001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.camel.util; 018 019import java.io.Closeable; 020import java.io.IOException; 021import java.util.Iterator; 022import java.util.concurrent.atomic.AtomicBoolean; 023 024/** 025 * Skip based {@link Iterator} which skips the given {@link Iterator} a number of times. 026 */ 027public final class SkipIterator implements Iterator<Object>, Closeable { 028 029 private final Iterator<?> it; 030 private final int skip; 031 private boolean closed; 032 private final AtomicBoolean hasSkip = new AtomicBoolean(); 033 034 /** 035 * Creates a new skip iterator 036 * 037 * @param it the iterator 038 * @param skip number of times to skip 039 * @throws IllegalArgumentException is thrown if skip is not a positive number 040 */ 041 public SkipIterator(Iterator<?> it, int skip) { 042 this.it = it; 043 this.skip = skip; 044 if (skip < 0) { 045 throw new IllegalArgumentException("Skip must not be a negative number, was: " + skip); 046 } 047 } 048 049 @Override 050 public void close() throws IOException { 051 try { 052 IOHelper.closeIterator(it); 053 } finally { 054 // we are now closed 055 closed = true; 056 } 057 } 058 059 @Override 060 public boolean hasNext() { 061 if (closed) { 062 return false; 063 } 064 065 if (hasSkip.compareAndSet(false, true)) { 066 doSkip(); 067 } 068 069 boolean answer = it.hasNext(); 070 if (!answer) { 071 // auto close 072 try { 073 close(); 074 } catch (IOException e) { 075 // ignore 076 } 077 } 078 return answer; 079 } 080 081 @Override 082 public Object next() { 083 if (hasSkip.compareAndSet(false, true)) { 084 doSkip(); 085 } 086 087 return it.next(); 088 } 089 090 private void doSkip() { 091 for (int i = 0; i < skip; i++) { 092 if (it.hasNext()) { 093 // skip 094 it.next(); 095 } 096 } 097 } 098 099 @Override 100 public void remove() { 101 it.remove(); 102 } 103}