FileChannel和MappedByteBuffer

Posted 2020-06-08

使用内存映射文件可以高效访问文件。下面代码做了一个示例，对比内存映射文件的操作和FileOutputStream写文件的效率差异。

import java.io.File;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.RandomAccessFile;

import java.nio.MappedByteBuffer;

import java.nio.channels.FileChannel;

import java.nio.channels.FileChannel.MapMode;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

public class FileClient {

private FileChannel fileChannel;

private MappedByteBuffer mappedByteBuffer;

private File file;

private static int mapedFileSizeCommitLog = 1024 * 1024 * 1024;

private static final String fileName = "D:\\temp\\testfilecache\\a.dat";

private static final String fileName2 = "D:\\temp\\testfilecache\\b.dat";

private static final Logger logger = LoggerFactory.getLogger(FileClient.class.getName());

public static void main(String[] args) throws IOException {

FileClient fclient = new FileClient();

fclient.start();

fclient.start2();

}

@SuppressWarnings("resource")

public void start() throws IOException {

file = new File(fileName);

String testString = "hello";

boolean ok = false;

try {

this.fileChannel = new RandomAccessFile(this.file, "rw").getChannel();

this.mappedByteBuffer = this.fileChannel.map(MapMode.READ_WRITE, 0, mapedFileSizeCommitLog);

int curPos = 0;

long startTime = System.currentTimeMillis();

for (int i = 0; i < 1000000; i++) {

this.mappedByteBuffer.position(curPos);

this.mappedByteBuffer.put(testString.getBytes());

curPos += 6;

}

this.mappedByteBuffer.force();

this.fileChannel.close();

long stopTime = System.currentTimeMillis();

logger.debug("time :  " + (stopTime - startTime));

ok = true;

} catch (FileNotFoundException e) {

logger.error("create file channel " + fileName + " Failed. ", e);

throw e;

} catch (IOException e) {

logger.error("map file " + fileName + " Failed. ", e);

throw e;

} finally {

if (!ok && this.fileChannel != null) {

this.fileChannel.close();

}

}

}

public void start2() throws IOException {

FileOutputStream fos = new FileOutputStream(fileName2);

String testString = "hello";

long startTime = System.currentTimeMillis();

for (int i = 0; i < 1000000; i++) {

fos.write(testString.getBytes());

}

fos.close();

long stopTime = System.currentTimeMillis();

logger.debug("time2 :  " + (stopTime - startTime));

}

}

服务器sata盘，写入性能：

[[email protected] ~]# dd if=/dev/zero of=kwxgd bs=64k count=4k oflag=dsync

4096+0 records in

4096+0 records out

268435456 bytes (268 MB) copied, 8.93065 seconds, 30.1 MB/s

运行后，可以看到对比结果：

[[email protected] ~]# java -jar filechannel-test.jar 

17:56:46.987 [main] DEBUG o.l.filechannel_test.FileClient - time :  207

17:56:48.670 [main] DEBUG o.l.filechannel_test.FileClient - time2 :  1675

性能相差8倍

代码可以从https://github.com/mfcliu/netty-learning下载。

本文出自 “勤似春芽” 博客，请务必保留此出处http://leo01.blog.51cto.com/694903/1738057