系统启动并解析Manifest的流程(转)

最近有同学问我关于Manifest何时被系统解析的问题，正好也分析到这一块了，索性这一章就讲解一下android系统何时解析Manifest吧，这里的Manifest指的是android安装文件apk中的androidManifest.xml文件是何时被解析的。
大家应该都知道，Android系统启动之后，我们就可以在一个应用中打开另一个从未打开过的应用，或者是在一个应用中发送广播，如果另外一个应用设置了这个广播的接收器，那么这个应用进程就会被启动并接收该广播并作出相应的处理，这样的例子很多，我们可以猜测到Android系统在启动的时候就会抓取到了系统中所有安装的应用信息（应该是解析apk文件的Manifest信息），即在Android系统的启动过程中就已经解析了系统中安装应用的androidManifest.xml文件并保存起来了，那么这个过程具体是如何的呢?

其实android系统启动过程中解析Manifest的流程是通过PackageManagerService服务来实现的。这里我们重点分析一下PackageManagerService服务是如何解析Manifest的。

首先看一下在SystemServer进程启动过程中是如何启动PackageManagerService服务的：

private void startBootstrapServices() {
		...
        mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
                mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
        mFirstBoot = mPackageManagerService.isFirstBoot();
        mPackageManager = mSystemContext.getPackageManager();

        ...
    }

在SystemServer进程启动过程中会调用SystemServer类的startBootstrapServices方法（主要用于启动ActivityManagerService服务和PackageManagerService服务），然后会在这个方法中会调用PackageManagerService.main静态方法，这个方法主要是用来初始化PackageManagerService服务并执行相关逻辑的。下面我来看一下main方法的具体逻辑：

public static PackageManagerService main(Context context, Installer installer,
            boolean factoryTest, boolean onlyCore) {
        PackageManagerService m = new PackageManagerService(context, installer,
                factoryTest, onlyCore);
        ServiceManager.addService("package", m);
        return m;
    }

可以发现main方法的实现逻辑主要是创建了一个PackageManagerService对象，并将这个对象添加到ServierManager中为其他组件提供服务。好吧，看来PackageManagerService的初始化操作主要是在PackageManagerService的构造方法中了，下面我们来看一下其构造方法的实现逻辑：

File dataDir = Environment.getDataDirectory();
            mAppDataDir = new File(dataDir, "data");
            mAppInstallDir = new File(dataDir, "app");
            mAppLib32InstallDir = new File(dataDir, "app-lib");
            mAsecInternalPath = new File(dataDir, "app-asec").getPath();
            mUserAppDataDir = new File(dataDir, "user");
            mDrmAppPrivateInstallDir = new File(dataDir, "app-private");

PackageManagerService的构造方法代码量比较大，这里就不贴出所有的代码了，我们主要和解析Manifest相关的主要代码，在构造方法中有这样几段代码。可以发现在构造方法中，解析了系统中几个apk的安装目录，这几个目录就是系统中安装apk的目录，android系统会默认解析这几个目录下apk文件，也就是说如果我们android手机在其他的目录下存在apk文件系统是不会默认解析的，反过来说，如果我们把我们的apk文件移动到这几个目录下，那么重新启动操作系统，该apk文件就会被系统解析并执行相关的逻辑操作，具体做什么操作呢？我们看下面的实现。

/ overlay packages if they reside in VENDOR_OVERLAY_DIR.
            File vendorOverlayDir = new File(VENDOR_OVERLAY_DIR);
            scanDirLI(vendorOverlayDir, PackageParser.PARSE_IS_SYSTEM
                    | PackageParser.PARSE_IS_SYSTEM_DIR, scanFlags | SCAN_TRUSTED_OVERLAY, 0);

            // Find base frameworks (resource packages without code).
            scanDirLI(frameworkDir, PackageParser.PARSE_IS_SYSTEM
                    | PackageParser.PARSE_IS_SYSTEM_DIR
                    | PackageParser.PARSE_IS_PRIVILEGED,
                    scanFlags | SCAN_NO_DEX, 0);

