感谢以下链接：https://blog.csdn.net/houdada_/article/details/107587762 ，此方法参考了链接上的大部分代码

近期有一个上传PDF文件的需求，因此做了一个选择手机系统文件的功能，期间遇到过几个问题，在此记录一下，归根结底其本质还是适配Android10和Android11的问题

主要问题：拿不到返回的路径、拿不到返回的真实路径

跳转到系统选择文件：

  private fun selectFile()
    {
        val intent = Intent(Intent.ACTION_GET_CONTENT)
        intent.type = "*/*" //无类型限制
        intent.addCategory(Intent.CATEGORY_OPENABLE)
        startActivityForResult(intent, 1)
    }

根据Uri获取文件路径：

import android.content.ContentResolver;
import android.content.ContentUris;
import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.os.Build;
import android.os.Environment;
import android.os.FileUtils;
import android.provider.DocumentsContract;
import android.provider.MediaStore;
import android.provider.OpenableColumns;
import android.text.TextUtils;
import android.util.Log;

import androidx.annotation.RequiresApi;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class GetFilePathFromUri {


    /**
     * 根据Uri获取文件绝对路径，解决Android4.4以上版本Uri转换 兼容Android 10
     *
     * @param context
     * @param imageUri
     */
    public static String getFileAbsolutePath(Context context, Uri imageUri) {
        if (context == null || imageUri == null) {
            return null;
        }

        //4.4以下的版本
        if (android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.KITKAT) {
            return getRealFilePath(context, imageUri);
        }

        //大于4.4，小于10
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.KITKAT
                && android.os.Build.VERSION.SDK_INT < Build.VERSION_CODES.Q
                && DocumentsContract.isDocumentUri(context, imageUri)) {

            if (isExternalStorageDocument(imageUri)) {
                String docId = DocumentsContract.getDocumentId(imageUri);
                String[] split = docId.split(":");
                String type = split[0];
                if ("primary".equalsIgnoreCase(type)) {
                    return Environment.getExternalStorageDirectory() + "/" + split[1];
                }
            } else if (isDownloadsDocument(imageUri)) {
                String id = DocumentsContract.getDocumentId(imageUri);
                Uri contentUri = ContentUris.withAppendedId(Uri.parse("content://downloads/public_downloads"), Long.valueOf(id));
                return getDataColumn(context, contentUri, null, null);
            } else if (isMediaDocument(imageUri)) {
                String docId = DocumentsContract.getDocumentId(imageUri);
                String[] split = docId.split(":");
                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;
                }
                String selection = MediaStore.Images.Media._ID + "=?";
                String[] selectionArgs = new String[]{split[1]};
                return getDataColumn(context, contentUri, selection, selectionArgs);
            }
        }

        // MediaStore (and general)  大于等于10
        if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q){
            return uriToFileApiQ(context,imageUri);
        }
        else if ("content".equalsIgnoreCase(imageUri.getScheme())) {
            // Return the remote address
            if (isGooglePhotosUri(imageUri)) {
                return imageUri.getLastPathSegment();
            }
            if (Build.VERSION.SDK_INT >= 24)
            {
                return getFilePathFromUri(context,imageUri); //content 类型
            }else {
                return getDataColumn(context, imageUri, null, null);
            }
        }
        // File
        else if ("file".equalsIgnoreCase(imageUri.getScheme())) {
            return imageUri.getPath();
        }
        return null;
    }

    private static String getRealFilePath(final Context context, final Uri uri) {
        if (null == uri) {
            return null;
        }
        final String scheme = uri.getScheme();
        String data = null;
        if (scheme == null) {
            data = uri.getPath();
        } else if (ContentResolver.SCHEME_FILE.equals(scheme)) {
            data = uri.getPath();
        } else if (ContentResolver.SCHEME_CONTENT.equals(scheme)) {
            String[] projection = {MediaStore.Images.ImageColumns.DATA};
            Cursor cursor = context.getContentResolver().query(uri, projection, null, null, null);
            if (null != cursor) {
                if (cursor.moveToFirst()) {
                    int index = cursor.getColumnIndex(MediaStore.Images.ImageColumns.DATA);
                    if (index > -1) {
                        data = cursor.getString(index);
                    }
                }
                cursor.close();
            }
        }
        return data;
    }


