Android使用DocumentFile读写外置存储的问题

最近在维护项目，app遇到安装在高版本的Android时，以往直接授权和new File(path)的形式不再支持，日志也是说Permission denied。。。。。好吧，换为DocumentFile。

经过一番操作，也终于实再对存储目录的读和写了，下面记录一下：

首先建一个DocumentFile的Utils类：

import android.annotation.TargetApi;
import android.content.Context;
import android.content.SharedPreferences;
import android.net.Uri;
import android.os.Build;
import android.os.ParcelFileDescriptor;
import android.preference.PreferenceManager;
import android.provider.DocumentsContract;
import android.util.Log;

import androidx.documentfile.provider.DocumentFile;

import java.io.File;
import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.util.ArrayList;
import java.util.List;

public class DocumentsUtils {

    private static final String TAG = DocumentsUtils.class.getSimpleName();

    public static final int OPEN_DOCUMENT_TREE_CODE = 8000;

    private static List<String> sExtSdCardPaths = new ArrayList<>();

    private DocumentsUtils() {

    }

    public static void cleanCache() {
        sExtSdCardPaths.clear();
    }

    /**
     * Get a list of external SD card paths. (Kitkat or higher.)
     *
     * @return A list of external SD card paths.
     */
    @TargetApi(Build.VERSION_CODES.KITKAT)
    private static String[] getExtSdCardPaths(Context context) {
        if (sExtSdCardPaths.size() > 0) {
            return sExtSdCardPaths.toArray(new String[0]);
        }
        for (File file : context.getExternalFilesDirs("external")) {
            if (file != null && !file.equals(context.getExternalFilesDir("external"))) {
                int index = file.getAbsolutePath().lastIndexOf("/Android/data");
                if (index < 0) {
                    Log.w(TAG, "Unexpected external file dir: " + file.getAbsolutePath());
                } else {
                    String path = file.getAbsolutePath().substring(0, index);
                    try {
                        path = new File(path).getCanonicalPath();
                    } catch (IOException e) {
                        // Keep non-canonical path.
                    }
                    sExtSdCardPaths.add(path);
                }
            }
        }
        if (sExtSdCardPaths.isEmpty()) sExtSdCardPaths.add("/storage/sdcard1");
        return sExtSdCardPaths.toArray(new String[0]);
    }

    /**
     * Determine the main folder of the external SD card containing the given file.
     *
     * @param file the file.
     * @return The main folder of the external SD card containing this file, if the file is on an SD
     * card. Otherwise,
     * null is returned.
     */
    @TargetApi(Build.VERSION_CODES.KITKAT)
    private static String getExtSdCardFolder(final File file, Context context) {
        String[] extSdPaths = getExtSdCardPaths(context);
        try {
            for (int i = 0; i < extSdPaths.length; i++) {
                if (file.getCanonicalPath().startsWith(extSdPaths[i])) {
                    return extSdPaths[i];
                }
            }
        } catch (IOException e) {
            return null;
        }
        return null;
    }

    /**
     * Determine if a file is on external sd card. (Kitkat or higher.)
     *
     * @param file The file.
     * @return true if on external sd card.
     */
    @TargetApi(Build.VERSION_CODES.KITKAT)
    public static boolean isOnExtSdCard(final File file, Context c) {
        return getExtSdCardFolder(file, c) != null;
    }

    /**
     * Get a DocumentFile corresponding to the given file (for writing on ExtSdCard on Android 5).
     * If the file is not
     * existing, it is created.
     *
     * @param file        The file.
     * @param isDirectory flag indicating if the file should be a directory.
     * @return The DocumentFile
     */
    public static DocumentFile getDocumentFile(final File file, final boolean isDirectory,
                                               Context context) {

        if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.KITKAT) {
            return DocumentFile.fromFile(file);
        }

        String baseFolder = getExtSdCardFolder(file, context);
    //    Log.i(TAG,"lum_ baseFolder " + baseFolder);
        boolean originalDirectory = false;
        if (baseFolder == null) {
            return null;
        }

        String relativePath = null;
        try {
            String fullPath = file.getCanonicalPath();
            if (!baseFolder.equals(fullPath)) {
                relativePath = fullPath.substring(baseFolder.length() + 1);
            } else {
                originalDirectory = true;
            }
        } catch (IOException e) {
            return null;
        } catch (Exception f) {
            originalDirectory = true;
            //continue
        }
        String as = PreferenceManager.getDefaultSharedPreferences(context).getString(baseFolder,
                null);

        Uri treeUri = null;
        if (as != null) treeUri = Uri.parse(as);
        if (treeUri == null) {
            return null;
        }

