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原作者：ShinyZeng
版权声明：未经玉刚说许可，不得以任何形式转载
前言：这篇文章在一个月之前已经发布到玉刚说微信公众号。Gradle 这一块对于我们Android开发来说，一直是比较无人问津的一块，平日的开发中也比较少涉及，即使涉及也是网上查查资料就可以解决，并不会深入理解原理，即使深入了，过一段时间不接触也容易忘记，譬如我今日再看这篇文章，就发现有很多已经忘记了…真是汗颜啊…所以简书中再发出来，做个备忘吧。
一、源码依赖
本文基于:
android gradle plugin版本：com.android.tools.build:gradle:2.3.0
gradle 版本：4.1
Gradle源码总共30个G，为简单起见，方便大家看源码，此处通过gradle依赖的形式来查看源码，依赖源码姿势：
创建一个新工程，app 项目目录中删除所有文件，仅留下gradle文件，依赖
apply plugin: 'java'
sourceCompatibility = 1.8
dependencies {
compile gradleApi()
compile 'com.android.tools.build:gradle:2.3.0'
}
将跟目录下的gradle文件，删除掉gradle依赖
buildscript {
repositories {
google()
jcenter()
}
dependencies {
// compile 'com.android.tools.build:gradle:2.3.0'
}
}
然后rebuild一下，就可以在External Libraries中查看到android gradle的源码已经依赖了
二、Android Gradle Plugin简介
我们知道Android gradle plugin是用来构建Android工程的gradle插件，在Android gradle 插件中，可以看到app工程和library工程所依赖的plugin是不一样的
// app 工程
apply plugin: 'com.android.application'
// library 工程
apply plugin: 'com.android.library'
而对应填写andorid块中所填写的配置也不同，这就是区分Application和Library的插件的extension块
分别为：
app工程 -> AppPlugin -> AppExtension
librar工程 -> LibraryPlugin -> LibraryExtension
对应的是AppPlugin和AppExtension，这两个插件构建的流程大抵是相同的，只是各自插件生成的任务不同，接下来我们着重分析Application插件是如何构建我们的Android应用的
三、AppPlugin的构建流程
我们先看下app工程中gradle的文件格式
apply plugin: 'com.android.application'
android {
compileSdkVersion 25
buildToolsVersion '26.0.2'
defaultConfig {
applicationId "com.zengshaoyi.gradledemo"
minSdkVersion 15
targetSdkVersion 25
versionCode project.ext.versionCode
versionName project.ext.versionName
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
lintOptions {
abortOnError false
}
}
跟踪apply方法，其实是进入到
AppPlugin的apply的方法，我们可以看到内部实现是直接调用父类BasePlugin的apply方法
protected void apply(@NonNull Project project) {
checkPluginVersion();
this.project = project;
ExecutionConfigurationUtil.setThreadPoolSize(project);
checkPathForErrors();
checkModulesForErrors();
ProfilerInitializer.init(project);
threadRecorder = ThreadRecorder.get();
ProcessProfileWriter.getProject(project.getPath())
.setAndroidPluginVersion(Version.ANDROID_GRADLE_PLUGIN_VERSION)
.setAndroidPlugin(getAnalyticsPluginType())
.setPluginGeneration(GradleBuildProject.PluginGeneration.FIRST);
threadRecorder.record(
ExecutionType.BASE_PLUGIN_PROJECT_CONFIGURE,
project.getPath(),
null,
this::configureProject);
threadRecorder.record(
ExecutionType.BASE_PLUGIN_PROJECT_BASE_EXTENSION_CREATION,
project.getPath(),
null,
this::configureExtension);
threadRecorder.record(
ExecutionType.BASE_PLUGIN_PROJECT_TASKS_CREATION,
project.getPath(),
null,
this::createTasks);
// Apply additional plugins
for (String plugin : AndroidGradleOptions.getAdditionalPlugins(project)) {
project.apply(ImmutableMap.of("plugin", plugin));
}
}
threadRecoirder.recode()是记录最后一个参数的路径和执行的时间点，前面做了一些必要性的信息检测之前，其实主要做了以下几件事情：
// 配置项目，设置构建回调
this::configureProject
// 配置Extension
this::configureExtension
// 创建任务
this::createTasks
::是java 8引入的特性，详情可以查看java8特性 ，这里就是方法的调用
configureProject
直接来看源码
private void configureProject() {
extraModelInfo = new ExtraModelInfo(project);
checkGradleVersion();
AndroidGradleOptions.validate(project);
// Android SDK处理类
sdkHandler = new SdkHandler(project, getLogger());
// 设置项目评估阶段回调
project.afterEvaluate(p -> {
// TODO: Read flag from extension.
