Add support for generating methods

Add `GeneratedMethods` and `GeneratedMethod` support classes which
can be used during code generation to generation additional methods
that will ultimately be included in a `JavaFile`.

See gh-28414

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

@@ -0,0 +1,96 @@
+/*
+ * 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.function.Consumer;
+
+import org.springframework.javapoet.MethodSpec;
+import org.springframework.javapoet.MethodSpec.Builder;
+import org.springframework.util.Assert;
+
+/**
+ * A generated method.
+ *
+ * @author Phillip Webb
+ * @since 6.0
+ * @see GeneratedMethods
+ * @see MethodGenerator
+ */
+public final class GeneratedMethod {
+
+	private final String name;
+
+	private MethodSpec spec;
+
+
+	/**
+	 * Create a new {@link GeneratedMethod} instance with the given name. This
+	 * constructor is package-private since names should only be generated via a
+	 * {@link GeneratedMethods}.
+	 * @param name the generated name
+	 */
+	GeneratedMethod(String name) {
+		this.name = name;
+	}
+
+
+	/**
+	 * Return the generated name of the method.
+	 * @return the name of the generated method
+	 */
+	public String getName() {
+		return this.name;
+	}
+
+	/**
+	 * Return the {@link MethodSpec} for this generated method.
+	 * @return the method spec
+	 * @throws IllegalStateException if one of the {@code generateBy(...)}
+	 * methods has not been called
+	 */
+	public MethodSpec getSpec() {
+		Assert.state(this.spec != null,
+				() -> String.format("Method '%s' has no method spec defined", this.name));
+		return this.spec;
+	}
+
+	/**
+	 * Generate the method using the given consumer.
+	 * @param builder a consumer that will accept a method spec builder and
+	 * configure it as necessary
+	 * @return this instance
+	 */
+	public GeneratedMethod using(Consumer<MethodSpec.Builder> builder) {
+		Builder builderToUse = MethodSpec.methodBuilder(this.name);
+		builder.accept(builderToUse);
+		MethodSpec spec = builderToUse.build();
+		assertNameHasNotBeenChanged(spec);
+		this.spec = spec;
+		return this;
+	}
+
+	private void assertNameHasNotBeenChanged(MethodSpec spec) {
+		Assert.isTrue(this.name.toString().equals(spec.name), () -> String
+				.format("'spec' must use the generated name \"%s\"", this.name));
+	}
+
+	@Override
+	public String toString() {
+		return (this.spec != null) ? this.spec.toString() : this.name.toString();
+	}
+
+}

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

@@ -0,0 +1,102 @@
+/*
+ * 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.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.function.Consumer;
+import java.util.stream.Stream;
+
+import org.springframework.javapoet.MethodSpec;
+import org.springframework.util.Assert;
+
+/**
+ * A managed collection of generated methods.
+ *
+ * @author Phillip Webb
+ * @since 6.0
+ * @see GeneratedMethod
+ */
+public class GeneratedMethods implements Iterable<GeneratedMethod>, MethodGenerator {
+
+	private final MethodNameGenerator methodNameGenerator;
+
+	private final List<GeneratedMethod> generatedMethods = new ArrayList<>();
+
+
+	/**
+	 * Create a new {@link GeneratedMethods} instance backed by a new
+	 * {@link MethodNameGenerator}.
+	 */
+	public GeneratedMethods() {
+		this(new MethodNameGenerator());
+	}
+
+	/**
+	 * Create a new {@link GeneratedMethods} instance backed by the given
+	 * {@link MethodNameGenerator}.
+	 * @param methodNameGenerator the method name generator
+	 */
+	public GeneratedMethods(MethodNameGenerator methodNameGenerator) {
+		Assert.notNull(methodNameGenerator, "'methodNameGenerator' must not be null");
+		this.methodNameGenerator = methodNameGenerator;
+	}
+
+
+	@Override
+	public GeneratedMethod generateMethod(Object... methodNameParts) {
+		return add(methodNameParts);
+	}
+
+	/**
+	 * Add a new {@link GeneratedMethod}. The returned instance must define the
+	 * method spec by calling {@code using(builder -> ...)}.
+	 * @param methodNameParts the method name parts that should be used to
+	 * generate a unique method name
+	 * @return the newly added {@link GeneratedMethod}
+	 */
+	public GeneratedMethod add(Object... methodNameParts) {
+		GeneratedMethod method = new GeneratedMethod(
+				this.methodNameGenerator.generateMethodName(methodNameParts));
+		this.generatedMethods.add(method);
+		return method;
+	}
+
+	/**
+	 * Call the given action with each of the {@link MethodSpec MethodSpecs}
+	 * that have been added to this collection.
+	 * @param action the action to perform
+	 */
+	public void doWithMethodSpecs(Consumer<MethodSpec> action) {
+		stream().map(GeneratedMethod::getSpec).forEach(action);
+	}
+
+	@Override
+	public Iterator<GeneratedMethod> iterator() {
+		return this.generatedMethods.iterator();
+	}
+
+	/**
+	 * Return a {@link Stream} of all the methods in this collection.
+	 * @return a stream of {@link GeneratedMethod} instances
+	 */
+	public Stream<GeneratedMethod> stream() {
+		return this.generatedMethods.stream();
+	}
+
+}

