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PMS解析AndroidManifest.xml文件的过程

發(fā)布時間：2023/12/20 Android 37 豆豆

生活随笔收集整理的這篇文章主要介紹了 PMS解析AndroidManifest.xml文件的过程小編覺得挺不錯的,現(xiàn)在分享給大家,幫大家做個參考.

一、前言

???????前段時間在看當下主流的安卓插件化技術(shù)原理的時候，發(fā)現(xiàn)目前插件化技術(shù)對于四大組件的處理基本都是通過代理來實現(xiàn)的（動態(tài)注冊的廣播接收器除外）。簡單說就是需要先在主包里預埋一個注冊在AndroidManifest.xml中的組件，再由這個組件來連接SystemServer和插件中的業(yè)務邏輯。

???????這里難免就會有一些疑問，系統(tǒng)從AndroidManifest.xml文件解析出來的四大組件的信息存放在哪里？能否不利用預埋+代理的技術(shù)，直接通過修改中間的存儲容器來實現(xiàn)四大組件的插件化？
???????要想解答這些疑惑，我們就得知道系統(tǒng)是如何從AndroidManifest.xml中解析出四大組件的？以及解析后的組件信息又是如何保存的？

???????系統(tǒng)中負責解析AndroidManifest.xml文件的系統(tǒng)服務是PackageManagerService（以下簡稱PMS）。PMS中關(guān)于AndroidManifest.xml文件的處理邏輯入口主要有兩處，一個是SystemServer進程啟動時，另一個則是應用安裝/更新時。兩個入口對于xml的解析流程大體上是一致的，本篇文章只分析SystemServer進程啟動時，PMS對AndroidManifest.xml的解析流程。

二、相關(guān)知識

2.1 方法后綴LI、LIF、LPr、LPw的含義

??????PMS中有很多方法的名字后綴都是LI/LIF/LPr/LPw，因此我們需要先簡單了解下這些后綴的含義是什么。這些后綴涉及到PMS兩個很重要的鎖mPackages和mInstallLock以及一個mFrozenPackages變量。相關(guān)后綴的含義見下表。詳見：https://blog.csdn.net/u013553529/article/details/61962439。

三、調(diào)用流程

SystemServer的啟動屬于開機流程中的一步，入口如下：

SystemServer.main()

/*** The main entry point from zygote.* zygote進程會調(diào)用該方法*/public static void main(String[] args) {new SystemServer().run();}

??????main()方法中new了一個SystemServer對象，并調(diào)用了它的run()方法

SystemServer.run()

private void run() {try {// 省略部分代碼，只列出關(guān)鍵部分的代碼// The system server should never make non-oneway callsBinder.setWarnOnBlocking(true);// Initialize native services.System.loadLibrary("android_servers");// Create the system service manager.// SystemServiceManager是整個Service的大管家mSystemServiceManager = new SystemServiceManager(mSystemContext);mSystemServiceManager.setStartInfo(mRuntimeRestart,mRuntimeStartElapsedTime, mRuntimeStartUptime);LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);} finally {t.traceEnd(); // InitBeforeStartServices}// Start services.try {t.traceBegin("StartServices");// start critical services, include PMS/AMSstartBootstrapServices(t);// start essential servicesstartCoreServices(t);// start other servicestartOtherServices(t);} catch (Throwable ex) {Slog.e("System", "******************************************");Slog.e("System", "************ Failure starting system services", ex);throw ex;} finally {t.traceEnd(); // StartServices}}

??????run()方法中主要做了一些系統(tǒng)啟動時的初始化工作，其中很關(guān)鍵的一步就是啟動各項service服務。PMS就是在startBootstrapServices()中初始化的。

SystemServer.startBootstrapServices(@NonNull TimingsTraceAndSlog t)

/*** Starts the small tangle of critical services that are needed to get the system off the* ground. These services have complex mutual dependencies which is why we initialize them all* in one place here. Unless your service is also entwined in these dependencies, it should be* initialized in one of the other functions.*/private void startBootstrapServices(@NonNull TimingsTraceAndSlog t) {// 省略部分代碼t.traceBegin("StartPackageManagerService");try {Watchdog.getInstance().pauseWatchingCurrentThread("packagemanagermain");mPackageManagerService = PackageManagerService.main(mSystemContext, installer,mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);} finally {Watchdog.getInstance().resumeWatchingCurrentThread("packagemanagermain");}// Now that the package manager has started, register the dex load reporter to capture any// dex files loaded by system server.// These dex files will be optimized by the BackgroundDexOptService.SystemServerDexLoadReporter.configureSystemServerDexReporter(mPackageManagerService);mFirstBoot = mPackageManagerService.isFirstBoot();mPackageManager = mSystemContext.getPackageManager();// 省略部分代碼}

