Develop Reference

Querying Android ContentResolver for gallery files and determining image vs video

I'm trying to make a simple Android app for my own phone that looks at my Gallery, and for each image/video file:
creates a Bitmap thumbnail of the file
records the file's absolute path on the phone
Essentially, I'll have the following data model:
public class MediaFileModel {
private Bitmap thumbnail;
private String absPath;
// ctor, getters and setters omitted for brevity
}
And I need something that looks at all the files in my Gallery and yields a List<MediaFileModel>. My best attempt is here:
public List<MediaFileModel> getAllGalleryMedia() {
String[] projection = { MediaStore.MediaColumns.DATA };
List<MediaFileModel> galleryMedia = new ArrayList<>();
Cursor cursor = getActivity().getContentResolver().query(
MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
projection,
null,
null,
null);
// I believe here I'm iterating over all the gallery files (???)
while(cursor.moveToNext()) {
MediaFileModel next = new MediaFileModel();
// is this how I get the abs path of the current file?!?
String absPath = cursor.getString(cursor.getColumnIndex(MediaStore.MediaColumns.DATA));
Bitmap thumbnail = null;
if (true /* ??? cursor is pointing to a media file that is an image/photo ??? */) {
thumbnail = ThumbnailUtils.extractThumbnail(BitmapFactory.decodeFile(absPath), 64, 64);
} else {
// else we have a video (I assume???)
thumbnail = ThumbnailUtils.createVideoThumbnail(absPath, MediaStore.Images.Thumbnails.MINI_KIND);
}
next.setThumbnail(thumbnail);
next.setAbsPath(absPath);
galleryMedia.add(next);
}
return galleryMedia;
}
However I'm not sure if my media query is setup correctly and I'm definitely not sure how to determine whether the file is an image/photo of a video, which I (believe I) need so that I can use the correct method for obtaining the thumbnail Bitmap.
Can anyone help nudge me over the finish line here?

Here is a code I was using for something similar, I hope this will help:
//The code has been removed
Note: Sorry I've removed the code because I am not sure if it has some portion copied from other open-sourced codes, I am using it in my apps but I can't remember if it is quoted from other source, so I've removed it, also it could be auto-completed using github copilot

Brother SDK Calling PrintImage causes JNI DETECTED ERROR IN APPLICATION: GetStringUTFChars received NULL jstring

Currently working with the Brother SDK for a label Printer and when I call Asset Manager, the Bitmap appears but when it is parsed to print image it crashes.
if (myPrinter.startCommunication()) {
AssetManager assetManager = getAssets();
Bitmap bitmap = null;
try{
bitmap = BitmapFactory.decodeStream(new BufferedInputStream(assetManager.open("meme.bmp")));
}catch(Exception e){
e.printStackTrace();
}
PrinterStatus result = myPrinter.printImage(bitmap);
if (result.errorCode != ErrorCode.ERROR_NONE) {
Log.d("TAG", "ERROR - " + result.errorCode);
}
myPrinter.endCommunication();
}
Stack Readout
Debugger printout, with Image Preview.

For anyone got stuck even if they made sure they have the write permission granted, it was about the working path b-PAC trying to create.
The default path is: /storage/emulated/0/com.brother.ptouch.sdk/template
Just define your own path in PrinterInfo object. Set the workPath variable as such:
PrinterInfo mPrintSettings = mPrinter.getPrinterInfo();
mPrintSettings.workPath = "your/custom/work/path";
It says in the document that you don't even need the permission if you do so. But I'm going to keep it anyway.

I had this issue as well. Have you made sure that the android.permission.WRITE_EXTERNAL_STORAGE permisson is granted.
Having this in the manifest file wasn't enough, but by requesting permisson from the user, this specific error went away.
Credit to this post on SO

Why is DocumentFile so slow, and what should I use instead?

I want to create something like "PDF Viewer app". Application will search for all *.pdf files in location chosen by user. User can choose this folder by this function:
Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
startActivityForResult(intent, REQUEST_CODE);
Then I get DocumentFile (folder):
#Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
if (resultCode == getActivity().RESULT_OK && requestCode == REQUEST_CODE) {
Uri uriTree = data.getData();
DocumentFile documentFile = DocumentFile.fromTreeUri(getActivity(), uriTree);
//rest of code here
}
}
Why I chose this method of selecting folder? Because I want to make possible to choose Secondary Storage (you know, in Android >= 5.0, you can't access Secondary Storage with Java.io.file).
Ok, so I get folder with all *.pdf as DocumentFile. Then I call:
for(DocumentFile file: documentFile.listFiles()){
String fileNameToDisplay = file.getName();
}
And this is VERY SLOW. It takes almost 30 seconds when there are ~600 files in chosen folder. To prove it, I chose directory from External Storage (not secondary storage), and then I tried two solutions: DocumentFile and File.
File version looks like it:
File f = new File(Environment.getExternalStorageDirectory()+"/pdffiles");
for(File file: f.listFiles()){
String fileNameToDisplay = file.getName();
}
}
Second version works about 500x faster. There is almost no time in displaying all files on List View.
Why is DocumentFile so slow?

