get to here, then hasNext() has given us an item to return.
070        // we want to return the item and then null out the next pointer, so
071        // we use a temporary variable.
072        Result temp = next;
073        next = null;
074        return temp;
075      }
076    };
077  }
078
079  /**
080   * Grab the next row's worth of values. The scanner will return a Result.
081   * @return Result object if there is another row, null if the scanner is exhausted.
082   * @throws IOException e
083   */
084  Result next() throws IOException;
085
086  /**
087   * Get nbRows rows. How many RPCs are made is determined by the {@link Scan#setCaching(int)}
088   * setting (or hbase.client.scanner.caching in hbase-site.xml).
089   * @param nbRows number of rows to return
090   * @return Between zero and nbRows rowResults. Scan is done if returned array is of zero-length
091   *         (We never return null).
092   * @throws IOException
093   */
094  default Result[] next(int nbRows) throws IOException {
095    List<Result> resultSets = new ArrayList<>(nbRows);
096    for (int i = 0; i < nbRows; i++) {
097      Result next = next();
098      if (next != null) {
099        resultSets.add(next);
100      } else {
101        break;
102      }
103    }
104    return resultSets.toArray(new Result[0]);
105  }
106
107  /**
108   * Closes the scanner and releases any resources it has allocated
109   */
110  @Override
111  void close();
112
113  /**
114   * Allow the client to renew the scanner's lease on the server.
115   * @return true if the lease was successfully renewed, false otherwise.
116   */
117  boolean renewLease();
118
119  /**
120   * @return the scan metrics, or {@code null} if we do not enable metrics.
121   */
122  ScanMetrics getScanMetrics();
123}