正如标题所说,我正在寻找将整数数组写入文件的最快速的方法.阵列的大小会有所不同,并且实际上可以包含2500到25 000 000个内部的任何地方.
以下是我目前使用的代码：
DataOutputStream writer = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(filename))); for (int d : data) writer.writeInt(d);
鉴于DataOutputStream有一个写入字节数组的方法,我已经尝试将int数组转换为字节数组,如下所示：
private static byte[] integersToBytes(int[] values) throws IOException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
DataOutputStream dos = new DataOutputStream(baos);
for (int i = 0; i < values.length; ++i) {
dos.writeInt(values[i]);
}
return baos.toByteArray();
}
就像这样：
private static byte[] integersToBytes2(int[] src) {
int srcLength = src.length;
byte[] dst = new byte[srcLength << 2];
for (int i = 0; i < srcLength; i++) {
int x = src[i];
int j = i << 2;
dst[j++] = (byte) ((x >>> 0) & 0xff);
dst[j++] = (byte) ((x >>> 8) & 0xff);
dst[j++] = (byte) ((x >>> 16) & 0xff);
dst[j++] = (byte) ((x >>> 24) & 0xff);
}
return dst;
}
两者似乎都稍微增加了一点,约占5％.我没有严格测试他们,以确认.
解决方法
我看了三个选择：
>使用DataOutputStream;
>使用ObjectOutputStream(对于Serializable对象,int []是);和
>使用FileChannel.
结果是
DataOutputStream wrote 1,000,000 ints in 3,159.716 ms ObjectOutputStream wrote 1,000 ints in 295.602 ms FileChannel wrote 1,000 ints in 110.094 ms
所以NIO版本是最快的.它还具有允许编辑的优点,这意味着您可以轻松地更改一个int,而ObjectOutputStream将需要读取整个数组,修改它并将其写入文件.
代码如下：
private static final int NUM_INTS = 1000000;
interface IntWriter {
void write(int[] ints);
}
public static void main(String[] args) {
int[] ints = new int[NUM_INTS];
Random r = new Random();
for (int i=0; i<NUM_INTS; i++) {
ints[i] = r.nextInt();
}
time("DataOutputStream",new IntWriter() {
public void write(int[] ints) {
storeDO(ints);
}
},ints);
time("ObjectOutputStream",new IntWriter() {
public void write(int[] ints) {
storeOO(ints);
}
},ints);
time("FileChannel",new IntWriter() {
public void write(int[] ints) {
storeFC(ints);
}
},ints);
}
private static void time(String name,IntWriter writer,int[] ints) {
long start = System.nanoTime();
writer.write(ints);
long end = System.nanoTime();
double ms = (end - start) / 1000000d;
System.out.printf("%s wrote %,d ints in %,.3f ms%n",name,ints.length,ms);
}
private static void storeOO(int[] ints) {
ObjectOutputStream out = null;
try {
out = new ObjectOutputStream(new FileOutputStream("object.out"));
out.writeObject(ints);
} catch (IOException e) {
throw new RuntimeException(e);
} finally {
safeClose(out);
}
}
private static void storeDO(int[] ints) {
DataOutputStream out = null;
try {
out = new DataOutputStream(new FileOutputStream("data.out"));
for (int anInt : ints) {
out.write(anInt);
}
} catch (IOException e) {
throw new RuntimeException(e);
} finally {
safeClose(out);
}
}
private static void storeFC(int[] ints) {
FileOutputStream out = null;
try {
out = new FileOutputStream("fc.out");
FileChannel file = out.getChannel();
ByteBuffer buf = file.map(FileChannel.MapMode.READ_WRITE,4 * ints.length);
for (int i : ints) {
buf.putInt(i);
}
file.close();
} catch (IOException e) {
throw new RuntimeException(e);
} finally {
safeClose(out);
}
}
private static void safeClose(OutputStream out) {
try {
if (out != null) {
out.close();
}
} catch (IOException e) {
// do nothing
}
}