            // Collected privileged system packages.
            final File privilegedAppDir = new File(Environment.getRootDirectory(), "priv-app");
            scanDirLI(privilegedAppDir, PackageParser.PARSE_IS_SYSTEM
                    | PackageParser.PARSE_IS_SYSTEM_DIR
                    | PackageParser.PARSE_IS_PRIVILEGED, scanFlags, 0);

            // Collect ordinary system packages.
            final File systemAppDir = new File(Environment.getRootDirectory(), "app");
            scanDirLI(systemAppDir, PackageParser.PARSE_IS_SYSTEM
                    | PackageParser.PARSE_IS_SYSTEM_DIR, scanFlags, 0);

            // Collect all vendor packages.
            File vendorAppDir = new File("/vendor/app");
            try {
                vendorAppDir = vendorAppDir.getCanonicalFile();
            } catch (IOException e) {
                // failed to look up canonical path, continue with original one
            }
            scanDirLI(vendorAppDir, PackageParser.PARSE_IS_SYSTEM
                    | PackageParser.PARSE_IS_SYSTEM_DIR, scanFlags, 0);

            // Collect all OEM packages.
            final File oemAppDir = new File(Environment.getOemDirectory(), "app");
            scanDirLI(oemAppDir, PackageParser.PARSE_IS_SYSTEM
                    | PackageParser.PARSE_IS_SYSTEM_DIR, scanFlags, 0);

在我们刚刚的PackageManagerService.mani方法中，解析完刚刚的几个系统目录之后系统会调用scanDirLI方法，那么这个方法主要是做什么用的呢？看它的名字应该是遍历这个系统目录。好吧，这个方法主要就是用于解析上面几个目录下的apk文件的。不信？我们看一下scanDirLI方法的具体实现：

private void scanDirLI(File dir, int parseFlags, int scanFlags, long currentTime) {
        final File[] files = dir.listFiles();
        if (ArrayUtils.isEmpty(files)) {
            Log.d(TAG, "No files in app dir " + dir);
            return;
        }

        if (DEBUG_PACKAGE_SCANNING) {
            Log.d(TAG, "Scanning app dir " + dir + " scanFlags=" + scanFlags
                    + " flags=0x" + Integer.toHexString(parseFlags));
        }

        for (File file : files) {
            final boolean isPackage = (isApkFile(file) || file.isDirectory())
                    && !PackageInstallerService.isStageName(file.getName());
            if (!isPackage) {
                // Ignore entries which are not packages
                continue;
            }
            try {
                scanPackageLI(file, parseFlags | PackageParser.PARSE_MUST_BE_APK,
                        scanFlags, currentTime, null);
            } catch (PackageManagerException e) {
                Slog.w(TAG, "Failed to parse " + file + ": " + e.getMessage());

                // Delete invalid userdata apps
                if ((parseFlags & PackageParser.PARSE_IS_SYSTEM) == 0 &&
                        e.error == PackageManager.INSTALL_FAILED_INVALID_APK) {
                    logCriticalInfo(Log.WARN, "Deleting invalid package at " + file);
                    if (file.isDirectory()) {
                        mInstaller.rmPackageDir(file.getAbsolutePath());
                    } else {
                        file.delete();
                    }
                }
            }
        }
    }

可以放下其首先会遍历该目录下的所有文件，并判断是否是apk文件，如果是apk文件则调用scanPackageLI方法，scanPackageLI方法的名字很明显，就是用于解析这个apk文件的。

继续看一下scanPakcageLI方法的实现：

private PackageParser.Package scanPackageLI(File scanFile, int parseFlags, int scanFlags,
            long currentTime, UserHandle user) throws PackageManagerException {
        if (DEBUG_INSTALL) Slog.d(TAG, "Parsing: " + scanFile);
        parseFlags |= mDefParseFlags;
        PackageParser pp = new PackageParser();
        pp.setSeparateProcesses(mSeparateProcesses);
        pp.setOnlyCoreApps(mOnlyCore);
        pp.setDisplayMetrics(mMetrics);

        if ((scanFlags & SCAN_TRUSTED_OVERLAY) != 0) {
            parseFlags |= PackageParser.PARSE_TRUSTED_OVERLAY;
        }

        final PackageParser.Package pkg;
        try {
            pkg = pp.parsePackage(scanFile, parseFlags);
        } catch (PackageParserException e) {
            throw PackageManagerException.from(e);
        }
		...
}

