java8，测试1g文件copy和4g文件拷贝时效率
vm参数设置： -XX:+PrintGCDetails -Xmx1G -Xms1G
源码
import java.io.*;
import java.nio.IntBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.text.DecimalFormat;
import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
/**
* 4g文件，copy测试
*/
public class FileCopyTest extends AbstractTest {
private String source = "D:\\test\\bigfile.txt";
@Override
protected void head() {
try {
//创建文件,1g(1L<<30) 4g(1L<<32)
create(source, 1L << 30);
//文件复制方式第一种，stream直接buffer，1g->5s 4g->33s
streamCopy(source, "D:\\test\\streamCopy.txt");
//文件复制方式Files.copy,用户态文件copy，1g->11s 4g->40s
toolCopy(source, "D:\\test\\toolCopy.txt");
//文件复制方式Channel复制，1g->3s 4g->38s
channelCopy(source, "D:\\test\\channelCopy.txt");
//文件复制方式MappedByteBuffer复制,1g->6s 4g->42s
mappedByteBufferCopy(source, "D:\\test\\mappedByteBufferCopy.txt");
//文件复制通道RandomAccessFile,1g->3s 4g->38s
channelRandomCopy(source, "D:\\test\\channelRandomCopy.txt");
//多线程复制，跟gc和线程切换有关,1g->5s ,4g->40-60
multiThreadCopy(source, "D:\\test\\multiThreadCopy.txt");
} catch (IOException e) {
e.printStackTrace();
}
}
private void create(String target, long size) throws IOException {
Path path = Paths.get(target);
if (Files.isDirectory(path)) {
throw new IOException("不是有效的文件" + target);
}
if (Files.exists(path)) {
Files.delete(path);
Files.createFile(path);
}
//512m
long stepLength = 1L << 29;
long cur = 0L;
MappedByteBuffer mappedByteBuffer;
Random random = new Random();
while (cur < size) {
mappedByteBuffer = new RandomAccessFile(target, "rw").getChannel()
.map(FileChannel.MapMode.READ_WRITE, cur, stepLength);
IntBuffer intBuffer = mappedByteBuffer.asIntBuffer();
while (intBuffer.position() < intBuffer.capacity()) {
intBuffer.put(random.nextInt());
}
cur += stepLength;
}
}
private void multiThreadCopy(String source, String target) throws IOException {
long start = System.currentTimeMillis();
RandomAccessFile in = new RandomAccessFile(source, "r");
RandomAccessFile out = new RandomAccessFile(target, "rw");
ExecutorService executorService = Executors.newFixedThreadPool(4);
long size = in.length();
//512m
long stepLength = 1L << 29;
int partition = (int) (size / stepLength);
System.out.println("分块：" + partition);
System.out.println("步长：" + FileUtils.size(stepLength));
CountDownLatch countDownLatch = new CountDownLatch(partition);
FileChannel fileChannel = in.getChannel();
for (int i = 0; i < partition; i++) {
long cur = i * stepLength;
executorService.execute(new CopyTask(fileChannel, cur, stepLength, out, countDownLatch));
}
try {
countDownLatch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
executorService.shutdown();
long end = System.currentTimeMillis();
System.out.println("multiThreadCopy耗时:" + (end - start) / 1000L);
}
private static class CopyTask implements Runnable {
private long cur;
private RandomAccessFile out;
private CountDownLatch countDownLatch;
private FileChannel fileChannel;
private long stepLength;
public CopyTask(FileChannel fileChannel, long cur, long stepLength, RandomAccessFile out, CountDownLatch countDownLatch) {
this.cur = cur;
this.out = out;
this.countDownLatch = countDownLatch;
this.stepLength = stepLength;
this.fileChannel = fileChannel;
}
@Override
public void run() {
try {
MappedByteBuffer mappedByteBuffer = fileChannel.map(FileChannel.MapMode.READ_ONLY, cur, stepLength);
out.getChannel().write(mappedByteBuffer, cur);
} catch (IOException e) {
e.printStackTrace();
}
countDownLatch.countDown();
}
}
/**
* mappedByteBuffer,涉及到GC，空间没有重复使用
*
* @throws IOException
*/
private void mappedByteBufferCopy(String source, String target) throws IOException {
long start = System.currentTimeMillis();
RandomAccessFile in = new RandomAccessFile(source, "r");
RandomAccessFile out = new RandomAccessFile(target, "rw");
MappedByteBuffer inMappedByteBuffer;
long cur = 0L;
long stepLength = 1L << 29;
while (cur < in.length()) {
inMappedByteBuffer =
