Add language abstraction

This commit adds a `Language` on the JVM abstraction with well known
concepts such as `Annotation`, `Parameter`, `CompilationUnit` and
`TypeDeclaration` that concrete language implementations can reuse.

See gh-813

Co-authored-by: Stephane Nicoll <snicoll@pivotal.io>

initializr-generator/src/main/java/io/spring/initializr/generator/language/AbstractLanguage.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2012-2019 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
+ *
+ *      http://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 io.spring.initializr.generator.language;
+
+/**
+ * Base {@link Language} implementation.
+ *
+ * @author Stephane Nicoll
+ */
+public abstract class AbstractLanguage implements Language {
+
+	private final String id;
+
+	private final String jvmVersion;
+
+	protected AbstractLanguage(String id, String jvmVersion) {
+		this.id = id;
+		this.jvmVersion = (jvmVersion != null) ? jvmVersion : DEFAULT_JVM_VERSION;
+	}
+
+	@Override
+	public String id() {
+		return this.id;
+	}
+
+	@Override
+	public String jvmVersion() {
+		return this.jvmVersion;
+	}
+
+	@Override
+	public String toString() {
+		return id();
+	}
+
+}

initializr-generator/src/main/java/io/spring/initializr/generator/language/Annotatable.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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 io.spring.initializr.generator.language;
+
+import java.util.List;
+
+/**
+ * A representation of something that can be annotated.
+ *
+ * @author Andy Wilkinson
+ */
+public interface Annotatable {
+
+	void annotate(Annotation annotation);
+
+	List<Annotation> getAnnotations();
+
+}

initializr-generator/src/main/java/io/spring/initializr/generator/language/Annotation.java

@@ -0,0 +1,116 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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 io.spring.initializr.generator.language;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Consumer;
+
+/**
+ * An annotation.
+ *
+ * @author Andy Wilkinson
+ * @author Stephane Nicoll
+ */
+public final class Annotation {
+
+	private final String name;
+
+	private final List<Attribute> attributes;
+
+	private Annotation(Builder builder) {
+		this.name = builder.name;
+		this.attributes = Collections
+				.unmodifiableList(new ArrayList<>(builder.attributes.values()));
+	}
+
+	public String getName() {
+		return this.name;
+	}
+
+	public List<Attribute> getAttributes() {
+		return this.attributes;
+	}
+
+	public static Annotation name(String name) {
+		return name(name, null);
+	}
+
+	public static Annotation name(String name, Consumer<Builder> annotation) {
+		Builder builder = new Builder(name);
+		if (annotation != null) {
+			annotation.accept(builder);
+		}
+		return new Annotation(builder);
+	}
+
+	/**
+	 * Builder for creating an {@link Annotation}.
+	 */
+	public static final class Builder {
+
+		private final String name;
+
+		private final Map<String, Attribute> attributes = new LinkedHashMap<>();
+
+		private Builder(String name) {
+			this.name = name;
+		}
+
+		public Builder attribute(String name, Class<?> type, String... values) {
+			this.attributes.put(name, new Attribute(name, type, values));
+			return this;
+		}
+
+	}
+
+	/**
+	 * Define an attribute of an annotation.
+	 */
+	public static final class Attribute {
+
+		private final String name;
+
+		private final Class<?> type;
+
+		private final List<String> values;
+
+		private Attribute(String name, Class<?> type, String... values) {
+			this.name = name;
+			this.type = type;
+			this.values = Arrays.asList(values);
+		}
+
+		public String getName() {
+			return this.name;
+		}
+
+		public Class<?> getType() {
+			return this.type;
+		}
+
+		public List<String> getValues() {
+			return this.values;
+		}
+
+	}
+
+}