好吧，这个方法也比较复杂，这里只是列出重点相关的代码，我们可以发现在这个方法中创建了一个PackagerParser对象，并调用了parsePackage方法，这个方法其实就是解析Manifest的主要方法，我们可以看一下其具体的实现：

public Package parsePackage(File packageFile, int flags) throws PackageParserException {
        if (packageFile.isDirectory()) {
            return parseClusterPackage(packageFile, flags);
        } else {
            return parseMonolithicPackage(packageFile, flags);
        }
    }

可以发现，若我们解析的File对象是一个文件夹则执行调用parseClusterPackage方法，否则调用执行parseMonolithicPackage方法，很明显的因为我们这里解析的是apk文件（在上一方法中我们循环遍历得到了apk文件，这里的File对象就代表了一个个的apk文件信息），所以这里会执行parseMonolithicPackage方法，然后我们来看一下parseMonolithicPackage方法：

public Package parseMonolithicPackage(File apkFile, int flags) throws PackageParserException {
        if (mOnlyCoreApps) {
            final PackageLite lite = parseMonolithicPackageLite(apkFile, flags);
            if (!lite.coreApp) {
                throw new PackageParserException(INSTALL_PARSE_FAILED_MANIFEST_MALFORMED,
                        "Not a coreApp: " + apkFile);
            }
        }

        final AssetManager assets = new AssetManager();
        try {
            final Package pkg = parseBaseApk(apkFile, assets, flags);
            pkg.codePath = apkFile.getAbsolutePath();
            return pkg;
        } finally {
            IoUtils.closeQuietly(assets);
        }
    }

可以看出，这里又调用了parseBaseApk方法：

private Package parseBaseApk(File apkFile, AssetManager assets, int flags)
			...
            final Package pkg = parseBaseApk(res, parser, flags, outError);
            ...
    }

可以看出，这个parseBaseApk方法调用了其重载的parseBaseApk方法：

while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
                && (type != XmlPullParser.END_TAG || parser.getDepth() > outerDepth)) {
            if (type == XmlPullParser.END_TAG || type == XmlPullParser.TEXT) {
                continue;
            }

            String tagName = parser.getName();
            if (tagName.equals("application")) {
                if (foundApp) {
                    if (RIGID_PARSER) {
                        outError[0] = "<manifest> has more than one <application>";
                        mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
                        return null;
                    } else {
                        Slog.w(TAG, "<manifest> has more than one <application>");
                        XmlUtils.skipCurrentTag(parser);
                        continue;
                    }
                }

                foundApp = true;
                if (!parseBaseApplication(pkg, res, parser, attrs, flags, outError)) {
                    return null;
                }
            } else if (tagName.equals("overlay")) {
                pkg.mTrustedOverlay = trustedOverlay;

                sa = res.obtainAttributes(attrs,
                        com.android.internal.R.styleable.AndroidManifestResourceOverlay);
                pkg.mOverlayTarget = sa.getString(
                        com.android.internal.R.styleable.AndroidManifestResourceOverlay_targetPackage);
                pkg.mOverlayPriority = sa.getInt(
                        com.android.internal.R.styleable.AndroidManifestResourceOverlay_priority,
                        -1);
                sa.recycle();

                if (pkg.mOverlayTarget == null) {
                    outError[0] = "<overlay> does not specify a target package";
                    mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
                    return null;
                }
                if (pkg.mOverlayPriority < 0 || pkg.mOverlayPriority > 9999) {
                    outError[0] = "<overlay> priority must be between 0 and 9999";
                    mParseError =
                        PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
                    return null;
                }
                XmlUtils.skipCurrentTag(parser);