if (!p.getGradle().getStartParameter().isOffline()
&& AndroidGradleOptions.getUseSdkDownload(p)) {
// 相关配置依赖的下载处理
SdkLibData sdkLibData =
SdkLibData.download(getDownloader(), getSettingsController());
dependencyManager.setSdkLibData(sdkLibData);
sdkHandler.setSdkLibData(sdkLibData);
}
});
// 创建AndroidBuilder
androidBuilder = new AndroidBuilder(
project == project.getRootProject() ? project.getName() : project.getPath(),
creator,
new GradleProcessExecutor(project),
new GradleJavaProcessExecutor(project),
extraModelInfo,
getLogger(),
isVerbose());
// dataBinding的相关处理
dataBindingBuilder = new DataBindingBuilder();
dataBindingBuilder.setPrintMachineReadableOutput(
extraModelInfo.getErrorFormatMode() ==
ExtraModelInfo.ErrorFormatMode.MACHINE_PARSABLE);
// Apply the Java and Jacoco plugins.
project.getPlugins().apply(JavaBasePlugin.class);
project.getPlugins().apply(JacocoPlugin.class);
// 给assemble任务添加描述
project.getTasks()
.getByName("assemble")
.setDescription(
"Assembles all variants of all applications and secondary packages.");
...
可以看到 configureProject 方法中在 project.afterEvaluate 设置了回调，当项目评估结束时，根据项目配置情况，设置 dependece 依赖；创建了 AndroidBuilder 对象，这个对象是用来合并manifest 和创建 dex 等作用，后面在创建任务的过程中会使用到，结下来继续看 configureProject 的源码
// call back on execution. This is called after the whole build is done (not
// after the current project is done).
// This is will be called for each (android) projects though, so this should support
// being called 2+ times.
// 设置构建回调
project.getGradle()
.addBuildListener(
new BuildListener() {
private final LibraryCache libraryCache = LibraryCache.getCache();
@Override
public void buildStarted(Gradle gradle) {}
@Override
public void settingsEvaluated(Settings settings) {}
@Override
public void projectsLoaded(Gradle gradle) {}
@Override
public void projectsEvaluated(Gradle gradle) {}
@Override
public void buildFinished(BuildResult buildResult) {
ExecutorSingleton.shutdown();
sdkHandler.unload();
threadRecorder.record(
ExecutionType.BASE_PLUGIN_BUILD_FINISHED,
project.getPath(),
null,
() -> {
// 当任务执行完成时，清楚dex缓存
PreDexCache.getCache()
.clear(
FileUtils.join(
project.getRootProject()
.getBuildDir(),
FD_INTERMEDIATES,
"dex-cache",
"cache.xml"),
getLogger());
JackConversionCache.getCache()
.clear(
FileUtils.join(
project.getRootProject()
.getBuildDir(),
FD_INTERMEDIATES,
"jack-cache",
"cache.xml"),
getLogger());
libraryCache.unload();
Main.clearInternTables();
});
}
});
// 设置创建有向图任务回调
project.getGradle()
.getTaskGraph()
.addTaskExecutionGraphListener(
taskGraph -> {
for (Task task : taskGraph.getAllTasks()) {
// TransformTask是class编译成dex的重要任务
if (task instanceof TransformTask) {
Transform transform = ((TransformTask) task).getTransform();
if (transform instanceof DexTransform) {
PreDexCache.getCache()
.load(
FileUtils.join(
project.getRootProject()
.getBuildDir(),
FD_INTERMEDIATES,
"dex-cache",
"cache.xml"));
break;
} else if (transform instanceof JackPreDexTransform) {
JackConversionCache.getCache()
.load(
FileUtils.join(
project.getRootProject()
.getBuildDir(),
FD_INTERMEDIATES,
"jack-cache",
"cache.xml"));
break;
}
}
}
});
这里在添加了 BuildListener，在 buildFinished 的时候清楚了dex缓存，而在任务有向图创建的回调中，判断是否是 DexTransfrom，从而从缓存中加载dex。
总结一下 configureProject 做的事情，主要是进行版本有效性的判断，创建了 AndroidBuilder 对象，并设置了构建流程的回调来处理依赖和dex的加载和缓存清理。
configureExtension
这个阶段就是配置 extension 的阶段，就是创建我们 android 块中的可配置的对象
private void configureExtension() {
final NamedDomainObjectContainer<BuildType> buildTypeContainer =
project.container(
BuildType.class,
new BuildTypeFactory(instantiator, project, project.getLogger()));
final NamedDomainObjectContainer<ProductFlavor> productFlavorContainer =
project.container(
ProductFlavor.class,
new ProductFlavorFactory(
instantiator, project, project.getLogger(), extraModelInfo));
final NamedDomainObjectContainer<SigningConfig> signingConfigContainer =
project.container(SigningConfig.class, new SigningConfigFactory(instantiator));
extension =
createExtension(
project,
instantiator,
androidBuilder,
sdkHandler,
buildTypeContainer,
productFlavorContainer,
signingConfigContainer,
extraModelInfo);
...