initializr-generator/src/main/java/io/spring/initializr/generator/language/CompilationUnit.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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 io.spring.initializr.generator.language;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * A compilation unit that represents an individual source file.
+ *
+ * @param <T> the concrete type declaration supported by the compilation unit
+ * @author Andy Wilkinson
+ */
+public abstract class CompilationUnit<T extends TypeDeclaration> {
+
+	private final String packageName;
+
+	private final String name;
+
+	private final List<T> typeDeclarations = new ArrayList<>();
+
+	public CompilationUnit(String packageName, String name) {
+		this.packageName = packageName;
+		this.name = name;
+	}
+
+	public String getPackageName() {
+		return this.packageName;
+	}
+
+	public String getName() {
+		return this.name;
+	}
+
+	public T createTypeDeclaration(String name) {
+		T typeDeclaration = doCreateTypeDeclaration(name);
+		this.typeDeclarations.add(typeDeclaration);
+		return typeDeclaration;
+	}
+
+	public List<T> getTypeDeclarations() {
+		return Collections.unmodifiableList(this.typeDeclarations);
+	}
+
+	protected abstract T doCreateTypeDeclaration(String name);
+
+}

initializr-generator/src/main/java/io/spring/initializr/generator/language/Language.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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 io.spring.initializr.generator.language;
+
+import java.util.Objects;
+
+import org.springframework.core.io.support.SpringFactoriesLoader;
+
+/**
+ * A language in which a generated project can be written.
+ *
+ * @author Andy Wilkinson
+ */
+public interface Language {
+
+	/**
+	 * The default JVM version to use if none is specified.
+	 */
+	String DEFAULT_JVM_VERSION = "1.8";
+
+	String id();
+
+	String jvmVersion();
+
+	static Language forId(String id, String jvmVersion) {
+		return SpringFactoriesLoader
+				.loadFactories(LanguageFactory.class,
+						LanguageFactory.class.getClassLoader())
+				.stream().map((factory) -> factory.createLanguage(id, jvmVersion))
+				.filter(Objects::nonNull).findFirst()
+				.orElseThrow(() -> new IllegalStateException(
+						"Unrecognized language id '" + id + "'"));
+	}
+
+}

initializr-generator/src/main/java/io/spring/initializr/generator/language/LanguageFactory.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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 io.spring.initializr.generator.language;
+
+/**
+ * A factory for creating a {@link Language}.
+ *
+ * @author Andy Wilkinson
+ */
+public interface LanguageFactory {
+
+	/**
+	 * Creates and returns a {@link Language} for the given id and JVM version. If the
+	 * factory does not recognise the given {@code id}, {@code null} should be returned.
+	 * @param id the id of the language
+	 * @param jvmVersion the jvm version or {@code null} to use the default
+	 * @return the language or {@code null}
+	 */
+	Language createLanguage(String id, String jvmVersion);
+
+}

initializr-generator/src/main/java/io/spring/initializr/generator/language/Parameter.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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 io.spring.initializr.generator.language;
+
+/**
+ * A parameter, typically of a method or function.
+ *
+ * @author Andy Wilkinson
+ */
+public class Parameter {
+
+	private final String type;
+
+	private final String name;
+
+	public Parameter(String type, String name) {
+		this.type = type;
+		this.name = name;
+	}
+
+	public String getType() {
+		return this.type;
+	}
+
+	public String getName() {
+		return this.name;
+	}
+
+}

initializr-generator/src/main/java/io/spring/initializr/generator/language/SourceCode.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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 io.spring.initializr.generator.language;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.function.BiFunction;
+
+/**
+ * Representation of application source code.
+ *
+ * @param <T> types
+ * @param <C> compilation units
+ * @author Andy Wilkinson
+ */
+public abstract class SourceCode<T extends TypeDeclaration, C extends CompilationUnit<T>> {
+
+	private final List<C> compilationUnits = new ArrayList<>();
+
+	private final BiFunction<String, String, C> compilationUnitFactory;
+
+	protected SourceCode(BiFunction<String, String, C> compilationUnitFactory) {
+		this.compilationUnitFactory = compilationUnitFactory;
+	}
+
+	public C createCompilationUnit(String packageName, String name) {
+		C compilationUnit = this.compilationUnitFactory.apply(packageName, name);
+		this.compilationUnits.add(compilationUnit);
+		return compilationUnit;
+	}
+
+	/**
+	 * Returns an unmodifiable view of the {@link CompilationUnit compilation units}.
+	 * @return the compilation units
+	 */
+	public List<C> getCompilationUnits() {
+		return Collections.unmodifiableList(this.compilationUnits);
+	}
+
+}

