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FastAccessFile.java
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FastAccessFile.java
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/*
* Copyright 2011-2021 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.appng.application.manager.business.webservice;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.StandardCharsets;
import java.util.Iterator;
import java.util.NoSuchElementException;
class FastAccessFile {
public static final char LF = '\n';
private ByteBuffer cb;
private long size;
public FastAccessFile(File file) throws IOException {
try (FileInputStream is = new FileInputStream(file); FileChannel fc = is.getChannel();) {
size = fc.size();
cb = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
}
}
public Iterator<String> tail(long lines) {
long cnt = 0;
long i = 0;
for (i = size - 1; i >= 0; i--) {
if (cb.get((int) i) == LF) {
cnt++;
if (cnt == lines + 1)
break;
}
}
return new LineIterator((int) i + 1);
}
private class LineIterator implements Iterator<String> {
private static final char CR = '\r';
private int offset;
public LineIterator(int offset) {
this.offset = offset;
}
public boolean hasNext() {
return offset < cb.limit();
}
public String next() {
if (offset >= cb.limit()) {
throw new NoSuchElementException();
}
ByteArrayOutputStream sb = new ByteArrayOutputStream();
for (; offset < cb.limit(); offset++) {
byte c = (cb.get(offset));
if (c == LF) {
offset++;
break;
}
if (c != CR) {
sb.write(c);
}
}
try {
return sb.toString(StandardCharsets.UTF_8.name());
} catch (UnsupportedEncodingException e) {
}
return sb.toString();
}
@Override
public void remove() {
// not needed
}
}
}