src/main/java/org/apache/freemarker/generator/OutputGenerator.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.freemarker.generator;

import freemarker.template.Configuration;
import freemarker.template.Template;

import java.io.File;
import java.io.FileWriter;
import java.nio.file.Path;
import java.util.HashMap;
import java.util.Map;

/**
 * Knows how to generate an output file given five things:
 * <ul>
 * <li>The latest update time of the <b>pom file(s)</b> for the project</li>
 * <li>The location of the <b>generator file</b></li>
 * <li>The location of the <b>template file</b></li>
 * <li>The location of the <b>output file</b></li>
 * <li>A <b>data model<b> used to fill out the template.</li>
 * </ul>
 *<p>Given these five pieces of information, the generator will generate a new output file, but only if any existing
 * generated file is not newer than the inputs (pom, generator, and template).</p>
 */
class OutputGenerator {
	public final long pomModifiedTimestamp;
	public final Path generatorLocation;
	public final Path templateLocation;
	public final Path outputLocation;
	public final Map<String,Object> dataModel;
	private OutputGenerator(
		 long pomModifiedTimestamp,
		 Path generatorLocation,
		 Path templateLocation,
		 Path outputLocation,
		 Map<String, Object> dataModel) {
		this.pomModifiedTimestamp = pomModifiedTimestamp;
		this.generatorLocation = generatorLocation;
		this.templateLocation = templateLocation;
		this.outputLocation = outputLocation;
		this.dataModel = dataModel;
	}

	/**
	 * Uses a fluent builder to make the code more legible in place.
	 * Also allows the output generator to be built from multiple locations in source by passing the builder.
	 * @return A new fluent builder for the OutputGenerator class.
	 */
	public static OutputGeneratorBuilder builder() {
		return new OutputGeneratorBuilder();
	}

	public static class OutputGeneratorBuilder {
		private long pomModifiedTimestamp = Long.MAX_VALUE;
		private Path generatorLocation = null;
		private Path templateLocation = null;
		private Path outputLocation = null;
		private Map<String,Object> dataModel = null;

		public OutputGeneratorBuilder addPomLastModifiedTimestamp(long pomModifiedTimestamp) {
			this.pomModifiedTimestamp = pomModifiedTimestamp;
			return this;
		}

		public OutputGeneratorBuilder addGeneratorLocation(Path generatorLocation) {
			this.generatorLocation = generatorLocation;
			return this;
		}

		public OutputGeneratorBuilder addTemplateLocation(Path templateLocation) {
			this.templateLocation = templateLocation;
			return this;
		}

		public OutputGeneratorBuilder addOutputLocation(Path outputLocation) {
			this.outputLocation = outputLocation;
			return this;
		}

		public OutputGeneratorBuilder addDataModel(Map<String,Object> dataModel) {
			this.dataModel = dataModel;
			return this;
		}

		public OutputGeneratorBuilder addToDataModel(String key, Object val) {
			if (this.dataModel == null) {
				this.dataModel = new HashMap<>(4);
			}
			this.dataModel.put(key,val);
			return this;
		}

		/**
		 * @throws IllegalStateException if any of the parts of the OutputGenerator were not set.
		 * @return A new output generator (which is immutable).
		 */
		public OutputGenerator create() {
			if (pomModifiedTimestamp == Long.MAX_VALUE) throw new IllegalStateException("Must set the pomModifiedTimestamp");
			if (generatorLocation == null) throw new IllegalStateException("Must set a non-null generatorLocation");
			if (templateLocation == null) throw new IllegalStateException("Must set a non-null templateLocation");
			if (outputLocation == null) throw new IllegalStateException("Must set a non-null outputLocation");
			if (dataModel == null) throw new IllegalStateException("Must set a non-null dataModel");
			return new OutputGenerator(pomModifiedTimestamp, generatorLocation, templateLocation, outputLocation, dataModel);
		}
	}

	/**
	 * <p>Generates an output by applying the model to the template.</p>
	 * <p>Checks the ages of the inputs against an existing output file to early exit if there is no update.</p>
	 * @param config Used to load the template from the template name.
	 */
	public void generate(Configuration config) {
		//Use "createFile" for testing purposes only
		File outputFile = FactoryUtil.createFile(outputLocation.toFile().toString());
		File templateFile = templateLocation.toFile();
		File generatorFile = generatorLocation.toFile();
		if (outputFile.exists()) {
			//early exit only if the output file is newer than all files that contribute to its generation
			if (outputFile.lastModified() > generatorFile.lastModified()
				 && outputFile.lastModified() > templateFile.lastModified()
				 && outputFile.lastModified() > pomModifiedTimestamp) {
				return;
			}
		} else {
			File parentDir = outputFile.getParentFile();
			if (parentDir.isFile()) {
				throw new RuntimeException("Parent directory of output file is a file: " + parentDir.getAbsoluteFile());
			}
			parentDir.mkdirs();
			if (!parentDir.isDirectory()) {
				throw new RuntimeException("Could not create directory: " + parentDir.getAbsoluteFile());
			}
		}

		Template template;
		try {
			template = config.getTemplate(templateFile.getName());
		} catch (Throwable t) {
			throw new RuntimeException("Could not read template: " + templateFile.getName(), t);
		}

		try (FileWriter writer = new FileWriter(outputFile)) {
			template.process(dataModel, writer);
		} catch (Throwable t) {
			throw new RuntimeException("Could not process template associated with data file: " + generatorLocation, t);
		}
	}
}