Java对证书的操作

1 Java程序从证书文件读取证书

import java.io.*;

import java.security.cert.*;

public class PrintCert{

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

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

        FileInputStream in=new FileInputStream("my.cer");

        Certificate c=cf.generateCertificate(in);

        in.close();

        String s=c.toString( );

        // 显示证书

  FileOutputStream fout=new FileOutputStream("tmp.txt");

         BufferedWriter out= new BufferedWriter(new OutputStreamWriter(fout));

        out.write(s,0,s.length( )); 

        out.close();   

}

}  

2 Java程序从密钥库直接读取证书

import java.io.*;

import java.security.*;

import java.security.cert.Certificate;

public class PrintCert2{

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

          String pass="080302";

          String alias="mykey";

          String name=".keystore";

          FileInputStream in=new FileInputStream(name);

          KeyStore ks=KeyStore.getInstance("JKS");           

          ks.load(in,pass.toCharArray());

          Certificate c=ks.getCertificate(alias);

          in.close();

         System.out.println(c.toString( ));

    }

}  

3 Java程序显示证书指定信息（全名/公钥/签名等）

import java.io.*;

import java.security.*;

import java.security.cert.*;

import java.math.*;

public class ShowCertInfo{

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

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

        FileInputStream in=new FileInputStream("my.cer");

        java.security.cert.Certificate c=cf.generateCertificate(in);

        in.close();

        X509Certificate t=(X509Certificate) c;

        System.out.println("版本号 "+t.getVersion());

        System.out.println("序列号 "+t.getSerialNumber().toString(16));

        System.out.println("全名 "+t.getSubjectDN());

        System.out.println("签发者全名n"+t.getIssuerDN());

        System.out.println("有效期起始日 "+t.getNotBefore());

        System.out.println("有效期截至日 "+t.getNotAfter());

        System.out.println("签名算法 "+t.getSigAlgName());

        byte[] sig=t.getSignature();

        System.out.println("签名n"+new BigInteger(sig).toString(16));

        PublicKey pk=t.getPublicKey();

        byte[ ] pkenc=pk.getEncoded();

        System.out.println("公钥");

        for(int i=0;i< div=""> 

        System.out.print(pkenc[i]+",");

        }

}

}