什么是最简单的方法从android.net.Uri对象持有一个文件:类型转换为java.io.File对象在Android?
我尝试了下面的方法，但不管用:
File file = new File(Environment.getExternalStorageDirectory(), "read.me");
Uri uri = Uri.fromFile(file);
File auxFile = new File(uri.toString());
assertEquals(file.getAbsolutePath(), auxFile.getAbsolutePath());
当前回答
你想要的是…
new File(uri.getPath());
．.． ,而不是……
new File(uri.toString());
笔记
对于android.net.Uri对象，它被命名为uri并完全按照问题中创建，uri. tostring()返回一个“file:///mnt/sdcard/myPicture.jpg”格式的字符串，而uri. getpath()返回一个“/mnt/sdcard/myPicture.jpg”格式的字符串。 我知道在Android系统中文件存储有一些细微差别。在这个回答中，我的意图是准确地回答提问者所问的问题，而不是深究其中的细微差别。
其他回答
在寻找了很长一段时间后，这对我来说是有效的:
File file = new File(getPath(uri));
public String getPath(Uri uri)
{
String[] projection = { MediaStore.Images.Media.DATA };
Cursor cursor = getContentResolver().query(uri, projection, null, null, null);
if (cursor == null) return null;
int column_index = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
cursor.moveToFirst();
String s=cursor.getString(column_index);
cursor.close();
return s;
}
使用
InputStream inputStream = getContentResolver().openInputStream(uri);
直接复制文件。还看到:
https://developer.android.com/guide/topics/providers/document-provider.html
一些库需要文件对象的过程，如改造，一些图像编辑器等。 将URI转换为文件对象或任何类似的东西，我们有一种方法，这是支持所有android旧版本和即将到来的版本。
步骤1:
你必须在FilesDir中创建一个新文件，这个文件对于其他与我们的文件和扩展名相同的应用程序是不可读的。
步骤2:
您必须通过使用InputStream复制URI的内容来创建一个文件。
File f = getFile(getApplicationContext(), uri);
public static File getFile(Context context, Uri uri) throws IOException {
File destinationFilename = new File(context.getFilesDir().getPath() + File.separatorChar + queryName(context, uri));
try (InputStream ins = context.getContentResolver().openInputStream(uri)) {
createFileFromStream(ins, destinationFilename);
} catch (Exception ex) {
Log.e("Save File", ex.getMessage());
ex.printStackTrace();
}
return destinationFilename;
}
public static void createFileFromStream(InputStream ins, File destination) {
try (OutputStream os = new FileOutputStream(destination)) {
byte[] buffer = new byte[4096];
int length;
while ((length = ins.read(buffer)) > 0) {
os.write(buffer, 0, length);
}
os.flush();
} catch (Exception ex) {
Log.e("Save File", ex.getMessage());
ex.printStackTrace();
}
}
private static String queryName(Context context, Uri uri) {
Cursor returnCursor =
context.getContentResolver().query(uri, null, null, null, null);
assert returnCursor != null;
int nameIndex = returnCursor.getColumnIndex(OpenableColumns.DISPLAY_NAME);
returnCursor.moveToFirst();
String name = returnCursor.getString(nameIndex);
returnCursor.close();
return name;
}
在这种情况下，特别是在Android上，使用字节的方式通常更快。
有了这个，我通过设置一个类FileHelper来解决这个问题，它被赋予了处理通过流从/向文件读取/写入字节的责任，以及一个类UriHelper，它被赋予了计算Uri路径和权限的责任。
就我们所知，字符串。getBytes((charset == null) ?DEFAULT_CHARSET:charset)可以帮助我们将你想要的字符串转换为你需要的字节。
如何让UriHelper和FileHelper你复制一个图片的Uri到一个文件，你可以运行:
FileHelper.getInstance().copy(UriHelper.getInstance().toFile(uri_of_a_picture)
, FileHelper.getInstance().createExternalFile(null, UriHelper.getInstance().generateFileNameBasedOnTimeStamp()
+ UriHelper.getInstance().getFileName(uri_of_a_picture, context), context)
);
关于我的UriHelper:
public class UriHelper {
private static UriHelper INSTANCE = new UriHelper();
public static UriHelper getInstance() {
return INSTANCE;
}
@SuppressLint("SimpleDateFormat")
public String generateFileNameBasedOnTimeStamp() {
return new SimpleDateFormat("yyyyMMdd_hhmmss").format(new Date()) + ".jpeg";
}
/**
* if uri.getScheme.equals("content"), open it with a content resolver.
