I have a keystore.jks file with multiple certificate including public and private key

This "all-public-cert.crt" file contain only certificate (public key only) . should not contain any private key in this file.

String keystorePath = ....
InputStream is = new FileInputStream(new File(keystorePath));
KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());
keystore.load(is, "keystorePassword".toCharArray());

Enumeration e = ks.aliases();
Set<Certificate> certs = new HashSet<Certificate>();
while (e.hasMoreElements()) {
  Certificate cert = ks.getCertificate((String) enumeration.nextElement());
  certs.add(cert);
}

String pathToStoreTheCerts = ...
File path = new File(pathToStoreTheCerts);
OutputStream os = null;
for (X509Certificate cert : certs) {
  File certFile = new File(path, cert.getSubjectX500Principal().getName() + ".crt");
  os = new FileOutputStream(certFile);
  os.write(cert.getEncoded());
  os.flush();
}
os.close();