How to use java.util.zip for epub

Question

I have to edit the html files of epubs programmatically so what I did was to unzip the .epub and create a parser to make the necessary edits for the html files. However, when I convert them back into an .epub using my code, EpubChecker shows that:

Error: Required META-INF/container.xml resource is missing

When I uncompressed my edited .epub, the container.xml is present and is not missing.

I understand that the mimetype and META-INF has to be zipped first. Here is my code to convert the files back to epub:

    FileOutputStream fos = new FileOutputStream(zipFile);
    ZipOutputStream zos = new ZipOutputStream(fos);

    System.out.println("Output to Zip : " + zipFile);
    writeMimeType(zos);
    ZipEntry container = new ZipEntry("META-INF\\container.xml");
    zos.putNextEntry(container);
    FileInputStream inMime2 = new FileInputStream(SOURCE_FOLDER + File.separator + "META-INF\\container.xml");
    int len2;
    while((len2 = inMime2.read(buffer)) > 0){
        zos.write(buffer, 0, len2);
    }
    inMime2.close();
    for(String file : this.fileList){
            if(!file.toString().equals("mimetype") && !file.toString().equals("META-INF\\container.xml")){
                System.out.println("File Added : " + file);
                ZipEntry ze= new ZipEntry(file);
                zos.putNextEntry(ze);

                FileInputStream in = 
                    new FileInputStream(SOURCE_FOLDER + File.separator + file);

                int len;
                while ((len = in.read(buffer)) > 0) {
                        zos.write(buffer, 0, len);
                }

                in.close();
           }
    }

    zos.closeEntry();
    zos.close();

When I manually zip the directory using WinRar, no errors are seen and it works properly. I don't know what I am doing wrong. Can somebody please help me?Thank you.

Answer 1

Looks like you're on Windows, so your FileInputStream(SOURCE_FOLDER + File.separator + "META-INF\\container.xml"); statement is correct for the OS, but I'd guess you need to change the other 2 strings to use the forward slash for the zipentry path.

ZipEntry container = new ZipEntry("META-INF\\container.xml");

try instead as

ZipEntry container = new ZipEntry("META-INF/container.xml");

and change

if(!file.toString().equals("mimetype") && !file.toString().equals("META-INF\\container.xml")){

to

if(!file.toString().equals("mimetype") && !file.toString().equals("META-INF/container.xml")){

accordingly.

You may need to adjust your other ZipEntry's as well. From the ZIP spec (section "4.4.17 file name"):

All slashes MUST be forward slashes '/' as opposed to backwards slashes '\'