* if the uri.Scheme.equals("file"), open it using normal file methods.
*/
//
public File toFile(Uri uri) {
if (uri == null) return null;
Logger.d(">>> uri path:" + uri.getPath());
Logger.d(">>> uri string:" + uri.toString());
return new File(uri.getPath());
}
public DocumentFile toDocumentFile(Uri uri) {
if (uri == null) return null;
Logger.d(">>> uri path:" + uri.getPath());
Logger.d(">>> uri string:" + uri.toString());
return DocumentFile.fromFile(new File(uri.getPath()));
}
public Uri toUri(File file) {
if (file == null) return null;
Logger.d(">>> file path:" + file.getAbsolutePath());
return Uri.fromFile(file); //returns an immutable URI reference representing the file
}
public String getPath(Uri uri, Context context) {
if (uri == null) return null;
if (uri.getScheme() == null) return null;
Logger.d(">>> uri path:" + uri.getPath());
Logger.d(">>> uri string:" + uri.toString());
String path;
if (uri.getScheme().equals("content")) {
//Cursor cursor = context.getContentResolver().query(uri, new String[] {MediaStore.Images.ImageColumns.DATA}, null, null, null);
Cursor cursor = context.getContentResolver().query(uri, null, null, null, null);
if (cursor == null) {
Logger.e("!!! cursor is null");
return null;
}
if (cursor.getCount() >= 0) {
Logger.d("... the numbers of rows:" + cursor.getCount()
+ "and the numbers of columns:" + cursor.getColumnCount());
if (cursor.isBeforeFirst()) {
while (cursor.moveToNext()) {
StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i<cursor.getColumnCount(); i++) {
stringBuilder.append("... iterating cursor.getString(" + i +"(" + cursor.getColumnName(i) + ")):" + cursor.getString(i));
stringBuilder.append("\n");
}
Logger.d(stringBuilder.toString());
}
} else {
cursor.moveToFirst();
do {
StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i<cursor.getColumnCount(); i++) {
stringBuilder.append("... iterating cursor.getString(" + i +"(" + cursor.getColumnName(i) + ")):" + cursor.getString(i));
stringBuilder.append("\n");
}
Logger.d(stringBuilder.toString());
} while (cursor.moveToNext());
}
path = uri.getPath();
cursor.close();
Logger.d("... content scheme:" + uri.getScheme() + " and return:" + path);
return path;
} else {
path = uri.getPath();
Logger.d("... content scheme:" + uri.getScheme()
+ " but the numbers of rows in the cursor is < 0:" + cursor.getCount()
+ " and return:" + path);
return path;
}
} else {
path = uri.getPath();
Logger.d("... not content scheme:" + uri.getScheme() + " and return:" + path);
return path;
}
}
public String getFileName(Uri uri, Context context) {
if (uri == null) return null;
if (uri.getScheme() == null) return null;
Logger.d(">>> uri path:" + uri.getPath());
Logger.d(">>> uri string:" + uri.toString());
String path;
if (uri.getScheme().equals("content")) {
//Cursor cursor = context.getContentResolver().query(uri, new String[] {MediaStore.Images.ImageColumns.DATA}, null, null, null);
Cursor cursor = context.getContentResolver().query(uri, null, null, null, null);
if (cursor == null) {
Logger.e("!!! cursor is null");
return null;
}
if (cursor.getCount() >= 0) {
Logger.d("... the numbers of rows:" + cursor.getCount()
+ "and the numbers of columns:" + cursor.getColumnCount());
if (cursor.isBeforeFirst()) {
while (cursor.moveToNext()) {
StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i<cursor.getColumnCount(); i++) {
stringBuilder.append("... iterating cursor.getString(" + i +"(" + cursor.getColumnName(i) + ")):" + cursor.getString(i));
stringBuilder.append("\n");
}
Logger.d(stringBuilder.toString());
}
} else {
cursor.moveToFirst();
do {
StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i<cursor.getColumnCount(); i++) {
stringBuilder.append("... iterating cursor.getString(" + i +"(" + cursor.getColumnName(i) + ")):" + cursor.getString(i));
stringBuilder.append("\n");
}
Logger.d(stringBuilder.toString());
} while (cursor.moveToNext());
}
cursor.moveToFirst();
path = cursor.getString(cursor.getColumnIndex(MediaStore.Images.ImageColumns.DISPLAY_NAME));
cursor.close();
Logger.d("... content scheme:" + uri.getScheme() + " and return:" + path);
return path;
} else {
path = uri.getLastPathSegment();
Logger.d("... content scheme:" + uri.getScheme()
+ " but the numbers of rows in the cursor is < 0:" + cursor.getCount()
+ " and return:" + path);
return path;
}
} else {
path = uri.getLastPathSegment();
Logger.d("... not content scheme:" + uri.getScheme() + " and return:" + path);
return path;
}
}
}
关于我的FileHelper:
public class FileHelper {
private static final String DEFAULT_DIR_NAME = "AmoFromTaiwan";
private static final int DEFAULT_BUFFER_SIZE = 1024;
private static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");
private static final int EOF = -1;
private static FileHelper INSTANCE = new FileHelper();
public static FileHelper getInstance() {
return INSTANCE;
}
private boolean isExternalStorageWritable(Context context) {
/*
String state = Environment.getExternalStorageState();
return Environment.MEDIA_MOUNTED.equals(state);
*/
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (context.checkSelfPermission(android.Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) {
return true;
} else {
Logger.e("!!! checkSelfPermission() not granted");
return false;
}
} else { //permission is automatically granted on sdk<23 upon installation
return true;
}
}
private boolean isExternalStorageReadable(Context context) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (context.checkSelfPermission(android.Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) {
return true;
} else {
Logger.e("!!! checkSelfPermission() not granted");
return false;
}
} else { //permission is automatically granted on sdk<23 upon installation
return true;
}
}
@SuppressLint("SimpleDateFormat")
private String generateFileNameBasedOnTimeStamp() {
return new SimpleDateFormat("yyyyMMdd_hhmmss").format(new Date()) + ".jpeg";
}
public File createExternalFile(String dir_name, String file_name, Context context) {
String dir_path;
String file_path;
File dir ;
File file;
if (!isExternalStorageWritable(context)) {
Logger.e("!!! external storage not writable");
return null;
}
if (dir_name == null) {
dir_path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).getAbsolutePath() + File.separator + DEFAULT_DIR_NAME;
} else {
dir_path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).getAbsolutePath() + File.separator + dir_name;
}
Logger.d("... going to access an external dir:" + dir_path);
dir = new File(dir_path);
if (!dir.exists()) {
Logger.d("... going to mkdirs:" + dir_path);
if (!dir.mkdirs()) {
Logger.e("!!! failed to mkdirs");
return null;
}
}
if (file_name == null) {
file_path = dir_path + File.separator + generateFileNameBasedOnTimeStamp();
} else {
file_path = dir_path + File.separator + file_name;
}
Logger.d("... going to return an external dir:" + file_path);
file = new File(file_path);
if (file.exists()) {
Logger.d("... before creating to delete an external dir:" + file.getAbsolutePath());
if (!file.delete()) {
Logger.e("!!! failed to delete file");
return null;
}
}
return file;
}
public File createInternalFile(String dir_name, String file_name, Context context) {
