前言
在使用 Android Studio 以后，基本新的 Android 项目都是用 Gradle 作为构建工具，关于 Gradle 的介绍不在本文范畴，当新建一个 Android 项目时，默认只会有个 module 使用com.android.application 插件，Gradle 的核心在于 task，即从 java 源文件和资源文件编译成 apk 文件（编译过程），就是由一系列的 task 组成，task 可以相互依赖，比如最基本的 Task.dependsOn()，所以理解 Android 编译过程就是理解各个 task 的作用。
本文涉及的源码：
- com.android.tools.build:gradle:3.1.4
- gradle-api-4.4
AppPlugin
com.android.application 的源码位于 com.android.build.gradle.AppPlugin，AppPlugin 继承于 BasePlugin，BasePlugin 封装了大部分通用的逻辑：
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| @Override
public void apply(@NonNull Project project) {
if (!projectOptions.get(BooleanOption.ENABLE_NEW_DSL_AND_API)) {
TaskInputHelper.enableBypass();
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);
} else {
}
}
|
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| private void createTasks() {
threadRecorder.record(
ExecutionType.TASK_MANAGER_CREATE_TASKS,
project.getPath(),
null,
() -> taskManager.createTasksBeforeEvaluate());
project.afterEvaluate(
project ->
threadRecorder.record(
ExecutionType.BASE_PLUGIN_CREATE_ANDROID_TASKS,
project.getPath(),
null,
() -> createAndroidTasks(false)));
}
|
从 createTasks() 可以看到，createAndroidTasks() 是在 afterEvaluate() 中执行的，evaluate 是 Gradle 一个执行的过程
Gradle 编译的三个阶段：Initialization、Configuration、Execution。具体可以阅读 build_lifecycle
createAndroidTasks() 这个方法较长，但是我们关心的是 VariantManager.createAndroidTasks()
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| public void createAndroidTasks() {
variantFactory.validateModel(this);
variantFactory.preVariantWork(project);
if (variantScopes.isEmpty()) {
recorder.record(
ExecutionType.VARIANT_MANAGER_CREATE_VARIANTS,
project.getPath(),
null ,
this::populateVariantDataList);
}
recorder.record(
ExecutionType.VARIANT_MANAGER_CREATE_TESTS_TASKS,
project.getPath(),
null ,
() -> taskManager.createTopLevelTestTasks(!productFlavors.isEmpty()));
for (final VariantScope variantScope : variantScopes) {
recorder.record(
ExecutionType.VARIANT_MANAGER_CREATE_TASKS_FOR_VARIANT,
project.getPath(),
variantScope.getFullVariantName(),
() -> createTasksForVariantData(variantScope));
}
taskManager.createReportTasks(variantScopes);
}
|
调用 populateVariantDataList() 来生成 VariantScopes，它是由 ProductFlavors、BuildType、VariantType 组合
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| public void createTasksForVariantData(final VariantScope variantScope) {
final BaseVariantData variantData = variantScope.getVariantData();
final VariantType variantType = variantData.getType();
final GradleVariantConfiguration variantConfig = variantScope.getVariantConfiguration();
final BuildTypeData buildTypeData = buildTypes.get(variantConfig.getBuildType().getName());
if (buildTypeData.getAssembleTask() == null) {
buildTypeData.setAssembleTask(taskManager.createAssembleTask(buildTypeData));
}
taskManager
.getTaskFactory()
.configure(
"assemble",
task -> {
assert buildTypeData.getAssembleTask() != null;
task.dependsOn(buildTypeData.getAssembleTask().getName());
});
createAssembleTaskForVariantData(variantData);
if (variantType.isForTesting()) {
} else {
taskManager.createTasksForVariantScope(variantScope);
}
}
|
assemble task 用于将源文件编译为最终产物，比如 jar、aar、apk 等，在 createTasksForVariantData() 中会生成对应 BuildType 的 assemble task，比如 assembleDebug 和 assembleRelease ，接着设置 assemble 依赖于这两个 task，最后根据 variant 生成对应的 assemble task，比如 assembleTestDebug
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| private void createAssembleTaskForVariantData(final BaseVariantData variantData) {
final VariantScope variantScope = variantData.getScope();
if (variantData.getType().isForTesting()) {
variantScope.setAssembleTask(taskManager.createAssembleTask(variantData));
} else {
BuildTypeData buildTypeData =
buildTypes.get(variantData.getVariantConfiguration().getBuildType().getName());
Preconditions.checkNotNull(buildTypeData.getAssembleTask());
