Convert certificate into base64 encoded string

In my previous post, I explained how to create and export a self-signed certificate using ‘keytool’ command. In this post, I am going to show you how to convert the certificate into base64 encoded string.

To run this program, you need to create a self-signed certificate and pass the path of the file as an input to the application Test.java.

CertificateUtil.java

package com.sample.util;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.util.Base64;
import java.util.Base64.Encoder;

public class CertificateUtil {
 private static final int BUFFER_SIZE = 65535;

 /**
  * 
  * 
  * @param certificateFilePath
  * @return the base64 encoded array from given certificate content.
  * 
  * @throws Exception
  */
 public static byte[] convertCertificateToByteArray(String certificateFilePath) throws Exception {
  if (certificateFilePath == null || certificateFilePath.isEmpty()) {
   throw new Exception("certificateFilePath should not be null or empty");
  }

  File file = new File(certificateFilePath);

  if (!file.exists()) {
   throw new Exception("File not exist : " + file.getAbsolutePath());
  }

  if (file.isDirectory()) {
   throw new Exception("File shouldn't be a directory : " + file.getAbsolutePath());
  }

  try (InputStream inputStream = new FileInputStream(file)) {

   ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
   byte[] buffer = new byte[BUFFER_SIZE];
   int numberOfReadBytes;

   while ((numberOfReadBytes = inputStream.read(buffer)) > 0) {
    byteArrayOutputStream.write(buffer, 0, numberOfReadBytes);
   }

   byte[] certificateInBytes = byteArrayOutputStream.toByteArray();

   Encoder encoder = Base64.getEncoder();
   byte[] encodedBytes = encoder.encode(certificateInBytes);
   return encodedBytes;

  }
 }

 /**
  * Convert the certificate into base64 encoded string.
  * 
  * @param certificateFilePath
  * @return
  * @throws Exception
  */
 public static String convertCertificateToString(String certificateFilePath) throws Exception {

  byte[] encodedBytes = convertCertificateToByteArray(certificateFilePath);
  String str = new String(encodedBytes);

  return str;

 }
}

Test.java

package com.sample.test;

import com.sample.util.CertificateUtil;

public class Test {
 public static void main(String args[]) throws Exception {
  String certificateFilePath = "C:\\Users\\krishna\\myCert.cer";
  
  String certificateInfo = CertificateUtil.convertCertificateToString(certificateFilePath);
  
  System.out.println(certificateInfo);
 }
}

Output

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

In my next post, I am going to show how to convert the above generated string to certificate.

You may like

Miscellaneous

Interview Questions

ProgrammingQuestions

Reading pkcs12 certificate information

Java cacerts file

Load Client Certificates from Windows Operating system

Load Client Certificates from MAC Operating system

Export public key certificate from keystore

Convert byte array to private, public keys

Digital Signature

Keytool:Create and export self-signed certificate

Convert certificate into base64 encoded array

Convert encoded byte array to certificate