String dir_path;
String file_path;
File dir ;
File file;
if (dir_name == null) {
dir = new ContextWrapper(context).getDir(DEFAULT_DIR_NAME, Context.MODE_PRIVATE);
} else {
dir = new ContextWrapper(context).getDir(dir_name, Context.MODE_PRIVATE);
}
dir_path = dir.getAbsolutePath();
Logger.d("... going to access an internal dir:" + dir_path);
if (!dir.exists()) {
Logger.d("... going to mkdirs:" + dir_path);
if (!dir.mkdirs()) {
Logger.e("!!! mkdirs failed");
return null;
}
}
if (file_name == null) {
file = new File(dir, generateFileNameBasedOnTimeStamp());
} else {
file = new File(dir, file_name);
}
file_path = file.getAbsolutePath();
Logger.d("... going to return an internal dir:" + file_path);
if (file.exists()) {
Logger.d("... before creating to delete an external dir:" + file.getAbsolutePath());
if (!file.delete()) {
Logger.e("!!! failed to delete file");
return null;
}
}
return file;
}
public File getExternalFile(String dir_name, String file_name, Context context) {
String dir_path;
String file_path;
File file;
if (!isExternalStorageWritable(context)) {
Logger.e("!!! external storage not writable");
return null;
}
if (dir_name == null) {
dir_path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).getAbsolutePath() + File.separator + DEFAULT_DIR_NAME;
} else {
dir_path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).getAbsolutePath() + File.separator + dir_name;
}
if (file_name == null) {
file_path = dir_path;
} else {
file_path = dir_path + File.separator + file_name;
}
Logger.d("... going to return an external file:" + file_path);
file = new File(file_path);
if (file.exists()) {
Logger.d("... file exists:" + file.getAbsolutePath());
} else {
Logger.e("!!! file does't exist:" + file.getAbsolutePath());
}
return file;
}
public File getInternalFile(String dir_name, String file_name, Context context) {
String file_path;
File dir ;
File file;
if (dir_name == null) {
dir = new ContextWrapper(context).getDir(DEFAULT_DIR_NAME, Context.MODE_PRIVATE);
} else {
dir = new ContextWrapper(context).getDir(dir_name, Context.MODE_PRIVATE);
}
if (file_name == null) {
file = new File(dir.getAbsolutePath());
} else {
file = new File(dir, file_name);
}
file_path = file.getAbsolutePath();
Logger.d("... going to return an internal dir:" + file_path);
if (file.exists()) {
Logger.d("... file exists:" + file.getAbsolutePath());
} else {
Logger.e("!!! file does't exist:" + file.getAbsolutePath());
}
return file;
}
private byte[] readBytesFromFile(File file) {
Logger.d(">>> path:" + file.getAbsolutePath());
FileInputStream fis;
long file_length;
byte[] buffer;
int offset = 0;
int next = 0;
if (!file.exists()) {
Logger.e("!!! file doesn't exists");
return null;
}
if (file.length() > Integer.MAX_VALUE) {
Logger.e("!!! file length is out of max of int");
return null;
} else {
file_length = file.length();
}
try {
fis = new FileInputStream(file);
//buffer = new byte[(int) file_length];
buffer = new byte[(int) file.length()];
long time_start = System.currentTimeMillis();
while (true) {
Logger.d("... now next:" + next + " and offset:" + offset);
if (System.currentTimeMillis() - time_start > 1000) {
Logger.e("!!! left due to time out");
break;
}
next = fis.read(buffer, offset, (buffer.length-offset));
if (next < 0 || offset >= buffer.length) {
Logger.d("... completed to read");
break;
}
offset += next;
}
//if (offset < buffer.length) {
if (offset < (int) file_length) {
Logger.e("!!! not complete to read");
return null;
}
fis.close();
return buffer;
} catch (IOException e) {
e.printStackTrace();
Logger.e("!!! IOException");
