Copy a ZipEntry into another zip file

[Wang Weijun]

Hi Sherman

The jarsigner tool contains these 2 methods to copy a ZipEntry into the signer 
jar:

private void writeEntry(ZipFile zf, ZipOutputStream os, ZipEntry ze)
throws IOException
{
    ZipEntry ze2 = new ZipEntry(ze.getName());
    ze2.setMethod(ze.getMethod());
    ze2.setTime(ze.getTime());
    ze2.setComment(ze.getComment());
    ze2.setExtra(ze.getExtra());
    if (ze.getMethod() == ZipEntry.STORED) {
        ze2.setSize(ze.getSize());
        ze2.setCrc(ze.getCrc());
    }
    os.putNextEntry(ze2);
    writeBytes(zf, ze, os);
}

/**
 * Writes all the bytes for a given entry to the specified output stream.
 */
private synchronized void writeBytes
    (ZipFile zf, ZipEntry ze, ZipOutputStream os) throws IOException {
    int n;

    InputStream is = null;
    try {
        is = zf.getInputStream(ze);
        long left = ze.getSize();

        while((left > 0) && (n = is.read(buffer, 0, buffer.length)) != -1) {
            os.write(buffer, 0, n);
            left -= n;
        }
    } finally {
        if (is != null) {
            is.close();
        }
    }
}

Several questions:

1. Why cannot I just call os.putNextEntry(ze) or at least os.putNextEntry(new 
ZipEntry(ze))? Maybe some fields (say, compressed size) should not be copied 
over? If ze2 must be this way, shall I also copy the flag field?

2. In writeBytes(), why does the getSize() return value need to be used? 
Shouldn't we just transfer all bytes from is to os?

Thanks
Max