Preferred way to use Java ZipOutputStream and BufferedOutputStream

Question

In Java does it matter whether I instantiate a ZipOutputStream first, or the BufferedOutputStream first? Example:

FileOutputStream dest = new FileOutputStream(fi         


        

Answer 1

You should always wrap the BufferedOutputStream with the ZipOutputStream, never the other way around. See the below code:

FileOutputStream fos = new FileOutputStream("hello-world.zip");
BufferedOutputStream bos = new BufferedOutputStream(fos);
ZipOutputStream zos = new ZipOutputStream(bos);

try {
    for (int i = 0; i < 10; i++) {
        // not available on BufferedOutputStream
        zos.putNextEntry(new ZipEntry("hello-world." + i + ".txt"));
        zos.write("Hello World!".getBytes());
        // not available on BufferedOutputStream
        zos.closeEntry();
    }
}
finally {
    zos.close();
}

As the comments say the putNextEntry() and closeEntry() methods are not available on the BufferedOutputStream. Without calling those methods ZipOutputStream throws an exception java.util.zip.ZipException: no current ZIP entry.

For the sake of completeness, it is worth noting that the finally clause only calls close() on the ZipOutputStream. This is because by convention all built-in Java output stream wrapper implementations propagate closing.

EDIT

I just tested it the other way around. It turns out that wrapping a ZipOutputStream with BufferedOutputStream and then only calling write() on it (without creating / closing entries) will not throw a ZipException. Instead the resulting ZIP file will be corrupt, without any entries inside it.

Answer 2

You should:

ZipOutputStream out =  new ZipOutputStream(new BufferedOutputStream(dest));

because you want to buffer the writing to the disc (because this is much more efficient in big data blocks than in a lot of little ones).

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This

new BufferedOutputStream(new ZipOutputStream(dest));

would buffer before zip compression. But this all happens in the memory and does not need buffering because a lot of little memory accesses are about the same speed as a few big ones. In memory general the needed time is proportional to the number of bytes read/write.

As mentioned in the comments:

The methods of ZipOutputStream which are not part of BufferedOutputStream would not be available also. E.g. putNextEntry and closeEntry.