in.getChannel().map(FileChannel.MapMode.READ_ONLY, cur, stepLength);
out.getChannel().write(inMappedByteBuffer, cur);
cur += stepLength;
}
long end = System.currentTimeMillis();
System.out.println("channelCopy耗时:" + (end - start) / 1000L);
}
/**
* 理论上是最快的
*
* @throws IOException
*/
private void channelCopy(String source, String target) throws IOException {
long start = System.currentTimeMillis();
File in = new File(source);
FileInputStream fileInputStream = new FileInputStream(in);
File out = new File(target);
if (!out.exists()) {
out.createNewFile();
}
FileOutputStream fileOutputStream = new FileOutputStream(out);
long fileLength = in.length();
long cur = 0L;
//1G
long stepLength = 1L << 30;
while (cur < fileLength) {
fileInputStream.getChannel().transferTo(cur, stepLength, fileOutputStream.getChannel());
cur += stepLength;
}
fileInputStream.close();
fileOutputStream.close();
long end = System.currentTimeMillis();
System.out.println("channelCopy耗时:" + (end - start) / 1000L);
}
/**
* 和直接使用file.getChannel应该是一样的
*
* @throws IOException
*/
private void channelRandomCopy(String source, String target) throws IOException {
long start = System.currentTimeMillis();
RandomAccessFile in = new RandomAccessFile(source, "r");
RandomAccessFile out = new RandomAccessFile(target, "rw");
long fileLength = in.length();
long cur = 0L;
long stepLength = 1L << 30;
while (cur < fileLength) {
in.getChannel().transferTo(cur, stepLength, out.getChannel());
cur += stepLength;
}
in.close();
out.close();
long end = System.currentTimeMillis();
System.out.println("channelRandomCopy耗时:" + (end - start) / 1000L);
}
/**
* 直接调用底层C++代码复制，用户态-内核态切换
*
* @throws IOException
*/
private void toolCopy(String source, String target) throws IOException {
long start = System.currentTimeMillis();
File out = new File(target);
FileOutputStream fileOutputStream = new FileOutputStream(out);
Files.copy(Paths.get(source), fileOutputStream);
fileOutputStream.close();
long end = System.currentTimeMillis();
System.out.println("toolCopy耗时:" + (end - start) / 1000L);
}
/**
* 分析，重复使用buffer，没有gc
*
* @throws IOException
*/
private void streamCopy(String source, String target) throws IOException {
long start = System.currentTimeMillis();
File in = new File(source);
FileInputStream fileInputStream = new FileInputStream(in);
File out = new File(target);
if (!out.exists()) {
out.createNewFile();
}
FileOutputStream fileOutputStream = new FileOutputStream(out);
//1M
byte[] buffer = new byte[1 << 20];
int length;
while ((length = fileInputStream.read(buffer)) != -1) {
fileOutputStream.write(buffer, 0, length);
}
fileOutputStream.flush();
fileOutputStream.close();
fileInputStream.close();
long end = System.currentTimeMillis();
System.out.println("streamCopy耗时:" + (end - start) / 1000L);
}
private static class FileUtils {
private static final long B = 1024L;
private static final long K = 1048576L;
private static final long M = 1073741824L;
private static final long G = 1099511627776L;
private static final long T = 1125899906842624L;
private static final long P = 1152921504606846976L;
/**
* 单位换算，（这里如果想用stringbuilder来appen也是可以的
* ，如果您javap 命令反编译出class文件，会发现其实底层优化，自动使用了stringbuilder）
*
* @param size
* @return
*/
public static String size(long size) {
DecimalFormat df = new DecimalFormat("#.00");
String fileSizeString = "";
String kSize = df.format((double) size / B) + "K";
if (size < B) {
fileSizeString = kSize + "(" + df.format((double) size) + "B" + ")";
} else if (size < K) {
fileSizeString = df.format((double) size / B) + "K";
} else if (size < M) {
fileSizeString = kSize + "(" + df.format((double) size / K) + "M" + ")";
} else if (size < G) {
fileSizeString = kSize + "(" + df.format((double) size / M) + "G" + ")";
} else if (size < T) {
fileSizeString = kSize + "(" + df.format((double) size / G) + "T)";
} else if (size < P) {
fileSizeString = kSize + "(" + df.format((double) size / T) + "P)";
} else {
