How to Read File Bytes in an Android Application

How do I read a file in bytes in my Android application after selecting it from the SD card?

private List<String> getListOfFiles(String path) {

   File files = new File(path);

   FileFilter filter = new FileFilter() {

      private final List<String> exts = Arrays.asList("jpeg", "jpg", "png", "bmp", "gif","mp3");

      public boolean accept(File pathname) {
         String ext;
         String path = pathname.getPath();
         ext = path.substring(path.lastIndexOf(".") + 1);
         return exts.contains(ext);
      }
   };

   final File [] filesFound = files.listFiles(filter);
   List<String> list = new ArrayList<String>();
   if (filesFound != null && filesFound.length > 0) {
      for (File file : filesFound) {
         list.add(file.getName());
      }
   }
   return list;
}

To read file content as bytes in an Android application, you can utilize Java's File and FileInputStream classes. Below is a step-by-step guide to read the selected file from the SD card and convert its contents into a byte array.

import java.io.*;

public byte[] readFileInBytes(String filePath) throws IOException {
    File file = new File(filePath);
    byte[] bytes = new byte[(int) file.length()];

    try (FileInputStream fis = new FileInputStream(file);
         ByteArrayOutputStream bos = new ByteArrayOutputStream()) {
         int bytesRead;
         while ((bytesRead = fis.read(bytes)) != -1) {
             bos.write(bytes, 0, bytesRead);
         }
         bos.flush();
    }
    return bos.toByteArray();
}

Causes

• The file may not exist at the provided path.
• Permission issues might prevent accessing files on the SD card.
• Incorrect handling of the input stream might lead to exceptions.

Solutions

• Use FileInputStream to read the file.
• Wrap the FileInputStream with ByteArrayOutputStream to convert to byte array.
• Ensure that your app has appropriate permissions to read external storage.

Mistake: Not checking for null when trying to list files.

Solution: Always check if the returned array of files is null before processing.

Mistake: Lack of permissions for accessing external storage.

Solution: Ensure the app has READ_EXTERNAL_STORAGE permission in the manifest and handle runtime permission requests.

Mistake: Assuming the file size will always fit in memory.

Solution: For very large files, consider reading in chunks instead of loading into a byte array directly.