Android APK应用安装原理(1)-解析AndroidManifest原理-PackageParser.parserPackage

Android  安装一个 APK 的时候首先会解析 APK ，这里要做很多事情，其中一个事情就是解析 Manifest.xml 文件，并将所有 APK 的 Manifest 封装到各种对象中并保存在内存当中

解析Manifest的类是非常重要的，该类就是frameworks\base\core\java\android\content\pm\PackageParser

PackageManagerService会调用PackageParser.parserPackage方法来解析APK清单，下面开始分析PackageParser的实现：

PackageParser是使用的XMLPullParser工具来对XML进行解析的，然后分别通过android.content.pm下各种xxxInfo类来进行封装：

public Package parsePackage(File sourceFile, String destCodePath,
            DisplayMetrics metrics, int flags) {
    	//最后要跑出的解析错误信息
        mParseError = PackageManager.INSTALL_SUCCEEDED;

        //获得要解析的文件的路径
        mArchiveSourcePath = sourceFile.getPath();
        
        //如果要解析的不是文件类型就跳过并且返回该方法
        if (!sourceFile.isFile()) {
            Log.w(TAG, "Skipping dir: " + mArchiveSourcePath);
            //更新错误信息
            mParseError = PackageManager.INSTALL_PARSE_FAILED_NOT_APK;
            return null;
        }
        
        //如果文件不是以.apk结尾并且flag没有确定一定是APK，那么也返回
        if (!isPackageFilename(sourceFile.getName())
                && (flags&PARSE_MUST_BE_APK) != 0) {
            if ((flags&PARSE_IS_SYSTEM) == 0) {
                // We expect to have non-.apk files in the system dir,
                // so don't warn about them.
                Log.w(TAG, "Skipping non-package file: " + mArchiveSourcePath);
            }
            //更新错误信息
            mParseError = PackageManager.INSTALL_PARSE_FAILED_NOT_APK;
            return null;
        }

        if ((flags&PARSE_CHATTY) != 0 && Config.LOGD) Log.d(
            TAG, "Scanning package: " + mArchiveSourcePath);

        XmlResourceParser parser = null;
        AssetManager assmgr = null;
        boolean assetError = true;
        try {
            assmgr = new AssetManager();
            
            //将一个文件添加到AssetManager中并返回一个唯一标识
            int cookie = assmgr.addAssetPath(mArchiveSourcePath);
            if(cookie != 0) {
            	//通过标识去AssetManager中找到标识对应资源中的Manifest清单文件，并返回一个XML的解析器
                parser = assmgr.openXmlResourceParser(cookie, "AndroidManifest.xml");
                //走到这里证明一切顺利
                assetError = false;
            } else {
                Log.w(TAG, "Failed adding asset path:"+mArchiveSourcePath);
            }
        } catch (Exception e) {
            Log.w(TAG, "Unable to read AndroidManifest.xml of "
                    + mArchiveSourcePath, e);
        }
        if(assetError) {
            if (assmgr != null) assmgr.close();
            mParseError = PackageManager.INSTALL_PARSE_FAILED_BAD_MANIFEST;
            return null;
        }
        String[] errorText = new String[1];
        Package pkg = null;
        Exception errorException = null;
        try {
            // XXXX todo: need to figure out correct configuration.
            Resources res = new Resources(assmgr, metrics, null);
            //这个是真正在解析的package的方法，是private method
            pkg = parsePackage(res, parser, flags, errorText);
        } catch (Exception e) {
            errorException = e;
            mParseError = PackageManager.INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION;
        }


        if (pkg == null) {
            if (errorException != null) {
                Log.w(TAG, mArchiveSourcePath, errorException);
            } else {
                Log.w(TAG, mArchiveSourcePath + " (at "
                        + parser.getPositionDescription()
                        + "): " + errorText[0]);
            }
            parser.close();
            assmgr.close();
            if (mParseError == PackageManager.INSTALL_SUCCEEDED) {
                mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
            }
            return null;
        }

parserPackage调用了重载的另外一个parserPackage

private Package parsePackage(
        Resources res, XmlResourceParser parser, int flags, String[] outError)
        throws XmlPullParserException, IOException {
        AttributeSet attrs = parser;

        //每次调用这个方法时候清空这些变量
        mParseInstrumentationArgs = null;
        mParseActivityArgs = null;
        mParseServiceArgs = null;
        mParseProviderArgs = null;
        
        //这里调用这个方法获得包名
        String pkgName = parsePackageName(parser, attrs, flags, outError);
        if (pkgName == null) {
            mParseError = PackageManager.INSTALL_PARSE_FAILED_BAD_PACKAGE_NAME;
            return null;
        }
        int type;

        final Package pkg = new Package(pkgName);
        boolean foundApp = false;
        
        //从资源里获得AndroidManifest的数组
        TypedArray sa = res.obtainAttributes(attrs,
                com.android.internal.R.styleable.AndroidManifest);
        
        //继续挖掘出版本号
        pkg.mVersionCode = sa.getInteger(
                com.android.internal.R.styleable.AndroidManifest_versionCode, 0);
        
        //获取版本名
        pkg.mVersionName = sa.getNonConfigurationString(
                com.android.internal.R.styleable.AndroidManifest_versionName, 0);
        if (pkg.mVersionName != null) {
            pkg.mVersionName = pkg.mVersionName.intern();
        }
        
        //获得sharedUserId
        String str = sa.getNonConfigurationString(
                com.android.internal.R.styleable.AndroidManifest_sharedUserId, 0);
        if (str != null && str.length() > 0) {
        	//验证包名是否符合规则
            String nameError = validateName(str, true);
            if (nameError != null && !"android".equals(pkgName)) {
                outError[0] = "<manifest> specifies bad sharedUserId name \""
                    + str + "\": " + nameError;
                mParseError = PackageManager.INSTALL_PARSE_FAILED_BAD_SHARED_USER_ID;
                return null;
            }
            pkg.mSharedUserId = str.intern();
            pkg.mSharedUserLabel = sa.getResourceId(
                    com.android.internal.R.styleable.AndroidManifest_sharedUserLabel, 0);
        }
        sa.recycle();

        //安装的位置
        pkg.installLocation = sa.getInteger(
                com.android.internal.R.styleable.AndroidManifest_installLocation,
                PARSE_DEFAULT_INSTALL_LOCATION);

        // Resource boolean are -1, so 1 means we don't know the value.
        int supportsSmallScreens = 1;
        int supportsNormalScreens = 1;
        int supportsLargeScreens = 1;
        int resizeable = 1;
        int anyDensity = 1;
        
        int outerDepth = parser.getDepth();
        
        //关键时刻到了，真正的开始解析了
        while ((type=parser.next()) != parser.END_DOCUMENT
               && (type != parser.END_TAG || parser.getDepth() > outerDepth)) {
            if (type == parser.END_TAG || type == parser.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 {
                        Log.w(TAG, "<manifest> has more than one <application>");
                        XmlUtils.skipCurrentTag(parser);
                        continue;
                    }
                }

                foundApp = true;
                if (!parseApplication(pkg, res, parser, attrs, flags, outError)) {
                    return null;
                }
            } else if (tagName.equals("permission-group")) {
                if (parsePermissionGroup(pkg, 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")) {
                sa = res.obtainAttributes(attrs,
                        com.android.internal.R.styleable.AndroidManifestUsesPermission);

                // 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.AndroidManifestUsesPermission_name);

                sa.recycle();

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这里分别把每种不同的element用不同的小方法去解析，他们的调用顺序是：






这些小方法里其实还是有很多小技巧的，有兴趣的话可以细细品位