fileSizeString = kSize + "(" + df.format((double) size / P) + "E)";
}
return fileSizeString;
}
}
}
1.InputStream和OutputStream
1G文件
streamCopy耗时:4
Heap
def new generation total 314560K, used 22398K [0x04800000, 0x19d50000, 0x19d50000)
eden space 279616K, 8% used [0x04800000, 0x05ddfbc0, 0x15910000)
from space 34944K, 0% used [0x15910000, 0x15910000, 0x17b30000)
to space 34944K, 0% used [0x17b30000, 0x17b30000, 0x19d50000)
tenured generation total 699072K, used 0K [0x19d50000, 0x44800000, 0x44800000)
the space 699072K, 0% used [0x19d50000, 0x19d50000, 0x19d50200, 0x44800000)
Metaspace used 3984K, capacity 4024K, committed 4032K, reserved 4480K4G文件
streamCopy耗时:34
Heap
def new generation total 314560K, used 22398K [0x04800000, 0x19d50000, 0x19d50000)
eden space 279616K, 8% used [0x04800000, 0x05ddfbc0, 0x15910000)
from space 34944K, 0% used [0x15910000, 0x15910000, 0x17b30000)
to space 34944K, 0% used [0x17b30000, 0x17b30000, 0x19d50000)
tenured generation total 699072K, used 0K [0x19d50000, 0x44800000, 0x44800000)
the space 699072K, 0% used [0x19d50000, 0x19d50000, 0x19d50200, 0x44800000)
Metaspace used 3984K, capacity 4024K, committed 4032K, reserved 4480K2.Files.copy()
1G文件
toolCopy耗时:5
Heap
def new generation total 314560K, used 22398K [0x04e00000, 0x1a350000, 0x1a350000)
eden space 279616K, 8% used [0x04e00000, 0x063dfbc0, 0x15f10000)
from space 34944K, 0% used [0x15f10000, 0x15f10000, 0x18130000)
to space 34944K, 0% used [0x18130000, 0x18130000, 0x1a350000)
tenured generation total 699072K, used 0K [0x1a350000, 0x44e00000, 0x44e00000)
the space 699072K, 0% used [0x1a350000, 0x1a350000, 0x1a350200, 0x44e00000)
Metaspace used 4198K, capacity 4248K, committed 4288K, reserved 4480K4G文件
toolCopy耗时:41
Heap
def new generation total 314560K, used 22398K [0x04800000, 0x19d50000, 0x19d50000)
eden space 279616K, 8% used [0x04800000, 0x05ddfbc0, 0x15910000)
from space 34944K, 0% used [0x15910000, 0x15910000, 0x17b30000)
to space 34944K, 0% used [0x17b30000, 0x17b30000, 0x19d50000)
tenured generation total 699072K, used 0K [0x19d50000, 0x44800000, 0x44800000)
the space 699072K, 0% used [0x19d50000, 0x19d50000, 0x19d50200, 0x44800000)
Metaspace used 4198K, capacity 4248K, committed 4288K, reserved 4480K3.FileChannel.transferTo()
1G文件
channelCopy耗时:3
Heap
def new generation total 314560K, used 22398K [0x04a00000, 0x19f50000, 0x19f50000)
eden space 279616K, 8% used [0x04a00000, 0x05fdfbc0, 0x15b10000)
from space 34944K, 0% used [0x15b10000, 0x15b10000, 0x17d30000)
to space 34944K, 0% used [0x17d30000, 0x17d30000, 0x19f50000)
tenured generation total 699072K, used 0K [0x19f50000, 0x44a00000, 0x44a00000)
the space 699072K, 0% used [0x19f50000, 0x19f50000, 0x19f50200, 0x44a00000)
Metaspace used 4065K, capacity 4123K, committed 4160K, reserved 4480K4G文件
channelCopy耗时:37
Heap
def new generation total 314560K, used 22398K [0x04a00000, 0x19f50000, 0x19f50000)
eden space 279616K, 8% used [0x04a00000, 0x05fdfbc0, 0x15b10000)
from space 34944K, 0% used [0x15b10000, 0x15b10000, 0x17d30000)
to space 34944K, 0% used [0x17d30000, 0x17d30000, 0x19f50000)
tenured generation total 699072K, used 0K [0x19f50000, 0x44a00000, 0x44a00000)
the space 699072K, 0% used [0x19f50000, 0x19f50000, 0x19f50200, 0x44a00000)
Metaspace used 4067K, capacity 4123K, committed 4160K, reserved 4480K4.RandomAccessFile
1G文件
channelRandomCopy耗时:3
Heap
def new generation total 314560K, used 22398K [0x04800000, 0x19d50000, 0x19d50000)
eden space 279616K, 8% used [0x04800000, 0x05ddfbc0, 0x15910000)
from space 34944K, 0% used [0x15910000, 0x15910000, 0x17b30000)
to space 34944K, 0% used [0x17b30000, 0x17b30000, 0x19d50000)
tenured generation total 699072K, used 0K [0x19d50000, 0x44800000, 0x44800000)
the space 699072K, 0% used [0x19d50000, 0x19d50000, 0x19d50200, 0x44800000)
Metaspace used 4077K, capacity 4123K, committed 4160K, reserved 4480K4G文件
channelRandomCopy耗时:38
Heap
