Codename One API to append / merge files - codenameone

Question

To merge Storage files in Codename One I elaborated this solution:
/**
* Merges the given list of Storage files in the output Storage file.
* #param toBeMerged
* #param output
* #throws IOException
*/
public static synchronized void mergeStorageFiles(List<String> toBeMerged, String output) throws IOException {
if (toBeMerged.contains(output)) {
throw new IllegalArgumentException("The output file cannot be contained in the toBeMerged list of input files.");
}
// Note: the temporary file used for merging is placed in the FileSystemStorage because it offers the method
// openOutputStream(String file, int offset) that allows appending to a stream. Storage doesn't have a such method.
long writtenBytes = 0;
String tempFile = FileSystemStorage.getInstance().getAppHomePath() + "/tempFileUsedInMerge";
for (String partialFile : toBeMerged) {
InputStream in = Storage.getInstance().createInputStream(partialFile);
OutputStream out = FileSystemStorage.getInstance().openOutputStream(tempFile, (int) writtenBytes);
Util.copy(in, out);
writtenBytes = FileSystemStorage.getInstance().getLength(tempFile);
}
Util.copy(FileSystemStorage.getInstance().openInputStream(tempFile), Storage.getInstance().createOutputStream(output));
FileSystemStorage.getInstance().delete(tempFile);
}
This solution is based on the API FileSystemStorage.openOutputStream(String file, int offset), that is the only API that I found to allow to append the content of a file to another.
Are there other API that can be used to append or merge files?
Thank you

Answer 1

Since you end up copying everything to a Storage entry I don't see the value of using FileSystemStorage as an intermediate merging tool.
The only reason I can think of is integrity of the output file (e.g. if failure happens while writing) but that can happen here too. You can guarantee integrity by setting a flag e.g. creating a file called "writeLock" and deleting it when write has finished successfully.
To be clear I would copy like this which is simpler/faster:
try(OutputStream out = Storage.getInstance().createOutputStream(output)) {
for (String partialFile : toBeMerged) {
try(InputStream in = Storage.getInstance().createInputStream(partialFile)) {
Util.copyNoClose(in, out, 8192);
}
}
}