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public class FileRead {
private static final Logger LOGGER = LoggerFactory.getLogger(FileRead.class);
private static final Charset UTF8 = StandardCharsets.UTF_8;
// 回车符
private static final int LF = 10;
// 换行符
private static final int CR = 13;
public static void main(String[] args) {
String file = "C:\\ProgramData\\chocolatey\\logs\\chocolatey.log";
StopWatch stopWatch = StopWatch.create("1");
// run(() -> byteRead(file), stopWatch);
run(() -> bufferedRead(file), stopWatch);
run(() -> streamRead(file), stopWatch);
run(() -> scannerRead(file), stopWatch);
run(() -> readLine(file), stopWatch);
LOGGER.info(stopWatch.prettyPrint());
}
/**
* 按字节读取
*/
// public static void byteRead(String file) {
// try (InputStream is = new FileInputStream(new File(file))) {
// while (is.read() != -1) {
// // do something
// }
// } catch (Exception e) {
// LOGGER.error("错误", e);
// }
// }
/**
* BufferReader按行读取
*/
public static void bufferedRead(String file) {
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
while (br.readLine() != null) {
// do something
}
} catch (IOException e) {
LOGGER.error("错误", e);
}
}
/**
* Stream按行读取
*/
public static void streamRead(String file) {
try (Stream<String> stream = Files.lines(Paths.get(file))) {
} catch (IOException e) {
LOGGER.error("错误", e);
}
}
/**
* Scanner按行读取
*/
public static void scannerRead(String file) {
try (Scanner scan = new Scanner(new File(file))) {
while (scan.hasNextLine()) {
scan.nextLine();
}
} catch (IOException e) {
LOGGER.error("错误", e);
}
}
/**
* NIO按行读取
*/
public static void readLine(String fileName) {
try (RandomAccessFile randomAccessFile = new RandomAccessFile(fileName, "rw");
FileChannel channel = randomAccessFile.getChannel()) {
// 每次读取的buffer
ByteBuffer buffer = ByteBuffer.allocate(1024 * 1024);
// 期望每行占用的buffer
ByteBuffer stringBuffer = ByteBuffer.allocate(20);
// 从文件中读数据到buffer中
while (channel.read(buffer) != -1) {
// 切换模式，写->读
buffer.flip();
while (buffer.hasRemaining()) {
byte b = buffer.get();
// 换行或回车
if (b == LF || b == CR) {
stringBuffer.flip();
// 解码已经读到的一行所对应的字节
UTF8.decode(stringBuffer).toString();
// System.out.println(line + "----------");
stringBuffer.clear();
} else {
// 空间不够扩容
if (!stringBuffer.hasRemaining()) {
stringBuffer = reAllocate(stringBuffer);
}
stringBuffer.put(b);
}
}
// 清空,position位置为0，limit=capacity
buffer.clear();
}
} catch (Exception e) {
LOGGER.error("错误", e);
}
}
private static ByteBuffer reAllocate(ByteBuffer stringBuffer) {
final int capacity = stringBuffer.capacity();
// 扩容至两倍
byte[] newBuffer = new byte[capacity * 2];
System.arraycopy(stringBuffer.array(), 0, newBuffer, 0, capacity);
// 生成新的ByteBuffer，并移动到position
return (ByteBuffer) ByteBuffer.wrap(newBuffer).position(capacity);
}
private static void run(Runnable r, StopWatch sw) {
sw.start();
r.run();
sw.stop();
}
}
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