KeyStore getCertificate() method in Java with Examples

The getCertificate() method of java.security.KeyStore class is used to provide the certificate for the requested alias. .
Syntax:

public final Certificate
  getCertificate(String alias)
  throws KeyStoreException

Parameter: This method accepts the name of the alias as a parameter whose certificate is to be fetched.
Return Value: This method returns the certificate for the requested alias if it exists.
Exception: This method throws KeyStoreException if you don’t initialize this keystore.
Note: All the programs in this article won’t run on online IDE as no ‘privatekey’ Keystore exists. You can check this code on Java compiler on your system. To check this code, create a Keystore ‘privatekey’ on your system and set your own keystore password to access that keystore.
Below are the examples to illustrate the getCertificate() method:
Example 1:

Java

// Java program to demonstrate
// getCertificate() method

import java.security.*;
import java.security.cert.*;
import java.util.*;
import java.io.*;

public class GFG {
    public static void main(String[] argv)
    {
        try {

            // creating the object of KeyStore
            // and getting instance
            // By using getInstance() method
            KeyStore sr = KeyStore.getInstance("JKS");

            // keystore password is required to access keystore
            char[] pass = ("123456").toCharArray();

            // creating and initializing object of InputStream
            InputStream is
                = new FileInputStream(
                    "f:/java/private key.store");

            // initializing keystore object
            sr.load(is, pass);

            // getting the certificate
            // using getCertificate() method
            X509Certificate cert
                = (X509Certificate)sr
                      .getCertificate("ftpkey");

            // display the result
            System.out.println("Certificate version : "
                               + cert.getVersion());
        }

        catch (NoSuchAlgorithmException e) {

            System.out.println("Exception thrown : " + e);
        }
        catch (NullPointerException e) {

            System.out.println("Exception thrown : " + e);
        }
        catch (KeyStoreException e) {

            System.out.println("Exception thrown : " + e);
        }
        catch (FileNotFoundException e) {

            System.out.println("Exception thrown : " + e);
        }
        catch (IOException e) {

            System.out.println("Exception thrown : " + e);
        }
        catch (CertificateException e) {

            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

Certificate version : 3

Example 2: For KeyStoreException

Java

// Java program to demonstrate
// getCertificate() method

import java.security.*;
import java.security.cert.*;
import java.util.*;
import java.io.*;

public class GFG {
    public static void main(String[] argv)
    {
        try {

            // creating the object of KeyStore
            // and getting instance
            // By using getInstance() method
            KeyStore sr = KeyStore.getInstance("JKS");

            // initializing keystore object
            // sr.load(is, pass);

            // getting the certificate
            // using getCertificate() method
            X509Certificate cert
                = (X509Certificate)sr
                      .getCertificate("ftpkey");

            // display the result
            System.out.println("Certificate version : "
                               + cert.getVersion());
        }
        catch (NullPointerException e) {

            System.out.println("Exception thrown : " + e);
        }
        catch (KeyStoreException e) {

            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

Exception thrown :
 java.security.KeyStoreException:
 Uninitialized keystore

Reference: https://docs.oracle.com/javase/9/docs/api/java/security/KeyStore.html#getCertificate-java.lang.String-