搬运自：https://stackoverflow.com/questions/12501117/programmatically-obtain-keystore-from-pem

protected static SSLSocketFactory getSocketFactoryPEM(String pemPath) throws Exception {
    byte[] certAndKey = fileToBytes(new File(pemPath));
    
    byte[] certBytes = parseDERFromPEM(certAndKey, "-----BEGIN CERTIFICATE-----", "-----END CERTIFICATE-----");
    byte[] keyBytes = parseDERFromPEM(certAndKey, "-----BEGIN PRIVATE KEY-----", "-----END PRIVATE KEY-----");

    X509Certificate cert = generateCertificateFromDER(certBytes);              
    RSAPrivateKey key  = generatePrivateKeyFromDER(keyBytes);  

    KeyStore keystore = KeyStore.getInstance("JKS");
    keystore.load(null);
    keystore.setCertificateEntry("cert-alias", cert);
    keystore.setKeyEntry("key-alias", key, "<password>".toCharArray(), new Certificate[] {cert});

    KeyManagerFactory kmf = KeyManagerFactory.getInstance("SunX509");
    kmf.init(keystore, "<password>".toCharArray());

    KeyManager[] km = kmf.getKeyManagers(); 

    SSLContext context = SSLContext.getInstance("TLS");
    context.init(km, null, null);

    return context.getSocketFactory();
}

protected static byte[] parseDERFromPEM(byte[] pem, String beginDelimiter, String endDelimiter) {
    String data = new String(pem);
    String[] tokens = data.split(beginDelimiter);
    tokens = tokens[1].split(endDelimiter);
    return DatatypeConverter.parseBase64Binary(tokens[0]);        
}

protected static RSAPrivateKey generatePrivateKeyFromDER(byte[] keyBytes) throws InvalidKeySpecException, NoSuchAlgorithmException {
    PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(keyBytes);

    KeyFactory factory = KeyFactory.getInstance("RSA");

    return (RSAPrivateKey)factory.generatePrivate(spec);        
}

protected static X509Certificate generateCertificateFromDER(byte[] certBytes) throws CertificateException {
    CertificateFactory factory = CertificateFactory.getInstance("X.509");

    return (X509Certificate)factory.generateCertificate(new ByteArrayInputStream(certBytes));      
}

此代码适合于读取pem格式的证书，需要私钥和公钥证书两个pem文件。
同样也适用于将pem内容去掉首尾的文件说明，把中间的内容拼或不拼成一行字符串来使用，只需要略微调整一下代码即可。