Make classes final where possible

Update classes that have private constructors so that they are also
declared final. In a few cases, inner-classes used private constructors
but were subclassed. These have now been changed to have package-private
constructors.

Issue gh-8945

crypto/src/main/java/org/springframework/security/crypto/encrypt/CipherUtils.java

@@ -36,7 +36,10 @@ import javax.crypto.spec.PBEParameterSpec;
  *
  * @author Keith Donald
  */
-class CipherUtils {
+final class CipherUtils {
+
+	private CipherUtils() {
+	}
 
 	/**
 	 * Generates a SecretKey.
@@ -138,7 +141,4 @@ class CipherUtils {
 		}
 	}
 
-	private CipherUtils() {
-	}
-
 }

crypto/src/main/java/org/springframework/security/crypto/encrypt/Encryptors.java

@@ -24,7 +24,10 @@ import org.springframework.security.crypto.keygen.KeyGenerators;
  *
  * @author Keith Donald
  */
-public class Encryptors {
+public final class Encryptors {
+
+	private Encryptors() {
+	}
 
 	/**
 	 * Creates a standard password-based bytes encryptor using 256 bit AES encryption with
@@ -112,9 +115,6 @@ public class Encryptors {
 		return NO_OP_TEXT_INSTANCE;
 	}
 
-	private Encryptors() {
-	}
-
 	private static final TextEncryptor NO_OP_TEXT_INSTANCE = new NoOpTextEncryptor();
 
 	private static final class NoOpTextEncryptor implements TextEncryptor {

crypto/src/main/java/org/springframework/security/crypto/factory/PasswordEncoderFactories.java

@@ -32,7 +32,10 @@ import org.springframework.security.crypto.scrypt.SCryptPasswordEncoder;
  * @author Rob Winch
  * @since 5.0
  */
-public class PasswordEncoderFactories {
+public final class PasswordEncoderFactories {
+
+	private PasswordEncoderFactories() {
+	}
 
 	/**
 	 * Creates a {@link DelegatingPasswordEncoder} with default mappings. Additional
@@ -79,7 +82,4 @@ public class PasswordEncoderFactories {
 		return new DelegatingPasswordEncoder(encodingId, encoders);
 	}
 
-	private PasswordEncoderFactories() {
-	}
-
 }

crypto/src/main/java/org/springframework/security/crypto/keygen/KeyGenerators.java

@@ -23,7 +23,10 @@ import java.security.SecureRandom;
  *
  * @author Keith Donald
  */
-public class KeyGenerators {
+public final class KeyGenerators {
+
+	private KeyGenerators() {
+	}
 
 	/**
 	 * Create a {@link BytesKeyGenerator} that uses a {@link SecureRandom} to generate
@@ -59,9 +62,4 @@ public class KeyGenerators {
 		return new HexEncodingStringKeyGenerator(secureRandom());
 	}
 
-	// internal helpers
-
-	private KeyGenerators() {
-	}
-
 }

crypto/src/main/java/org/springframework/security/crypto/password/PasswordEncoderUtils.java

@@ -24,7 +24,10 @@ import org.springframework.security.crypto.codec.Utf8;
  *
  * @author Rob Winch
  */
-class PasswordEncoderUtils {
+final class PasswordEncoderUtils {
+
+	private PasswordEncoderUtils() {
+	}
 
 	/**
 	 * Constant time comparison to prevent against timing attacks.
@@ -43,12 +46,9 @@ class PasswordEncoderUtils {
 		if (s == null) {
 			return null;
 		}
-
-		return Utf8.encode(s); // need to check if Utf8.encode() runs in constant time
-								// (probably not). This may leak length of string.
-	}
-
-	private PasswordEncoderUtils() {
+		// need to check if Utf8.encode() runs in constant time (probably not).
+		// This may leak length of string.
+		return Utf8.encode(s);
 	}
 
 }

crypto/src/main/java/org/springframework/security/crypto/util/EncodingUtils.java

@@ -22,7 +22,10 @@ package org.springframework.security.crypto.util;
  *
  * @author Keith Donald
  */
-public class EncodingUtils {
+public final class EncodingUtils {
+
+	private EncodingUtils() {
+	}
 
 	/**
 	 * Combine the individual byte arrays into one array.
@@ -54,7 +57,4 @@ public class EncodingUtils {
 		return subarray;
 	}
 
-	private EncodingUtils() {
-	}
-
 }