how to populate a jsonwebkey from a generated ecdsa key

I try to generate a public/private key pair which i will use for digital signature of a JWT with jose4j. I use Elliptic Curve Digital Signature Algorithm

My problem is that i don't know how to get the parameters representing the edcsa key meaning:

• crv
• x
• y

• d

   KeyPairGenerator g = KeyPairGenerator.getInstance("EC");
   ECGenParameterSpec kpgparams = new ECGenParameterSpec("secp256r1");
   g.initialize(kpgparams);
  
   KeyPair pair = g.generateKeyPair();
   // Instance of signature class with SHA256withECDSA algorithm
   Signature ecdsaSign = Signature.getInstance("SHA256withECDSA");
   ecdsaSign.initSign(pair.getPrivate());
  
   System.out.println("Private Keys is::" + pair.getPrivate());
   System.out.println("Public Keys is::" + pair.getPublic());
  
  JsonWebKeySet jsonWebKeySet = new JsonWebKeySet();
  PrivateKey privateKey = pair.getPrivate();
  JsonWebKey webKey = new  JsonWebKey(privateKey) {
  
      @Override
      public String getKeyType() {
          // TODO Auto-generated method stub
          return "EC";
      }
  
      @Override
      protected void fillTypeSpecificParams(Map<String, Object> params,
              OutputControlLevel outputLevel) {
          params.put("use", "sig");
          params.put("key_ops", "sign");
          params.put("alg", "ES256");
          params.put("kid", "kukuPrivateKey");
  
      }
  };
  jsonWebKeySet.addJsonWebKey(webKey);
  System.out.println("aaaa"+jsonWebKeySet.toJson());
  

You can create a JsonWebKey directly with the public key you generated and jose4j will take care of the parameters and encoding.

    KeyPairGenerator g = KeyPairGenerator.getInstance("EC");
    ECGenParameterSpec kpgparams = new ECGenParameterSpec("secp256r1");
    g.initialize(kpgparams);

    KeyPair keyPair = g.generateKeyPair();

    PublicJsonWebKey jwk = PublicJsonWebKey.Factory.newPublicJwk(keyPair.getPublic());
    jwk.setPrivateKey(keyPair.getPrivate());
    jwk.setUse(Use.SIGNATURE);

    System.out.println(jwk.toJson(JsonWebKey.OutputControlLevel.PUBLIC_ONLY));
    System.out.println(jwk.toJson(JsonWebKey.OutputControlLevel.INCLUDE_PRIVATE)); // to include the private key 'd'

You can also use the EcJwkGenerator utility in jose4j to generate the key pair and wrap it in a JsonWebKey,

    EllipticCurveJsonWebKey jwk = EcJwkGenerator.generateJwk(EllipticCurves.P256);
    jwk.setUse(Use.SIGNATURE);

    System.out.println(jwk.toJson(JsonWebKey.OutputControlLevel.PUBLIC_ONLY));
    System.out.println(jwk.toJson(JsonWebKey.OutputControlLevel.INCLUDE_PRIVATE)); // to include the private key 'd'