步骤1 -使用隐式Intent：

要从设备中选择文件，应使用隐式Intent

Intent chooseFile = new Intent(Intent.ACTION_GET_CONTENT);
chooseFile.setType("*/*");
chooseFile = Intent.createChooser(chooseFile, "Choose a file");
startActivityForResult(chooseFile, PICKFILE_RESULT_CODE);

步骤2 -获取绝对文件路径：

要从Uri获取文件路径，首先尝试使用

Uri uri = data.getData();
String src = uri.getPath();

其中data是onActivityResult()中返回的Intent。
如果不起作用，请使用以下方法：

public String getPath(Uri uri) {

    String path = null;
    String[] projection = { MediaStore.Files.FileColumns.DATA };
    Cursor cursor = getContentResolver().query(uri, projection, null, null, null);

    if(cursor == null){
        path = uri.getPath()
    }
    else{
        cursor.moveToFirst();
        int column_index = cursor.getColumnIndexOrThrow(projection[0]);
        path = cursor.getString(column_index);
        cursor.close();
    }

    return ((path == null || path.isEmpty()) ? (uri.getPath()) : path);
}

这两种方法中至少有一种方法可以为您获取正确的完整路径。

步骤3 -复制文件：

我相信，您想要的是将文件从一个位置复制到另一个位置。
为此，必须具有源位置和目标位置的 * 绝对文件路径 *。
首先，使用我的getPath()方法或uri.getPath()获取绝对文件路径：

String src = getPath(uri);    /* Method defined above. */

或

Uri uri = data.getData();
String src = uri.getPath();

然后，建立两个File对象，如下所示：

File source = new File(src);
String filename = uri.getLastPathSegment();
File destination = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + "/CustomFolder/" + filename);

其中CustomFolder是外部驱动器上要将文件复制到的目录。
然后使用以下方法将文件从一个位置复制到另一个位置：

private void copy(File source, File destination) {

   FileChannel in = new FileInputStream(source).getChannel();
   FileChannel out = new FileOutputStream(destination).getChannel();

   try {
      in.transferTo(0, in.size(), out);
   } catch(Exception){
      // post to log
   } finally {
      if (in != null)
         in.close();
      if (out != null)
         out.close();
   }
}

试试这个，应该能用.

**注：**与Lukas的答案不同，他所做的是使用一个名为openInputStream()的方法，该方法返回Uri的 * 内容 *，无论Uri表示文件还是URL。
另一种有前途的方法-FileProvider：

如果一个应用通过FileProvider共享它的文件，那么它就有可能获得一个FileDescriptor对象，这个对象保存了关于这个文件的特定信息。
为此，请使用以下Intent：

Intent mRequestFileIntent = new Intent(Intent.ACTION_GET_CONTENT);
mRequestFileIntent.setType("*/*");
startActivityForResult(mRequestFileIntent, 0);

在onActivityResult()中：

@Override
public void onActivityResult(int requestCode, int resultCode,
        Intent returnIntent) {
    // If the selection didn't work
    if (resultCode != RESULT_OK) {
        // Exit without doing anything else
        return;
    } else {
        // Get the file's content URI from the incoming Intent
        Uri returnUri = returnIntent.getData();
        /*
         * Try to open the file for "read" access using the
         * returned URI. If the file isn't found, write to the
         * error log and return.
         */
        try {
            /*
             * Get the content resolver instance for this context, and use it
             * to get a ParcelFileDescriptor for the file.
             */
            mInputPFD = getContentResolver().openFileDescriptor(returnUri, "r");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
            Log.e("MainActivity", "File not found.");
            return;
        }
        // Get a regular file descriptor for the file
        FileDescriptor fd = mInputPFD.getFileDescriptor();
        ...
    }
}

其中mInputPFD是ParcelFileDescriptor。

参考资料：
**1.**共同目的-文件存储.

我的天
我的天啊
我的天啊！

正如**@CommonsWare**所指出的，Android返回给您的是Uri，这是一个比文件路径更抽象的概念。
它也可以描述一个简单的文件路径，但它也可以描述一个通过应用程序访问的资源（如content://media/external/audio/media/710）。
如果您希望用户从手机中选取任何文件，以便从应用程序中读取该文件，您可以通过请求该文件（正如您所做的那样），然后使用ContentResolver为选取器返回的Uri获取InputStream。
以下是一个示例：

Intent chooseFile = new Intent(Intent.ACTION_GET_CONTENT);
// Ask specifically for something that can be opened:
chooseFile.addCategory(Intent.CATEGORY_OPENABLE);
chooseFile.setType("*/*");
startActivityForResult(
        Intent.createChooser(chooseFile, "Choose a file"),
        PICKFILE_REQUEST_CODE
);

