Add support for generating class names

Add `ClassNameGenerator` to support generation of class names.

See gh-28414

spring-core/src/main/java/org/springframework/aot/generate/ClassNameGenerator.java

@@ -0,0 +1,108 @@
+/*
+ * Copyright 2002-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.aot.generate;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.springframework.javapoet.ClassName;
+import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.StringUtils;
+
+/**
+ * Generates unique class names that can be used in ahead-of-time generated
+ * source code. This class is stateful so the same instance should be used for
+ * all name generation. Most commonly the class name generator is obtained via a
+ * {@link GenerationContext}.
+ *
+ * @author Phillip Webb
+ * @since 6.0
+ * @see GeneratedClassName
+ */
+public final class ClassNameGenerator {
+
+	private static final String SEPARATOR = "__";
+
+	private static final String AOT_PACKAGE = "__";
+
+
+	private final Map<String, AtomicInteger> sequenceGenerator = new ConcurrentHashMap<>();
+
+
+	/**
+	 * Generate a new class name for the given {@code target} /
+	 * {@code featureName} combination.
+	 * @param target the target of the newly generated class
+	 * @param featureName the name of the feature that the generated class
+	 * supports
+	 * @return a unique generated class name
+	 */
+	public ClassName generateClassName(Class<?> target, String featureName) {
+		Assert.notNull(target, "'target' must not be null");
+		String rootName = target.getName().replace("$", "_");
+		return generateSequencedClassName(rootName, featureName);
+	}
+
+	/**
+	 * Generate a new class name for the given {@code name} /
+	 * {@code featureName} combination.
+	 * @param target the target of the newly generated class. When possible,
+	 * this should be a class name
+	 * @param featureName the name of the feature that the generated class
+	 * supports
+	 * @return a unique generated class name
+	 */
+	public ClassName generateClassName(String target, String featureName) {
+		Assert.hasLength(target, "'target' must not be empty");
+		target = clean(target);
+		String rootName = AOT_PACKAGE + "." + ((!target.isEmpty()) ? target : "Aot");
+		return generateSequencedClassName(rootName, featureName);
+	}
+
+	private String clean(String name) {
+		StringBuilder rootName = new StringBuilder();
+		boolean lastNotLetter = true;
+		for (char ch : name.toCharArray()) {
+			if (!Character.isLetter(ch)) {
+				lastNotLetter = true;
+				continue;
+			}
+			rootName.append(lastNotLetter ? Character.toUpperCase(ch) : ch);
+			lastNotLetter = false;
+		}
+		return rootName.toString();
+	}
+
+	private ClassName generateSequencedClassName(String rootName, String featureName) {
+		Assert.hasLength(featureName, "'featureName' must not be empty");
+		Assert.isTrue(featureName.chars().allMatch(Character::isLetter),
+				"'featureName' must contain only letters");
+		String name = addSequence(
+				rootName + SEPARATOR + StringUtils.capitalize(featureName));
+		return ClassName.get(ClassUtils.getPackageName(name),
+				ClassUtils.getShortName(name));
+	}
+
+	private String addSequence(String name) {
+		int sequence = this.sequenceGenerator
+				.computeIfAbsent(name, key -> new AtomicInteger()).getAndIncrement();
+		return (sequence > 0) ? name + sequence : name;
+	}
+
+}