Android中获取文件（夹）属性

在Android中如果需要获取一个文件（夹）的属性，可以直接使用File等获取，这些API都有说明，但也仅限于获取一般可以见的属性，如读写权限修改时间等，但涉及到文件系统的属性（如inode,blocksize）等就不能直接获取。当然使用第三方工具命令,像stat（in busybox）还是可以的

但这种方式却不太方便（命令非系统自带，app中使用获取数据也比较麻烦），这种方法基本上可以抛弃。

到头来还是得看源码，在frameworks\base\core\java\android\os目录下有一个定义如下:

/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.os;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.util.regex.Pattern;
import java.util.zip.CRC32;
import java.util.zip.CheckedInputStream;

/**
 * Tools for managing files.  Not for public consumption.
 * @hide
 */
public class FileUtils {
    public static final int S_IRWXU = 00700;
    public static final int S_IRUSR = 00400;
    public static final int S_IWUSR = 00200;
    public static final int S_IXUSR = 00100;

    public static final int S_IRWXG = 00070;
    public static final int S_IRGRP = 00040;
    public static final int S_IWGRP = 00020;
    public static final int S_IXGRP = 00010;

    public static final int S_IRWXO = 00007;
    public static final int S_IROTH = 00004;
    public static final int S_IWOTH = 00002;
    public static final int S_IXOTH = 00001;

    /**
     * File status information. This class maps directly to the POSIX stat structure.
     * @hide
     */
    public static final class FileStatus {
        public int dev;
        public int ino;
        public int mode;
        public int nlink;
        public int uid;
        public int gid;
        public int rdev;
        public long size;
        public int blksize;
        public long blocks;
        public long atime;
        public long mtime;
        public long ctime;
    }

    /**
     * Get the status for the given path. This is equivalent to the POSIX stat(2) system call. 
     * @param path The path of the file to be stat'd.
     * @param status Optional argument to fill in. It will only fill in the status if the file
     * exists. 
     * @return true if the file exists and false if it does not exist. If you do not have 
     * permission to stat the file, then this method will return false.
     */
    public static boolean getFileStatus(String path, FileStatus status) {
        StrictMode.noteDiskRead();
        return getFileStatusNative(path, status);
    }

    private static native boolean getFileStatusNative(String path, FileStatus status);

    /** Regular expression for safe filenames: no spaces or metacharacters */
    private static final Pattern SAFE_FILENAME_PATTERN = Pattern.compile("[\\w%+,./=_-]+");

    public static native int setPermissions(String file, int mode, int uid, int gid);

    public static native int getPermissions(String file, int[] outPermissions);

    public static native int setUMask(int mask);

    /** returns the FAT file system volume ID for the volume mounted 
     * at the given mount point, or -1 for failure
     * @param mountPoint point for FAT volume
     * @return volume ID or -1
     */
    public static native int getFatVolumeId(String mountPoint);

    /**
     * Perform an fsync on the given FileOutputStream.  The stream at this
     * point must be flushed but not yet closed.
     */
    public static boolean sync(FileOutputStream stream) {
        try {
            if (stream != null) {
                stream.getFD().sync();
            }
            return true;
        } catch (IOException e) {
        }
        return false;
    }

    // copy a file from srcFile to destFile, return true if succeed, return
    // false if fail
    public static boolean copyFile(File srcFile, File destFile) {
        boolean result = false;
        try {
            InputStream in = new FileInputStream(srcFile);
            try {
                result = copyToFile(in, destFile);
            } finally  {
                in.close();
            }
        } catch (IOException e) {
            result = false;
        }
        return result;
    }

    /**
     * Copy data from a source stream to destFile.
     * Return true if succeed, return false if failed.
     */
    public static boolean copyToFile(InputStream inputStream, File destFile) {
        try {
            if (destFile.exists()) {
                destFile.delete();
            }
            FileOutputStream out = new FileOutputStream(destFile);
            try {
                byte[] buffer = new byte[4096];
                int bytesRead;
                while ((bytesRead = inputStream.read(buffer)) >= 0) {
                    out.write(buffer, 0, bytesRead);
                }
            } finally {
                out.flush();
                try {
                    out.getFD().sync();
                } catch (IOException e) {
                }
                out.close();
            }
            return true;
        } catch (IOException e) {
            return false;
        }
    }