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

    private static String getDataColumn(Context context, Uri uri, String selection, String[] selectionArgs) {
        Cursor cursor = null;
        String column = MediaStore.Images.Media.DATA;
        String[] projection = {column};
        try {
            cursor = context.getContentResolver().query(uri, projection, selection, selectionArgs, null);
            if (cursor != null && cursor.moveToFirst()) {
                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 MediaProvider.
     */
    private 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.
     */
    private static boolean isGooglePhotosUri(Uri uri) {
        return "com.google.android.apps.photos.content".equals(uri.getAuthority());
    }


    /**
     * Android 10 以上适配 另一种写法
     * @param context
     * @param uri
     * @return
     */
    private static String getFileFromContentUri(Context context, Uri uri) {
        if (uri == null) {
            return null;
        }
        String filePath;
        String[] filePathColumn = {MediaStore.MediaColumns.DATA, MediaStore.MediaColumns.DISPLAY_NAME};
        ContentResolver contentResolver = context.getContentResolver();
        Cursor cursor = contentResolver.query(uri, filePathColumn, null,
                null, null);
        if (cursor != null) {
            cursor.moveToFirst();
            try {
                filePath = cursor.getString(cursor.getColumnIndex(filePathColumn[0]));
                return filePath;
            } catch (Exception e) {
            } finally {
                cursor.close();
            }
        }
        return "";
    }

    /**
     * Android 10 以上适配
     * @param context
     * @param uri
     * @return
     */
    private static String uriToFileApiQ(Context context, Uri uri) {
        File file = null;
        //android10以上转换
        if (uri.getScheme().equals(ContentResolver.SCHEME_FILE)) {
            file = new File(uri.getPath());
        } else if (uri.getScheme().equals(ContentResolver.SCHEME_CONTENT)) {
            //把文件复制到沙盒目录
            ContentResolver contentResolver = context.getContentResolver();
            Cursor cursor = contentResolver.query(uri, null, null, null, null);
            if (cursor.moveToFirst()) {
                String displayName = cursor.getString(cursor.getColumnIndex(OpenableColumns.DISPLAY_NAME));
                try {
                    InputStream is = contentResolver.openInputStream(uri);
                    File file1 = new File(context.getExternalCacheDir().getAbsolutePath()+"/"+System.currentTimeMillis());
                    if (!file1.exists())
                    {
                        file1.mkdir();
                    }
                    File cache = new File(file1.getPath(), displayName);
                    FileOutputStream fos = new FileOutputStream(cache);
                    FileUtils.copy(is, fos);
                    file = cache;
                    fos.close();
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return file.getAbsolutePath();
    }

    private static String getFilePathFromUri(Context context,Uri uri)
    {
        String realFilePath = getRealFilePath(context,uri); //防止获取不到真实的地址，因此这里需要进行判断
        if (!TextUtils.isEmpty(realFilePath))
        {
            return realFilePath;
        }
        File filesDir = context.getApplicationContext().getFilesDir();
        String fileName = getFileName(uri);
        if (!TextUtils.isEmpty(fileName))
        {
            File copyFile1 = new File(filesDir + File.separator + fileName);
            copyFile(context,uri,copyFile1);
            return copyFile1.getAbsolutePath();
        }
        return null;
    }
    private static String getFileName(Uri uri)
    {
        if (uri == null)
        {
            return null;
        }
        String fileName = null;
        String path = uri.getPath();
        int cut = path.lastIndexOf('/');
        if (cut != -1)
        {
            fileName = path.substring(cut+1);
        }
        return fileName;
    }
    private static void copyFile(Context context, Uri srcUri, File dstFile) {
        try {
            InputStream inputStream = context.getContentResolver().openInputStream(srcUri);
            if (inputStream == null)
            {
                return;
            }
            OutputStream outputStream = new FileOutputStream(dstFile);
            copyStream(inputStream, outputStream);
            inputStream.close();
            outputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }


    private static int copyStream(InputStream input, OutputStream output){
        final int BUFFER_SIZE = 1024 * 2;
        byte[] buffer = new byte[BUFFER_SIZE];
        BufferedInputStream in = new BufferedInputStream(input, BUFFER_SIZE);
        BufferedOutputStream out = new BufferedOutputStream(output, BUFFER_SIZE);
        int count = 0, n = 0;
        try {
            while ((n = in.read(buffer, 0, BUFFER_SIZE)) != -1) {
                out.write(buffer, 0, n);
                count += n;
            }
            out.flush();
        }
        catch (Exception e)
        {
        }finally {
            try {
                out.close();
                in.close();
            } catch (Exception e) {
            }
        }
        return count;
    }

}