initializr-generator/src/main/java/io/spring/initializr/generator/language/SourceCodeWriter.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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 io.spring.initializr.generator.language;
+
+import java.io.IOException;
+import java.nio.file.Path;
+
+/**
+ * A writer for some {@link SourceCode}.
+ *
+ * @param <S> the type of source code that can be written by this writer
+ * @author Andy Wilkinson
+ */
+public interface SourceCodeWriter<S extends SourceCode<?, ?>> {
+
+	/**
+	 * Writes, to the given {@code directory}, the given {@code sourceCode}.
+	 * @param directory the root directory beneath which the source code is written
+	 * @param sourceCode the source code to write
+	 * @throws IOException if writing fails
+	 */
+	void writeTo(Path directory, S sourceCode) throws IOException;
+
+}

initializr-generator/src/main/java/io/spring/initializr/generator/language/TypeDeclaration.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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 io.spring.initializr.generator.language;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * A type declared in a {@link CompilationUnit}.
+ *
+ * @author Andy Wilkinson
+ */
+public class TypeDeclaration implements Annotatable {
+
+	private final List<Annotation> annotations = new ArrayList<>();
+
+	private final String name;
+
+	private String extendedClassName;
+
+	public TypeDeclaration(String name) {
+		this.name = name;
+	}
+
+	public void extend(String name) {
+		this.extendedClassName = name;
+	}
+
+	@Override
+	public void annotate(Annotation annotation) {
+		this.annotations.add(annotation);
+	}
+
+	@Override
+	public List<Annotation> getAnnotations() {
+		return Collections.unmodifiableList(this.annotations);
+	}
+
+	public String getName() {
+		return this.name;
+	}
+
+	public String getExtends() {
+		return this.extendedClassName;
+	}
+
+}

initializr-generator/src/main/java/io/spring/initializr/generator/language/package-info.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2019 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
+ *
+ *      http://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.
+ */
+
+/**
+ * Language abstraction.
+ */
+package io.spring.initializr.generator.language;

initializr-generator/src/test/java/io/spring/initializr/generator/language/AnnotationTests.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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 io.spring.initializr.generator.language;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link Annotation}.
+ *
+ * @author Stephane Nicoll
+ */
+class AnnotationTests {
+
+	@Test
+	void annotationWithNoAttribute() {
+		Annotation annotation = Annotation.name("com.example.Test");
+		assertThat(annotation.getName()).isEqualTo("com.example.Test");
+		assertThat(annotation.getAttributes()).isEmpty();
+	}
+
+	@Test
+	void annotationWithSingleAttribute() {
+		Annotation annotation = Annotation.name("com.example.Test",
+				(builder) -> builder.attribute("test", Enum.class,
+						"com.example.Unit.CENTURIES, com.example.Unit.NANOS"));
+		assertThat(annotation.getName()).isEqualTo("com.example.Test");
+		assertThat(annotation.getAttributes()).hasSize(1);
+		Annotation.Attribute attribute = annotation.getAttributes().get(0);
+		assertThat(attribute.getName()).isEqualTo("test");
+		assertThat(attribute.getType()).isEqualTo(Enum.class);
+		assertThat(attribute.getValues())
+				.containsExactly("com.example.Unit.CENTURIES, com.example.Unit.NANOS");
+	}
+
+}