??????startBootstrapServices()方法中調(diào)用了PMS的main()方法來初始化PMS服務

PackageManagerService.main()

public static PackageManagerService main(Context context, Installer installer,boolean factoryTest, boolean onlyCore) {// 省略部分代碼// new一個Java層的PMS對象PackageManagerService m = new PackageManagerService(injector, onlyCore, factoryTest);// 省略部分代碼// 將new出來的PMS對象注冊到ServiceManager中，之后我們便能夠通過Context對象的getPackageManager()來獲取PM對象了，這部分源碼在Context.getPackageManager()/ContextImpl.getPackageManager()中m.installWhitelistedSystemPackages();ServiceManager.addService("package", m);final PackageManagerNative pmn = m.new PackageManagerNative();ServiceManager.addService("package_native", pmn);return m;}

??????這里我們主要關(guān)注PMS的實例化過程，PMS的構(gòu)造函數(shù)如下：

PackageManagerService.PackageManagerService()

/** Directory where installed applications are stored */private static final File sAppInstallDir =new File(Environment.getDataDirectory(), "app");public PackageManagerService(Injector injector, boolean onlyCore, boolean factoryTest) {// 省略部分代碼if (!mOnlyCore) {EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_PMS_DATA_SCAN_START,SystemClock.uptimeMillis());scanDirTracedLI(sAppInstallDir, 0, scanFlags | SCAN_REQUIRE_KNOWN, 0,packageParser, executorService);}// 省略部分代碼}

??????PMS的構(gòu)造函數(shù)中通過scanDirTracedLI()來掃描已安裝的三方App apk信息，路徑為/data/app/

PackageManagerService.scanDirTracedLI()

private void scanDirTracedLI(File scanDir, final int parseFlags, int scanFlags,long currentTime, PackageParser2 packageParser, ExecutorService executorService) {Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "scanDir [" + scanDir.getAbsolutePath() + "]");try {scanDirLI(scanDir, parseFlags, scanFlags, currentTime, packageParser, executorService);} finally {Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);}}

PackageManagerService.scanDirLI()

private void scanDirLI(File scanDir, int parseFlags, int scanFlags, long currentTime,PackageParser2 packageParser, ExecutorService executorService) {ParallelPackageParser parallelPackageParser =new ParallelPackageParser(packageParser, executorService);// Submit files for parsing in parallelint fileCount = 0;for (File file : files) {final boolean isPackage = (isApkFile(file) || file.isDirectory())&& !PackageInstallerService.isStageName(file.getName());if (!isPackage) {// Ignore entries which are not packagescontinue;}// 繼續(xù)往下調(diào)用了parallelPackageParser.submit()parallelPackageParser.submit(file, parseFlags);fileCount++;}}

ParallelPackageParser.submit(File scanFile, int parseFlags)

/*** Submits the file for parsing* @param scanFile file to scan* @param parseFlags parse flags*/public void submit(File scanFile, int parseFlags) {mExecutorService.submit(() -> {ParseResult pr = new ParseResult();Trace.traceBegin(TRACE_TAG_PACKAGE_MANAGER, "parallel parsePackage [" + scanFile + "]");try {pr.scanFile = scanFile;// 繼續(xù)往下調(diào)用了parserPackage()pr.parsedPackage = parsePackage(scanFile, parseFlags);} catch (Throwable e) {pr.throwable = e;} finally {Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);}try {mQueue.put(pr);} catch (InterruptedException e) {Thread.currentThread().interrupt();// Propagate result to callers of take().// This is helpful to prevent main thread from getting stuck waiting on// ParallelPackageParser to finish in case of interruptionmInterruptedInThread = Thread.currentThread().getName();}});}

ParallelPackageParser.parsePackage(File scanFile, int parseFlags)

protected ParsedPackage parsePackage(File scanFile, int parseFlags)throws PackageParser.PackageParserException {return mPackageParser.parsePackage(scanFile, parseFlags, true);}

PackageParser2.parsePackage(File packageFile, int flags, boolean useCaches)

/*** TODO(b/135203078): Document new package parsing*/@AnyThreadpublic ParsedPackage parsePackage(File packageFile, int flags, boolean useCaches)throws PackageParserException {// 有緩存的話優(yōu)先使用緩存if (useCaches && mCacher != null) {ParsedPackage parsed = mCacher.getCachedResult(packageFile, flags);if (parsed != null) {return parsed;}}long parseTime = LOG_PARSE_TIMINGS ? SystemClock.uptimeMillis() : 0;ParseInput input = mSharedResult.get().reset();// 繼續(xù)往下調(diào)用了parsePackage()ParseResult<ParsingPackage> result = parsingUtils.parsePackage(input, packageFile, flags);// 省略部分代碼return parsed;}

ParsingPackageUtils.parsePackage(ParseInput input, File packageFile, int flags)

public ParseResult<ParsingPackage> parsePackage(ParseInput input, File packageFile,int flags)throws PackageParserException {if (packageFile.isDirectory()) {// 如果給定的路徑是文件夾，則循環(huán)解析其中的所有apk文件return parseClusterPackage(input, packageFile, flags);} else {// 如果給定的路徑是文件，則調(diào)用parseMonolithicPackage()解析文件return parseMonolithicPackage(input, packageFile, flags);} }

注： Android5.0引入了Split APK機制，這是為了解決65536上限以及APK安裝包越來越大等問題。Split APK機制可以將一個APK，拆分成多個獨立APK。
在引入了Split APK機制后，APK有兩種分類：

Single APK：安裝文件為一個完整的APK，即base APK。Android稱其為Monolithic。

Mutiple APK：安裝文件在一個文件目錄中，其內(nèi)部有多個被拆分的APK，這些APK由一個 base APK和一個或多個split APK組成。Android稱其為Cluster。

??????我們直接看解析Single APK文件的邏輯

ParsingPackageUtils.parseMonolithicPackage(ParseInput input, File apkFile, int flags)

/*** Parse the given APK file, treating it as as a single monolithic package.* * Note that this does not perform signature verification; that* must be done separately in {@link #getSigningDetails(ParsingPackageRead, boolean)}.*/private ParseResult<ParsingPackage> parseMonolithicPackage(ParseInput input, File apkFile,int flags) throws PackageParserException {// 省略部分代碼final SplitAssetLoader assetLoader = new DefaultSplitAssetLoader(lite, flags);try {// 真正開始解析apk信息ParseResult<ParsingPackage> result = parseBaseApk(input,apkFile,apkFile.getCanonicalPath(),assetLoader.getBaseAssetManager(), flags);if (result.isError()) {return input.error(result);}return input.success(result.getResult().setUse32BitAbi(lite.use32bitAbi));} catch (IOException e) {return input.error(INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION,"Failed to get path: " + apkFile, e);} finally {IoUtils.closeQuietly(assetLoader);}}

parsingPackageUtils.parseBaseApk(ParseInput input, File apkFile, String codePath, AssetManager assets, int flags)

private ParseResult<ParsingPackage> parseBaseApk(ParseInput input, File apkFile,String codePath, AssetManager assets, int flags) {final String apkPath = apkFile.getAbsolutePath();// 省略部分代碼// 打開apk的AndroidManifest.xml文件try (XmlResourceParser parser = assets.openXmlResourceParser(cookie,PackageParser.ANDROID_MANIFEST_FILENAME)) {final Resources res = new Resources(assets, mDisplayMetrics, null);// 開始解析AndroidManifest.xml的信息ParseResult<ParsingPackage> result = parseBaseApk(input, apkPath, codePath, res,parser, flags);// 省略部分代碼ApkAssets apkAssets = assets.getApkAssets()[0];if (apkAssets.definesOverlayable()) {SparseArray<String> packageNames = assets.getAssignedPackageIdentifiers();int size = packageNames.size();for (int index = 0; index < size; index++) {String packageName = packageNames.get(index);Map<String, String> overlayableToActor = assets.getOverlayableMap(packageName);if (overlayableToActor != null && !overlayableToActor.isEmpty()) {for (String overlayable : overlayableToActor.keySet()) {pkg.addOverlayable(overlayable, overlayableToActor.get(overlayable));}}}}pkg.setVolumeUuid(volumeUuid);if ((flags & PackageParser.PARSE_COLLECT_CERTIFICATES) != 0) {pkg.setSigningDetails(getSigningDetails(pkg, false));} else {pkg.setSigningDetails(SigningDetails.UNKNOWN);}return input.success(pkg);} catch (Exception e) {return input.error(INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION,"Failed to read manifest from " + apkPath, e);}}

parsingPackageUtils.parseBaseApk(ParseInput input, String apkPath, String codePath, Resources res, XmlResourceParser parser, int flags)

/*** Parse the manifest of a base APK. When adding new features you* need to consider whether they should be supported by split APKs and child* packages.** @param apkPath The package apk file path* @param res The resources from which to resolve values* @param parser The manifest parser* @param flags Flags how to parse* @return Parsed package or null on error.*/private ParseResult<ParsingPackage> parseBaseApk(ParseInput input, String apkPath,String codePath, Resources res, XmlResourceParser parser, int flags)throws XmlPullParserException, IOException, PackageParserException {// 省略部分代碼final TypedArray manifestArray = res.obtainAttributes(parser, R.styleable.AndroidManifest);try {final boolean isCoreApp =parser.getAttributeBooleanValue(null, "coreApp", false);final ParsingPackage pkg = mCallback.startParsingPackage(pkgName, apkPath, codePath, manifestArray, isCoreApp);// 繼續(xù)往下調(diào)用了parseBaseApkTags()final ParseResult<ParsingPackage> result =parseBaseApkTags(input, pkg, manifestArray, res, parser, flags);if (result.isError()) {return result;}return input.success(pkg);} finally {manifestArray.recycle();}}

parsingPackageUtils.parseBaseApkTags(ParseInput input, ParsingPackage pkg, TypedArray sa, Resources res, XmlResourceParser parser, int flags)

private ParseResult<ParsingPackage> parseBaseApkTags(ParseInput input, ParsingPackage pkg,TypedArray sa, Resources res, XmlResourceParser parser, int flags)throws XmlPullParserException, IOException {//省略部分代碼while ((type = parser.next()) != XmlPullParser.END_DOCUMENT&& (type != XmlPullParser.END_TAG|| parser.getDepth() > depth)) {if (type != XmlPullParser.START_TAG) {continue;}String tagName = parser.getName();final ParseResult result;if (PackageParser.TAG_APPLICATION.equals(tagName)) {// 找到<applicaton>標簽，四大組件的聲明都在里面if (foundApp) {if (PackageParser.RIGID_PARSER) {result = input.error("<manifest> has more than one <application>");} else {Slog.w(TAG, "<manifest> has more than one <application>");result = input.success(null);}} else {foundApp = true;// 關(guān)鍵在這里result = parseBaseApplication(input, pkg, res, parser, flags);}} else {// 解析除<application>外的其他標簽result = parseBaseApkTag(tagName, input, pkg, res, parser, flags);}if (result.isError()) {return input.error(result);}}// 省略部分代碼return input.success(pkg);}

parsingPackageUtils.parseBaseApplication(ParseInput input, ParsingPackage pkg, Resources res, XmlResourceParser parser, int flags)

private ParseResult<ParsingPackage> parseBaseApplication(ParseInput input,ParsingPackage pkg, Resources res, XmlResourceParser parser, int flags)throws XmlPullParserException, IOException {// 省略部分代碼boolean hasActivityOrder = false;boolean hasReceiverOrder = false;boolean hasServiceOrder = false;final int depth = parser.getDepth();int type;while ((type = parser.next()) != XmlPullParser.END_DOCUMENT&& (type != XmlPullParser.END_TAG|| parser.getDepth() > depth)) {if (type != XmlPullParser.START_TAG) {continue;}final ParseResult result;String tagName = parser.getName();boolean isActivity = false;switch (tagName) {case "activity":isActivity = true;// fall-throughcase "receiver":ParseResult<ParsedActivity> activityResult =ParsedActivityUtils.parseActivityOrReceiver(mSeparateProcesses, pkg,res, parser, flags, PackageParser.sUseRoundIcon, input);if (activityResult.isSuccess()) {ParsedActivity activity = activityResult.getResult();if (isActivity) {hasActivityOrder |= (activity.getOrder() != 0);pkg.addActivity(activity);} else {hasReceiverOrder |= (activity.getOrder() != 0);pkg.addReceiver(activity);}}result = activityResult;break;case "service":ParseResult<ParsedService> serviceResult =ParsedServiceUtils.parseService(mSeparateProcesses, pkg, res, parser,flags, PackageParser.sUseRoundIcon, input);if (serviceResult.isSuccess()) {ParsedService service = serviceResult.getResult();hasServiceOrder |= (service.getOrder() != 0);pkg.addService(service);}result = serviceResult;break;case "provider":// Provider的解析ParseResult<ParsedProvider> providerResult =ParsedProviderUtils.parseProvider(mSeparateProcesses, pkg, res, parser,flags, PackageParser.sUseRoundIcon, input);if (providerResult.isSuccess()) {// 注冊provider信息pkg.addProvider(providerResult.getResult());}result = providerResult;break;case "activity-alias":activityResult = ParsedActivityUtils.parseActivityAlias(pkg, res,parser, PackageParser.sUseRoundIcon, input);if (activityResult.isSuccess()) {ParsedActivity activity = activityResult.getResult();hasActivityOrder |= (activity.getOrder() != 0);pkg.addActivity(activity);}result = activityResult;break;default:result = parseBaseAppChildTag(input, tagName, pkg, res, parser, flags);break;}if (result.isError()) {return input.error(result);}}if (TextUtils.isEmpty(pkg.getStaticSharedLibName())) {// Add a hidden app detail activity to normal apps which forwards user to App Details// page.// 如果App沒有入口Activity，就將其入口設(shè)置為App詳情頁ParseResult<ParsedActivity> a = generateAppDetailsHiddenActivity(input, pkg);if (a.isError()) {return input.error(a);}pkg.addActivity(a.getResult());}return input.success(pkg);}

??????parseBaseApplication()方法中PMS根據(jù)tag來區(qū)分四大組件，并調(diào)用相應的方法做進一步的解析。最終PMS會通過ParsingPackage的addXXX()方法將解析到的組件信息添加到對應的List中。ParsingPackage是一個接口，對應的實現(xiàn)類為ParsingPackageImpl

ParsingPackageImpl.addXXX()

@NonNullprotected List<ParsedActivity> activities = emptyList();@NonNullprotected List<ParsedActivity> receivers = emptyList();@NonNullprotected List<ParsedService> services = emptyList();@NonNullprotected List<ParsedProvider> providers = emptyList();@Overridepublic ParsingPackageImpl addActivity(ParsedActivity parsedActivity) {this.activities = CollectionUtils.add(this.activities, parsedActivity);addMimeGroupsFromComponent(parsedActivity);return this;}@Overridepublic ParsingPackageImpl addReceiver(ParsedActivity parsedReceiver) {this.receivers = CollectionUtils.add(this.receivers, parsedReceiver);addMimeGroupsFromComponent(parsedReceiver);return this;}@Overridepublic ParsingPackageImpl addService(ParsedService parsedService) {this.services = CollectionUtils.add(this.services, parsedService);addMimeGroupsFromComponent(parsedService);return this;}@Overridepublic ParsingPackageImpl addProvider(ParsedProvider parsedProvider) {this.providers = CollectionUtils.add(this.providers, parsedProvider);addMimeGroupsFromComponent(parsedProvider);return this;}

??????至此，四大組件的信息就都被解析并且保存下來了。

三、小結(jié)

??????整個流程看下來我們會發(fā)現(xiàn)，PMS對四大組件信息的處理采用的是實時解析AndroidManifest.xml文件的方式，中間并沒有多余的轉(zhuǎn)存邏輯。因此，想要通過修改中間容器的方式來實現(xiàn)四大組件的插件化看起來是不太可行的。只能老老實實走預埋+代理的邏輯。
??????但是，實時解析的方式雖然安全準確，但是速度慢呀。當你手機里安裝的App越來越多，設(shè)備的開機速度就會變得越來越慢。因此，新版本上安卓系統(tǒng)為了提升設(shè)備的啟動速度，在PMS解析AndroidManifest.xml文件的流程中引入了相應的緩存邏輯來優(yōu)化解析速度。

總結(jié)

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