if (productFlavors.isEmpty()) {
variantScope.setAssembleTask(buildTypeData.getAssembleTask());
variantData.addTask(
TaskContainer.TaskKind.ASSEMBLE, buildTypeData.getAssembleTask());
} else {
variantScope.setAssembleTask(taskManager.createAssembleTask(variantData));
buildTypeData.getAssembleTask().dependsOn(variantScope.getAssembleTask());
GradleVariantConfiguration variantConfig = variantData.getVariantConfiguration();
for (CoreProductFlavor flavor : variantConfig.getProductFlavors()) {
ProductFlavorData productFlavorData = productFlavors.get(flavor.getName());
DefaultTask flavorAssembleTask = productFlavorData.getAssembleTask();
if (flavorAssembleTask == null) {
flavorAssembleTask = taskManager.createAssembleTask(productFlavorData);
productFlavorData.setAssembleTask(flavorAssembleTask);
}
flavorAssembleTask.dependsOn(variantScope.getAssembleTask());
}
if (variantConfig.getProductFlavors().size() > 1) {
final String name = StringHelper.capitalize(variantConfig.getFlavorName());
final String variantAssembleTaskName =
StringHelper.appendCapitalized("assemble", name);
if (!taskManager.getTaskFactory().containsKey(variantAssembleTaskName)) {
Task task = taskManager.getTaskFactory().create(variantAssembleTaskName);
task.setDescription("Assembles all builds for flavor combination: " + name);
task.setGroup("Build");
task.dependsOn(variantScope.getAssembleTask().getName());
}
taskManager
.getTaskFactory()
.configure(
"assemble", task1 -> task1.dependsOn(variantAssembleTaskName));
}
}
}
}
|
上面会生成包括 BuildType、Flavor、BuildType + Flavor + VariantType 的 assemble task，同时 task 之间存在依赖关系：assemble > buildType/flavor > 具体
除了上面所说的 assemble task，还将生成以下 task：
| task |
impl |
dependsOn |
| assemble{variant} |
DefaultTask |
compile{variant}Sources，package{variant} |
| pre{variant}Build |
AppPreBuildTask |
preBuild，extractProguardFiles(可能) |
| extractProguardFiles |
ExtractProguardFiles |
|
| generate{variant}Sources |
DefaultTask |
compile{variant}Renderscript，generate{variant}BuildConfig，bundle{variant}Resources，compile{variant}Aidl |
| generate{variant}Resources |
DefaultTask |
generate{variant}ResValues，compile{variant}Renderscript |
| generate{variant}Assets |
DefaultTask |
compile{variant}Shaders |
| compile{variant}Sources |
DefaultTask |
compile{variant}Ndk，compile{variant}JavaWithJavac |
| check{variant}Manifest |
CheckManifest |
pre{variant}Build |
| write{variant}ApplicationId |
ApplicationIdIdWriteTask |
|
| mainApkListPersistence{variant} |
MainApkListPersistence |
|
| reportBuildArtifacts{variant} |
BuildArtifactReportTask |
|
| create{variant}CompatibleScreenManifests |
CompatibleScreensManifest |
|
| process{variant}Manifest |
MergeManifests |
check{variant}Manifest |
| generate{variant}ResValues |
GenerateResValues |
|
| compile{variant}Renderscript |
RenderscriptCompile |
pre{variant}Build |
| merge{variant}Resources |
MergeResources |
generate{variant}Resources |
| merge{variant}Shaders |
MergeSourceSetFolders |
|
| compile{variant}Shaders |
ShaderCompile |
merge{variant}Shaders |
| merge{variant}Assets |
MergeSourceSetFolders |
generate{variant}Assets |
| generate{variant}BuildConfig |
GenerateBuildConfig |
check{variant}Manifest |
| splitsDiscoveryTask{variant} |
SplitsDiscovery |
|
| process{variant}JavaRes |
Sync |
pre{variant}Build |
| process{variant}Resources |
LinkApplicationAndroidResourcesTask |
|
| bundle{variant}Resources |
LinkAndroidResForBundleTask |
|
| compile{variant}Aidl |
AidlCompile |
pre{variant}Build |
| compile{variant}Ndk |
NdkCompile |
pre{variant}Build |
| merge{variant}JniLibFolders |
MergeSourceSetFolders |
generate{variant}Assets |
| javaPreCompile{variant} |
JavaPreCompileTask |
pre{variant}Build |
| compile{variant}JavaWithJavac |
AndroidJavaCompile |
generate{variant}Sources |
| bundleAppClasses{variant} |
Jar |
|
| transformResourcesWithMergeJavaResFor{variant} |
TransformTask |
|
| transformClassesWithMultidexlistFor{variant} |
TransformTask |
|
| transformClassesWithDexBuilderFor{variant} |
TransformTask |
|
| transformDexArchiveWithDexMergerFor{variant} |
TransformTask |
transformClassesWithMultidexlistFor{variant} |
| preparePUBLISHED_JAVA_RES{variant}ForPublishing |
PipelineToPublicationTask |
|
| package{variant} |
PackageApplication |
merge{variant}Assets，process{variant}Resources，validateSigning{variant}，compile{variant}JavaWithJavac |
| validateSigning{variant} |
ValidateSigningTask |
|
| install{variant} |
InstallVariantTask |
assemble{variant} |
| uninstall{variant} |
UninstallTask |
|
| lint{variant} |
LintPerVariantTask |
|
以 assembleProdRelease 命令，依次执行的 task：
prod 是 product flavor
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| preBuild
extractProguardFiles
preProdReleaseBuild
compileProdReleaseRenderscript
checkProdReleaseManifest
generateProdReleaseBuildConfig
prepareLintJar
mainApkListPersistenceProdRelease
generateProdReleaseResValues
generateProdReleaseResources
compileProdReleaseAidl
createProdReleaseCompatibleScreenManifests
processProdReleaseManifest
mergeProdReleaseResources // 合并资源
splitsDiscoveryTaskProdRelease
processProdReleaseResources
generateProdReleaseSources
javaPreCompileProdRelease
compileProdReleaseJavaWithJavac // javac
compileProdReleaseNdk
compileProdReleaseSources
mergeProdReleaseShaders
compileProdReleaseShaders
generateProdReleaseAssets
mergeProdReleaseAssets
transformClassesWithComponentCodeForProdRelease
processProdReleaseJavaRes
transformResourcesWithMergeJavaResForProdRelease
transformClassesAndResourcesWithProguardForProdRelease // 混淆
transformClassesWithMultidexlistForProdRelease
transformClassesWithDexForProdRelease // dex
transformClassesWithShrinkResForProdRelease
mergeProdReleaseJniLibFolders
transformNativeLibsWithMergeJniLibsForProdRelease
validateSigningProdRelease
packageProdRelease
|
接下来分析下比较重要的几个 task
接下来的分析，因为对应的源码比较复杂，所以只会简短介绍结果，没有详细过程，推荐 debug 整个流程
CompileJavaWithJavac
首先找到执行的 AndroidJavaCompile
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|
@Override
protected void compile(IncrementalTaskInputs inputs) {
if (isPostN()) {
if (!JavaVersion.current().isJava8Compatible()) {
throw new RuntimeException("compileSdkVersion '" + compileSdkVersion + "' requires "
+ "JDK 1.8 or later to compile.");
}
}
processAnalytics();
FileUtils.mkdirs(annotationProcessorOutputFolder);
mInstantRunBuildContext.startRecording(InstantRunBuildContext.TaskType.JAVAC);
super.compile(inputs);
mInstantRunBuildContext.stopRecording(InstantRunBuildContext.TaskType.JAVAC);
}
|
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@TaskAction
protected void compile(IncrementalTaskInputs inputs) {
if (!this.compileOptions.isIncremental()) {
this.compile();
} else {
DefaultJavaCompileSpec spec = this.createSpec();
CompileCaches compileCaches = this.createCompileCaches();
IncrementalCompilerFactory factory = new IncrementalCompilerFactory(this.getFileOperations(), this.getStreamHasher(), this.getCachingFileHasher(), this.getPath(), this.createCompiler(spec), this.source, compileCaches, (IncrementalTaskInputsInternal)inputs, this.getEffectiveAnnotationProcessorPath());
Compiler<JavaCompileSpec> compiler = factory.createCompiler();
this.performCompilation(spec, compiler);
}
}
|
不管是增量编译还是全量编译，最后都会调用 performCompilation
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| private void performCompilation(JavaCompileSpec spec, Compiler<JavaCompileSpec> compiler) {
WorkResult result = compiler.execute(spec);
this.setDidWork(result.getDidWork());
}
|
Compiler 采用装饰者设计模式，最外层是 CleaningJavaCompilerSupport 会先删除编译目录，再调用 JdkJavaCompiler 执行 javac 过程，具体为，创建一个 JavacTaskImpl 然后 JavacTask 会调用 com.sun.tools.javac.main.Main 进行处理，其中创建 JavacTask 的任务是由 JavacTool 完成