return null;
}
}
public byte[] readBytesFromFile(File file, boolean is_fis_fos_only) {
if (file == null) return null;
if (is_fis_fos_only) {
return readBytesFromFile(file);
}
Logger.d(">>> path:" + file.getAbsolutePath());
FileInputStream fis;
BufferedInputStream bis;
ByteArrayOutputStream bos;
byte[] buf = new byte[(int) file.length()];
int num_read;
if (!file.exists()) {
Logger.e("!!! file doesn't exists");
return null;
}
try {
fis = new FileInputStream(file);
bis = new BufferedInputStream(fis);
bos = new ByteArrayOutputStream();
long time_start = System.currentTimeMillis();
while (true) {
if (System.currentTimeMillis() - time_start > 1000) {
Logger.e("!!! left due to time out");
break;
}
num_read = bis.read(buf, 0, buf.length); //1024 bytes per call
if (num_read < 0) break;
bos.write(buf, 0, num_read);
}
buf = bos.toByteArray();
fis.close();
bis.close();
bos.close();
return buf;
} catch (FileNotFoundException e) {
e.printStackTrace();
Logger.e("!!! FileNotFoundException");
return null;
} catch (IOException e) {
e.printStackTrace();
Logger.e("!!! IOException");
return null;
}
}
/**
* streams (InputStream and OutputStream) transfer binary data
* if to write a string to a stream, must first convert it to bytes, or in other words encode it
*/
public boolean writeStringToFile(File file, String string, Charset charset) {
if (file == null) return false;
if (string == null) return false;
return writeBytesToFile(file, string.getBytes((charset == null) ? DEFAULT_CHARSET:charset));
}
public boolean writeBytesToFile(File file, byte[] data) {
if (file == null) return false;
if (data == null) return false;
FileOutputStream fos;
BufferedOutputStream bos;
try {
fos = new FileOutputStream(file);
bos = new BufferedOutputStream(fos);
bos.write(data, 0, data.length);
bos.flush();
bos.close();
fos.close();
} catch (IOException e) {
e.printStackTrace();
Logger.e("!!! IOException");
return false;
}
return true;
}
/**
* io blocks until some input/output is available.
*/
public boolean copy(File source, File destination) {
if (source == null || destination == null) return false;
Logger.d(">>> source:" + source.getAbsolutePath() + ", destination:" + destination.getAbsolutePath());
try {
FileInputStream fis = new FileInputStream(source);
FileOutputStream fos = new FileOutputStream(destination);
byte[] buffer = new byte[(int) source.length()];
int len;
while (EOF != (len = fis.read(buffer))) {
fos.write(buffer, 0, len);
}
if (true) { //debug
byte[] copies = readBytesFromFile(destination);
if (copies != null) {
int copy_len = copies.length;
Logger.d("... stream read and write done for " + copy_len + " bytes");
}
}
return destination.length() != 0;
} catch (IOException e) {
e.printStackTrace();
return false;
}
}
public void list(final String path, final String end, final List<File> files) {
Logger.d(">>> path:" + path + ", end:" + end);
File file = new File(path);
if (file.isDirectory()) {
for (File child : file.listFiles()){
list(child.getAbsolutePath(), end, files);
}
} else if (file.isFile()) {
if (end.equals("")) {
files.add(file);
} else {
if (file.getName().endsWith(end)) files.add(file);
}
}
}
public String[] splitFileName(File file, String split) {
String path;
String ext;
int lastIndexOfSplit = file.getAbsolutePath().lastIndexOf(split);
if (lastIndexOfSplit < 0) {
path = file.getAbsolutePath();
ext = "";
} else {
path = file.getAbsolutePath().substring(0, lastIndexOfSplit);
ext = file.getAbsolutePath().substring(lastIndexOfSplit);
}
return new String[] {path, ext};
}
public File rename(File old_file, String new_name) {