If you read the source code of TreeDocumentFile, you will find that each call to listFiles() and getName() invokes ContentResolver#query() under the hood. Like CommonsWare said, this would perform hundreds of queries, which is very inefficient.
Here is the source code of listFiles():
#Override
public DocumentFile[] listFiles() {
final ContentResolver resolver = mContext.getContentResolver();
final Uri childrenUri = DocumentsContract.buildChildDocumentsUriUsingTree(mUri,
DocumentsContract.getDocumentId(mUri));
final ArrayList<Uri> results = new ArrayList<>();
Cursor c = null;
try {
c = resolver.query(childrenUri, new String[] {
DocumentsContract.Document.COLUMN_DOCUMENT_ID }, null, null, null);
while (c.moveToNext()) {
final String documentId = c.getString(0);
final Uri documentUri = DocumentsContract.buildDocumentUriUsingTree(mUri,
documentId);
results.add(documentUri);
}
} catch (Exception e) {
Log.w(TAG, "Failed query: " + e);
} finally {
closeQuietly(c);
}
final Uri[] result = results.toArray(new Uri[results.size()]);
final DocumentFile[] resultFiles = new DocumentFile[result.length];
for (int i = 0; i < result.length; i++) {
resultFiles[i] = new TreeDocumentFile(this, mContext, result[i]);
}
return resultFiles;
}
In this function call, listFiles() made a query that only selects the document ID column. However, in your case you also want the file name for each file. Therefore, you can add the column COLUMN_DISPLAY_NAME to the query. This would retrieve the filename and document ID (which later you will convert it into Uri) in a single query and is much more efficient. There are also many other columns available such as file type, file size, and last modified time, which you may want to retrieve them as well.
c = resolver.query(mUri, new String[] {
DocumentsContract.Document.COLUMN_DOCUMENT_ID,
DocumentsContract.Document.COLUMN_DISPLAY_NAME
}, null, null, null);
Within the while loop, retrieve the filename by
final String filename = c.getString(1);
The above modified code is able to instantly retrieve the Uri and filename of a directory with 1000+ files.
In summary, my recommendation is to avoid using DocumentFile if you are working with more than just a few files. Instead use ContentResolver#query() to retrieve the Uri and other information by selecting multiple columns in the query. For file operations, use the static methods in the DocumentsContract class by passing the appropriate Uri's.
By the way, it seems that the sortOrder parameter of ContentResolver#query() gets completely ignored in the above code snippet when tested on Android 11 and Android 9. I would manually sort the results instead of relying on the query order.

Why is DocumentFile so slow?
For ~600 files you are performing ~600 requests of a ContentProvider to get the display name, which means ~600 IPC transactions.
Instead, use MediaStore to query for all indexed media with the application/pdf MIME type.

In case someone comes up here still looking for a solution,
I built a wrapper over this with some pretty good performance.
You can check the wrapper & performance info. here:
https://github.com/ItzNotABug/DocumentFileCompat

To use DocumentsContract to obtain children documents, see https://developer.android.com/reference/android/provider/DocumentsContract.html#buildChildDocumentsUriUsingTree(android.net.Uri, java.lang.String).
The Uri returned from ACTION_OPEN_DOCUMENT_TREE is a tree document URI. Use the above method to build the Uri to query all children documents.
The root document ID can be obtained using https://developer.android.com/reference/android/provider/DocumentsContract.html#getTreeDocumentId(android.net.Uri) with the Uri returned from ACTION_OPEN_TREE_DOCUMENT.

To obtain a speed little less than the one from File use DocumentsContract instead of DocumentFile to list the content of trees obtained with Intent.ACTION_OPEN_DOCUMENT_TREE.

