I have java app that pulls records from a database table that has a VARBINARY column that contains data for a file.

After pulling the records, the app then creates a ZipEntry for each record, adds it to a ZipOutputStream, and then writes the whole thing to a zip file that is downloaded to the user’s Downloads folder.

Then it is supposed to unzip the zip file.

Here’s the problem – although it is all in one function and the unzipping code occurs after the write code, it always tries to unzip BEFORE the ZipOutputStream has finished creating the zip file, and thus the unzipping never occurs.

I’ve confirmed that this is what happens by putting a wait() condition to force it to wait for a specified period of time after the writing to the ZipOutputStream begins – but it would really be best to do this programmatically such that the completion of the writing to the zip file is the signal to begin unzipping.

This is my code so far:

public void downloadDocuments(HttpServletResponse response) throws IOException, AuthException {

    //Add the files to a ZipOutputStream and save as a zip file
    response.setContentType("application/zip");
    response.setHeader("Content-Disposition", "attachment; filename="allfiles.zip"");
    ZipOutputStream zipOutput = null;

    try {
        zipOutput = new ZipOutputStream(new BufferedOutputStream(response.getOutputStream()));
        List<SupportingDocEntity> docs = documentDao.getDocuments();

        for (int ii=0; ii<docs.size(); ii++) {                
            SupportingDocEntity docEntity = docs.get(ii);
            ZipEntry zipEntry = new ZipEntry(docEntity.getFileName() + docEntity.getFileExtension());
            zipOutput.putNextEntry(new ZipEntry(zipEntry));
            zipOutput.write(docEntity.getContent());
            zipOutput.closeEntry();
        }
        
    } finally {
        if (zipOutput != null) try { zipOutput.close(); } catch (IOException logOrIgnore) { /**/ }
    }



    //How can I make it wait until the zip file is fully created before executing the code below???


    //Unzip the newly-created zip file
    byte[] buffer = new byte[2048];
    ZipInputStream zipInput = new ZipInputStream(new FileInputStream("C:/Users/mydirectory/Downloads/allfiles.zip"));
    try {
        ZipEntry zipEntry;
        while((zipEntry = zipInput.getNextEntry())!=null) {

            String outpath = "C:/Users/mydirectory/Downloads/" + zipEntry.getName();
            FileOutputStream fileOutput = null;
            try {
                fileOutput = new FileOutputStream(outpath);
                int len = 0;
                while ((len = zipInput.read(buffer)) > 0) {
                    fileOutput.write(buffer, 0, len);
                }
            }
            finally {
                // we must always close the output file
                if(fileOutput!=null) fileOutput.close();
            }
        }
    }
    finally {
        // we must always close the zip file.
        zipInput.close();
    }
}

Thanks in advance