In my android App I download some photographs from the internet.How can I verify that an image from the web is correctly downloaded? I've thought of checking the file's size I've just written on sd is greater that zero, but I don't know if this is sufficient. this is my code
String filename =title.replace(" ","")+j+".nomedia";
File destination = new File(MyApplication.getPhotoStorage() ,filename);
URL url = new URL (url_image);
InputStream is = url.openStream();
OutputStream os = new FileOutputStream(destination);
byte[] b = new byte[2048];
int length;
while ((length = is.read(b)) != -1) {
os.write(b, 0, length);
}
is.close();
os.close();
localPhotosUrl.add(destination.getAbsolutePath());
The only possibility I can think of is comparing the files checksums. Thus the server would have to provide the checksums for the files it provides. Then youl would download the file and the checksum, generate the checksum for the downloaded file locally and then compare the downloaded checksum with the generated. The checksums can be generated for example with MD5 but there are other hashing algorithms, too.
Here is shown how you can generate the MD5 checksum for files in Java without much overhead: Getting a File's MD5 Checksum in Java
For your code it would be applied like this:
String filename =title.replace(" ","")+j+".nomedia";
File destination = new File(MyApplication.getPhotoStorage() ,filename);
URL url = new URL (url_image);
OutputStream os = new FileOutputStream(destination);
MessageDigest md = MessageDigest.getInstance("MD5");
try (InputStream is = url.openStream()) {
DigestInputStream dis = new DigestInputStream(is, md);
byte[] b = new byte[2048];
int length;
while ((length = dis.read(b)) != -1) {
os.write(b, 0, length);
}
}
byte[] digest = md.digest();
os.close();
localPhotosUrl.add(destination.getAbsolutePath());
I guess the easiest way here would be to try to decode it with Bitmap.DecodeFile. If your bitmap can properly be loaded, then it has been downloaded successfully.
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(path, options);
int width = opts.outWidth;
int height = opts.outHeight;
We use options.inJustDecodeBounds so that as to keep memory usage low. We don't want a copy of the bitmap but just to check the decoder knows what to do with the file.
If width and height are greater than zero, your bitmap is not corrupted.
Obviously this only works because you are downloading photos and not some random files. If these can ben any kind of files then the md5 answer is a good one.
Unless the server also provides some sort of hash value alongside the files (SHA1, MD5, etc.), you can't really. You could try parsing the image file (create a Bitmap, etc.) object, but that could be too memory intensive if you are downloading a lot of files. Just keep it best effort :)
Related
Suppose I have the following code that will download something from my website.
URL website = new URL(url);
ReadableByteChannel rbc = Channels.newChannel(website.openStream());
FileOutputStream fos = new FileOutputStream("something.zip");
fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
fos.close();
I want to make a JProgressBar that would display the progress of the file that is being downloaded. To achieve this, I know that one way is to get the total size of the file and the currently downloaded bytes of the file, then get the percent. Here is the following code for getting the size of the file:
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("HEAD");
long fileSize = conn.getContentLengthLong();
However, getting the downloaded bytes of FileOutputStream is difficult, because you have to make loop that keeps track of the current bytes that are being downloaded. How would you be able to achieve this then?
Note: The algorithm should be suitable for very large files, as the files I am downloading from the internet are one gigabyte in size.
I provide below the code snippet you can look into it. Basically, you have to calculate the number of bytes and then make a calculation by diving into 100 to make some percentage.
InputStream inputStream = util.getInputStream();
// opens an output stream to save into file
FileOutputStream outputStream = new FileOutputStream(saveFilePath);
byte[] buffer = new byte[BUFFER_SIZE];
int bytesRead = -1;
long totalBytesRead = 0;
int percentCompleted = 0;
long fileSize = util.getContentLength();
while ((bytesRead = inputStream.read(buffer)) != -1) {
outputStream.write(buffer, 0, bytesRead);
totalBytesRead += bytesRead;
percentCompleted = (int) (totalBytesRead * 100 / fileSize);
setProgress(percentCompleted);
For more details, refer this link
I'm trying to get the url of a range of images like that:
for(Element img : document.select(".left-column .strillo-content .lazy img[src]")) {
InputStream input = new java.net.URL(imageMainUrl).openStream();
Bitmap bitmap = BitmapFactory.decodeStream(input);
images.add(bitmap);
}
but everytime I trying to run my app I get this warning:
java.net.MalformedURLException: Unknown protocol: data
at java.net.URL.<init>(URL.java:184)
at java.net.URL.<init>(URL.java:127)
so I have tried to print the URL and I get this:
data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7
and I can figure out why, because I'm 100% sure that the element I select is corrent and also I do the same process with other section of the website and it works..
