java - 获取读取文件的进度

Question

这是我的java代码的一部分，我想获取从文件读取的字节数，我在每个循环周期中增加4个字节，因为整数的大小是4个字节，但是这段代码无法正常工作，该代码的循环运行超出了文件的大小。请解决问题。

import java.io.File;
import java.util.Scanner;



public class S {


    public S() throws Exception {

        Scanner sc = new Scanner(new File("file.txt"));

        for(int i=0; sc.hasNext(); i+=4) {
            sc.nextInt();
            System.out.println("Read = "+i+" bytes");
        }

        System.out.println("done");
    }


    public static void main(String arg[]) throws Exception {
        new S();
    }

}

Answer 1

扫描仪不是为此类用例而设计的。扫描仪将读取比当前使用的更多的数据 - 如果您跟踪写入的字节，您将获得预期的其他结果:

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.Scanner;



public class S {


    private final static class ProgressStream extends FileInputStream {
        private int bytesRead;

        private ProgressStream(File file) throws FileNotFoundException {
            super(file);
        }

        @Override
        public int read() throws IOException {
            int b = super.read();
            if (b != -1)
                bytesRead++;
            return b;
        }

        @Override
        public int read(byte[] b) throws IOException {
            int read = super.read(b);
            if (read != -1)
                bytesRead += read;
            return read;
        }

        @Override
        public int read(byte[] b, int off, int len) throws IOException {
            int read = super.read(b, off, len);
            if (read != -1)
                bytesRead += read;
            return read;
        }
    }

    public S() throws Exception {

        ProgressStream progressStream = new ProgressStream(new File("file.txt"));

        Scanner sc = new Scanner(progressStream);

        while (sc.hasNext()) {
            sc.nextInt();
            System.out.println("Read = " + progressStream.bytesRead + " bytes");
        }

        System.out.println("done");
    }


    public static void main(String arg[]) throws Exception {
        new S();
    }

}

对于输入文件

123 456   789

输出

Read = 13 bytes
Read = 13 bytes
Read = 13 bytes
done

<小时/>

因此，您必须自己实现类似扫描仪的功能...

import java.io.File;
import java.io.FileInputStream;



public class S {

    public S() throws Exception {

        FileInputStream stream = new FileInputStream(new File("file.txt"));

        int b;
        StringBuilder lastDigits = new StringBuilder();
        int read = 0;
        while ((b = stream.read()) != -1) {
            read++;
            char c = (char) b;
            if (Character.isDigit(c)) {
                lastDigits.append(c);
            } else if (lastDigits.length() > 0) {
                System.out.println("found int "+Integer.parseInt(lastDigits.toString()));
                System.out.println("Read = "+read+" bytes");
                lastDigits = new StringBuilder();
            }
        }

        if (lastDigits.length() > 0) {
            System.out.println("found int "+Integer.parseInt(lastDigits.toString()));
            System.out.println("Read = "+read+" bytes");
        }

        System.out.println("done");
    }


    public static void main(String arg[]) throws Exception {
        new S();
    }

}

将输出

found int 123
Read = 4 bytes
found int 456
Read = 8 bytes
found int 789
Read = 13 bytes
done