Write Object from List to File, using ObjectOutputStream

Question

I'm trying to write the content of a list (object) to disk using ObjectOutputStream.

This is the relevant code:

//Input Filetype is .xlsx with an embedded File (also .xlsx), Output Filetype should be .xlsx (Type of embedded File)
//This code should save the embedded File to D:\\...

List<HSSFObjectData> extrList = new ArrayList<HSSFObjectData>();

HSSFWorkbook embeddedWorkbook = new HSSFWorkbook(pPart.getInputStream());
extrList = embeddedWorkbook.getAllEmbeddedObjects();
ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("D:\\scan_temp\\emb.xlsx"));

oos.writeObject(extrList);
oos.flush();
oos.close();

This code creates a file called emb.xlsx, but the content is not what I expected. If I try to open using notepad, it's something like:

¬í sr java.util.ArrayListxÒ™Ça I sizexp    w    x

What am I doing wrong here? Thanks for any help.

Answer 1

What am I doing wrong here?

You are doing several things wrong:

1. You are misusing the .xlsx extension for a file of serialized objects. That extension is for Excel spreadsheets in XML format. You should use something like .bin , .data , .ser , etc.
2. You are using Serialization when you should be using the I/O facilities built into POI.
3. You are trying to read a binary file with a text editor.
4. You are redundantly callling flush() before close() .

Answer 2

If anyone else is trying the same thing as I did, use the following code (works!):

HSSFWorkbook embeddedWorkbook = new HSSFWorkbook(InputStream);

FileOutputStream fileOut = new FileOutputStream("/outputfilepath.xls");
embeddedWorkbook.write(fileOut);
fileOut.close();

Don't try to get the embedded objects into a list. Just use .write() and that's all. :-)