Cannot access application.properties property in AttributeConverter implementation

I am trying to access my encrypt key stored in application.properties and set it as SECRET property in my AttributeEncryptor.

This is the class:

package com.nimesia.sweetvillas.encryptors;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.spec.SecretKeySpec;
import javax.persistence.AttributeConverter;
import java.security.InvalidKeyException;
import java.security.Key;
import java.util.Base64;

@Component
public class AttributeEncryptor implements AttributeConverter<String, String> {

    private static final String AES = "AES";
    @Value("${datasource.encryptkey}")
    private String SECRET;

    private final Key key;
    private final Cipher cipher;

    public AttributeEncryptor() throws Exception {
        key = new SecretKeySpec(SECRET.getBytes(), AES);
        cipher = Cipher.getInstance(AES);
    }

    @Override
    public String convertToDatabaseColumn(String attribute) {
        try {
            cipher.init(Cipher.ENCRYPT_MODE, key);
            return Base64.getEncoder().encodeToString(cipher.doFinal(attribute.getBytes()));
        } catch (IllegalBlockSizeException | BadPaddingException | InvalidKeyException e) {
            throw new IllegalStateException(e);
        }
    }

    @Override
    public String convertToEntityAttribute(String dbData) {
        try {
            cipher.init(Cipher.DECRYPT_MODE, key);
            return new String(cipher.doFinal(Base64.getDecoder().decode(dbData)));
        } catch (InvalidKeyException | BadPaddingException | IllegalBlockSizeException e) {
            throw new IllegalStateException(e);
        }
    }
}

datasource.encryptkey is in application.properties.
I have tried to access it from a controller and it worked. But when I try and use it in here it gives me a NullPointerException.

Hope I was clear.
Thanks in advance

>Solution :

The class is created before the property is set!

You should add it to the constructor instead:

private final String SECRET;

private final Key key;
private final Cipher cipher;

public AttributeEncryptor(@Value("${datasource.encryptkey}") String secret) throws Exception {
    SECRET = secret;
    key = new SecretKeySpec(SECRET.getBytes(), AES);
    cipher = Cipher.getInstance(AES);

}