def new generation total 314560K, used 22398K [0x04a00000, 0x19f50000, 0x19f50000)
eden space 279616K, 8% used [0x04a00000, 0x05fdfbc0, 0x15b10000)
from space 34944K, 0% used [0x15b10000, 0x15b10000, 0x17d30000)
to space 34944K, 0% used [0x17d30000, 0x17d30000, 0x19f50000)
tenured generation total 699072K, used 0K [0x19f50000, 0x44a00000, 0x44a00000)
the space 699072K, 0% used [0x19f50000, 0x19f50000, 0x19f50200, 0x44a00000)
Metaspace used 4077K, capacity 4123K, committed 4160K, reserved 4480K5.MappedByteBuffer
1G文件
[Full GC (System.gc()) [Tenured: 0K->1823K(699072K), 0.0141744 secs] 22398K->1823K(1013632K), [Metaspace: 4065K->4065K(4480K)], 0.0169870 secs] [Times: user=0.02 sys=0.00, real=0.01 secs]
channelCopy耗时:6
Heap
def new generation total 314560K, used 11184K [0x04800000, 0x19d50000, 0x19d50000)
eden space 279616K, 4% used [0x04800000, 0x052ec320, 0x15910000)
from space 34944K, 0% used [0x15910000, 0x15910000, 0x17b30000)
to space 34944K, 0% used [0x17b30000, 0x17b30000, 0x19d50000)
tenured generation total 699072K, used 1823K [0x19d50000, 0x44800000, 0x44800000)
the space 699072K, 0% used [0x19d50000, 0x19f17db0, 0x19f17e00, 0x44800000)
Metaspace used 4072K, capacity 4120K, committed 4160K, reserved 4480K4G文件
[Full GC (System.gc()) [Tenured: 0K->1823K(699072K), 0.0281413 secs] 22398K->1823K(1013632K), [Metaspace: 4065K->4065K(4480K)], 0.0311212 secs] [Times: user=0.01 sys=0.02, real=0.03 secs]
[Full GC (System.gc()) [Tenured: 1823K->1824K(699072K), 0.0048135 secs] 13008K->1824K(1013632K), [Metaspace: 4066K->4066K(4480K)], 0.0048608 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1824K->1824K(699072K), 0.0093538 secs] 13008K->1824K(1013632K), [Metaspace: 4066K->4066K(4480K)], 0.0094431 secs] [Times: user=0.02 sys=0.00, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1824K->1163K(699072K), 0.0075926 secs] 7417K->1163K(1013632K), [Metaspace: 4066K->4066K(4480K)], 0.0076662 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1163K->1163K(699072K), 0.0115011 secs] 6755K->1163K(1013632K), [Metaspace: 4066K->4066K(4480K)], 0.0116041 secs] [Times: user=0.01 sys=0.00, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1163K->1164K(699072K), 0.0082543 secs] 6756K->1164K(1013632K), [Metaspace: 4066K->4066K(4480K)], 0.0083320 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1164K->1165K(699072K), 0.0129058 secs] 6756K->1165K(1013632K), [Metaspace: 4066K->4066K(4480K)], 0.0130133 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
channelCopy耗时:42
Heap
def new generation total 314560K, used 5592K [0x04800000, 0x19d50000, 0x19d50000)
eden space 279616K, 2% used [0x04800000, 0x04d761a8, 0x15910000)
from space 34944K, 0% used [0x15910000, 0x15910000, 0x17b30000)
to space 34944K, 0% used [0x17b30000, 0x17b30000, 0x19d50000)
tenured generation total 699072K, used 1165K [0x19d50000, 0x44800000, 0x44800000)
the space 699072K, 0% used [0x19d50000, 0x19e734c8, 0x19e73600, 0x44800000)
Metaspace used 4073K, capacity 4120K, committed 4160K, reserved 4480K6.多线程复制
1G文件
分块：8
步长：131072.00K(128.00M)
[Full GC (System.gc()) [Tenured: 0K->1870K(699072K), 0.0112641 secs] 44768K->1870K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0113534 secs] [Times: user=0.01 sys=0.02, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1870K->1871K(699072K), 0.0070772 secs] 24240K->1871K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0071387 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
multiThreadCopy耗时:5
Heap
def new generation total 314560K, used 33554K [0x04a00000, 0x19f50000, 0x19f50000)
eden space 279616K, 12% used [0x04a00000, 0x06ac4960, 0x15b10000)
from space 34944K, 0% used [0x15b10000, 0x15b10000, 0x17d30000)
to space 34944K, 0% used [0x17d30000, 0x17d30000, 0x19f50000)
tenured generation total 699072K, used 1871K [0x19f50000, 0x44a00000, 0x44a00000)
the space 699072K, 0% used [0x19f50000, 0x1a123ed8, 0x1a124000, 0x44a00000)
