在Java中实现ECDSA密钥生成、签名和验证的过程，可以参考下面的代码示例：

import java.security.*;
import java.security.spec.ECGenParameterSpec;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;

public class ECDSAExample {

    public static void main(String[] args) throws Exception {
        String message = "Hello, ECDSA!";
        KeyPair keyPair = generateKeyPair();

        byte[] signature = sign(message, keyPair.getPrivate());
        boolean verified = verify(message, signature, keyPair.getPublic());
        System.out.println("Signature verified: " + verified);
    }

    public static KeyPair generateKeyPair() throws Exception {
        ECGenParameterSpec ecSpec = new ECGenParameterSpec("secp256r1");
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("EC");
        keyPairGenerator.initialize(ecSpec);
        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        return keyPair;
    }

    public static byte[] sign(String message, PrivateKey privateKey) throws Exception {
        Signature signature = Signature.getInstance("SHA256withECDSA");
        signature.initSign(privateKey);
        signature.update(message.getBytes("UTF-8"));
        byte[] signatureBytes = signature.sign();
        return signatureBytes;
    }

    public static boolean verify(String message, byte[] signatureBytes, PublicKey publicKey) throws Exception {
        Signature signature = Signature.getInstance("SHA256withECDSA");
        signature.initVerify(publicKey);
        signature.update(message.getBytes("UTF-8"));
        boolean verified = signature.verify(signatureBytes);
        return verified;
    }

    public static PublicKey decodePublicKey(String publicKeyString) throws Exception {
        byte[] publicKeyBytes = Base64.getDecoder().decode(publicKeyString);
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(publicKeyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("EC");
        PublicKey publicKey = keyFactory.generatePublic(keySpec);
        return publicKey;
    }

    public static PrivateKey decodePrivateKey(String privateKeyString) throws Exception {
        byte[] privateKeyBytes = Base64.getDecoder().decode(privateKeyString);
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(privateKeyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("EC");
        PrivateKey privateKey = keyFactory.generatePrivate(keySpec);
        return privateKey;
    }
}

使用该代码示例，您可以生成公私钥对，并使用私钥对消息进行签名。请确保使用与您的CA证书相同的椭圆曲线和哈希算法进行签名。验证签名时，您需要使用公钥和签名字节。