    /**
     * Check if a filename is "safe" (no metacharacters or spaces).
     * @param file  The file to check
     */
    public static boolean isFilenameSafe(File file) {
        // Note, we check whether it matches what's known to be safe,
        // rather than what's known to be unsafe.  Non-ASCII, control
        // characters, etc. are all unsafe by default.
        return SAFE_FILENAME_PATTERN.matcher(file.getPath()).matches();
    }

    /**
     * Read a text file into a String, optionally limiting the length.
     * @param file to read (will not seek, so things like /proc files are OK)
     * @param max length (positive for head, negative of tail, 0 for no limit)
     * @param ellipsis to add of the file was truncated (can be null)
     * @return the contents of the file, possibly truncated
     * @throws IOException if something goes wrong reading the file
     */
    public static String readTextFile(File file, int max, String ellipsis) throws IOException {
        InputStream input = new FileInputStream(file);
        try {
            long size = file.length();
            if (max > 0 || (size > 0 && max == 0)) {  // "head" mode: read the first N bytes
                if (size > 0 && (max == 0 || size < max)) max = (int) size;
                byte[] data = new byte[max + 1];
                int length = input.read(data);
                if (length <= 0) return "";
                if (length <= max) return new String(data, 0, length);
                if (ellipsis == null) return new String(data, 0, max);
                return new String(data, 0, max) + ellipsis;
            } else if (max < 0) {  // "tail" mode: keep the last N
                int len;
                boolean rolled = false;
                byte[] last = null, data = null;
                do {
                    if (last != null) rolled = true;
                    byte[] tmp = last; last = data; data = tmp;
                    if (data == null) data = new byte[-max];
                    len = input.read(data);
                } while (len == data.length);

                if (last == null && len <= 0) return "";
                if (last == null) return new String(data, 0, len);
                if (len > 0) {
                    rolled = true;
                    System.arraycopy(last, len, last, 0, last.length - len);
                    System.arraycopy(data, 0, last, last.length - len, len);
                }
                if (ellipsis == null || !rolled) return new String(last);
                return ellipsis + new String(last);
            } else {  // "cat" mode: size unknown, read it all in streaming fashion
                ByteArrayOutputStream contents = new ByteArrayOutputStream();
                int len;
                byte[] data = new byte[1024];
                do {
                    len = input.read(data);
                    if (len > 0) contents.write(data, 0, len);
                } while (len == data.length);
                return contents.toString();
            }
        } finally {
            input.close();
        }
    }

   /**
     * Writes string to file. Basically same as "echo -n $string > $filename"
     *
     * @param filename
     * @param string
     * @throws IOException
     */
    public static void stringToFile(String filename, String string) throws IOException {
        FileWriter out = new FileWriter(filename);
        try {
            out.write(string);
        } finally {
            out.close();
        }
    }

    /**
     * Computes the checksum of a file using the CRC32 checksum routine.
     * The value of the checksum is returned.
     *
     * @param file  the file to checksum, must not be null
     * @return the checksum value or an exception is thrown.
     */
    public static long checksumCrc32(File file) throws FileNotFoundException, IOException {
        CRC32 checkSummer = new CRC32();
        CheckedInputStream cis = null;

        try {
            cis = new CheckedInputStream( new FileInputStream(file), checkSummer);
            byte[] buf = new byte[128];
            while(cis.read(buf) >= 0) {
                // Just read for checksum to get calculated.
            }
            return checkSummer.getValue();
        } finally {
            if (cis != null) {
                try {
                    cis.close();
                } catch (IOException e) {
                }
            }
        }
    }
}

从注释可知，这是一个隐藏的类，于是很自然就想到了反射了，我们的目标是要获取到FileStatus的内容，

try {
    // 获取FileUtils类
    Class<?> fileUtilClass = Class.forName("android.os.FileUtils");

    // 获取FileStatus类
    Class<?> fileStatusClass = Class.forName("android.os.FileUtils$FileStatus");

    // getFileStatus是一个native方法，意义如方法名
    Method getFileStatus = fileUtilClass.getMethod("getFileStatus", String.class, fileStatusClass);

    // 传入的status方法是一个引用，在getFileStatus方法内会修改status对象的内容
    Object status = fileStatusClass.newInstance();
    boolean invokeSuc = (Boolean) getFileStatus.invoke(fileUtilClass.newInstance(), path, status);

    if (invokeSuc) {
        // 如果调用成功就可以直接获取对应的成员变量了
        Field field = fileStatusClass.getField("ino");

        inode = field.getInt(status);
    }
} catch (Exception e) {

}

当然也可以获取其他成员，不再赘述。

写完了