在软件系统中。IO速度比内存速度慢，IO读写在非常多情况下会是系统的瓶颈。
在java标准IO操作中，InputStream和OutputStream提供基于流的IO操作。以字节为处理单位；Reader和Writer实现了Buffered缓存，以字符为处理单位。
从Java1.4開始，添加NIO（New IO），添加缓存Buffer和通道Channel，以块为处理单位。是双向通道（可读可写。类似RandomAccessFile），支持锁和内存映射文件訪问接口。大大提升了IO速度。
下面样例简单測试常见IO操作的性能速度。
/**
* 測试不同io操作速度
*
* @author peter_wang
* @create-time 2014-6-4 下午12:52:48
*/
public class SpeedTest {
private static final String INPUT_FILE_PATH = "io_speed.txt";
private static final String OUTPUT_FILE_PATH = "io_speed_copy.txt";
/**
* @param args
*/
public static void main(String[] args) {
long ioStreamTime1 = ioStreamCopy();
System.out.println("io stream copy:" + ioStreamTime1);
long ioStreamTime2 = bufferedStreamCopy();
System.out.println("buffered stream copy:" + ioStreamTime2);
long ioStreamTime3 = nioStreamCopy();
System.out.println("nio stream copy:" + ioStreamTime3);
long ioStreamTime4 = nioMemoryStreamCopy();
System.out.println("nio memory stream copy:" + ioStreamTime4);
}
/**
* 普通文件流读写
*
* @return 操作的时间
*/
private static long ioStreamCopy() {
long costTime = -1;
FileInputStream is = null;
FileOutputStream os = null;
try {
long startTime = System.currentTimeMillis();
is = new FileInputStream(INPUT_FILE_PATH);
os = new FileOutputStream(OUTPUT_FILE_PATH);
int read = is.read();
while (read != -1) {
os.write(read);
read = is.read();
}
long endTime = System.currentTimeMillis();
costTime = endTime - startTime;
}
catch (FileNotFoundException e) {
e.printStackTrace();
}
catch (IOException e) {
e.printStackTrace();
}
finally {
try {
if (is != null) {
is.close();
}
if (os != null) {
os.close();
}
}
catch (IOException e) {
e.printStackTrace();
}
}
return costTime;
}
/**
* 增加缓存的文件流读写， Reader默认实现缓存。仅仅能读取字符文件，无法准确读取字节文件如图片视频等
*
* @return 操作的时间
*/
private static long bufferedStreamCopy() {
long costTime = -1;
FileReader reader = null;
FileWriter writer = null;
try {
long startTime = System.currentTimeMillis();
reader = new FileReader(INPUT_FILE_PATH);
writer = new FileWriter(OUTPUT_FILE_PATH);
int read = -1;
while ((read = reader.read()) != -1) {
writer.write(read);
}
writer.flush();
long endTime = System.currentTimeMillis();
costTime = endTime - startTime;
}
catch (FileNotFoundException e) {
e.printStackTrace();
}
catch (IOException e) {
e.printStackTrace();
}
finally {
try {
if (reader != null) {
reader.close();
}
if (writer != null) {
writer.close();
}
}
catch (IOException e) {
e.printStackTrace();
}
}
return costTime;
}
/**
* nio操作数据流
*
* @return 操作的时间
*/
private static long nioStreamCopy() {
long costTime = -1;
FileInputStream is = null;
FileOutputStream os = null;
FileChannel fi = null;
FileChannel fo = null;
try {
long startTime = System.currentTimeMillis();
is = new FileInputStream(INPUT_FILE_PATH);
os = new FileOutputStream(OUTPUT_FILE_PATH);
fi = is.getChannel();
fo = os.getChannel();
ByteBuffer buffer = ByteBuffer.allocate(1024);
while (true) {
buffer.clear();
int read = fi.read(buffer);
if (read == -1) {
break;
}
buffer.flip();
fo.write(buffer);
}
long endTime = System.currentTimeMillis();
costTime = endTime - startTime;
}
catch (FileNotFoundException e) {
e.printStackTrace();
}
catch (IOException e) {
e.printStackTrace();
}
finally {
try {
if (fi != null) {
fi.close();
}
if (fo != null) {
fo.close();
}
if (is != null) {
is.close();
}
if (os != null) {
os.close();
}
}
catch (IOException e) {
e.printStackTrace();
}
}
return costTime;
}
/**
* nio内存映射操作数据流
*
* @return 操作的时间
*/
private static long nioMemoryStreamCopy() {
long costTime = -1;
FileInputStream is = null;
//映射文件输出必须用RandomAccessFile
RandomAccessFile os = null;
FileChannel fi = null;
FileChannel fo = null;
try {
long startTime = System.currentTimeMillis();
is = new FileInputStream(INPUT_FILE_PATH);
os = new RandomAccessFile(OUTPUT_FILE_PATH, "rw");
fi = is.getChannel();
fo = os.getChannel();
IntBuffer iIb=fi.map(FileChannel.MapMode.READ_ONLY, 0, fi.size()).asIntBuffer();
IntBuffer oIb = fo.map(FileChannel.MapMode.READ_WRITE, 0, fo.size()).asIntBuffer();
while(iIb.hasRemaining()){
int read = iIb.get();
oIb.put(read);
}
long endTime = System.currentTimeMillis();
costTime = endTime - startTime;
}
catch (FileNotFoundException e) {
e.printStackTrace();
}
catch (IOException e) {
e.printStackTrace();
}
finally {
try {
if (fi != null) {
fi.close();
}
if (fo != null) {
fo.close();
}
if (is != null) {
is.close();
}
if (os != null) {
os.close();
}
}
catch (IOException e) {
e.printStackTrace();
}
}
return costTime;
}
}
执行结果：
io stream copy:384 buffered stream copy:125 nio stream copy:12 nio memory stream copy:10
结论分析：
最普通的InputStream操作耗时较长。添加了缓存后速度添加了，用了nio和内存映射訪问文件。速度最快。
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