首先创建了 BuildType、ProductFlavor、SigningConfig 三个类型的Container，接着传入到了createExtension方法中，点入查看是个抽象的方法，各自的实现在子类中，这里也就是我们的AppPlugin 中
@NonNull
@Override
protected BaseExtension createExtension(
@NonNull Project project,
@NonNull Instantiator instantiator,
@NonNull AndroidBuilder androidBuilder,
@NonNull SdkHandler sdkHandler,
@NonNull NamedDomainObjectContainer<BuildType> buildTypeContainer,
@NonNull NamedDomainObjectContainer<ProductFlavor> productFlavorContainer,
@NonNull NamedDomainObjectContainer<SigningConfig> signingConfigContainer,
@NonNull ExtraModelInfo extraModelInfo) {
return project.getExtensions()
.create(
"android",
AppExtension.class,
project,
instantiator,
androidBuilder,
sdkHandler,
buildTypeContainer,
productFlavorContainer,
signingConfigContainer,
extraModelInfo);
}
这里也就是可以看到我们android块配置是如何来的了，对应的Extension也确实是AppExtension，继续查看 configureExtension 的源码
dependencyManager = new DependencyManager(
project,
extraModelInfo,
sdkHandler);
ndkHandler = new NdkHandler(
project.getRootDir(),
null, /* compileSkdVersion, this will be set in afterEvaluate */
"gcc",
"" /*toolchainVersion*/);
taskManager =
createTaskManager(
project,
androidBuilder,
dataBindingBuilder,
extension,
sdkHandler,
ndkHandler,
dependencyManager,
registry,
threadRecorder);
variantFactory = createVariantFactory(instantiator, androidBuilder, extension);
variantManager =
new VariantManager(
project,
androidBuilder,
extension,
variantFactory,
taskManager,
instantiator,
threadRecorder);
// Register a builder for the custom tooling model
ModelBuilder modelBuilder = new ModelBuilder(
androidBuilder,
variantManager,
taskManager,
extension,
extraModelInfo,
ndkHandler,
new NativeLibraryFactoryImpl(ndkHandler),
getProjectType(),
AndroidProject.GENERATION_ORIGINAL);
registry.register(modelBuilder);
// Register a builder for the native tooling model
NativeModelBuilder nativeModelBuilder = new NativeModelBuilder(variantManager);
registry.register(nativeModelBuilder);
这一部分主要是创建一些管理类，其中 createTaskManager、createVariantFactory 都是抽象方法，对应的实现类
createTaskManager
AppPlugin -> ApplicationTaskManager
LibraryPlugin -> LibraryTaskManager
createVariantFactory
AppPlugin -> ApplicationVariantFactory
LibraryPlugin -> LibraryVariantFactory
这里简单介绍一下 TaskManager 就是创建具体任务的管理类，app 工程和库 library 工程所需的构建任务是不同的，后面我们会介绍 app 工程创建的构建任务；VariantFactory 就是我们常说的构建变体的工厂类，主要是生成Variant（构建变体）的对象。我们回到 createExtension 的源码中
// map the whenObjectAdded callbacks on the containers.
signingConfigContainer.whenObjectAdded(variantManager::addSigningConfig);
buildTypeContainer.whenObjectAdded(
buildType -> {
SigningConfig signingConfig =
signingConfigContainer.findByName(BuilderConstants.DEBUG);
buildType.init(signingConfig);
variantManager.addBuildType(buildType);
});
productFlavorContainer.whenObjectAdded(variantManager::addProductFlavor);
...
// create default Objects, signingConfig first as its used by the BuildTypes.
variantFactory.createDefaultComponents(
buildTypeContainer, productFlavorContainer, signingConfigContainer);
这一部分做得事情，配置了 BuildTypeContainer、ProductFlavorContainer、SigningConfigContainer 这三个配置项的 whenObjectAdded 的回调，每个配置的添加都会加入到 variantManager 中；创建默认配置，下面是 ApplicationVariantFactory 的 createDefaultComponents 代码
@Override
public void createDefaultComponents(
@NonNull NamedDomainObjectContainer<BuildType> buildTypes,
@NonNull NamedDomainObjectContainer<ProductFlavor> productFlavors,
@NonNull NamedDomainObjectContainer<SigningConfig> signingConfigs) {
// must create signing config first so that build type 'debug' can be initialized
// with the debug signing config.
signingConfigs.create(DEBUG);
buildTypes.create(DEBUG);
buildTypes.create(RELEASE);
}
总结一下 configureExtension 方法的作用，主要是创建 Android 插件的扩展对象，对配置项 BuildType、ProductFlavor、SigningConfig 做了统一的创建和回调处理， 创建taskManager、variantFactory、variantManager。
createTasks
private void createTasks() {
threadRecorder.record(
ExecutionType.TASK_MANAGER_CREATE_TASKS,
project.getPath(),
null,
() -> // 在项目评估之前创建任务
taskManager.createTasksBeforeEvaluate(
new TaskContainerAdaptor(project.getTasks())));
project.afterEvaluate(
project ->
threadRecorder.record(
ExecutionType.BASE_PLUGIN_CREATE_ANDROID_TASKS,
project.getPath(),
null,
// 在项目评估完成之后创建 androidTask
() -> createAndroidTasks(false)));
}
这里主要是分两块，一个是在 beforeEvaluate 创建任务；一个是在 afterEvaluate 创建任务。这里的区别是 AndroidTask 是依赖配置项的配置才能生成相应任务，所以是需要在 afterEvaluate 之后创建，如果对项目评估回调不理解的话，可以查阅Project文档。beforeEvaluate 创建的任务跟我们编译没有太大关系，我们重点查看一下 afterEvaluate 创建的任务 createAndroidTasks
@VisibleForTesting
final void createAndroidTasks(boolean force) {
...