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

@@ -0,0 +1,72 @@
+/*
+ * 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;
+
+/**
+ * Generates new {@link GeneratedMethod} instances.
+ *
+ * @author Phillip Webb
+ * @since 6.0
+ * @see GeneratedMethods
+ */
+@FunctionalInterface
+public interface MethodGenerator {
+
+	/**
+	 * Generate a new {@link GeneratedMethod}. The returned instance must define
+	 * the method spec by calling {@code using(builder -> ...)}.
+	 * @param methodNameParts the method name parts that should be used to
+	 * generate a unique method name
+	 * @return the newly added {@link GeneratedMethod}
+	 */
+	GeneratedMethod generateMethod(Object... methodNameParts);
+
+	/**
+	 * Return a new {@link MethodGenerator} instance that generates method with
+	 * additional implicit method name parts. The final generated name will be
+	 * of the following form:
+	 * <p>
+	 * <table border="1">
+	 * <tr>
+	 * <th>Original</th>
+	 * <th>Updated</th>
+	 * </tr>
+	 * <tr>
+	 * <td>run</td>
+	 * <td>&lt;name&gt;Run</td>
+	 * </tr>
+	 * <tr>
+	 * <td>getValue</td>
+	 * <td>get&lt;Name&gt;Value</td>
+	 * </tr>
+	 * <tr>
+	 * <td>setValue</td>
+	 * <td>set&lt;Name&gt;Value</td>
+	 * </tr>
+	 * <tr>
+	 * <td>isEnabled</td>
+	 * <td>is&lt;Name&gt;Enabled</td>
+	 * </tr>
+	 * </table>
+	 * @param nameParts the implicit name parts
+	 * @return a new {@link MethodGenerator} instance
+	 */
+	default MethodGenerator withName(Object... nameParts) {
+		return new MethodGeneratorWithName(this, nameParts);
+	}
+
+}

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

@@ -0,0 +1,71 @@
+/*
+ * 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 org.springframework.util.ObjectUtils;
+import org.springframework.util.StringUtils;
+
+/**
+ * Internal class used to support {@link MethodGenerator#withName(Object...)}.
+ *
+ * @author Phillip Webb
+ * @since 6.0
+ */
+class MethodGeneratorWithName implements MethodGenerator {
+
+	private static final String[] PREFIXES = { "get", "set", "is" };
+
+	private final MethodGenerator methodGenerator;
+
+	private final Object[] nameParts;
+
+
+	MethodGeneratorWithName(MethodGenerator methodGenerator, Object[] nameParts) {
+		this.methodGenerator = methodGenerator;
+		this.nameParts = nameParts;
+	}
+
+
+	@Override
+	public GeneratedMethod generateMethod(Object... methodNameParts) {
+		return this.methodGenerator.generateMethod(generateName(methodNameParts));
+	}
+
+	private Object[] generateName(Object... methodNameParts) {
+		String joined = MethodNameGenerator.join(methodNameParts);
+		String prefix = getPrefix(joined);
+		String suffix = joined.substring(prefix.length());
+		Object[] result = this.nameParts;
+		if (StringUtils.hasLength(prefix)) {
+			result = ObjectUtils.addObjectToArray(result, prefix, 0);
+		}
+		if (StringUtils.hasLength(suffix)) {
+			result = ObjectUtils.addObjectToArray(result, suffix);
+		}
+		return result;
+	}
+
+	private String getPrefix(String name) {
+		for (String candidate : PREFIXES) {
+			if (name.startsWith(candidate)) {
+				return candidate;
+			}
+		}
+		return "";
+	}
+
+}