replace usage of google Hashing with java built in MessageDigest

preferencesfx/src/main/java/com/dlsc/preferencesfx/util/StorageHandlerImpl.java

@@ -13,9 +13,7 @@
 import static com.dlsc.preferencesfx.util.Constants.WINDOW_WIDTH;
 
 import com.dlsc.preferencesfx.model.Setting;
-import com.google.common.hash.Hashing;
 import com.google.gson.Gson;
-import java.nio.charset.StandardCharsets;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.util.ArrayList;
@@ -261,10 +259,7 @@ private String deprecatedHash(String key) {
    * @return SHA-256 representation of breadcrumb
    */
   public String hash(String key) {
-    Objects.requireNonNull(key);
-    return Hashing.sha256()
-        .hashString(key, StandardCharsets.UTF_8)
-        .toString();
+    return Strings.sha256(key);
   }
 
   public Preferences getPreferences() {

preferencesfx/src/main/java/com/dlsc/preferencesfx/util/Strings.java

@@ -1,12 +1,61 @@
 package com.dlsc.preferencesfx.util;
 
+import static java.util.Objects.requireNonNull;
+
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+
 /**
  * Helper methods for working with strings.
  */
 public class Strings {
 
+  private static final char[] HEX_ARRAY = "0123456789abcdef".toCharArray();
+
+  /**
+   * Checks if a string is null or empty.
+   *
+   * @param string the string to test, may be {@code null}.
+   * @return {@code true} iff the string is not null and not empty
+   */
   public static boolean isNullOrEmpty(String string) {
     return string == null || string.isEmpty();
   }
 
+  /**
+   * Calculates the SHA-256 digest of a string.
+   *
+   * @param string the string to digest, must not be {@code null}.
+   * @return the SHA-256 digest of the input string
+   */
+  public static String sha256(String string) {
+    requireNonNull(string);
+    try {
+      final MessageDigest digest = MessageDigest.getInstance("sha-256");
+      final byte[] hash = digest.digest(string.getBytes(StandardCharsets.UTF_8));
+      return hexString(hash);
+    } catch (NoSuchAlgorithmException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  /**
+   * Calculates the HEX representation of a byte array.
+   *
+   * @param bytes the byte array, must not be {@code null}.
+   * @return the HEX representation of the byte array.
+   */
+  public static String hexString(byte[] bytes) {
+    requireNonNull(bytes);
+    final int numBytes = bytes.length;
+    char[] hexChars = new char[numBytes * 2];
+    for (int i = 0; i < numBytes; i++) {
+      int v = bytes[i] & 0xFF;
+      hexChars[i * 2] = HEX_ARRAY[v >>> 4];
+      hexChars[(i * 2) + 1] = HEX_ARRAY[v & 0x0F];
+    }
+    return new String(hexChars);
+  }
+
 }