ZipFile中ZipOutputStream.EOCD_SIG字段代表什么意思

private void positionAtCentralDirectory() throws IOException {
        boolean found = false;
        long off = this.archive.length() - 22L;
        byte[] sig;
        if (off >= 0L) {
            this.archive.seek(off);
            sig = ZipOutputStream.EOCD_SIG;

            for(int curr = this.archive.read(); curr != -1; curr = this.archive.read()) {
                if (curr == sig[0]) {
                    curr = this.archive.read();
                    if (curr == sig[1]) {
                        curr = this.archive.read();
                        if (curr == sig[2]) {
                            curr = this.archive.read();
                            if (curr == sig[3]) {
                                found = true;
                                break;
                            }
                        }
                    }
                }

                this.archive.seek(--off);
            }
        }

        if (!found) {
            throw new ZipException("archive is not a ZIP archive");
        } else {
            this.archive.seek(off + 16L);
            sig = new byte[4];
            this.archive.readFully(sig);
            this.archive.seek(ZipLong.getValue(sig));
        }
    }