从单独方法调用时，getKey（alias，keyPassword）返回密钥的空值

我正在尝试检索Java密钥存储区中的存储密钥。我写了下面的代码。

public class clientEncryptionUtility
{

    public static void generateKeyAndStoreOnKeyStore(String _keyStorePassword, String _keyStorePath, String _keyPassword, String keyAlias) throws Exception // take the keystore path, alias, password
    {
        KeyStore keyStore = KeyStore.getInstance("JCEKS");
        char[] keyStorePassword = _keyStorePassword.toCharArray();
        String path = _keyStorePath;
        FileInputStream fis = new FileInputStream(path);
        //load keystore
        keyStore.load(fis, keyStorePassword);
        //Loading the KeyStore object
        KeyStore.ProtectionParameter protectionParam = new KeyStore.PasswordProtection(keyStorePassword);

        //Generate the symmetric key for encryption
        KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");

        SecureRandom secureRandom = new SecureRandom();

        int keyBitSize = 128;

        keyGenerator.init(keyBitSize, secureRandom);

        SecretKey secretKey = keyGenerator.generateKey();   //Secret encryption key is genereated

        //setting the password for the key stored in keystore
        System.out.println("Algorithm used to generate key : "+secretKey.getAlgorithm()); 

        char[] keyPassword = _keyPassword.toCharArray();

        KeyStore.ProtectionParameter entryPassword = new KeyStore.PasswordProtection(keyPassword);

        KeyStore.SecretKeyEntry secretKeyEntry = new KeyStore.SecretKeyEntry(secretKey);

        keyStore.setEntry(keyAlias, secretKeyEntry, entryPassword);
        SecretKey newSecretKey = (SecretKey) keyStore.getKey(keyAlias, keyPassword);
        String stringKey = newSecretKey.toString();
        System.out.println("The encryption key at the alias is: " + stringKey);
    }
    public static void getKeyFromKeyStore(String _keyStorePassword, String _keyStorePath, String keyAlias, String _keyPassword) throws Exception
    {
        KeyStore keyStore = KeyStore.getInstance("JCEKS");
        char[] keyStorePassword = _keyStorePassword.toCharArray();
        String path = _keyStorePath;
        FileInputStream fis = new FileInputStream(path);

        //load keystore
        keyStore.load(fis, keyStorePassword);
        char[] keyPassword = _keyPassword.toCharArray();
        SecretKey secretKey = (SecretKey) keyStore.getKey(keyAlias, keyPassword);
        // Key key = keyStore.getKey(keyAlias, keyPassword);
        String stringKey = secretKey.toString();
        System.out.println("The encryption key at the alias is: " + stringKey);

    }
}

-如果我调用generateKeyAndStoreOnKeyStore（）方法，并存储密钥并在同一函数中检索密钥，则检索密钥。

-但是，如果我从另一个方法getKeyFromKeyStore（）中执行相同的操作，其中我只是试图从梯形畸变中检索别名处的密钥，则会得到nullPointerException。

我哪里错了？