java - 如何以编程方式比较两个 java.io.File

Question

有什么方法可以在 Android 中比较两个文件？

For example: I am having two files under same folder, which are same. They are same(also in size), but their namea are like myFileA.pdf and myFileB.pdf. So how can I identify that they are same or not.

我已经尝试过的:

• compareTo() 方法:尝试了 myFileA.compare(myFileB)，但这给出了一些奇怪的值，例如 -1、-2、等。我认为这些值是文件的 PATH 相关的。
• myFile.length():但在一些极少数情况下(非常罕见的情况下)，两个不同的文件可以具有相同的大小，所以我认为这不是正确的方法。

NOTE: I told that files are under same folder for just example, they can be anywhere like myFileA.pdf can be in NewFolder1 and myFileB.pdf can be in NewFolder2.

Answer 1

前段时间我编写了一个实用程序来以高效的方式比较两个流的内容:当发现第一个差异时停止比较。 这是我认为很容易 self 解释的代码:

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Arrays;
import java.util.Comparator;

public class FileComparator implements Comparator<File> {

    @Override
    public int compare(File file1, File file2) {

        // one or both null
        if (file1 == file2) {
            return 0;
        } else if (file1 == null && file2 != null) {
            return -1;
        } else if (file1 != null && file2 == null) {
            return 1;
        }

        if (file1.isDirectory() || file2.isDirectory()) {
            throw new IllegalArgumentException("Unable to compare directory content");
        }

        // not same size
        if (file1.length() < file2.length()) {
            return -1;
        } else if (file1.length() > file2.length()) {
            return 1;
        }

        try {
            return compareContent(file1, file2);
        } catch (IOException e) {
            throw new RuntimeException(e.getMessage(), e);
        }

    }

    private int bufferSize(long fileLength) {
        int multiple = (int) (fileLength / 1024);
        if (multiple <= 1) {
            return 1024;
        } else if (multiple <= 8) {
            return 1024 * 2;
        } else if (multiple <= 16) {
            return 1024 * 4;
        } else if (multiple <= 32) {
            return 1024 * 8;
        } else if (multiple <= 64) {
            return 1024 * 16;
        } else {
            return 1024 * 64;
        }
    }

    private int compareContent(File file1, File file2) throws IOException {

        final int BUFFER_SIZE = bufferSize(file1.length());

        // check content
        try (BufferedInputStream is1 = new BufferedInputStream(new FileInputStream(file1), BUFFER_SIZE); BufferedInputStream is2 = new BufferedInputStream(new FileInputStream(file2), BUFFER_SIZE);) {

            byte[] b1 = new byte[BUFFER_SIZE];
            byte[] b2 = new byte[BUFFER_SIZE];

            int read1 = -1;
            int read2 = -1;
            int read = -1;

            do {
                read1 = is1.read(b1);
                read2 = is2.read(b2);

                if (read1 < read2) {
                    return -1;
                } else if (read1 > read2) {
                    return 1;
                } else {
                    // read1 is equals to read2
                    read = read1;
                }

                if (read >= 0) {
                    if (read != BUFFER_SIZE) {
                        // clear the buffer not filled from the read
                        Arrays.fill(b1, read, BUFFER_SIZE, (byte) 0);
                        Arrays.fill(b2, read, BUFFER_SIZE, (byte) 0);
                    }
                    // compare the content of the two buffers
                    if (!Arrays.equals(b1, b2)) {
                        return new String(b1).compareTo(new String(b2));
                    }
                }
            } while (read >= 0);

            // no difference found
            return 0;
        }
    }
}