用过的读写

1、从文件中读取三行数据

String[] lines = new String[3];
boolean readPointerFileSuccess = true;

try (Scanner scanner = new Scanner(pointerFile)) {
    for (int i = 0; i < lines.length; i++) {
        if (scanner.hasNextLine()) {
            lines[i] = scanner.nextLine();
        } else {
            readPointerFileSuccess = false;
        }
    }
}

 2、写入文件

try(PrintWriter writer = new PrintWriter(pointerFile)){
    writer.println(logFileName);
    writer.println(pointer);
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    String time = sdf.format(readDate);
    writer.println(time);
    writer.flush();//立即写入
}

3、RandomAccessFile读取数据

RandomAccessFile randAccessFile = new RandomAccessFile(fileName, "r");
// 定位到文件的 pointer
randAccessFile.seek(pointer);

String line = readLine(randAccessFile, "GBK");
        
        
public String readLine(RandomAccessFile randAccessFile, String charset) throws IOException {

ByteArrayOutputStream baos = new ByteArrayOutputStream();

int c = -1;
boolean eol = false;

while (!eol) {
    switch (c = randAccessFile.read()) {
    case -1:
    case '
':
        eol = true;
        break;
    case '
':
        eol = true;
        long cur = randAccessFile.getFilePointer();
        if ((randAccessFile.read()) != '
') {
            randAccessFile.seek(cur);
        }
        break;
    default:
        baos.write(c);
        break;
    }
}

if ((c == -1) && (baos.size() == 0)) {
    return null;
}

return new String(baos.toByteArray(), charset);
}

4、RandomAccessFile读取数据

    File file = new File(info.getName());

    RandomAccessFile raf = null;
    try {
        raf = new RandomAccessFile(file, "rw");
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }

    FileChannel cha = raf.getChannel();

    ByteBuffer buf = ByteBuffer.allocate(1024);

    int size = 0;

    StringBuffer sb = new StringBuffer();

    try {
        while ((size = cha.read(buf)) != -1) {

            buf.flip();

            byte[] buff = new byte[size];

            buf.get(buff);

            sb.append(new String(buff, 0, size));

        }
    } catch (IOException e) {
        e.printStackTrace();
    }

    String[] s = sb.toString().split("\}\,\{");