Metaspace used 4155K, capacity 4184K, committed 4288K, reserved 4480K
4G文件
分块：32
步长：131072.00K(128.00M)
[Full GC (System.gc()) [Tenured: 0K->1872K(699072K), 0.0186461 secs] 44768K->1872K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0187987 secs] [Times: user=0.02 sys=0.01, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1872K->1872K(699072K), 0.0131360 secs] 18649K->1872K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0132463 secs] [Times: user=0.02 sys=0.02, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1872K->1873K(699072K), 0.0070749 secs] 18649K->1873K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0071370 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1873K->1211K(699072K), 0.0064547 secs] 13058K->1211K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0065091 secs] [Times: user=0.02 sys=0.00, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1211K->1211K(699072K), 0.0067938 secs] 12395K->1211K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0068554 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1211K->1212K(699072K), 0.0046318 secs] 12396K->1212K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0046733 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1212K->1213K(699072K), 0.0050816 secs] 12397K->1213K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0051401 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1213K->1210K(699072K), 0.0123529 secs] 12398K->1210K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0124787 secs] [Times: user=0.01 sys=0.02, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1210K->1211K(699072K), 0.0121111 secs] 12395K->1211K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0122155 secs] [Times: user=0.02 sys=0.01, real=0.01 secs]
[Full GC (System.gc()) [Tenured: 1211K->1212K(699072K), 0.0119589 secs] 12396K->1212K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0120655 secs] [Times: user=0.01 sys=0.00, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1212K->1213K(699072K), 0.0050013 secs] 12397K->1213K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0050459 secs] [Times: user=0.02 sys=0.00, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1213K->1210K(699072K), 0.0096042 secs] 12397K->1210K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0096898 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1210K->1211K(699072K), 0.0127724 secs] 12395K->1211K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0128951 secs] [Times: user=0.02 sys=0.02, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1211K->1212K(699072K), 0.0069125 secs] 12396K->1212K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0069763 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1212K->1212K(699072K), 0.0123873 secs] 12396K->1212K(1013632K), [Metaspace: 4146K->4146K(4480K)], 0.0124939 secs] [Times: user=0.02 sys=0.02, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1212K->1211K(699072K), 0.0125100 secs] 17989K->1211K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0126220 secs] [Times: user=0.02 sys=0.00, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1211K->1212K(699072K), 0.0099254 secs] 12396K->1212K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0100129 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1212K->1213K(699072K), 0.0090147 secs] 12397K->1213K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0090928 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1213K->1213K(699072K), 0.0066715 secs] 12397K->1213K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0067331 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1213K->1211K(699072K), 0.0118469 secs] 12398K->1211K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0119464 secs] [Times: user=0.02 sys=0.02, real=0.01 secs]