        // start with root of SD card and then parse through document tree.
        DocumentFile document = DocumentFile.fromTreeUri(context, treeUri);
        if (originalDirectory) return document;
        String[] parts = relativePath.split("/");
        for (int i = 0; i < parts.length; i++) {
            DocumentFile nextDocument = document.findFile(parts[i]);

            if (nextDocument == null) {
                if ((i < parts.length - 1) || isDirectory) {
                    nextDocument = document.createDirectory(parts[i]);
                } else {
                    nextDocument = document.createFile("image", parts[i]);
                }
            }
            document = nextDocument;
        }

        return document;
    }

    public static boolean mkdirs(Context context, File dir) {
        boolean res = dir.mkdirs();
        if (!res) {
            if (DocumentsUtils.isOnExtSdCard(dir, context)) {
                DocumentFile documentFile = DocumentsUtils.getDocumentFile(dir, true, context);
                res = documentFile != null && documentFile.canWrite();
            }
        }
        return res;
    }

    public static boolean delete(Context context, File file) {
        boolean ret = file.delete();

        if (!ret && DocumentsUtils.isOnExtSdCard(file, context)) {
            DocumentFile f = DocumentsUtils.getDocumentFile(file, false, context);
            if (f != null) {
                ret = f.delete();
            }
        }
        return ret;
    }

    public static boolean canWrite(File file) {
        boolean res = file.exists() && file.canWrite();

        if (!res && !file.exists()) {
            try {
                if (!file.isDirectory()) {
                    res = file.createNewFile() && file.delete();
                } else {
                    res = file.mkdirs() && file.delete();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return res;
    }

    public static boolean canWrite(Context context, File file) {
        boolean res = canWrite(file);

        if (!res && DocumentsUtils.isOnExtSdCard(file, context)) {
            DocumentFile documentFile = DocumentsUtils.getDocumentFile(file, true, context);
            res = documentFile != null && documentFile.canWrite();
        }
        return res;
    }

    /**
     * 重命名
     * @param context
     * @param src
     * @param dest
     * @return
     */
    public static boolean renameTo(Context context, File src, File dest) {
        boolean res = src.renameTo(dest);

        if (!res && isOnExtSdCard(dest, context)) {
            DocumentFile srcDoc;
            if (isOnExtSdCard(src, context)) {
                srcDoc = getDocumentFile(src, false, context);
            } else {
                srcDoc = DocumentFile.fromFile(src);
            }
            DocumentFile destDoc = getDocumentFile(dest.getParentFile(), true, context);
            if (srcDoc != null && destDoc != null) {
                try {
                    Log.i("renameTo", "src.getParent():" + src.getParent() + ",dest.getParent():" + dest.getParent());
                    if (src.getParent().equals(dest.getParent())) {//同一目录
                        res = srcDoc.renameTo(dest.getName());
                    } else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {//不同一目录
                        Uri renameSrcUri = DocumentsContract.renameDocument(context.getContentResolver(),//先重命名
                                srcDoc.getUri(), dest.getName());
                        res = DocumentsContract.moveDocument(context.getContentResolver(),//再移动
                                renameSrcUri,
                                srcDoc.getParentFile().getUri(),
                                destDoc.getUri()) != null;
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }

        return res;
    }

    public static InputStream getInputStream(Context context, File destFile) {
        InputStream in = null;
        try {
            if (!canWrite(destFile) && isOnExtSdCard(destFile, context)) {
                DocumentFile file = DocumentsUtils.getDocumentFile(destFile, false, context);
                if (file != null && file.canWrite()) {
                    in = context.getContentResolver().openInputStream(file.getUri());
                }
            } else {
                in = new FileInputStream(destFile);

            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        return in;
    }

    public static OutputStream getOutputStream(Context context, File destFile) {
        OutputStream out = null;
        try {
            if (!canWrite(destFile) && isOnExtSdCard(destFile, context)) {
                DocumentFile file = DocumentsUtils.getDocumentFile(destFile, false, context);
                if (file != null && file.canWrite()) {
                    out = context.getContentResolver().openOutputStream(file.getUri());
                }
            } else {
                out = new FileOutputStream(destFile);

            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        return out;
    }

    /**
     * 获取文件流
     * @param context
     * @param destFile 目标文件
     * @param mode May be "w", "wa", "rw", or "rwt".
     * @return
     */
    public static OutputStream getOutputStream(Context context, File destFile, String mode) {
        OutputStream out = null;
        try {
            if (!canWrite(destFile) && isOnExtSdCard(destFile, context)) {
                DocumentFile file = DocumentsUtils.getDocumentFile(destFile, false, context);
                if (file != null && file.canWrite()) {
                    out = context.getContentResolver().openOutputStream(file.getUri(), mode);
                }
            } else {
                out = new FileOutputStream(destFile, mode.equals("rw") || mode.equals("wa"));

