docs: add javadoc

Author: siujamo

key-pair-loader/src/main/java/com/onixbyte/security/KeyLoader.java

@@ -68,6 +68,19 @@ default RSAPublicKey loadPublicKey(String modulus, String exponent) {
         throw new KeyLoadingException("This key loader does not support loading an RSA public key.");
     }
 
+    /**
+     * Loads an EC public key using the provided x and y coordinates together with the curve name.
+     * <p>
+     * This default implementation throws a {@link KeyLoadingException} to signify that this key loader does not support
+     * loading an EC public key. Implementing classes are expected to override this method to supply their own
+     * loading logic.
+     *
+     * @param xHex      the hexadecimal string representing the x coordinate of the EC point
+     * @param yHex      the hexadecimal string representing the y coordinate of the EC point
+     * @param curveName the name of the elliptic curve
+     * @return the loaded {@link ECPublicKey} instance
+     * @throws KeyLoadingException if loading is not supported or fails
+     */
     default ECPublicKey loadPublicKey(String xHex, String yHex, String curveName) {
         throw new KeyLoadingException("This key loader does not support loading an EC public key.");
     }

key-pair-loader/src/main/java/com/onixbyte/security/impl/ECKeyLoader.java

@@ -131,6 +131,23 @@ public ECPublicKey loadPublicKey(String pemKeyText) {
         }
     }
 
+    /**
+     * Loads an EC public key from the given hexadecimal x and y coordinates alongside the curve name.
+     * <p>
+     * This method converts the hexadecimal string representations of the EC point coordinates into {@link BigInteger}
+     * instances, then constructs an {@link ECPoint} and retrieves the corresponding {@link ECParameterSpec} for the
+     * named curve. Subsequently, it utilises the {@link KeyFactory} to generate an {@link ECPublicKey}.
+     * <p>
+     * Only curves listed in {@link #SUPPORTED_CURVES} are supported. Should the specified curve name be unsupported,
+     * or if key construction fails due to invalid parameters or unsupported algorithms, a {@link KeyLoadingException}
+     * will be thrown.
+     *
+     * @param xHex      the hexadecimal string representing the x-coordinate of the EC point
+     * @param yHex      the hexadecimal string representing the y-coordinate of the EC point
+     * @param curveName the name of the elliptic curve
+     * @return the {@link ECPublicKey} generated from the specified coordinates and curve
+     * @throws KeyLoadingException if the curve is unsupported or key generation fails
+     */
     @Override
     public ECPublicKey loadPublicKey(String xHex, String yHex, String curveName) {
         if (!SUPPORTED_CURVES.contains(curveName)) {