// And then somewhere, in your activity:
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == PICKFILE_REQUEST_CODE && resultCode == RESULT_OK){
        Uri content_describer = data.getData();
        BufferedReader reader = null;
        try {
            // open the user-picked file for reading:
            InputStream in = getContentResolver().openInputStream(content_describer);
            // now read the content:
            reader = new BufferedReader(new InputStreamReader(in));
            String line;
            StringBuilder builder = new StringBuilder();
            while ((line = reader.readLine()) != null){
                builder.append(line);
            }
            // Do something with the content in
            some_view.setText(builder.toString());
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

重要提示：有些提供商（如Dropbox）在外部存储器上存储/缓存数据，你需要在清单中声明android.permission.READ_EXTERNAL_STORAGE-权限，否则即使文件在那里，你也会得到FileNotFoundException。
更新：可以，您可以通过从一个流阅读文件并将其写入另一个流来复制文件：

// Error handling is omitted for shorter code!
Uri content_describer = data.getData();
InputStream in = null;
OutputStream out = null;
try {
    // open the user-picked file for reading:
    in = getContentResolver().openInputStream(content_describer);
    // open the output-file:
    out = new FileOutputStream(new File("some/path/to/a/writable/file"));
    // copy the content:
    byte[] buffer = new byte[1024];
    int len;
    while ((len = in.read(buffer)) != -1) {
        out.write(buffer, 0, len);
    }
    // Contents are copied!
} finally {
    if (in != null) {
        in.close();
    }
    if (out != null){
        out.close();
    }
}

删除该文件可能是不可能的，因为该文件不属于您，它属于与您共享它的应用程序。因此，拥有该文件的应用程序负责删除该文件。

对于ActivityResultLauncher，它的工作方式类似于：

ActivityResultLauncher<Intent> startActivityForResult = requireActivity().registerForActivityResult(new ActivityResultContracts.StartActivityForResult(), result -> {
    if (result.getResultCode() == Activity.RESULT_OK) {
        Intent data = result.getData();
        Uri contentUri = data.getData();
        ...
    }
});

用法示例：

Intent data = new Intent(Intent.ACTION_GET_CONTENT);
data.addCategory(Intent.CATEGORY_OPENABLE);
data.setType("*/*");
Intent intent = Intent.createChooser(data, "Choose a file");
startActivityForResult.launch(intent);

需要下列相依性（含或不含-ktx）：

implementation "androidx.activity:activity:1.5.0"

我做了同样的操作，让用户从文件夹中选择图像：

1）有一个按钮OPEN：

@Override
public void onClick(View v) {
    switch (v.getId()) {
    case R.id.btn_open:
        myOpenImagePicker();
        break;
    }
}

2）打开图像文件夹功能：

@SuppressLint("InlinedApi")
public void myOpenImagePicker() {

    if (Build.VERSION.SDK_INT < 19) {
        Intent intent = new Intent();
        intent.setType("image/*");
        intent.setAction(Intent.ACTION_GET_CONTENT);
        startActivityForResult(
                Intent.createChooser(intent, "Select Picture"),
                SELECT_FOLDER);

    } else {
        Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
        intent.addCategory(Intent.CATEGORY_OPENABLE);
        intent.setType("image/*");
        startActivityForResult(intent, SELECT_FOLDER);
    }
}

3）活动结果，其中我获取映像文件路径并对映像路径执行任何操作：

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    switch (requestCode) {
    case SELECT_FOLDER:
        if (resultCode == RESULT_OK && data != null) {

            Uri originalUri = data.getData();
            String id01 = W_ImgFilePathUtil.getPath(
                    getApplicationContext(), originalUri);
            Bitmap unscaledBitmap = W_ImgScalingUtil.decodeResource(id01,
                    xdrawing.getViewWidth(), xdrawing.getViewHeight(),
                    ScalingLogic.FIT);
            if (unscaledBitmap == null) {
                zprefsutil.ShowToast("IMAGE ERROR", 1);
            } else {
                setExternalScaledBitmap(W_ImgScalingUtil
                        .createScaledBitmap(unscaledBitmap,
                                xdrawing.getViewWidth(),
                                xdrawing.getViewHeight(), ScalingLogic.FIT));
                unscaledBitmap.recycle();
                xdrawing.invalidate();
            }

