对于这种情况，尤其是在Android上，字节查找的方式通常更快。
这样，我通过设置一个类FileHelper来负责解决该问题，该类负责处理通过流从文件中读取/写入文件的字节，并UriHelper负责确定Uri的路径和权限。
据一般所知，string.getBytes((charset == null) ? DEFAULT_CHARSET:charset)可以帮助我们将所需的字符串转换为所需的字节。
如何让UriHelper和FileHelper将Uri记录的图片复制到文件中，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;
}
}
