Question

I’m writing a tool to do some minor text replacement in a DOCX file, which is a zipped format. My method is to copy ZipEntry contents from entries in the original file into the modified file using a ZipOutputStream. For most DOCX files this works well, but occasionally I will encounter ZipExceptions regarding discrepancies between the contents I’ve written and the meta-information contained in the ZipEntry (usually a difference in compressed size).

Here’s the code I’m using to copy over contents. I’ve stripped out error handling and document processing for brevity; I haven’t had issues with the document entry so far.

ZipFile         original = new ZipFile(INPUT_FILENAME);
ZipOutputStream outputStream = new ZipOutputStream(new FileOutputStream(OUTPUT_FILE));
Enumeration     entries = original.entries();
byte[]          buffer = new byte[512];
while (entries.hasMoreElements()) {
    ZipEntry    entry = (ZipEntry)entries.nextElement();
    if  ("word/document.xml".equalsIgnoreCase(entry.getName())) {
        //perform special processing
    }
    else{
        outputStream.putNextEntry(entry);
        InputStream in = original.getInputStream(entry);
        while (0 < in.available()){
            int read = in.read(buffer);
            outputStream.write(buffer,0,read);
        }
        in.close();
    }
    outputStream.closeEntry();
}
outputStream.close();

What is the proper or idiomatic way to directly copy ZipEntry objects from one ZipFile to another?

Answer 1

I have found a workaround that avoids the error. By creating a new ZipEntry with only the name field set I’m able to copy over contents without issue.

ZipFile         original = new ZipFile(INPUT_FILENAME);
ZipOutputStream outputStream = new ZipOutputStream(new FileOutputStream(OUTPUT_FILE));
Enumeration     entries = original.entries();
byte[]          buffer = new byte[512];
while (entries.hasMoreElements()) {
    ZipEntry    entry = (ZipEntry)entries.nextElement();
    if  ("word/document.xml".equalsIgnoreCase(entry.getName())) {
        //perform special processing
    }
    else{
        // create a new empty ZipEntry
        ZipEntry newEntry = new ZipEntry(entry.getName()); 
//      outputStream.putNextEntry(entry);
        outputStream.putNextEntry(newEntry);
        InputStream in = original.getInputStream(entry);
        while (0 < in.available()){
            int read = in.read(buffer);
            if (read > 0) {
              outputStream.write(buffer,0,read);
            }
        }
        in.close();
    }
    outputStream.closeEntry();
}
outputStream.close();

However, I this method loses any meta-information stored in the fields of original ZipEntry (e.g.: comment, extra). The API docs aren’t clear on whether this is important.