Java - Create a ZIP file with duplicate entries

Question

I'd like to create a zip which stores two different files with the same name, but I'm unable (using java.util.zip.ZipOutputStream) due to

java.util.zip.ZipException: duplicate entry:

exception. I know that it's possible, but I need an advise which library I can use for that purposes. Thanks!

UPD the code I'm using:

File zipFile = new File("C:\\Users\\user\\Desktop\\old.zip");
File outFile = new File("C:\\Users\\user\\Desktop\\new.zip");
if(!outFile.exists()) {
    outFile.getParentFile().mkdirs();
    outFile.createNewFile();
}

byte[] buf = new byte[1024];
ZipInputStream zin = new ZipInputStream(new FileInputStream(zipFile));
ZipOutputStream out = new ZipOutputStream(new FileOutputStream(outFile));

ZipEntry entry = zin.getNextEntry();
while (entry != null) {
    String name = entry.getName();
    out.putNextEntry(new ZipEntry(name));
    int len;
    while ((len = zin.read(buf)) > 0) {
        out.write(buf, 0, len);
    }
    entry = zin.getNextEntry();

    if("file".equals(name)) {
        File fakeFile = new File("C:\\Users\\user\\Desktop\\file");
        InputStream in = new FileInputStream(fakeFile);
        out.putNextEntry(new ZipEntry("file"));
        while ((len = in.read(buf)) > 0) {
            out.write(buf, 0, len);
        }
        out.closeEntry();
        in.close();
    }
} 
zin.close();
out.close();

Assonance

Please include a MCVE in your post – Solemnize

I do not think its possible with current Oracle JVM implementation. Why you need to do this? – Chalybeate

@Vampire, added – Assonance

You know that it's possible but you've just proven that it isn't possible. Make up your mind. – Longfellow

@JIV, to bypass a signature restriction (signature checker verifies the first entity, but installed installs the last) – Assonance

@EJP, a library does not allow duplicates. You may check sources hg.openjdk.java.net/jdk7/jdk7/jdk/file/9b8c96f96a0f/src/share/… line 214: if (! names.add(e.name)) { but you may check where names object is used and suddenly only to disallow duplicates. So it's possible but not with that library – Assonance

Answer 1

I was able to bypass restriction thru reflection api:

Field namesField = ZipOutputStream.class.getDeclaredField("names");
namesField.setAccessible(true);
HashSet<String> names = (HashSet<String>) namesField.get(out);

And clearing names after each putNextEntry call

Assonance

You must have really wanted to get those duplicate entries saved to figure out this technique! (p.s. thanks! very handy!) – Snowmobile

Yes, this is very handy if you want to prepare a JAR file for a test with e.g. multiple entries for ServiceLoader. – Pragmatics

@Julius Musseau Yepp, pkzip once used to maintain a folder structure and store file names, only instead of tons of redundant info. – Tmesis

Now that Java 17 bans the use of reflection into java.* packages we need a new way ! – Snowmobile

Answer 2

Putting Ivans answer in something performant.

static final Field zipNamesField = getZipNameField();

private static Field getZipNameField()
{
    try
    {
        Field res = ZipOutputStream.class.getDeclaredField("names");
        res.setAccessible(true);
        return res;
    }
    catch (NoSuchFieldException | SecurityException e)
    {
        e.printStackTrace();
        return null;
    }
}

...

// Loop
((HashSet<String>) zipNamesField.get(out)).clear();
entry = new ZipEntry(...);
out.putNextEntry(entry);

...

Tmesis

Answer 3

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

        HashSet<String> names = new HashSet<String>();
        for (String filePath : fileList) {
            if(names.add(filePath))
            {
            String name = filePath.substring(directory.getAbsolutePath()
                    .length() + 1, filePath.length());
            ZipEntry zipEntry = new ZipEntry(name);

            zos.putNextEntry(zipEntry);
            try (FileInputStream fis = new FileInputStream(filePath)) {
                byte[] buffer = new byte[1024];
                int length;
                while ((length = fis.read(buffer)) >= 0) {
                    zos.write(buffer, 0, length);
                }

            } catch (Exception e) {
                e.printStackTrace();
                throw new Exception();
            }
            zos.closeEntry();
            }

        }
        names.clear();
    } catch (IOException e) {
        e.printStackTrace();
        throw new Exception();
    }

By using HashSet solved my issue of zip duplicate entry

Tobin

Answer 4

This is my solution: adding postfixes for duplicate names:

String SPLIT_FILENAME_EXTENSION_REGEX = "\\.(?=[^\\.]+$)";
Map<String, Integer> namesPostfixes = new HashMap<>();


private void addZipPart(String fullName, InputStream attachmentStream, ZipOutputStream zos,
        Map<String, Integer> namesPostfixes)
        throws IOException, MessagingException {
    String generatedName;
    if (namesPostfixes.containsKey(fullName)) {
        String namePart;
        String extensionPart;
        if (fullName.contains(".")) {
            String[] splittedName = fullName.split(SPLIT_FILENAME_EXTENSION_REGEX);
            namePart = splittedName[0];
            extensionPart = "." + splittedName[1];
        } else {
            namePart = fullName;
            extensionPart = "";
        }
        Integer counter = namesPostfixes.get(fullName);
        generatedName = namePart + "_" + ++counter + extensionPart;
        namesPostfixes.put(fullName, counter);
    } else {
        generatedName = fullName;
        namesPostfixes.put(fullName, 0);
    }
    zos.putNextEntry(
            new ZipEntry(generatedName));
    IOUtils.copy(attachmentStream, zos);
    zos.closeEntry();
}

Ratel

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