1 /** 2 * Licensed to the Apache Software Foundation (ASF) under one 3 * or more contributor license agreements. See the NOTICE file 4 * distributed with this work for additional information 5 * regarding copyright ownership. The ASF licenses this file 6 * to you under the Apache License, Version 2.0 (the 7 * "License"); you may not use this file except in compliance 8 * with the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 package org.apache.hadoop.hbase.client; 19 20 import org.apache.hadoop.classification.InterfaceAudience; 21 import org.apache.hadoop.classification.InterfaceStability; 22 23 import java.io.IOException; 24 import java.util.Iterator; 25 26 /** 27 * Helper class for custom client scanners. 28 */ 29 @InterfaceAudience.Public 30 @InterfaceStability.Stable 31 public abstract class AbstractClientScanner implements ResultScanner { 32 33 @Override 34 public Iterator<Result> iterator() { 35 return new Iterator<Result>() { 36 // The next RowResult, possibly pre-read 37 Result next = null; 38 39 // return true if there is another item pending, false if there isn't. 40 // this method is where the actual advancing takes place, but you need 41 // to call next() to consume it. hasNext() will only advance if there 42 // isn't a pending next(). 43 public boolean hasNext() { 44 if (next == null) { 45 try { 46 next = AbstractClientScanner.this.next(); 47 return next != null; 48 } catch (IOException e) { 49 throw new RuntimeException(e); 50 } 51 } 52 return true; 53 } 54 55 // get the pending next item and advance the iterator. returns null if 56 // there is no next item. 57 public Result next() { 58 // since hasNext() does the real advancing, we call this to determine 59 // if there is a next before proceeding. 60 if (!hasNext()) { 61 return null; 62 } 63 64 // if we get to here, then hasNext() has given us an item to return. 65 // we want to return the item and then null out the next pointer, so 66 // we use a temporary variable. 67 Result temp = next; 68 next = null; 69 return temp; 70 } 71 72 public void remove() { 73 throw new UnsupportedOperationException(); 74 } 75 }; 76 } 77 }