threadRecorder.record(
ExecutionType.VARIANT_MANAGER_CREATE_ANDROID_TASKS,
project.getPath(),
null,
() -> {
// 创建AndroidTasks
variantManager.createAndroidTasks();
ApiObjectFactory apiObjectFactory =
new ApiObjectFactory(
androidBuilder, extension, variantFactory, instantiator);
for (BaseVariantData variantData : variantManager.getVariantDataList()) {
apiObjectFactory.create(variantData);
}
});
...
}
我们主要看下variantManager的createAndroidTasks的方法
/**
* Variant/Task creation entry point.
*
* Not used by gradle-experimental.
*/
public void createAndroidTasks() {
variantFactory.validateModel(this);
variantFactory.preVariantWork(project);
final TaskFactory tasks = new TaskContainerAdaptor(project.getTasks());
if (variantDataList.isEmpty()) {
recorder.record(
ExecutionType.VARIANT_MANAGER_CREATE_VARIANTS,
project.getPath(),
null /*variantName*/,
this::populateVariantDataList);
}
// Create top level test tasks.
recorder.record(
ExecutionType.VARIANT_MANAGER_CREATE_TESTS_TASKS,
project.getPath(),
null /*variantName*/,
() -> taskManager.createTopLevelTestTasks(tasks, !productFlavors.isEmpty()));
for (final BaseVariantData<? extends BaseVariantOutputData> variantData : variantDataList) {
recorder.record(
ExecutionType.VARIANT_MANAGER_CREATE_TASKS_FOR_VARIANT,
project.getPath(),
variantData.getName(),
() -> createTasksForVariantData(tasks, variantData));
}
taskManager.createReportTasks(tasks, variantDataList);
}
首先判断 variantDataList 是否是空，如果是空的就会进入到 populateVariantDataList 方法中
/**
* Create all variants.
*/
public void populateVariantDataList() {
if (productFlavors.isEmpty()) {
createVariantDataForProductFlavors(Collections.emptyList());
} else {
List<String> flavorDimensionList = extension.getFlavorDimensionList();
// Create iterable to get GradleProductFlavor from ProductFlavorData.
Iterable<CoreProductFlavor> flavorDsl =
Iterables.transform(
productFlavors.values(),
ProductFlavorData::getProductFlavor);
// Get a list of all combinations of product flavors.
List<ProductFlavorCombo<CoreProductFlavor>> flavorComboList =
ProductFlavorCombo.createCombinations(
flavorDimensionList,
flavorDsl);
for (ProductFlavorCombo<CoreProductFlavor> flavorCombo : flavorComboList) {
//noinspection unchecked
createVariantDataForProductFlavors(
(List<ProductFlavor>) (List) flavorCombo.getFlavorList());
}
}
}
从方法注释可以看到，这个方法主要的作用就是创建所有的 variants，试想一下该段代码会做哪些事情，是否是解析 buildType、productFlavor 配置？
创建构建变体（BuildVariant）
继续观察上面的代码，可以看到无论是否有配置productFlavor 子项，都会进入到 createVariantDataForProductFlavors 方法。如果有配置的话，通过获取配置的 flavorDimension 和 productFlavor 数组，调用 ProductFlavorCombo.createCombinations 组合出最后的产品风味数组 flavorComboList ，最后通过遍历调用 createVariantDataForProductFlavors 方法
/**
* Creates VariantData for a specified list of product flavor.
*
* This will create VariantData for all build types of the given flavors.
*
* @param productFlavorList the flavor(s) to build.
*/
private void createVariantDataForProductFlavors(
@NonNull List<ProductFlavor> productFlavorList) {
...
for (BuildTypeData buildTypeData : buildTypes.values()) {
boolean ignore = false;
...
if (!ignore) {
BaseVariantData<?> variantData = createVariantData(
buildTypeData.getBuildType(),
productFlavorList);
variantDataList.add(variantData);
...
}
}
...
}
看上述代码，通过 creatVariantData 方法，将 buildType 和 productFlavor 的作为参数传入，创建了 variantData，并且加入到了 variantDataList 集合中，这里我们就是将所有的构建变体集合到了 variantDataList 中。
接着我们返回继续看 createAndroidTasks 方法
/**
* Variant/Task creation entry point.
*
* Not used by gradle-experimental.
*/
public void createAndroidTasks() {
...
for (final BaseVariantData<? extends BaseVariantOutputData> variantData : variantDataList) {
recorder.record(
ExecutionType.VARIANT_MANAGER_CREATE_TASKS_FOR_VARIANT,
project.getPath(),
variantData.getName(),
() -> createTasksForVariantData(tasks, variantData));
}
...
}
通过上面拿到的variantDataList，遍历该集合来创建任务
/**
* Create tasks for the specified variantData.
*/
public void createTasksForVariantData(
final TaskFactory tasks,
final BaseVariantData<? extends BaseVariantOutputData> variantData) {
final BuildTypeData buildTypeData = buildTypes.get(
variantData.getVariantConfiguration().getBuildType().getName());
if (buildTypeData.getAssembleTask() == null) {
// 创建assemble + buildType任务
buildTypeData.setAssembleTask(taskManager.createAssembleTask(tasks, buildTypeData));
}
// Add dependency of assemble task on assemble build type task.
tasks.named("assemble", new Action<Task>() {
@Override
public void execute(Task task) {
assert buildTypeData.getAssembleTask() != null;
// 将 assemble 任务依赖于我们的 assemble + buildType 任务
task.dependsOn(buildTypeData.getAssembleTask().getName());
}
});
VariantType variantType = variantData.getType();
// 根据 variantData 创建 assemble + flavor + buildType 任务
createAssembleTaskForVariantData(tasks, variantData);
if (variantType.isForTesting()) {
...
} else {
// 根据 variantData 创建一系列任务
taskManager.createTasksForVariantData(tasks, variantData);
}
}
首先会先根据 buildType 信息创建 assemble + buildType 的任务，可以看下taskManager. createAssembleTask里的代码
@NonNull
public AndroidTask<DefaultTask> createAssembleTask(
@NonNull TaskFactory tasks,
@NonNull VariantDimensionData dimensionData) {
final String sourceSetName =
StringHelper.capitalize(dimensionData.getSourceSet().getName());
return androidTasks.create(
tasks,
// 设置任务名字为 assembleXXX
"assemble" + sourceSetName,
assembleTask -> {
// 设置描述和任务组
assembleTask.setDescription("Assembles all " + sourceSetName + " builds.");
assembleTask.setGroup(BasePlugin.BUILD_GROUP);
});
}
创建完任务之后，将assemble任务依赖于我们的assembleXXX任务，随后调用 createAssembleTaskForVariantData 方法，此方法是创建 assemble + flavor + buildType 任务，流程多了 productFlavor 任务的创建，这里就不赘述了。后面会执 createTasksForVariantData，这个方法就是根据 variant 生成一系列 Android 构建所需任务（后面会详细介绍），回到 createAndroidTasks 方法中
threadRecorder.record(
ExecutionType.VARIANT_MANAGER_CREATE_ANDROID_TASKS,
project.getPath(),
null,
() -> {
variantManager.createAndroidTasks();
ApiObjectFactory apiObjectFactory =
new ApiObjectFactory(
androidBuilder, extension, variantFactory, instantiator);
for (BaseVariantData variantData : variantManager.getVariantDataList()) {
// 创建variantApi，添加到extensions中
apiObjectFactory.create(variantData);
}
});
最后就遍历 variantDataList 通过 ApiObjectFactory 创建 variantApi，添加到 extensions 中；
至此，我们就已经将配置的构建变种任务已经添加到我们的任务列表中，并形成了相关依赖。
Application 的编译任务
我们继续查看createTasksForVariantData的最后一行，
taskManager.createTasksForVariantData，发现 createTasksForVariantData 是抽象方法，这里的 taskManager 具体实现是 ApplicationTaskManager，查看 ApplicationTaskManager 的 createTasksForVariantData 方法
/**
* Creates the tasks for a given BaseVariantData.
*/
@Override
public void createTasksForVariantData(
@NonNull final TaskFactory tasks,
@NonNull final BaseVariantData<? extends BaseVariantOutputData> variantData) {
assert variantData instanceof ApplicationVariantData;
final VariantScope variantScope = variantData.getScope();
//create sourceGenTask, resGenTask, assetGenTask
createAnchorTasks(tasks, variantScope);
createCheckManifestTask(tasks, variantScope);
handleMicroApp(tasks, variantScope);
// Create all current streams (dependencies mostly at this point)
createDependencyStreams(tasks, variantScope);
// Add a task to process the manifest(s)
// Add a task to create the res values
// Add a task to compile renderscript files.
// Add a task to merge the resource folders
// Add a task to merge the asset folders
// Add a task to create the BuildConfig class
// Add a task to process the Android Resources and generate source files
// Add a task to process the java resources
// Add a task to process this aidl file
// Add a task to process shader source
// Add NDK tasks
// Add external native build tasks
// Add a task to merge the jni libs folders
// Add a compile task
// Add data binding tasks if enabled
// create packaging task
// create the lint tasks.
...
}
代码实在太长了，我只留下了每段代码的注释，注释也已经非常清楚了，这个主要就是生成 variantData 的一系列像 compileXXX、generateXXX、processXXX、mergeXXX的任务，这一系列 task 就是构建一个可运行的完整APK的所需的所有task。下面介绍在编译dex中的过程，涉及的几个task。
Dex的编译过程
// Add a compile task
recorder.record(
ExecutionType.APP_TASK_MANAGER_CREATE_COMPILE_TASK,
project.getPath(),
variantScope.getFullVariantName(),
() -> {
CoreJackOptions jackOptions =
variantData.getVariantConfiguration().getJackOptions();
// create data binding merge task before the javac task so that it can
// parse jars before any consumer
createDataBindingMergeArtifactsTaskIfNecessary(tasks, variantScope);
AndroidTask<? extends JavaCompile> javacTask =
// 创建 javac 任务
createJavacTask(tasks, variantScope);
if (jackOptions.isEnabled()) {
AndroidTask<TransformTask> jackTask =
createJackTask(tasks, variantScope, true /*compileJavaSource*/);
setJavaCompilerTask(jackTask, tasks, variantScope);
} else {
...
addJavacClassesStream(variantScope);
setJavaCompilerTask(javacTask, tasks, variantScope);
getAndroidTasks()
.create(
tasks,
// 创建 AndroidJarTask ，生成classes.jar
new AndroidJarTask.JarClassesConfigAction(variantScope));
createPostCompilationTasks(tasks, variantScope);
}
});
我们直接查看 Add a compile task 注释下的代码，在执行 createPostCompilationTasks 之前，先创建了 javac 任务，任务名称为 compileXXXJavaWithJavac ，该任务是将 java 源文件编译成 class 文件，具体实现是在 JavaCompileConfigAction 类中。创建 javac 任务之后，接着创建了 AndroidJarTask 任务，该任务是将 class 文件整合输出 jar 包，具体实现就是在 AndroidJarTask 类中。
紧接着我们来看一下 createPostCompilationTasks 的方法
/**
* Creates the post-compilation tasks for the given Variant.
*
* These tasks create the dex file from the .class files, plus optional intermediary steps like
* proguard and jacoco
*
*/
public void createPostCompilationTasks(
@NonNull TaskFactory tasks,
@NonNull final VariantScope variantScope) {
checkNotNull(variantScope.getJavacTask());
variantScope.getInstantRunBuildContext().setInstantRunMode(
getIncrementalMode(variantScope.getVariantConfiguration()) != IncrementalMode.NONE);
final BaseVariantData<? extends BaseVariantOutputData> variantData = variantScope.getVariantData();
final GradleVariantConfiguration config = variantData.getVariantConfiguration();
TransformManager transformManager = variantScope.getTransformManager();
...
boolean isMinifyEnabled = isMinifyEnabled(variantScope);
boolean isMultiDexEnabled = config.isMultiDexEnabled();
// Switch to native multidex if possible when using instant run.
boolean isLegacyMultiDexMode = isLegacyMultidexMode(variantScope);
AndroidConfig extension = variantScope.getGlobalScope().getExtension();
// ----- External Transforms -----
// apply all the external transforms.
...
// ----- Minify next -----
if (isMinifyEnabled) {
boolean outputToJarFile = isMultiDexEnabled && isLegacyMultiDexMode;
// 内部会判断是否使用 proguard 来创建 proguard 任务和 shrinkResources 任务
createMinifyTransform(tasks, variantScope, outputToJarFile);
}
// ----- 10x support
...
// ----- Multi-Dex support
Optional<AndroidTask<TransformTask>> multiDexClassListTask;
// non Library test are running as native multi-dex
if (isMultiDexEnabled && isLegacyMultiDexMode) {
...
} else {
multiDexClassListTask = Optional.empty();
}
// create dex transform
// 从 extension 中获取 dexOptions 项的配置
DefaultDexOptions dexOptions = DefaultDexOptions.copyOf(extension.getDexOptions());
...
// 创建 DexTransform
DexTransform dexTransform = new DexTransform(
dexOptions,
config.getBuildType().isDebuggable(),
isMultiDexEnabled,
isMultiDexEnabled && isLegacyMultiDexMode ? variantScope.getMainDexListFile() : null,
variantScope.getPreDexOutputDir(),
variantScope.getGlobalScope().getAndroidBuilder(),
getLogger(),
variantScope.getInstantRunBuildContext(),
AndroidGradleOptions.getBuildCache(variantScope.getGlobalScope().getProject()));
// 创建 dexTask
Optional<AndroidTask<TransformTask>> dexTask =
transformManager.addTransform(tasks, variantScope, dexTransform);
// need to manually make dex task depend on MultiDexTransform since there's no stream
// consumption making this automatic
dexTask.ifPresent(t -> {
t.optionalDependsOn(tasks, multiDexClassListTask.orElse(null));
variantScope.addColdSwapBuildTask(t);
});
...
}
为了讲述主流程，我将一些 mutiDex 和 instantRun 判断的源码省略了，这里我们关注非mutiDex和非instantRun的情况。我们看到，如果我们设置了 minifyEnabled 为 true，那么这里就会去创建 createMinifyTransform ，如果use proguard，这里会创建 progruad 的任务和 shrinkResources 的任务。后面将创建 dexTask， 这个是 transfromTask 类型的任务，我们先来看下 transFromTask 类
/**
* A task running a transform.
