深入分析PMS服务(一)

在前面两篇自己动手编译最新Android源码及自己动手调试Android源码中,我们掌握了Android源码的编译以及调试,现在呢,我们在这基础上分析一些源码的实现.首先从PMS服务开始.

PMS服务即PackageManagerService,主要用来进行APK的管理任务.但是今天,我们并不直接分析PMS的源码,而是从一个工具类PackageParse说起.

首先来认识PackageParser类,它主要用来解析手机上的apk文件(支持Single APK和Multiple APK),主要包含两个过程

• APK->Package:解析APK文件为Package对象的过程
• Package->PackageInfo:由Package对象生成PackageInfo的过程

介于不少童鞋不了解Single APK和Multiple APK,在这里做个简单解释:

Single APK是我们通常所开发的APK,即一个应用只有一个apk文件.而Google Play还允许你为一个应用中发布不同的apk文件,这些apk文件适用于不同设备.举例说明,假设你现在开发了一款APP叫做Monkey,但是目前该APP由于体积太大或者其他因素导致不能同时适用于手机和平板,此时你就可将原先的Monkey.apk拆分为了Monkey-Phone.apk和Monkey-Tablet,分别用于运行在Android手机和Android平板,只要保存两者拥有相同的包名,并用相同key进行签名就可以在发布Monkey应用的时候,一同发布Monkey-Phone.apk和Moneky-Tablet.apk,那么这种一个应用拥有多个APK文件的程序就称之为Multiple APK.
更多信息查看官网:multiple-apks

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解析APK文件为Package对象

该过程目的是通过解析磁盘上的APK文件来生成与之相关的Package对象.而Pakcage对象是APK经过完整解析之后的结果.

该过程主要涉及到一系列parseXXX()格式的方法,起始方法是public Package parsePackage(File packageFile, int flags),那么我们就从该方法开始分析其流程:

public Package parsePackage(File packageFile, int flags) throws PackageParserException {        if (packageFile.isDirectory()) {            //多个apk文件的目录            return parseClusterPackage(packageFile, flags);        } else {            //单一APK文件            return parseMonolithicPackage(packageFile, flags);        }    }

该方法接受两个参数packageFile和flags.并根据packageFile是否是文件目录来确定具体的解析流程.通常我们都是Single APK,因此我们重点关注Single APK的解析,不难发现其具体解析过程给委托给parseMonolithicPackage(packageFile, flags)方法:

 public Package parseMonolithicPackage(File apkFile, int flags) throws PackageParserException {        //如果是核心应用则以更轻量级的方式进行解析后,判断是否是核心应用,非核心应用不执行解析过程        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 {            //调用parseBaseAPK()继续解析操作            final Package pkg = parseBaseApk(apkFile, assets, flags);            pkg.codePath = apkFile.getAbsolutePath();            return pkg;        } finally {            IoUtils.closeQuietly(assets);        }    }

在该方法中首先通过mOnlyCoreApps属性判断当前系统是不是只解析核心APK,默认是全部解析.至于什么是核心APK后面再说.现在我们继续关注其解析过程.
这里其解析操作继续由parseBaseApk(apkFile, assets, flags)完成:

 private Package parseBaseApk(File apkFile, AssetManager assets, int flags)            throws PackageParserException {                ...        final int cookie = loadApkIntoAssetManager(assets, apkPath, flags);        Resources res = null;        XmlResourceParser parser = null;        try {            res = new Resources(assets, mMetrics, null);            assets.setConfiguration(0, 0, null, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,                    Build.VERSION.RESOURCES_SDK_INT);            //为AndroidManifest.xml生成xml文件解析器            parser = assets.openXmlResourceParser(cookie, ANDROID_MANIFEST_FILENAME);            final String[] outError = new String[1];            final Package pkg = parseBaseApk(res, parser, flags, outError);                ...            pkg.baseCodePath = apkPath;            pkg.mSignatures = null;            return pkg;        }                 ...    }

而真正的解析又是通过该方法的同名函数:parseBaseApk(Resources res, XmlResourceParser parser, int flags,String[] outError)完成的,为了突出重点,我对其方法进行了简化:

    private Package parseBaseApk(Resources res, XmlResourceParser parser, int flags,            String[] outError) throws XmlPullParserException, IOException {             //....省略多行代码....       //循环解析AndroidManifest.xml中的元素       while ((type = parser.next()) != XmlPullParser.END_DOCUMENT                && (type != XmlPullParser.END_TAG || parser.getDepth() > outerDepth)) {                if (tagName.equals("application")) {                    //....省略多行代码,重点关注其中调用的parseBaseApplication()方法                }else if (tagName.equals("overlay")) {                    //....省略多行代码....                }else if (tagName.equals("key-sets")){                    //paseKeySets()                }else if (tagName.equals("permission-group")) {                    parsePermissionGroup(pkg, flags, res, parser, attrs,                 }else if (tagName.equals("permission")) {                    //parsePermission                }else if (tagName.equals("uses-configuration")) {                    //....省略多行代码....                }else if (tagName.equals("uses-feature")) {                    //parseUsesFeature()                }else if (tagName.equals("feature-group")) {                    //....省略多行代码....                }else if (tagName.equals("uses-sdk")) {                    //....省略多行代码....                }else if (tagName.equals("supports-screens")) {                    //....省略多行代码....                }else if (tagName.equals("protected-broadcast")) {                    //....省略多行代码....                }else if (tagName.equals("instrumentation")) {                    //....省略多行代码....                }else if (tagName.equals("original-package")) {                    //....省略多行代码....                }else if (tagName.equals("adopt-permissions")) {                    //....省略多行代码....                }              //....省略多行代码....            }        //....省略多汗代码....    }

不难发现这里通过很多parseXXX()方法解析相应的数据,比如:parseBaseApplication(),parseKeySets(),parsePermissionGroup(),parseUsesPermission()等等.
下面,我们重点关注Application标签的解析,即:parseBaseApplication()方法:

 private boolean parseBaseApplication(Package owner, Resources res,            XmlPullParser parser, AttributeSet attrs, int flags, String[] outError)        throws XmlPullParserException, IOException {        //....省略对Application元素属性解析多行代码....    //解析Application下的子元素结点,如activity,receiver,service等        while ((type = parser.next()) != XmlPullParser.END_DOCUMENT                && (type != XmlPullParser.END_TAG || parser.getDepth() > innerDepth)) {             if (tagName.equals("activity")) {                //....省略多行代码,主要关注parseActivity()....             } else if (tagName.equals("receiver")) {                //....省略多行代码,主要关注parseActivity()....             }else if (tagName.equals("service")) {                //....省略多行代码,主要关注parseService()....             }else if (tagName.equals("provider")) {                //....省略多行代码,主要关注parseProvider()....             }else if (tagName.equals("activity-alias")) {                //....省略多行代码,主要关注parseActivityAlias()...             }else if (parser.getName().equals("meta-data")) {                //....省略多行代码,重点关注parseMetaData()....             }else if (tagName.equals("library")) {                //....省略多行代码....             }else if (tagName.equals("uses-library")) {                //....省略多行代码....             }else if (tagName.equals("uses-package")) {                //....省略多行代码....             }else{                //....省略多行代码....             }         }       return true;      }

在解析Application下子元素结点时,同样也是通过很多parseXXX()方法来完成的.比如在解析activity结点时是通过parseActivity()来完成的,其余自行查阅代码.

另外你可能已经注意到对receiver的解析也是通过parseActivity()实现的.

到此为止,整个为止,解析的整个流程完成,并返回一个Package对象.

附:PackageParser中所有相关解析方法

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由Package对象生成PackageInfo

该过程的目的是从Package中提取相关属性,并封装成PackageInfo类型的对象.

该过程主要涉及到一系列generateXXXInfo()格式的方法,起始方法是generatePackageInfo(),那么我们就从该方法开始分析其流程:

 public static PackageInfo generatePackageInfo(PackageParser.Package p,            int gids[], int flags, long firstInstallTime, long lastUpdateTime,            ArraySet<String> grantedPermissions, PackageUserState state) {        return generatePackageInfo(p, gids, flags, firstInstallTime, lastUpdateTime,                grantedPermissions, state, UserHandle.getCallingUserId());    }

不难看出这里由调用了其同名方法generatePackageInfo(PackageParser.Package p,
int gids[], int flags, long firstInstallTime, long lastUpdateTime,
ArraySet<String> grantedPermissions, PackageUserState state, int userId)来进行继续解析工作:

public static PackageInfo generatePackageInfo(PackageParser.Package p,            int gids[], int flags, long firstInstallTime, long lastUpdateTime,            ArraySet<String> grantedPermissions, PackageUserState state, int userId)        if (!checkUseInstalledOrHidden(flags, state)) {            return null;        }        //从Package对象p中取出一系列的属性值用来初始化pi        PackageInfo pi = new PackageInfo();        pi.packageName = p.packageName;        pi.splitNames = p.splitNames;        pi.versionCode = p.mVersionCode;        pi.baseRevisionCode = p.baseRevisionCode;        pi.splitRevisionCodes = p.splitRevisionCodes;        pi.versionName = p.mVersionName;        pi.sharedUserId = p.mSharedUserId;        pi.sharedUserLabel = p.mSharedUserLabel;        pi.applicationInfo = generateApplicationInfo(p, flags, state, userId);        pi.installLocation = p.installLocation;        pi.coreApp = p.coreApp;        if ((pi.applicationInfo.flags&ApplicationInfo.FLAG_SYSTEM) != 0                || (pi.applicationInfo.flags&ApplicationInfo.FLAG_UPDATED_SYSTEM_APP) != 0) {            pi.requiredForAllUsers = p.mRequiredForAllUsers;        }        pi.restrictedAccountType = p.mRestrictedAccountType;        pi.requiredAccountType = p.mRequiredAccountType;        pi.overlayTarget = p.mOverlayTarget;        pi.firstInstallTime = firstInstallTime;        pi.lastUpdateTime = lastUpdateTime;        if ((flags&PackageManager.GET_GIDS) != 0) {            pi.gids = gids;        }        if ((flags&PackageManager.GET_CONFIGURATIONS) != 0) {            //....省略多行代码....        }        if ((flags&PackageManager.GET_ACTIVITIES) != 0) {            //....省略多行代码,关注generateActivityInfo()....        }        if ((flags&PackageManager.GET_RECEIVERS) != 0) {           //....省略多行代码,关注generateActivityInfo()....        }        if ((flags&PackageManager.GET_SERVICES) != 0) {            //....省略多行代码,关注generateServiceInfo()....        }        if ((flags&PackageManager.GET_PROVIDERS) != 0) {            //....省略多行代码,关注generateProviderInfo()....        }        if ((flags&PackageManager.GET_INSTRUMENTATION) != 0) {           //....省略多行代码,关注generateInstrumentationInfo()....        }        if ((flags&PackageManager.GET_PERMISSIONS) != 0) {            //....省略多行代码,generatePermissionInfo....        }        if ((flags&PackageManager.GET_SIGNATURES) != 0) {           //....省略多行代码....        }        return pi;    }

上面的过程主要从Package对象取出一系列的属性用来初始化PackageInfo对象,该过程不再涉及磁盘文件的解析操作.
和解析过程相对,该过程借助了很多generateXXXInfo()方法来实现.在解析过程中对于Application元素的解析提供了parseApplication(),而在该过程中也提供了generateApplicationInfo()来实现Application的取值操作

附:PackageParser中所有相关的generate方法

中途小结

到现在为止,我们已经了解Package的生成和PackageInfo生成,不难发现Package的生成是以磁盘APK文件作为输入,而PackageInfo是以Package对象作为输入.得益于Google工程师良好的设计,PackageParse具有非常好的对称性,非常容易理解.在这里,我只是简单的介绍了该类,对于具体的操作并没有深入的说明,其原因在于,其核心就是通过使用Pull Parser对xml文件进行解析的操作.

附:PackageParser所有内部类:

细心的同学已经发现在上面所示的内部类中也存在Activity,Service等类,要注意这些并不是我们平常使用的Activity组件.PackageParser中的内部类,如Activity,Service,Provider,Permission,皆对应于AndroidManifest.xml文件中的某个标签,用于存储解析出来相关的信息.

这里我们同样用类图来简单的描述期间的关系:

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相关实体类

接下来,我们来介绍与上述过程相关的几个实体类,以便你有一个宏观的认识,从而为理解后面的PMS打下基础.
对于这几个实体类,我们值做简单的说明,其具体的点还是需要我们自己进行深究.

Package

PackageParser的静态内部类,代表磁盘上APK文件完整解析后的对象,相当于在内存中Package的对象是对磁盘APK的描述.这里我们只需要关注其属性即可,大部分属性对你而来都是很熟悉的:

public final static class Package {        public String packageName;        /** Names of any split APKs, ordered by parsed splitName */        public String[] splitNames;        //apk文件在磁盘的路径.可能是一个apk的路径,也可能是包含多个apk文件的目录        public String codePath;        /** Path of base APK */        public String baseCodePath;        /** Paths of any split APKs, ordered by parsed splitName */        public String[] splitCodePaths;        /** Revision code of base APK */        public int baseRevisionCode;        /** Revision codes of any split APKs, ordered by parsed splitName */        public int[] splitRevisionCodes;        /** Flags of any split APKs; ordered by parsed splitName */        public int[] splitFlags;        public boolean baseHardwareAccelerated;        public final ApplicationInfo applicationInfo = new ApplicationInfo();        //权限        public final ArrayList<Permission> permissions = new ArrayList<Permission>(0);        public final ArrayList<PermissionGroup> permissionGroups = new ArrayList<PermissionGroup>(0);        //四大组件Activity,Receiver,Service,Provider        public final ArrayList<Activity> activities = new ArrayList<Activity>(0);        public final ArrayList<Activity> receivers = new ArrayList<Activity>(0);        public final ArrayList<Provider> providers = new ArrayList<Provider>(0);        public final ArrayList<Service> services = new ArrayList<Service>(0);        public final ArrayList<Instrumentation> instrumentation = new ArrayList<Instrumentation>(0);        public final ArrayList<String> requestedPermissions = new ArrayList<String>();        public final ArrayList<Boolean> requestedPermissionsRequired = new ArrayList<Boolean>();        public ArrayList<String> protectedBroadcasts;        public ArrayList<String> libraryNames = null;        public ArrayList<String> usesLibraries = null;        public ArrayList<String> usesOptionalLibraries = null;        public String[] usesLibraryFiles = null;        public ArrayList<ActivityIntentInfo> preferredActivityFilters = null;        public ArrayList<String> mOriginalPackages = null;        public String mRealPackage = null;        public ArrayList<String> mAdoptPermissions = null;        // We store the application meta-data independently to avoid multiple unwanted references        public Bundle mAppMetaData = null;        // The version code declared for this package.        public int mVersionCode;        // The version name declared for this package.        public String mVersionName;        // The shared user id that this package wants to use.        public String mSharedUserId;        // The shared user label that this package wants to use.        public int mSharedUserLabel;        // Signatures that were read from the package.        public Signature[] mSignatures;        public Certificate[][] mCertificates;        // For use by package manager service for quick lookup of        // preferred up order.        public int mPreferredOrder = 0;        // For use by package manager to keep track of where it needs to do dexopt.        public final ArraySet<String> mDexOptPerformed = new ArraySet<>(4);        // For use by package manager to keep track of when a package was last used.        public long mLastPackageUsageTimeInMills;        // // User set enabled state.        // public int mSetEnabled = PackageManager.COMPONENT_ENABLED_STATE_DEFAULT;        //        // // Whether the package has been stopped.        // public boolean mSetStopped = false;        // Additional data supplied by callers.        public Object mExtras;        // Whether an operation is currently pending on this package        public boolean mOperationPending;        // Applications hardware preferences        public ArrayList<ConfigurationInfo> configPreferences = null;        // Applications requested features        public ArrayList<FeatureInfo> reqFeatures = null;        // Applications requested feature groups        public ArrayList<FeatureGroupInfo> featureGroups = null;        public int installLocation;        public boolean coreApp;        /* An app that's required for all users and cannot be uninstalled for a user */        public boolean mRequiredForAllUsers;        /* The restricted account authenticator type that is used by this application */        public String mRestrictedAccountType;        /* The required account type without which this application will not function */        public String mRequiredAccountType;        /**         * 代表一个包文件的摘要,用于确定两个package是否不一致         */        public ManifestDigest manifestDigest;        public String mOverlayTarget;        public int mOverlayPriority;        public boolean mTrustedOverlay;        /**         * Data used to feed the KeySetManagerService         */        public ArraySet<PublicKey> mSigningKeys;        public ArraySet<String> mUpgradeKeySets;        public ArrayMap<String, ArraySet<PublicKey>> mKeySetMapping;        public String cpuAbiOverride;    }