            } else if (tagName.equals("key-sets")) {
                if (!parseKeySets(pkg, res, parser, attrs, outError)) {
                    return null;
                }
            } else if (tagName.equals("permission-group")) {
                if (parsePermissionGroup(pkg, flags, res, parser, attrs, outError) == null) {
                    return null;
                }
            } else if (tagName.equals("permission")) {
                if (parsePermission(pkg, res, parser, attrs, outError) == null) {
                    return null;
                }
            } else if (tagName.equals("permission-tree")) {
                if (parsePermissionTree(pkg, res, parser, attrs, outError) == null) {
                    return null;
                }
            } else if (tagName.equals("uses-permission")) {
                if (!parseUsesPermission(pkg, res, parser, attrs)) {
                    return null;
                }
            } else if (tagName.equals("uses-permission-sdk-m")
                    || tagName.equals("uses-permission-sdk-23")) {
                if (!parseUsesPermission(pkg, res, parser, attrs)) {
                    return null;
                }
            } else if (tagName.equals("uses-configuration")) {
                ConfigurationInfo cPref = new ConfigurationInfo();
                sa = res.obtainAttributes(attrs,
                        com.android.internal.R.styleable.AndroidManifestUsesConfiguration);
                cPref.reqTouchScreen = sa.getInt(
                        com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqTouchScreen,
                        Configuration.TOUCHSCREEN_UNDEFINED);
                cPref.reqKeyboardType = sa.getInt(
                        com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqKeyboardType,
                        Configuration.KEYBOARD_UNDEFINED);
                if (sa.getBoolean(
                        com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqHardKeyboard,
                        false)) {
                    cPref.reqInputFeatures |= ConfigurationInfo.INPUT_FEATURE_HARD_KEYBOARD;
                }
                cPref.reqNavigation = sa.getInt(
                        com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqNavigation,
                        Configuration.NAVIGATION_UNDEFINED);
                if (sa.getBoolean(
                        com.android.internal.R.styleable.AndroidManifestUsesConfiguration_reqFiveWayNav,
                        false)) {
                    cPref.reqInputFeatures |= ConfigurationInfo.INPUT_FEATURE_FIVE_WAY_NAV;
                }
                sa.recycle();
                pkg.configPreferences = ArrayUtils.add(pkg.configPreferences, cPref);

                XmlUtils.skipCurrentTag(parser);

            } else if (tagName.equals("uses-feature")) {
                FeatureInfo fi = parseUsesFeature(res, attrs);
                pkg.reqFeatures = ArrayUtils.add(pkg.reqFeatures, fi);

                if (fi.name == null) {
                    ConfigurationInfo cPref = new ConfigurationInfo();
                    cPref.reqGlEsVersion = fi.reqGlEsVersion;
                    pkg.configPreferences = ArrayUtils.add(pkg.configPreferences, cPref);
                }

                XmlUtils.skipCurrentTag(parser);

            } else if (tagName.equals("feature-group")) {
                FeatureGroupInfo group = new FeatureGroupInfo();
                ArrayList<FeatureInfo> features = null;
                final int innerDepth = parser.getDepth();
                while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
                        && (type != XmlPullParser.END_TAG || parser.getDepth() > innerDepth)) {
                    if (type == XmlPullParser.END_TAG || type == XmlPullParser.TEXT) {
                        continue;
                    }

                    final String innerTagName = parser.getName();
                    if (innerTagName.equals("uses-feature")) {
                        FeatureInfo featureInfo = parseUsesFeature(res, attrs);
                        // FeatureGroups are stricter and mandate that
                        // any <uses-feature> declared are mandatory.
                        featureInfo.flags |= FeatureInfo.FLAG_REQUIRED;
                        features = ArrayUtils.add(features, featureInfo);
                    } else {
                        Slog.w(TAG, "Unknown element under <feature-group>: " + innerTagName +
                                " at " + mArchiveSourcePath + " " +
                                parser.getPositionDescription());
                    }
                    XmlUtils.skipCurrentTag(parser);
                }

                if (features != null) {
                    group.features = new FeatureInfo[features.size()];
                    group.features = features.toArray(group.features);
                }
                pkg.featureGroups = ArrayUtils.add(pkg.featureGroups, group);

            } else if (tagName.equals("uses-sdk")) {
                if (SDK_VERSION > 0) {
                    sa = res.obtainAttributes(attrs,
                            com.android.internal.R.styleable.AndroidManifestUsesSdk);

                    int minVers = 0;
                    String minCode = null;
                    int targetVers = 0;
                    String targetCode = null;
                    
                    TypedValue val = sa.peekValue(
                            com.android.internal.R.styleable.AndroidManifestUsesSdk_minSdkVersion);
                    if (val != null) {
                        if (val.type == TypedValue.TYPE_STRING && val.string != null) {
                            targetCode = minCode = val.string.toString();
                        } else {
                            // If it's not a string, it's an integer.
                            targetVers = minVers = val.data;
                        }
                    }
                    
                    val = sa.peekValue(
                            com.android.internal.R.styleable.AndroidManifestUsesSdk_targetSdkVersion);
                    if (val != null) {
                        if (val.type == TypedValue.TYPE_STRING && val.string != null) {
                            targetCode = minCode = val.string.toString();
                        } else {
                            // If it's not a string, it's an integer.
                            targetVers = val.data;
                        }
                    }
                    
                    sa.recycle();

                    if (minCode != null) {
                        boolean allowedCodename = false;
                        for (String codename : SDK_CODENAMES) {
                            if (minCode.equals(codename)) {
                                allowedCodename = true;
                                break;
                            }
                        }
                        if (!allowedCodename) {
                            if (SDK_CODENAMES.length > 0) {
                                outError[0] = "Requires development platform " + minCode
                                        + " (current platform is any of "
                                        + Arrays.toString(SDK_CODENAMES) + ")";
                            } else {
                                outError[0] = "Requires development platform " + minCode
                                        + " but this is a release platform.";
                            }
                            mParseError = PackageManager.INSTALL_FAILED_OLDER_SDK;
                            return null;
                        }
                    } else if (minVers > SDK_VERSION) {
                        outError[0] = "Requires newer sdk version #" + minVers
                                + " (current version is #" + SDK_VERSION + ")";
                        mParseError = PackageManager.INSTALL_FAILED_OLDER_SDK;
                        return null;
                    }
                    
                    if (targetCode != null) {
                        boolean allowedCodename = false;
                        for (String codename : SDK_CODENAMES) {
                            if (targetCode.equals(codename)) {
                                allowedCodename = true;
                                break;
                            }
                        }
                        if (!allowedCodename) {
                            if (SDK_CODENAMES.length > 0) {
                                outError[0] = "Requires development platform " + targetCode
                                        + " (current platform is any of "
                                        + Arrays.toString(SDK_CODENAMES) + ")";
                            } else {
                                outError[0] = "Requires development platform " + targetCode
                                        + " but this is a release platform.";
                            }
                            mParseError = PackageManager.INSTALL_FAILED_OLDER_SDK;
                            return null;
                        }
                        // If the code matches, it definitely targets this SDK.
                        pkg.applicationInfo.targetSdkVersion
                                = android.os.Build.VERSION_CODES.CUR_DEVELOPMENT;
                    } else {
                        pkg.applicationInfo.targetSdkVersion = targetVers;
                    }
                }

                XmlUtils.skipCurrentTag(parser);

            } else if (tagName.equals("supports-screens")) {
                sa = res.obtainAttributes(attrs,
                        com.android.internal.R.styleable.AndroidManifestSupportsScreens);

                pkg.applicationInfo.requiresSmallestWidthDp = sa.getInteger(
                        com.android.internal.R.styleable.AndroidManifestSupportsScreens_requiresSmallestWidthDp,
                        0);
                pkg.applicationInfo.compatibleWidthLimitDp = sa.getInteger(
                        com.android.internal.R.styleable.AndroidManifestSupportsScreens_compatibleWidthLimitDp,
                        0);
                pkg.applicationInfo.largestWidthLimitDp = sa.getInteger(
                        com.android.internal.R.styleable.AndroidManifestSupportsScreens_largestWidthLimitDp,
                        0);

                // This is a trick to get a boolean and still able to detect
                // if a value was actually set.
                supportsSmallScreens = sa.getInteger(
                        com.android.internal.R.styleable.AndroidManifestSupportsScreens_smallScreens,
                        supportsSmallScreens);
                supportsNormalScreens = sa.getInteger(
                        com.android.internal.R.styleable.AndroidManifestSupportsScreens_normalScreens,
                        supportsNormalScreens);
                supportsLargeScreens = sa.getInteger(
                        com.android.internal.R.styleable.AndroidManifestSupportsScreens_largeScreens,
                        supportsLargeScreens);
                supportsXLargeScreens = sa.getInteger(
                        com.android.internal.R.styleable.AndroidManifestSupportsScreens_xlargeScreens,
                        supportsXLargeScreens);
                resizeable = sa.getInteger(
                        com.android.internal.R.styleable.AndroidManifestSupportsScreens_resizeable,
                        resizeable);
                anyDensity = sa.getInteger(
                        com.android.internal.R.styleable.AndroidManifestSupportsScreens_anyDensity,
                        anyDensity);

                sa.recycle();
                
                XmlUtils.skipCurrentTag(parser);
                
            } else if (tagName.equals("protected-broadcast")) {
                sa = res.obtainAttributes(attrs,
                        com.android.internal.R.styleable.AndroidManifestProtectedBroadcast);

                // Note: don't allow this value to be a reference to a resource
                // that may change.
                String name = sa.getNonResourceString(
                        com.android.internal.R.styleable.AndroidManifestProtectedBroadcast_name);

                sa.recycle();

                if (name != null && (flags&PARSE_IS_SYSTEM) != 0) {
                    if (pkg.protectedBroadcasts == null) {
                        pkg.protectedBroadcasts = new ArrayList<String>();
                    }
                    if (!pkg.protectedBroadcasts.contains(name)) {
                        pkg.protectedBroadcasts.add(name.intern());
                    }
                }

                XmlUtils.skipCurrentTag(parser);
                
            } else if (tagName.equals("instrumentation")) {
                if (parseInstrumentation(pkg, res, parser, attrs, outError) == null) {
                    return null;
                }
                
            } else if (tagName.equals("original-package")) {
                sa = res.obtainAttributes(attrs,
                        com.android.internal.R.styleable.AndroidManifestOriginalPackage);

                String orig =sa.getNonConfigurationString(
                        com.android.internal.R.styleable.AndroidManifestOriginalPackage_name, 0);
                if (!pkg.packageName.equals(orig)) {
                    if (pkg.mOriginalPackages == null) {
                        pkg.mOriginalPackages = new ArrayList<String>();
                        pkg.mRealPackage = pkg.packageName;
                    }
                    pkg.mOriginalPackages.add(orig);
                }

                sa.recycle();

                XmlUtils.skipCurrentTag(parser);
                
            } else if (tagName.equals("adopt-permissions")) {
                sa = res.obtainAttributes(attrs,
                        com.android.internal.R.styleable.AndroidManifestOriginalPackage);

                String name = sa.getNonConfigurationString(
                        com.android.internal.R.styleable.AndroidManifestOriginalPackage_name, 0);

                sa.recycle();

                if (name != null) {
                    if (pkg.mAdoptPermissions == null) {
                        pkg.mAdoptPermissions = new ArrayList<String>();
                    }
                    pkg.mAdoptPermissions.add(name);
                }

                XmlUtils.skipCurrentTag(parser);
                
            } else if (tagName.equals("uses-gl-texture")) {
                // Just skip this tag
                XmlUtils.skipCurrentTag(parser);
                continue;
                
            } else if (tagName.equals("compatible-screens")) {
                // Just skip this tag
                XmlUtils.skipCurrentTag(parser);
                continue;
            } else if (tagName.equals("supports-input")) {
                XmlUtils.skipCurrentTag(parser);
                continue;
                
            } else if (tagName.equals("eat-comment")) {
                // Just skip this tag
                XmlUtils.skipCurrentTag(parser);
                continue;
                
            } else if (RIGID_PARSER) {
                outError[0] = "Bad element under <manifest>: "
                    + parser.getName();
                mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
                return null;

            } else {
                Slog.w(TAG, "Unknown element under <manifest>: " + parser.getName()
                        + " at " + mArchiveSourcePath + " "
                        + parser.getPositionDescription());
                XmlUtils.skipCurrentTag(parser);
                continue;
            }
        }

在这个parseBaseApk方法中有一个while循环，该循环主要就是用于解析AndroidManifest.xml文件中的节点信息。在开始解析application节点的时候，同时调用了parseBaseApplication方法，该方法解析了application节点下的activity，service，broadcast，contentprovier等组件的定义信息：

while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
                && (type != XmlPullParser.END_TAG || parser.getDepth() > innerDepth)) {
            if (type == XmlPullParser.END_TAG || type == XmlPullParser.TEXT) {
                continue;
            }

            String tagName = parser.getName();
            if (tagName.equals("activity")) {
                Activity a = parseActivity(owner, res, parser, attrs, flags, outError, false,
                        owner.baseHardwareAccelerated);
                if (a == null) {
                    mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
                    return false;
                }

                owner.activities.add(a);

            } else if (tagName.equals("receiver")) {
                Activity a = parseActivity(owner, res, parser, attrs, flags, outError, true, false);
                if (a == null) {
                    mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
                    return false;
                }

                owner.receivers.add(a);

            } else if (tagName.equals("service")) {
                Service s = parseService(owner, res, parser, attrs, flags, outError);
                if (s == null) {
                    mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
                    return false;
                }

                owner.services.add(s);

            } else if (tagName.equals("provider")) {
                Provider p = parseProvider(owner, res, parser, attrs, flags, outError);
                if (p == null) {
                    mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
                    return false;
                }

                owner.providers.add(p);

            } else if (tagName.equals("activity-alias")) {
                Activity a = parseActivityAlias(owner, res, parser, attrs, flags, outError);
                if (a == null) {
                    mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
                    return false;
                }

                owner.activities.add(a);

            } else if (parser.getName().equals("meta-data")) {
                // note: application meta-data is stored off to the side, so it can
                // remain null in the primary copy (we like to avoid extra copies because
                // it can be large)
                if ((owner.mAppMetaData = parseMetaData(res, parser, attrs, owner.mAppMetaData,
                        outError)) == null) {
                    mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
                    return false;
                }

            } else if (tagName.equals("library")) {
                sa = res.obtainAttributes(attrs,
                        com.android.internal.R.styleable.AndroidManifestLibrary);

                // Note: don't allow this value to be a reference to a resource
                // that may change.
                String lname = sa.getNonResourceString(
                        com.android.internal.R.styleable.AndroidManifestLibrary_name);

                sa.recycle();

                if (lname != null) {
                    lname = lname.intern();
                    if (!ArrayUtils.contains(owner.libraryNames, lname)) {
                        owner.libraryNames = ArrayUtils.add(owner.libraryNames, lname);
                    }
                }

                XmlUtils.skipCurrentTag(parser);

            } else if (tagName.equals("uses-library")) {
                sa = res.obtainAttributes(attrs,
                        com.android.internal.R.styleable.AndroidManifestUsesLibrary);

                // Note: don't allow this value to be a reference to a resource
                // that may change.
                String lname = sa.getNonResourceString(
                        com.android.internal.R.styleable.AndroidManifestUsesLibrary_name);
                boolean req = sa.getBoolean(
                        com.android.internal.R.styleable.AndroidManifestUsesLibrary_required,
                        true);

                sa.recycle();

                if (lname != null) {
                    lname = lname.intern();
                    if (req) {
                        owner.usesLibraries = ArrayUtils.add(owner.usesLibraries, lname);
                    } else {
                        owner.usesOptionalLibraries = ArrayUtils.add(
                                owner.usesOptionalLibraries, lname);
                    }
                }

                XmlUtils.skipCurrentTag(parser);

            } else if (tagName.equals("uses-package")) {
                // Dependencies for app installers; we don't currently try to
                // enforce this.
                XmlUtils.skipCurrentTag(parser);

            } else {
                if (!RIGID_PARSER) {
                    Slog.w(TAG, "Unknown element under <application>: " + tagName
                            + " at " + mArchiveSourcePath + " "
                            + parser.getPositionDescription());
                    XmlUtils.skipCurrentTag(parser);
                    continue;
                } else {
                    outError[0] = "Bad element under <application>: " + tagName;
                    mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
                    return false;
                }
            }
        }

这样，经过这里循环遍历，整个androidManifest的节点信息就被解析并保存在了Package对象中。可以看到我们平时在Manifest中定义的各种节点，其实都是在这里有所体现。当androidManifest.xml文件被解析完成之后会调用我们刚刚介绍的scanPackageLI的重载方法，将解析完成的Package对象信息保存的Setting对象中，这个对象用于保存app的安装信息，具体实现是在方法：

private PackageParser.Package scanPackageLI(File scanFile, int parseFlags, int scanFlags,
            long currentTime, UserHandle user) throws PackageManagerException

当解析完成manifest文件之后会调用其重载方法：

// Note that we invoke the following method only if we are about to unpack an application
        PackageParser.Package scannedPkg = scanPackageLI(pkg, parseFlags, scanFlags
                | SCAN_UPDATE_SIGNATURE, currentTime, user);

这样，解析的manifest文件信息就会被保存到Settings中，并持久化，然后执行安装apk的操作，我们可以看一下该重载方法的具体实现：

private PackageParser.Package scanPackageLI(PackageParser.Package pkg, int parseFlags,
            int scanFlags, long currentTime, UserHandle user) throws PackageManagerException {
        boolean success = false;
        try {
            final PackageParser.Package res = scanPackageDirtyLI(pkg, parseFlags, scanFlags,
                    currentTime, user);
            success = true;
            return res;
        } finally {
            if (!success && (scanFlags & SCAN_DELETE_DATA_ON_FAILURES) != 0) {
                removeDataDirsLI(pkg.volumeUuid, pkg.packageName);
            }
        }
    }

可以发现其内部调用了scanPackageDirtyLI方法，这个方法就是实际实现持久化manifest信息并安装APK操作的：

private PackageParser.Package scanPackageDirtyLI(PackageParser.Package pkg, int parseFlags,
            int scanFlags, long currentTime, UserHandle user) throws PackageManagerException {
	...
	// And now re-install the app.
    ret = createDataDirsLI(pkg.volumeUuid, pkgName, pkg.applicationInfo.uid,
                  pkg.applicationInfo.seinfo);
	...
}

可以发现其内部调用了createDataDirLI，该方法主要实现安装apk的操作。

private int createDataDirsLI(String volumeUuid, String packageName, int uid, String seinfo) {
        int[] users = sUserManager.getUserIds();
        int res = mInstaller.install(volumeUuid, packageName, uid, uid, seinfo);
        if (res < 0) {
            return res;
        }
        for (int user : users) {
            if (user != 0) {
                res = mInstaller.createUserData(volumeUuid, packageName,
                        UserHandle.getUid(user, uid), user, seinfo);
                if (res < 0) {
                    return res;
                }
            }
        }
        return res;
    }

查看该方法的实现：

public int install(String uuid, String name, int uid, int gid, String seinfo) {
        StringBuilder builder = new StringBuilder("install");
        builder.append(' ');
        builder.append(escapeNull(uuid));
        builder.append(' ');
        builder.append(name);
        builder.append(' ');
        builder.append(uid);
        builder.append(' ');
        builder.append(gid);
        builder.append(' ');
        builder.append(seinfo != null ? seinfo : "!");
        return mInstaller.execute(builder.toString());
    }

怎么样？很熟悉吧，这里的Installer其实调用的就是我们平时运行android项目很熟悉的install命令，原来android系统安装apk文件底层都是调用的adb命令。

总结：

• android系统启动之后会解析固定目录下的apk文件，并执行解析，持久化apk信息，重新安装等操作；

• 解析Manifest流程：Zygote进程 –> SystemServer进程 –> PackgeManagerService服务 –> scanDirLI方法 –> scanPackageLI方法 –> PackageParser.parserPackage方法；

• 解析完成Manifest之后会将apk的Manifest信息保存在Settings对象中并持久化，然后执行重新安装的操作；

另外对android源码解析方法感兴趣的可参考我的：

android源码解析之（一）–>android项目构建过程

android源码解析之（二）–>异步消息机制

android源码解析之（三）–>异步任务AsyncTask

android源码解析之（四）–>HandlerThread

android源码解析之（五）–>IntentService

android源码解析之（六）–>Log

android源码解析之（七）–>LruCache

android源码解析之（八）–>Zygote进程启动流程

android源码解析之（九）–>SystemServer进程启动流程

android源码解析之（十）–>Launcher启动流程

android源码解析之（十一）–>应用进程启动流程