if (old_file == null || new_name == null) return null;
Logger.d(">>> old file path:" + old_file.getAbsolutePath() + ", new file name:" + new_name);
File new_file = new File(old_file, new_name);
if (!old_file.equals(new_file)) {
if (new_file.exists()) { //if find out previous file/dir at new path name exists
if (new_file.delete()) {
Logger.d("... succeeded to delete previous file at new abstract path name:" + new_file.getAbsolutePath());
} else {
Logger.e("!!! failed to delete previous file at new abstract path name");
return null;
}
}
if (old_file.renameTo(new_file)) {
Logger.d("... succeeded to rename old file to new abstract path name:" + new_file.getAbsolutePath());
} else {
Logger.e("!!! failed to rename old file to new abstract path name");
}
} else {
Logger.d("... new and old file have the equal abstract path name:" + new_file.getAbsolutePath());
}
return new_file;
}
public boolean remove(final String path, final String end) {
Logger.d(">>> path:" + path + ", end:" + end);
File file = new File(path);
boolean result = false;
if (file.isDirectory()) {
for (File child : file.listFiles()){
result = remove(child.getAbsolutePath(), end);
}
} else if (file.isFile()) {
if (end.equals("")) {
result = file.delete();
} else {
if (file.getName().endsWith(end)) result = file.delete();
}
} else {
Logger.e("!!! child is not file or directory");
}
return result;
}
@TargetApi(Build.VERSION_CODES.O)
public byte[] readNIOBytesFromFile(String path) throws IOException {
Logger.d(">>> path:" + path);
if (!Files.exists(Paths.get(path), LinkOption.NOFOLLOW_LINKS)) {
Logger.e("!!! file doesn't exists");
return null;
} else {
return Files.readAllBytes(Paths.get(path));
}
}
@TargetApi(Build.VERSION_CODES.O)
public File writeNIOBytesToFile(String dir, String name, byte[] data) {
Logger.d(">>> dir:" + dir + ", name:" + name);
Path path_dir;
Path path_file;
try {
if (!Files.exists(Paths.get(dir), LinkOption.NOFOLLOW_LINKS)) {
Logger.d("... make a dir");
path_dir = Files.createDirectories(Paths.get(dir));
if (path_dir == null) {
Logger.e("!!! failed to make a dir");
return null;
}
}
path_file = Files.write(Paths.get(name), data);
return path_file.toFile();
} catch (IOException e) {
e.printStackTrace();
Logger.e("!!! IOException");
return null;
}
}
@TargetApi(Build.VERSION_CODES.O)
public void listNIO(final String dir, final String end, final List<File> files) throws IOException {
Logger.d(">>> dir:" + dir + ", end:" + end);
Files.walkFileTree(Paths.get(dir), new FileVisitor<Path>() {
@Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) {
Logger.d("... file:" + dir.getFileName());
return FileVisitResult.CONTINUE;
}
@Override
public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) {
Logger.d("... file:" + file.getFileName());
if (end.equals("")) {
files.add(file.toFile());
} else {
if (file.endsWith(end)) files.add(file.toFile());
}
return FileVisitResult.CONTINUE;
}
@Override
public FileVisitResult visitFileFailed(Path file, IOException exc) {
Logger.d("... file:" + file.getFileName());
if (end.equals("")) {
files.add(file.toFile());
} else {
if (file.endsWith(end)) files.add(file.toFile());
}
return FileVisitResult.CONTINUE;
}
@Override
public FileVisitResult postVisitDirectory(Path dir, IOException exc) {
Logger.d("... file:" + dir.getFileName());
return FileVisitResult.CONTINUE;
}
});
}
/**
* recursion
*/
private int factorial (int x) {
if (x > 1) return (x*(factorial(x-1)));
else if (x == 1) return x;
else return 0;
}
}
安卓 + Kotlin
为Kotlin Android扩展添加依赖项: 实现“androidx.core: core-ktx: {latestVersion}’ 从uri获取文件: uri.toFile ()
