在軟體系統中。IO速度比記憶體速度慢,IO讀寫在非常多情況下會是系統的瓶頸。
在java标準IO操作中,InputStream和OutputStream提供基于流的IO操作。以位元組為處理機關;Reader和Writer實作了Buffered緩存,以字元為處理機關。
從Java1.4開始,添加NIO(New IO),添加緩存Buffer和通道Channel,以塊為處理機關。是雙向通道(可讀可寫。類似RandomAccessFile),支援鎖和記憶體映射檔案訪問接口。大大提升了IO速度。
下面樣例簡單測試常見IO操作的性能速度。
/**
* 測試不同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);
}
/**
* 普通檔案流讀寫
*
* @return 操作的時間
*/
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;
}
/**
* 增加緩存的檔案流讀寫, Reader預設實作緩存。僅僅能讀取字元檔案,無法準确讀取位元組檔案如圖檔視訊等
*
* @return 操作的時間
*/
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操作資料流
*
* @return 操作的時間
*/
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記憶體映射操作資料流
*
* @return 操作的時間
*/
private static long nioMemoryStreamCopy() {
long costTime = -1;
FileInputStream is = null;
//映射檔案輸出必須用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;
}
}
執行結果:
io stream copy:384
buffered stream copy:125
nio stream copy:12
nio memory stream copy:10
結論分析: