android/support/VersionFileWriterTask.java

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * 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 android.support;

import com.android.build.gradle.LibraryExtension;

import org.gradle.api.Action;
import org.gradle.api.DefaultTask;
import org.gradle.api.Project;
import org.gradle.api.tasks.Input;
import org.gradle.api.tasks.OutputFile;
import org.gradle.api.tasks.TaskAction;

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * Task that allows to write a version to a given output file.
 */
public class VersionFileWriterTask extends DefaultTask {
    public static final String RESOURCE_DIRECTORY = "generatedResources";
    public static final String VERSION_FILE_PATH =
            RESOURCE_DIRECTORY + "/META-INF/%s_%s.version";

    private String mVersion;
    private File mOutputFile;

    /**
     * Sets up Android Library project to have a task that generates a version file.
     *
     * @param project an Android Library project.
     */
    public static void setUpAndroidLibrary(Project project) {
        project.afterEvaluate(new Action<Project>() {
            @Override
            public void execute(Project project) {
                LibraryExtension library =
                        project.getExtensions().findByType(LibraryExtension.class);

                String group = (String) project.getProperties().get("group");
                String artifactId = (String) project.getProperties().get("name");
                String version = (String) project.getProperties().get("version");

                // Add a java resource file to the library jar for version tracking purposes.
                File artifactName = new File(project.getBuildDir(),
                        String.format(VersionFileWriterTask.VERSION_FILE_PATH,
                                group, artifactId));

                VersionFileWriterTask writeVersionFile =
                        project.getTasks().create("writeVersionFile", VersionFileWriterTask.class);
                writeVersionFile.setVersion(version);
                writeVersionFile.setOutputFile(artifactName);

                library.getLibraryVariants().all(
                        libraryVariant -> libraryVariant.getProcessJavaResources().dependsOn(
                                writeVersionFile));

                library.getSourceSets().getByName("main").getResources().srcDir(
                        new File(project.getBuildDir(), VersionFileWriterTask.RESOURCE_DIRECTORY)
                );
            }
        });
    }

    @Input
    public String getVersion() {
        return mVersion;
    }

    public void setVersion(String version) {
        mVersion = version;
    }

    @OutputFile
    public File getOutputFile() {
        return mOutputFile;
    }

    public void setOutputFile(File outputFile) {
        mOutputFile = outputFile;
    }

    /**
     * The main method for actually writing out the file.
     *
     * @throws IOException
     */
    @TaskAction
    public void run() throws IOException {
        PrintWriter writer = new PrintWriter(mOutputFile);
        writer.println(mVersion);
        writer.close();
    }
}