        }
        break;
    default:
        break;
    }
}

4），现在最重要的部分，W_ImgFilePathUtil类，代码不是从我，但它允许您检索任何选定文件的完整路径，无论是在sd卡上，谷歌驱动器，...：

public class W_ImgFilePathUtil {

    /**
     * Method for return file path of Gallery image
     * 
     * @param context
     * @param uri
     * @return path of the selected image file from gallery
     */
    @SuppressLint("NewApi")
    public static String getPath(final Context context, final Uri uri) {

        // check here to KITKAT or new version
        final boolean isKitKatorUp = Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT;

        // DocumentProvider
        if (isKitKatorUp && DocumentsContract.isDocumentUri(context, uri)) {

            // ExternalStorageProvider
            if (isExternalStorageDocument(uri)) {
                final String docId = DocumentsContract.getDocumentId(uri);
                final String[] split = docId.split(":");
                final String type = split[0];

                if ("primary".equalsIgnoreCase(type)) {
                    return Environment.getExternalStorageDirectory() + "/"
                            + split[1];
                }
            }
            // DownloadsProvider
            else if (isDownloadsDocument(uri)) {

                final String id = DocumentsContract.getDocumentId(uri);
                final Uri contentUri = ContentUris.withAppendedId(
                        Uri.parse("content://downloads/public_downloads"),
                        Long.valueOf(id));

                return getDataColumn(context, contentUri, null, null);
            }
            // MediaProvider
            else if (isMediaDocument(uri)) {
                final String docId = DocumentsContract.getDocumentId(uri);
                final String[] split = docId.split(":");
                final String type = split[0];

                Uri contentUri = null;
                if ("image".equals(type)) {
                    contentUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
                } else if ("video".equals(type)) {
                    contentUri = MediaStore.Video.Media.EXTERNAL_CONTENT_URI;
                } else if ("audio".equals(type)) {
                    contentUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
                }

                final String selection = "_id=?";
                final String[] selectionArgs = new String[] { split[1] };

                return getDataColumn(context, contentUri, selection,
                        selectionArgs);
            }
        }

        // MediaStore (and general)
        else if ("content".equalsIgnoreCase(uri.getScheme())) {

            // Return the remote address
            if (isGooglePhotosUri(uri))
                return uri.getLastPathSegment();

            return getDataColumn(context, uri, null, null);
        }
        // File
        else if ("file".equalsIgnoreCase(uri.getScheme())) {
            return uri.getPath();
        }

        return null;
    }

    /**
     * Get the value of the data column for this Uri. This is useful for
     * MediaStore Uris, and other file-based ContentProviders.
     * 
     * @param context
     *            The context.
     * @param uri
     *            The Uri to query.
     * @param selection
     *            (Optional) Filter used in the query.
     * @param selectionArgs
     *            (Optional) Selection arguments used in the query.
     * @return The value of the _data column, which is typically a file path.
     */
    public static String getDataColumn(Context context, Uri uri,
            String selection, String[] selectionArgs) {

        Cursor cursor = null;
        final String column = "_data";
        final String[] projection = { column };

        try {
            cursor = context.getContentResolver().query(uri, projection,
                    selection, selectionArgs, null);
            if (cursor != null && cursor.moveToFirst()) {
                final int index = cursor.getColumnIndexOrThrow(column);
                return cursor.getString(index);
            }
        } finally {
            if (cursor != null)
                cursor.close();
        }
        return null;
    }

    /**
     * @param uri
     *            The Uri to check.
     * @return Whether the Uri authority is ExternalStorageProvider.
     */
    public static boolean isExternalStorageDocument(Uri uri) {
        return "com.android.externalstorage.documents".equals(uri
                .getAuthority());
    }

    /**
     * @param uri
     *            The Uri to check.
     * @return Whether the Uri authority is DownloadsProvider.
     */
    public static boolean isDownloadsDocument(Uri uri) {
        return "com.android.providers.downloads.documents".equals(uri
                .getAuthority());
    }

    /**
     * @param uri
     *            The Uri to check.
     * @return Whether the Uri authority is MediaProvider.
     */
    public static boolean isMediaDocument(Uri uri) {
        return "com.android.providers.media.documents".equals(uri
                .getAuthority());
    }

    /**
     * @param uri
     *            The Uri to check.
     * @return Whether the Uri authority is Google Photos.
     */
    public static boolean isGooglePhotosUri(Uri uri) {
        return "com.google.android.apps.photos.content".equals(uri
                .getAuthority());
    }
}

结论：这段代码可以处理图像路径，但也可以处理任何类型的文件。
希望这有助于解决您的问题。
和平。

A Uri is not a file。Uri更接近于Web服务器URL。它是一个不透明的地址，仅对“服务器”（在本例中为ContentProvider）有意义。
就像使用InputStream读入Web URL表示的字节一样，使用InputStream读入Uri表示的字节。通过在ContentResolver上调用openInputStream()可以获得这样的流。