[Full GC (System.gc()) [Tenured: 1211K->1212K(699072K), 0.0094466 secs] 12396K->1212K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0095368 secs] [Times: user=0.01 sys=0.02, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1212K->1212K(699072K), 0.0118130 secs] 12397K->1212K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0119286 secs] [Times: user=0.02 sys=0.00, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1212K->1213K(699072K), 0.0082931 secs] 12397K->1213K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0083596 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1213K->1211K(699072K), 0.0130539 secs] 12398K->1211K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0131914 secs] [Times: user=0.01 sys=0.02, real=0.01 secs]
[Full GC (System.gc()) [Tenured: 1211K->1212K(699072K), 0.0133806 secs] 12396K->1212K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0135109 secs] [Times: user=0.02 sys=0.02, real=0.01 secs]
[Full GC (System.gc()) [Tenured: 1212K->1212K(699072K), 0.0132605 secs] 12396K->1212K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0134015 secs] [Times: user=0.02 sys=0.00, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1212K->1213K(699072K), 0.0123650 secs] 12397K->1213K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0124783 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1213K->1211K(699072K), 0.0150080 secs] 12398K->1211K(1013632K), [Metaspace: 4149K->4149K(4480K)], 0.0151485 secs] [Times: user=0.02 sys=0.02, real=0.01 secs]
multiThreadCopy耗时:56
Heap
def new generation total 314560K, used 27961K [0x05200000, 0x1a750000, 0x1a750000)
eden space 279616K, 10% used [0x05200000, 0x06d4e7e8, 0x16310000)
from space 34944K, 0% used [0x16310000, 0x16310000, 0x18530000)
to space 34944K, 0% used [0x18530000, 0x18530000, 0x1a750000)
tenured generation total 699072K, used 1211K [0x1a750000, 0x45200000, 0x45200000)
the space 699072K, 0% used [0x1a750000, 0x1a87ec90, 0x1a87ee00, 0x45200000)
Metaspace used 4157K, capacity 4187K, committed 4288K, reserved 4480KOhter.创建4g文件
[Full GC (System.gc()) [Tenured: 0K->1837K(699072K), 0.0096224 secs] 22398K->1837K(1013632K), [Metaspace: 4253K->4253K(4480K)], 0.0096961 secs] [Times: user=0.02 sys=0.00, real=0.02 secs]
[Full GC (System.gc()) [Tenured: 1837K->1838K(699072K), 0.0053253 secs] 13022K->1838K(1013632K), [Metaspace: 4253K->4253K(4480K)], 0.0053815 secs] [Times: user=0.02 sys=0.00, real=0.01 secs]
[Full GC (System.gc()) [Tenured: 1838K->1839K(699072K), 0.0088826 secs] 13023K->1839K(1013632K), [Metaspace: 4253K->4253K(4480K)], 0.0089286 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
[Full GC (System.gc()) [Tenured: 1839K->1177K(699072K), 0.0044623 secs] 7431K->1177K(1013632K), [Metaspace: 4253K->4253K(4480K)], 0.0044984 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
[Full GC (System.gc()) [Tenured: 1177K->1178K(699072K), 0.0067081 secs] 6769K->1178K(1013632K), [Metaspace: 4253K->4253K(4480K)], 0.0067496 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
[Full GC (System.gc()) [Tenured: 1178K->1179K(699072K), 0.0045560 secs] 6770K->1179K(1013632K), [Metaspace: 4253K->4253K(4480K)], 0.0046011 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System.gc()) [Tenured: 1179K->1180K(699072K), 0.0039339 secs] 6771K->1180K(1013632K), [Metaspace: 4253K->4253K(4480K)], 0.0039759 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
Heap
def new generation total 314560K, used 5592K [0x05400000, 0x1a950000, 0x1a950000)
eden space 279616K, 2% used [0x05400000, 0x059761a8, 0x16510000)
from space 34944K, 0% used [0x16510000, 0x16510000, 0x18730000)
to space 34944K, 0% used [0x18730000, 0x18730000, 0x1a950000)
tenured generation total 699072K, used 1180K [0x1a950000, 0x45400000, 0x45400000)
the space 699072K, 0% used [0x1a950000, 0x1aa77090, 0x1aa77200, 0x45400000)
Metaspace used 4260K, capacity 4312K, committed 4416K, reserved 4480K结论：
1.FileChannel.transferTo()在小于2G时，效率最高，跟直接内核态拷贝（零拷贝）的机制有关。
2.系统直接fullgc，是因为直接new的大数组对象做buffer
3.buffer重复利用，避免触发GC，消除stop the world 停顿时间
在Java9 以及高版本中使用xlog参数打印jvm日志。