Error: org.apache.pdfbox.pdmodel.graphics.xobject.PDXObjectForm cannot be cast to org.apache.pdfbox.pdmodel.graphics.xobject.PDXObjectImage

I am trying to extract image from the pdf using pdfbox. I have taken help from this post . It worked for some of the pdfs but for others/most it did not. For example, I am not able to extract the figures in this file
After doing some research I found that PDResources.getImages is deprecated. So, I am using PDResources.getXObjects(). With this, I am not able to extract any image from the PDF and instead get this message at the console:
org.apache.pdfbox.pdmodel.graphics.xobject.PDXObjectForm cannot be cast to org.apache.pdfbox.pdmodel.graphics.xobject.PDXObjectImage
Now I am stuck and unable to find the solution. Please assist if anyone can.
//////UPDATE AS REPLY ON COMMENTS///
I am using pdfbox-1.8.10
Here is the code:
public void getimg ()throws Exception {
try {
String sourceDir = "C:/Users/admin/Desktop/pdfbox/mypdfbox/pdfbox/inputs/Yavaa.pdf";
String destinationDir = "C:/Users/admin/Desktop/pdfbox/mypdfbox/pdfbox/outputs/";
File oldFile = new File(sourceDir);
if (oldFile.exists()){
PDDocument document = PDDocument.load(sourceDir);
List<PDPage> list = document.getDocumentCatalog().getAllPages();
String fileName = oldFile.getName().replace(".pdf", "_cover");
int totalImages = 1;
for (PDPage page : list) {
PDResources pdResources = page.getResources();
Map pageImages = pdResources.getXObjects();
if (pageImages != null){
Iterator imageIter = pageImages.keySet().iterator();
while (imageIter.hasNext()){
String key = (String) imageIter.next();
Object obj = pageImages.get(key);
if(obj instanceof PDXObjectImage) {
PDXObjectImage pdxObjectImage = (PDXObjectImage) obj;
pdxObjectImage.write2file(destinationDir + fileName+ "_" + totalImages);
totalImages++;
}
}
}
}
} else {
System.err.println("File not exist");
}
}
catch (Exception e){
System.err.println(e.getMessage());
}
}
//// PARTIAL SOLUTION/////
I have solved the problem of the error message. I have updated the correct code in the post as well. However, the problem remains the same. I am still not able to extract the images from few of the files. Like the one, I have mentioned in this post. Any solution in that regards.

The first problem with the original code is that XObjects can be PDXObjectImage or PDXObjectForm, so it is needed to check the instance. The second problem is that the code doesn't walk PDXObjectForm recursively, forms can have resources too. The third problem (only in 1.8) is that you used getResources() instead of findResources(), getResources() doesn't check higher levels.
Code for 1.8 can be found here:
https://svn.apache.org/viewvc/pdfbox/branches/1.8/pdfbox/src/main/java/org/apache/pdfbox/ExtractImages.java?view=markup
Code for 2.0 can be found here:
https://svn.apache.org/viewvc/pdfbox/trunk/tools/src/main/java/org/apache/pdfbox/tools/ExtractImages.java?view=markup&sortby=date
(Even these are not always perfect, see this answer)
The fourth problem is that your file doesn't have any XObjects at all. All "graphics" were really vector drawings, these can't be "extracted" like embedded images. All you could do is to convert the PDF pages to images, and then mark and cut what you need.

How to split the string a android?

I am working on android application. I am getting the image from gallery. Also I am getting the image path from gallery. Now my requirement is I want to get only the image name with the extension . How can I do that? Please help me.
String imgpath = "/mnt/sdcard/joke.png";
The image extension can be anything joke.png or joke.jpeg. I need to get the image name with extension finally.
i.e I want to split the above string and get only joke.png.
How can I achieve that? Please help me in this regard.

String imgpath = "/mnt/sdcard/joke.png";
String result = imgpath.substring(imgpath.lastIndexOf("/") + 1);
System.out.println("Image name " + result);
Output :-
Image name joke.png
You should read How do I get the file name from a String containing the Absolute file path?

You can do that in Android like in any Java program:
String[] parts = imagepath.split("/");
String result = parts[parts.length-1];

String s[] = imgpath.split("/");
String result = s[s.length-1];

String imgName = imgpath.substring((imgpath.lastIndexOf("/") + 1), imgpath.length());

You can get this with Regex too, if that is the hammer you have in your hands:
String fileName = null;
Pattern pattern = Pattern.compile("(^|.*/)([^/]*)$");
Matcher m = pattern.getMatcher(filenameWithPath);
if(matcher.matches()) {
fileName = matcher.group(2);
}
But don't be tempted to do this. This is less readable, and probably even slower than the other methods.