PackageInfo

该类代表包的整体描述信息,即AndroidManifest.xml中的信息.如果说Package在内存中代表完整的APK描述,那么PackageInfo则是其子集,来简单的看一下其代码:

public class PackageInfo implements Parcelable {    public String packageName;    public String[] splitNames;    public int versionCode;    public String versionName;    public int baseRevisionCode;    public int[] splitRevisionCodes;    public String sharedUserId;    public int sharedUserLabel;    public ApplicationInfo applicationInfo;    public long firstInstallTime;    public long lastUpdateTime;    public int[] gids;    public ActivityInfo[] activities;    public ActivityInfo[] receivers;    public ServiceInfo[] services;    public ProviderInfo[] providers;    public InstrumentationInfo[] instrumentation;    public PermissionInfo[] permissions;    public String[] requestedPermissions;    public int[] requestedPermissionsFlags;    public Signature[] signatures;    public ConfigurationInfo[] configPreferences;    public FeatureInfo[] reqFeatures;    public FeatureGroupInfo[] featureGroups;}

对比Package和PackageInfo很容易发现期间的关系,接下来顺便介绍PackageInfo中涉及到的实体类:

类名 描述 ActivityInfo 该实体类代表AndroidManiest.xml中的<activity>和<recevier>元素的信息 ServiceInfo 该实体类代表AndroidManiest.xml中的<service>元素中的信息 ProviderInfo 该实体类代表AndroidManiest.xml中的<provider>元素的信息 InstrumentationInfo 该实体类代表AndroidManiest.xml中的<instrumentation>元素的信息 PermissionInfo 该实体类代表AndroidManiest.xml中的<permission>元素的信息 ConfigurationInfo 关于程序要求的硬件信息,该实体类代表AndroidManiest.xml中<uses-configuration>和<uses-feature>元素的信息. FeatureInfo 该实体类代表AndroidManiest.xml中的<uses-feature>元素的信息 FeatureGroupInfo 该实体类代表AndroidManiest.xml中的<feature-group>元素的信息 ManifestDigest 代表一个包文件的摘要信息

这里我们用一张类图来描述其类间的关系:

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总结

到现在PackageParser的基本解释已经完成,之所以在分析PMS之前先来谈PackageParser的原因在于,该工具类可以脱离上下文,单独进行理解,而无关你目前的状态,这也就避免我们面对一大堆源码,在阅读过程找不到侧重点的问题.接下来,是对PackageManager的分析.