84 lines
2.8 KiB
Java
84 lines
2.8 KiB
Java
/* ====================================================================
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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==================================================================== */
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package org.apache.poi.hssf.util;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* Utility for delaying the concatenation of multiple byte arrays. Doing this up-front
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* causes significantly more copying, which for a large number of byte arrays can cost
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* a large amount of time.
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*/
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public class LazilyConcatenatedByteArray {
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private final List<byte[]> arrays = new ArrayList<byte[]>(1);
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/**
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* Clears the array (sets the concatenated length back to zero.
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*/
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public void clear() {
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arrays.clear();
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}
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/**
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* Concatenates an array onto the end of our array.
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* This is a relatively fast operation.
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*
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* @param array the array to concatenate.
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* @throws IllegalArgumentException if {@code array} is {@code null}.
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*/
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public void concatenate(byte[] array) {
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if (array == null) {
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throw new IllegalArgumentException("array cannot be null");
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}
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arrays.add(array);
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}
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/**
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* Gets the concatenated contents as a single byte array.
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*
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* This is a slower operation, but the concatenated array is stored off as a single
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* array again so that subsequent calls will not perform additional copying.
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*
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* @return the byte array. Returns {@code null} if no data has been placed into it.
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*/
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public byte[] toArray() {
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if (arrays.isEmpty()) {
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return null;
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} else if (arrays.size() > 1) {
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int totalLength = 0;
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for (byte[] array : arrays) {
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totalLength += array.length;
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}
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byte[] concatenated = new byte[totalLength];
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int destPos = 0;
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for (byte[] array : arrays) {
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System.arraycopy(array, 0, concatenated, destPos, array.length);
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destPos += array.length;
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}
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arrays.clear();
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arrays.add(concatenated);
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}
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return arrays.get(0);
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}
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}
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