这里是如何实现一个文件拾取器，并将选定的文件移动到另一个位置（如图片）。
首先，在代码中添加一个文件选择器，其中包含一个单击侦听器上的按钮，如下所示：
点取文件按钮：

@Override
public void onClick(View v) {
    switch (v.getId()) {
    case R.id.btn_choose_file:
        showFileChooser();
        break;
    }
}

private String filePath = null;
private File sourceFile;

private static final int FILE_SELECT_CODE = 0;

    private void showFileChooser() {
        Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
        intent.setType("*/*");
        intent.addCategory(Intent.CATEGORY_OPENABLE);

        try {
            startActivityForResult(
                    Intent.createChooser(intent, "Select a File to Copy"),
                    FILE_SELECT_CODE);
        } catch (android.content.ActivityNotFoundException ex) {
            Toast.makeText(this, "Please install a File Manager.",
                    Toast.LENGTH_SHORT).show();
        }
    }

然后按如下方式处理onActivityResult：

@Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        switch (requestCode) {
            case FILE_SELECT_CODE:
                if (resultCode == RESULT_OK) {
                    // Get the Uri of the selected file
                    Uri uri = data.getData();

                    File   file = new File(getCacheDir(), getFileName(uri));

                    int maxBufferSize = 1 * 1024 * 1024;

                    try {
                        InputStream inputStream = getContentResolver().openInputStream(uri);
                        Log.e("InputStream Size","Size " + inputStream);
                        int  bytesAvailable = inputStream.available();
                        int bufferSize = Math.min(bytesAvailable, maxBufferSize);
                        final byte[] buffers = new byte[bufferSize];

                        FileOutputStream outputStream = new FileOutputStream(file);
                        int read = 0;
                        while ((read = inputStream.read(buffers)) != -1) {
                            outputStream.write(buffers, 0, read);
                        }
                        Log.e("File Size","Size " + file.length());
                        inputStream.close();
                        outputStream.close();

                        file.getPath();
                        Log.e("File Path","Path " + file.getPath());
                        file.length();
                        Log.e("File Size","Size " + file.length());

                        if(file.length() > 0){

                            sourceFile = file;
                           saveFile(sourceFile);
                        }

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


                } else {

                }

                break;
        }
        super.onActivityResult(requestCode, resultCode, data);
    }



    private void saveFile (File sourceFile) {

                try {

                File currentFile = sourceFile;

                Bitmap myBitmap = BitmapFactory.decodeFile(currentFile.getAbsolutePath());

                String path = currentFile.getAbsolutePath();
                String idStr = path.substring(path.lastIndexOf('/') + 1);
                File filepath = Environment.getExternalStorageDirectory();
                File dir = new File(filepath.getAbsolutePath() + "/" + "yourFolderName" + "/");
                if (!dir.exists()) {
                    dir.mkdirs();
                }
                String fileName = currentFile.getName();
                file = new File(dir, fileName);
                if (file.exists()) file.delete();
                FileOutputStream fos = new FileOutputStream(file);
                myBitmap.compress(CompressFormat.JPEG, 65, fos);
                fos.flush();
                fos.close();

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

    }

注意：不要忘记将此权限添加到清单文件中。

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

希望这对你有帮助。

在此方法中传递onActivityResult中返回的URI

private String getPath(Uri contentURI) {

    String result;
    Cursor cursor = getActivity().getContentResolver().query(contentURI,
            null, null, null, null);

    if (cursor == null) {
        result = contentURI.getPath();
    } else {
        cursor.moveToFirst();
        int idx = cursor
                .getColumnIndex(MediaStore.Images.ImageColumns.DATA);
        result = cursor.getString(idx);
        cursor.close();
    }
    return result;
}

以下是在较新的Android版本中的操作方法：

private ActivityResultLauncher<String> filePicker;

//execute this in your AppCompatActivity onCreate
public void registerFilePicker() {
    filePicker = registerForActivityResult(
            new ActivityResultContracts.GetContent(), 
            uri -> onPickFile(uri)
    );
}

//execute this to launch the picker
public void openFilePicker() {
    String mimeType = "*/*";
    filePicker.launch(mimeType);
}

//this gets executed when the user picks a file
public void onPickFile(Uri uri) {
    try (InputStream inputStream = getContentResolver().openInputStream(uri)) {

    } catch (IOException exception) {

    }
}

更多信息：https://developer.android.com/training/basics/intents/result