*/
@ParallelizableTask
public class TransformTask extends StreamBasedTask implements Context {
private Transform transform;
...
public Transform getTransform() {
return transform;
}
...
@TaskAction
void transform(final IncrementalTaskInputs incrementalTaskInputs)
throws IOException, TransformException, InterruptedException {
...
recorder.record(
ExecutionType.TASK_TRANSFORM,
executionInfo,
getProject().getPath(),
getVariantName(),
new Recorder.Block<Void>() {
@Override
public Void call() throws Exception {
transform.transform(
new TransformInvocationBuilder(TransformTask.this)
.addInputs(consumedInputs.getValue())
.addReferencedInputs(referencedInputs.getValue())
.addSecondaryInputs(changedSecondaryInputs.getValue())
.addOutputProvider(
outputStream != null
? outputStream.asOutput()
: null)
.setIncrementalMode(isIncremental.getValue())
.build());
return null;
}
});
}
}
我们知道，自定义任务中，在任务执行阶段会去执行被 @TaskAction 注解的方法，这里也就是执行 transfrom 方法，而 transfrom 方法中最后又会调用到 transform 的 transfrom 方法，在我们 dexTask 中传入的 transfrom 是DexTransfrom，那我们就去看下 DexTransfrom 的 transfrom 具体实现
public class DexTransform extends Transform {
@Override
public void transform(@NonNull TransformInvocation transformInvocation)
throws TransformException, IOException, InterruptedException {
...
try {
// if only one scope or no per-scope dexing, just do a single pass that
// runs dx on everything.
if ((jarInputs.size() + directoryInputs.size()) == 1
|| !dexOptions.getPreDexLibraries()) {
// since there is only one dex file, we can merge all the scopes into the full
// application one.
File outputDir = outputProvider.getContentLocation("main",
getOutputTypes(),
TransformManager.SCOPE_FULL_PROJECT,
Format.DIRECTORY);
FileUtils.mkdirs(outputDir);
// first delete the output folder where the final dex file(s) will be.
FileUtils.cleanOutputDir(outputDir);
// gather the inputs. This mode is always non incremental, so just
// gather the top level folders/jars
final List<File> inputFiles =
Stream.concat(
jarInputs.stream().map(JarInput::getFile),
directoryInputs.stream().map(DirectoryInput::getFile))
.collect(Collectors.toList());
// 通过 AndroidBuilder 转化为 byte
androidBuilder.convertByteCode(
inputFiles,
outputDir,
multiDex,
mainDexListFile,
dexOptions,
outputHandler);
for (File file : Files.fileTreeTraverser().breadthFirstTraversal(outputDir)) {
if (file.isFile()) {
instantRunBuildContext.addChangedFile(FileType.DEX, file);
}
}
} else {
...
}
最后执行到androidBuilder.convertByteCode
/**
* Converts the bytecode to Dalvik format
* @param inputs the input files
* @param outDexFolder the location of the output folder
* @param dexOptions dex options
* @throws IOException
* @throws InterruptedException
* @throws ProcessException
*/
public void convertByteCode(
@NonNull Collection<File> inputs,
@NonNull File outDexFolder,
boolean multidex,
@Nullable File mainDexList,
@NonNull DexOptions dexOptions,
@NonNull ProcessOutputHandler processOutputHandler)
throws IOException, InterruptedException, ProcessException {checkNotNull(inputs, "inputs cannot be null.");
checkNotNull(outDexFolder, "outDexFolder cannot be null.");
checkNotNull(dexOptions, "dexOptions cannot be null.");
checkArgument(outDexFolder.isDirectory(), "outDexFolder must be a folder");
checkState(mTargetInfo != null,
"Cannot call convertByteCode() before setTargetInfo() is called.");
ImmutableList.Builder<File> verifiedInputs = ImmutableList.builder();
for (File input : inputs) {
if (checkLibraryClassesJar(input)) {
verifiedInputs.add(input);
}
}
//创建 DexProcessBuilder
DexProcessBuilder builder = new DexProcessBuilder(outDexFolder);
builder.setVerbose(mVerboseExec)
.setMultiDex(multidex)
.setMainDexList(mainDexList)
.addInputs(verifiedInputs.build());
runDexer(builder, dexOptions, processOutputHandler);
}
创建了 DexProcessBuilder ，随后执行到了 runDexer 方法中
public void runDexer(
@NonNull final DexProcessBuilder builder,
@NonNull final DexOptions dexOptions,
@NonNull final ProcessOutputHandler processOutputHandler)
throws ProcessException, IOException, InterruptedException {
initDexExecutorService(dexOptions);
if (dexOptions.getAdditionalParameters().contains("--no-optimize")) {
mLogger.warning(DefaultDexOptions.OPTIMIZE_WARNING);
}
if (shouldDexInProcess(dexOptions)) {
dexInProcess(builder, dexOptions, processOutputHandler);
} else {
dexOutOfProcess(builder, dexOptions, processOutputHandler);
}
}
进入到dexInProcess方法
private void dexInProcess(
@NonNull final DexProcessBuilder builder,
@NonNull final DexOptions dexOptions,
@NonNull final ProcessOutputHandler outputHandler)
throws IOException, ProcessException {
final String submission = Joiner.on(',').join(builder.getInputs());
mLogger.verbose("Dexing in-process : %1$s", submission);
try {
sDexExecutorService.submit(() -> {
Stopwatch stopwatch = Stopwatch.createStarted();
ProcessResult result = DexWrapper.run(builder, dexOptions, outputHandler);
result.assertNormalExitValue();
mLogger.verbose("Dexing %1$s took %2$s.", submission, stopwatch.toString());
return null;
}).get();
} catch (Exception e) {
throw new ProcessException(e);
}
}
/**
* Wrapper around the real dx classes.
