org.apache.poi.hssf.util.LazilyConcatenatedByteArray Maven / Gradle / Ivy
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(the "License"); you may not use this file except in compliance with
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http://www.apache.org/licenses/LICENSE-2.0
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limitations under the License.
==================================================================== */
package org.apache.poi.hssf.util;
import java.util.ArrayList;
import java.util.List;
/**
* Utility for delaying the concatenation of multiple byte arrays. Doing this up-front
* causes significantly more copying, which for a large number of byte arrays can cost
* a large amount of time.
*/
public class LazilyConcatenatedByteArray {
private final List arrays = new ArrayList(1);
/**
* Clears the array (sets the concatenated length back to zero.
*/
public void clear() {
arrays.clear();
}
/**
* Concatenates an array onto the end of our array.
* This is a relatively fast operation.
*
* @param array the array to concatenate.
* @throws IllegalArgumentException if {@code array} is {@code null}.
*/
public void concatenate(byte[] array) {
if (array == null) {
throw new IllegalArgumentException("array cannot be null");
}
arrays.add(array);
}
/**
* Gets the concatenated contents as a single byte array.
*
* This is a slower operation, but the concatenated array is stored off as a single
* array again so that subsequent calls will not perform additional copying.
*
* @return the byte array. Returns {@code null} if no data has been placed into it.
*/
public byte[] toArray() {
if (arrays.isEmpty()) {
return null;
} else if (arrays.size() > 1) {
int totalLength = 0;
for (byte[] array : arrays) {
totalLength += array.length;
}
byte[] concatenated = new byte[totalLength];
int destPos = 0;
for (byte[] array : arrays) {
System.arraycopy(array, 0, concatenated, destPos, array.length);
destPos += array.length;
}
arrays.clear();
arrays.add(concatenated);
}
return arrays.get(0);
}
}