java 讀取.cer證書公鑰字符串

import sun.misc.BASE64Encoder;

import java.io.FileInputStream;
import java.security.PublicKey;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;

  public class Demo {

    public static void main(String[] args) throws Exception{
        //獲取X.509對象工廠
        CertificateFactory cf = CertificateFactory.getInstance("X.509");
        //通過文件流讀取證書文件
        X509Certificate cert = (X509Certificate)cf.generateCertificate(new FileInputStream("證書存放的絕對路徑"));
        //獲取公鑰對象
        PublicKey publicKey = cert.getPublicKey();

        BASE64Encoder base64Encoder=new BASE64Encoder();
        String publicKeyString = base64Encoder.encode(publicKey.getEncoded());
        System.out.println("-----------------公鑰--------------------");
        System.out.println(publicKeyString);
        System.out.println("-----------------公鑰--------------------");
    }
}