            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        return out;
    }

    public static FileDescriptor getFileDescriptor(Context context, File destFile) {
        FileDescriptor fd = null;
        try {
            if (/*!canWrite(destFile) && */isOnExtSdCard(destFile, context)) {
                DocumentFile file = DocumentsUtils.getDocumentFile(destFile, false, context);
                if (file != null && file.canWrite()) {
                    ParcelFileDescriptor out = context.getContentResolver().openFileDescriptor(file.getUri(), "rw");
                    fd = out.getFileDescriptor();
                }
            } else {
                RandomAccessFile file = null;
                try {
                    file = new RandomAccessFile(destFile, "rws");
                    file.setLength(0);
                    fd = file.getFD();
                } catch (Exception e){
                    e.printStackTrace();
                } finally {
                    if (file != null) {
                        try {
                            file.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        return fd;
    }

    public static boolean saveTreeUri(Context context, String rootPath, Uri uri) {
        DocumentFile file = DocumentFile.fromTreeUri(context, uri);
        if (file != null && file.canWrite()) {
            SharedPreferences perf = PreferenceManager.getDefaultSharedPreferences(context);
            perf.edit().putString(rootPath, uri.toString()).apply();
            Log.e(TAG, "save uri" + rootPath);
            return true;
        } else {
            Log.e(TAG, "no write permission: " + rootPath);
        }
        return false;
    }

    /**
     * 返回true表示没有权限
     * @param context
     * @param rootPath
     * @return
     */
    public static boolean checkWritableRootPath(Context context, String rootPath) {
        File root = new File(rootPath);
        if (!root.canWrite()) {
            Log.e(TAG,"sd card can not write:" + rootPath + ",is on extsdcard:" + DocumentsUtils.isOnExtSdCard(root, context));
            if (DocumentsUtils.isOnExtSdCard(root, context)) {
                DocumentFile documentFile = DocumentsUtils.getDocumentFile(root, true, context);
                if (documentFile != null) {
                    Log.i(TAG, "get document file:" + documentFile.canWrite());
                }
                return documentFile == null || !documentFile.canWrite();
            } else {
                SharedPreferences perf = PreferenceManager.getDefaultSharedPreferences(context);
                String documentUri = perf.getString(rootPath, "");
                Log.i(TAG,"lum_2 get perf documentUri:" + documentUri);
                if (documentUri == null || documentUri.isEmpty()) {
                    return true;
                } else {
                    DocumentFile file = DocumentFile.fromTreeUri(context, Uri.parse(documentUri));
                    if (file != null)
                        Log.i(TAG,"lum get perf documentUri:" + file.canWrite());
                    return !(file != null && file.canWrite());
                }
            }
        }else{
            Log.e(TAG,"sd card can write...");
        }
        return false;
    }
}

然后在app启动的地方检查下是否需要授权才能操作：

if (DocumentsUtils.checkWritableRootPath(this, StringUtils.STORAGE_PATH)) {   //检查sd卡路径是否有 权限 没有显示dialog
      showOpenDocumentTree();
} 

private void showOpenDocumentTree() {
        Log.e("showOpenDocumentTree", "start check sd card...");
        Intent intent = null;
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.N) {
            StorageManager sm = getSystemService(StorageManager.class);
            StorageVolume volume = sm.getStorageVolume(new File(StringUtils.STORAGE_PATH));
            if (volume != null) {
                intent = volume.createAccessIntent(null);
            }
        }
        Log.e("showOpenDocumentTree", "intent=" + intent);
        if (intent == null) {
            intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
        }
        startActivityForResult(intent, DocumentsUtils.OPEN_DOCUMENT_TREE_CODE);
    }

//................................
@Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        switch (requestCode) {
            case DocumentsUtils.OPEN_DOCUMENT_TREE_CODE:
                if (data != null && data.getData() != null) {
                    Uri uri = data.getData();
                    DocumentsUtils.saveTreeUri(this, StringUtils.STORAGE_PATH, uri);
                    Log.i(TAG,"DocumentsUtils.OPEN_DOCUMENT_TREE_CODE ： "  + uri);
                }
                break;
        }
        super.onActivityResult(requestCode, resultCode, data);
    }
 

按以上代码，是可以实现对外置存储卡进行读和写操作了，只要机器没关机，多关打开关闭app，都不会弹下面这个授权框：

但是-----如果关机再重新开机，就要重新授权，这样很麻烦，用户体验也极其不好，所以又查询了很多资料，最后在stackoverflow上找到办法，关键是下面这句：

grantUriPermission(getPackageName(), uri, Intent.FLAG_GRANT_READ_URI_PERMISSION | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
                    getContentResolver().takePersistableUriPermission(uri, Intent.FLAG_GRANT_READ_URI_PERMISSION | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);

是在ActivityResult回调里，添加上面这两行代码，就不用每次都弹授权，影响体验了

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