how to generate a certificate

[swetha 255]

hai friends.
i got errors in generating a file.here is my codepublic
class certificate{

public static void main(String[] args) throws Exception {

CertificateFactory certFactory = CertificateFactory.getInstance("X.509");

FileInputStream fis = new FileInputStream("file");


CertificateFactory cf = CertificateFactory.getInstance("X.509");

while (fis.available() > 0) {
Certificate cert = cf.generateCertificate(fis);
System.out.println(cert.toString());
}



my error is:Exception in thread "main" java.security.cert.CertificateParsingException: invalid DER-encoded certificate data ...

what should my file contain (plaintext or some other encoded data).