由于OP渴望了解如何使用NIO来完成此操作。
由于文件很小，很难看到差异，但是可以测量。
public static void main(String... args) throws IOException {
PrintWriter pw = new PrintWriter("abc.log");
for (int i = 0; i < 100 * 1000; i++) {
pw.println("0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789");
}
pw.close();
long start2 = System.nanoTime();
int count2 = 0;
BufferedReader br = new BufferedReader(new FileReader("abc.log"));
while (br.readLine() != null) count2++;
br.close();
long time2 = System.nanoTime() - start2;
System.out.printf("IO: Took %,d ms to read %,d lines%n", time2 / 1000 / 1000, count2);
long start = System.nanoTime();
FileChannel fc = new FileInputStream("abc.log").getChannel();
ByteBuffer bb = ByteBuffer.allocateDirect((int) fc.size());
fc.read(bb);
fc.close();
bb.flip();
CharBuffer cb = ByteBuffer.allocateDirect(bb.remaining() * 2).order(ByteOrder.nativeOrder()).asCharBuffer();
CharsetDecoder cd = Charset.forName("UTF-8").newDecoder();
cd.decode(bb, cb, true);
cb.flip();
StringBuilder sb = new StringBuilder();
int count = 0;
while (cb.remaining() > 0) {
char ch = cb.get();
if (isEndOfLine(cb, ch)) {
// process sb
count++;
sb.setLength(0);
} else {
sb.append(ch);
}
}
long time = System.nanoTime() - start;
System.out.printf("NIO as UTF-8: Took %,d ms to read %,d lines%n", time / 1000 / 1000, count);
long start3 = System.nanoTime();
FileChannel fc2 = new FileInputStream("abc.log").getChannel();
MappedByteBuffer bb2 = fc2.map(FileChannel.MapMode.READ_ONLY, 0, fc2.size());
bb.flip();
StringBuilder sb3 = new StringBuilder();
int count3 = 0;
while (bb2.remaining() > 0) {
char ch = (char) bb2.get();
if (isEndOfLine(bb2, ch)) {
// process sb
count3++;
sb3.setLength(0);
} else {
sb3.append(ch);
}
}
fc2.close();
long time3 = System.nanoTime() - start3;
System.out.printf("NIO as ISO-8859-1: Took %,d ms to read %,d lines%n", time3 / 1000 / 1000, count3);
}
private static boolean isEndOfLine(CharBuffer cb, char ch) {
if (ch == '\r') {
if (cb.remaining() >= 1 && cb.get() == '\n') {
return true;
}
cb.position(cb.position() - 1);
return true;
} else if (ch == '\n') {
return true;
}
return false;
}
private static boolean isEndOfLine(ByteBuffer bb, char ch) {
if (ch == '\r') {
if (bb.remaining() >= 1 && bb.get() == '\n') {
return true;
}
bb.position(bb.position() - 1);
return true;
} else if (ch == '\n') {
return true;
}
return false;
}
打印每一行的长度为102字节，因此文件约为10 MB。
IO: Took 112 ms to read 100,000 lines
NIO as UTF-8: Took 207 ms to read 100,000 lines
NIO as ISO-8859-1: Took 87 ms to read 100,000 lines
如前所述，使用NIO节省35毫秒的额外复杂性不太值得。
顺便说一句：如果您有硬盘驱动器，并且文件不在内存中，则仅驱动器的速度至关重要。
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