Read different certificate/key file formats with Java

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

(...)

try {
	CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
	FileInputStream is = new FileInputStream("THE_X509_CERTIFICATE_PEM_FILE_PATH");
	X509Certificate cer = (X509Certificate) certFactory.generateCertificate(is);
	PublicKey key = cer.getPublicKey();
} catch (Exception e) {
	e.printStackTrace();
}

import java.io.FileReader;
import java.io.IOException;
import java.security.PrivateKey;
import org.bouncycastle.asn1.pkcs.PrivateKeyInfo;
import org.bouncycastle.openssl.PEMKeyPair;
import org.bouncycastle.openssl.PEMParser;
import org.bouncycastle.openssl.jcajce.JcaPEMKeyConverter;

(...)

PEMParser reader = null;
try {
	reader = new PEMParser(new FileReader("THE_PEM_ENCODED_FILE_PATH"));
	PrivateKeyInfo info = null;
	
	// the return type depends on whether the file contains a single key or a key pair 
	Object bouncyCastleResult = reader.readObject();
	
	if (bouncyCastleResult instanceof PrivateKeyInfo) {
		info = (PrivateKeyInfo) bouncyCastleResult;
	} else if ( bouncyCastleResult instanceof PEMKeyPair ) {
		PEMKeyPair keys = (PEMKeyPair) bouncyCastleResult;
		info = keys.getPrivateKeyInfo();
	} else {
		throw new Exception("No private key found in the provided file");
	}
	
	JcaPEMKeyConverter converter = new JcaPEMKeyConverter();
	PrivateKey privateKeyJava = converter.getPrivateKey(info);
} catch (Exception e) {
	e.printStackTrace();
} finally {
	if (reader != null) {
		try {
			reader.close();
		} catch (IOException e) {
		}
	}
}

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.PrivateKey;
import org.bouncycastle.asn1.ASN1Sequence;
import org.bouncycastle.asn1.DERNull;
import org.bouncycastle.asn1.pkcs.PKCSObjectIdentifiers;
import org.bouncycastle.asn1.pkcs.PrivateKeyInfo;
import org.bouncycastle.asn1.pkcs.RSAPrivateKey;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import org.bouncycastle.openssl.jcajce.JcaPEMKeyConverter;

(...)
try {
	String privateKeyFileName = "THE_BINARY_ENCODED_FILE_PATH";
	Path path = Paths.get(privateKeyFileName);
	byte[] privKeyByteArray = Files.readAllBytes(path);
	ASN1Sequence seq = ASN1Sequence.getInstance(privKeyByteArray);
	RSAPrivateKey bcPrivateKey = RSAPrivateKey.getInstance(seq);
	JcaPEMKeyConverter converter = new JcaPEMKeyConverter();
	AlgorithmIdentifier algId = new AlgorithmIdentifier(PKCSObjectIdentifiers.rsaEncryption, DERNull.INSTANCE);
	
	PrivateKey privateKeyJava = converter
			.getPrivateKey(new PrivateKeyInfo(algId, bcPrivateKey));
	
} catch (Exception e) {
	e.printStackTrace();
}

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.spec.PKCS8EncodedKeySpec;

(...)
try {
			 
	Path path = Paths.get(THE_BINARY_ENCODED_FILE_PATH);
	byte[] privKeyByteArray = Files.readAllBytes(path);
	PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(privKeyByteArray);
	KeyFactory keyFactory = KeyFactory.getInstance("RSA");
	PrivateKey privateKey= keyFactory.generatePrivate(keySpec);
	
} catch (Exception e) {
	e.printStackTrace();
}

import java.io.FileInputStream;
import java.security.Key;
import java.security.KeyStore;
(...)
try {
	KeyStore p12 = KeyStore.getInstance("pkcs12");
	// getPassword returns the password of the key / file. The password should not be hard coded. 
	p12.load(new FileInputStream("THE_PFX_FILE_PATH"),
			getPassword().toCharArray());
	// the key is ready to be used ! 
	Key key = p12.getKey("YOUR_KEY_ALIAS", getPassword().toCharArray());
	
} catch (Exception e) {
	e.printStackTrace();
}