UPDATE 1:
I have tried this method to decode the ´base64´ image:
byte[] decodedString = Base64.decode(imageMainUrl, Base64.DEFAULT);
Bitmap bitmap = BitmapFactory.decodeByteArray(decodedString, 0, decodedString.length);
but the result is the same..
It's the data URI scheme
http://en.wikipedia.org/wiki/Data_URI_scheme
It allows to add inline data in your URI.
Extract the base64 part of the URI and get a byte array with parseBase64Binary, more information here : http://docs.oracle.com/javase/7/docs/api/javax/xml/bind/DatatypeConverter.html#parseBase64Binary%28java.lang.String%29
Use this array to build a ByteArrayInputStream
Use your BitmapFactory to decode it into a Bitmap
edit
This code works, it give a 1px*1px gif image. I used org.apache.commons.codec.binary.Base64 from commons-codec
String uri = "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7";
byte[] decodedString = Base64.decodeBase64(uri.substring(uri.indexOf("data:image/gif;base64,") + "data:image/gif;base64,".length()));
ByteArrayInputStream is = new ByteArrayInputStream(decodedString);
FileOutputStream os = new FileOutputStream(new File("/tmp/test.gif"));
byte[] buffer = new byte[1024];
int length;
// copy the file content in bytes
while ((length = is.read(buffer)) > 0)
{
os.write(buffer, 0, length);
}
is.close();
os.close();
I want to use java(httpurlconnection class) to download a pdf file,but have some thing puzzle,the core code is:
BufferedInputStream inputStream = new BufferedInputStream(httpConn.getInputStream());
OutputStream output = new FileOutputStream("F:/httpclient-tutorial.pdf");
byte[] infoBytes = new byte[BUFFER];
while(inputStream.read(infoBytes) != -1){
output.write(infoBytes, 0, BUFFER);
}
Question:when the BUFFER is 1024,get the pdf file is larger than real one;but the BUFFER is 8,then it's ok. I don't know why it is? Has anyone know about that?
You're unconditionally writing out the whole of the buffer on each iteration. You should only write out as many bytes as you've just read:
int bytesRead;
while((bytesRead = inputStream.read(infoBytes)) != -1){
output.write(infoBytes, 0, bytesRead);
}
What is the efficient way to encode and decode an audio file in android
I have tried the Base64 as below but after decoding the file size get increased.
Encode
ByteArrayOutputStream objByteArrayOS = new ByteArrayOutputStream();
File file = new File(path);
FileInputStream objFileIS;
try {
objFileIS = new FileInputStream(file);
byte[] byteBufferString = new byte[1024];
for (int readNum; (readNum = objFileIS.read(byteBufferString)) != -1;) {
objByteArrayOS.write(byteBufferString, 0, readNum);
System.out.println("read " + readNum + " bytes,");
byte[] bytes = FileUtils.readFileToByteArray(file);
strAttachmentCoded = Base64.encodeToString(bytes,
Base64.DEFAULT);
Decode
byte[] decoded = Base64.decode(strAttachmentCoded,
Base64.DEFAULT);
// byte[] decoded1 = Base64.decode(byteBinaryData1, 0);
File file1 = new File(pathAudio);
FileOutputStream os = new FileOutputStream(file1, true);
os.write(decoded);
os.close();
i want audio in String format to send to server and retrieve the same as per the user requirement.
wikipedia:base64 (rfc3548) is the right method to choose I would think. It is most common now I think having taken over from wikipedia:uuencoding.
To answer the question . . .
You could add some padding. The wikipedia article on base64 gives a good example of padding.
Or you could add a header to your audio string including length. The header could also include other control data so it may be something you want to include anyway.
I have a FileInputStream created using Context.openFileInput(). I now want to convert the file into a byte array.
Unfortunately, I can't determine the size of the byte array required for FileInputStream.read(byte[]). The available() method doesn't work, and I can't create a File to check it's length using the specific pathname, probably because the path is inaccessible to non-root users.
I read about ByteArrayOutputStream, and it seems to dynamically adjust the byte array size to fit, but I can't get how to read from the FileInputStream to write to the ByteArrayOutputStream.
This should work.
InputStream is = Context.openFileInput(someFileName);
ByteArrayOutputStream bos = new ByteArrayOutputStream();
byte[] b = new byte[1024];
while ((int bytesRead = is.read(b)) != -1) {
bos.write(b, 0, bytesRead);
}
byte[] bytes = bos.toByteArray();
This is the easiest way
FileInputStream fis = openFileInput(fileName);
byte[] buffer = new byte[(int) fis.getChannel().size()];
fis.read(buffer);
You can pre-allocate the byte array using
int size = context.getFileStreamPath(filename).length();
This way, you will avoid allocating memory chunks every time your ByteArrayOutputStream fills up.
For the method to work on any device and aplication you just need to replace:
InputStream is = Context.getContentResolver().openInputStream(yourFileURi);
This way you can encode external files as well.