*/
public class DexWrapper {
/**
* Runs the dex command.
*
* @return the integer return code of com.android.dx.command.dexer.Main.run()
*/
public static ProcessResult run(
@NonNull DexProcessBuilder processBuilder,
@NonNull DexOptions dexOptions,
@NonNull ProcessOutputHandler outputHandler) throws IOException, ProcessException {
ProcessOutput output = outputHandler.createOutput();
int res;
try {
DxContext dxContext = new DxContext(output.getStandardOutput(), output.getErrorOutput());
// 构建 Main.Arguments 参数
Main.Arguments args = buildArguments(processBuilder, dexOptions, dxContext);
res = new Main(dxContext).run(args);
} finally {
output.close();
}
outputHandler.handleOutput(output);
return new DexProcessResult(res);
}
...
}
buildArguments方法通过传入的DexProcessBuilder、dexOptions、dxContext构建 arguments，后面使用的args的参数fileNames，outName，jarOutput都是从DexProcessBuilder来的，然后执行Main的run方法
package com.android.dx.command.dexer;
...
/**
* Main class for the class file translator.
*/
public class Main {
/**
* Run and return a result code.
* @param arguments the data + parameters for the conversion
* @return 0 if success > 0 otherwise.
*/
public int run(Arguments arguments) throws IOException {
// Reset the error count to start fresh.
errors.set(0);
// empty the list, so that tools that load dx and keep it around
// for multiple runs don't reuse older buffers.
libraryDexBuffers.clear();
args = arguments;
args.makeOptionsObjects(context);
OutputStream humanOutRaw = null;
if (args.humanOutName != null) {
humanOutRaw = openOutput(args.humanOutName);
humanOutWriter = new OutputStreamWriter(humanOutRaw);
}
try {
if (args.multiDex) {
return runMultiDex();
} else {
return runMonoDex();
}
} finally {
closeOutput(humanOutRaw);
}
}
}
这里我们关注非multiDex的情况，即执行了runMonoDex的方法
private int runMonoDex() throws IOException {
...
// 内部会创建dexFile，并填充class
if (!processAllFiles()) {
return 1;
}
if (args.incremental && !anyFilesProcessed) {
return 0; // this was a no-op incremental build
}
// this array is null if no classes were defined
byte[] outArray = null;
if (!outputDex.isEmpty() || (args.humanOutName != null)) {
// 内部通过Dex类toDex 方法将 class 文件转化dex byte[]
outArray = writeDex(outputDex);
if (outArray == null) {
return 2;
}
}
if (args.incremental) {
outArray = mergeIncremental(outArray, incrementalOutFile);
}
outArray = mergeLibraryDexBuffers(outArray);
if (args.jarOutput) {
// Effectively free up the (often massive) DexFile memory.
outputDex = null;
if (outArray != null) {
// 输出的文件名为 classes.dex
outputResources.put(DexFormat.DEX_IN_JAR_NAME, outArray);
}
if (!createJar(args.outName)) {
return 3;
}
} else if (outArray != null && args.outName != null) {
OutputStream out = openOutput(args.outName);
out.write(outArray);
closeOutput(out);
}
return 0;
}
上面的代码中，填充class以及dex流转换，内部流程较为复杂，就不再继续深入，简单做下总结：
1.通过执行 processAllFiles ，内部创建 DexFile 也就是outputDex，并且填充 class 文件
2.通过 writeDex 方法，将 outputDex 传入，方法内部执行的是 outputDex.toDex 方法，将 outputDex 内部填充的 class 转化为 dex 的 byte[] 返回
3.最后将 byte[] 数组创建 classes.dex 输出
总结：
Android Gradle Plugin源码繁多，以上文章只是对整体流程的简单梳理，其中简要介绍了构建变体任务的解析和添加 ，最后对编译dex流程做了简单分析。个人精力有限，这里的源码解析也只是九牛一毛，如有纰漏，欢迎大家拍砖，希望这篇文章能帮助到想了解 Android Gradle Plguin 原理的同学。
