在android的apk安装过程中，PMS会调用installPackageLI方法对apk进行解析，下面看看这个方法的具体实现：
http://androidxref.com/9.0.0_r3/xref/frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java
private void installPackageLI(InstallArgs args, PackageInstalledInfo res) {
...
PackageParser pp = new PackageParser();
...
final PackageParser.Package pkg;
try {
//关键代码1
pkg = pp.parsePackage(tmpPackageFile, parseFlags);
DexMetadataHelper.validatePackageDexMetadata(pkg);
} catch (PackageParserException e) {
res.setError("Failed parse during installPackageLI", e);
return;
} finally {
Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);
}
...
}
这个方法中，会先创建一个PackageParser对象，并调用PackageParser了的parsePackage方法对apk包进行解析。下面来看看PackageParser类的parsePackage方法的具体实现：
http://androidxref.com/9.0.0_r3/xref/frameworks/base/core/java/android/content/pm/PackageParser.java
public Package parsePackage(File packageFile, int flags) throws PackageParserException {
return parsePackage(packageFile, flags, false /* useCaches */);
}
public Package parsePackage(File packageFile, int flags, boolean useCaches)
throws PackageParserException {
Package parsed = useCaches ? getCachedResult(packageFile, flags) : null;
if (parsed != null) {
return parsed;
}
...
//关键代码
if (packageFile.isDirectory()) {
parsed = parseClusterPackage(packageFile, flags);
} else {
parsed = parseMonolithicPackage(packageFile, flags);
}
...
return parsed;
}
parsePackage方法内部，调用了其重载方法，这个重载方法内部，会判断packageFile是否是文件夹，而采用不同的解析方法对apk进行解析，之所以采用两种方式对apk包进行解析，是因为从android 5.0开始，为了解决单个包方法是数超过65535的限制，就采用了multiple apk，将一个apk拆分成多个apk,这样就解决了单个apk的方法数的限制。对于一个完整的未拆分的apk，集base APK，Andriod称之为Monolithic,对于多个apk，由一个base APK和多个split APK组成，Android 称之为Cluster。并且对于多个apk，它们是存储在一个目录下的，所以，上面的代码中会通过packageFile是否是目录来区分。从parseClusterPackage中带有Cluster这个单词，就知道这个方法是解析多个apk的，另外一个parseMonolithicPackage方法，就是解析一个base.apk的。由于解析多个apk的方法中是包含了解析一个apk的原理的，所以，下面以parseClusterPackage为例来分析，是如何具体的解析apk的。
http://androidxref.com/9.0.0_r3/xref/frameworks/base/core/java/android/content/pm/PackageParser.java
private Package parseClusterPackage(File packageDir, int flags) throws PackageParserException {
//关键代码1
final PackageLite lite = parseClusterPackageLite(packageDir, 0);
...
try {
final AssetManager assets = assetLoader.getBaseAssetManager();
final File baseApk = new File(lite.baseCodePath);
//关键代码2
final Package pkg = parseBaseApk(baseApk, assets, flags);
if (pkg == null) {
throw new PackageParserException(INSTALL_PARSE_FAILED_NOT_APK,
"Failed to parse base APK: " + baseApk);
}
if (!ArrayUtils.isEmpty(lite.splitNames)) {
final int num = lite.splitNames.length;
pkg.splitNames = lite.splitNames;
pkg.splitCodePaths = lite.splitCodePaths;
pkg.splitRevisionCodes = lite.splitRevisionCodes;
pkg.splitFlags = new int[num];
pkg.splitPrivateFlags = new int[num];
pkg.applicationInfo.splitNames = pkg.splitNames;
pkg.applicationInfo.splitDependencies = splitDependencies;
pkg.applicationInfo.splitClassLoaderNames = new String[num];
for (int i = 0; i < num; i++) {
final AssetManager splitAssets = assetLoader.getSplitAssetManager(i);
//关键代码3
parseSplitApk(pkg, i, splitAssets, flags);
}
}
...
return pkg;
} catch (IOException e) {
throw new PackageParserException(INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION,
"Failed to get path: " + lite.baseCodePath, e);
} finally {
IoUtils.closeQuietly(assetLoader);
}
}
这个方法中，关键代码1处，通过parseClusterPackageLite方法，获取到PackageLite类型的对象，这个方法的名称中包含了Lite，表示这个方法只是轻量的解析了apk包，因为apk的解析过程是很复制的，并且和耗时，所以这里只是轻量的解析apk,获取apk包中的少量的信息，后面用这个获取到的apk的少量信息来作为后面解析apk的参数使用，在关键代码2处，调用parseBaseApk方法来解析baseApk，在关键代码3处，调用parseSplitApk方法对split apk进行解析。下面先来看看parseBaseApk方法的具体实现：
http://androidxref.com/9.0.0_r3/xref/frameworks/base/core/java/android/content/pm/PackageParser.java
private Package parseBaseApk(File apkFile, AssetManager assets, int flags)
throws PackageParserException {
final String apkPath = apkFile.getAbsolutePath();
...
XmlResourceParser parser = null;
try {
final int cookie = assets.findCookieForPath(apkPath);
if (cookie == 0) {
throw new PackageParserException(INSTALL_PARSE_FAILED_BAD_MANIFEST,
"Failed adding asset path: " + apkPath);
}
parser = assets.openXmlResourceParser(cookie, ANDROID_MANIFEST_FILENAME);
final Resources res = new Resources(assets, mMetrics, null);
final String[] outError = new String[1];
//关键代码
final Package pkg = parseBaseApk(apkPath, res, parser, flags, outError);
if (pkg == null) {
throw new PackageParserException(mParseError,
apkPath + " (at " + parser.getPositionDescription() + "): " + outError[0]);
}
pkg.setVolumeUuid(volumeUuid);
pkg.setApplicationVolumeUuid(volumeUuid);
pkg.setBaseCodePath(apkPath);
pkg.setSigningDetails(SigningDetails.UNKNOWN);
return pkg;
} catch (PackageParserException e) {
throw e;
} catch (Exception e) {
throw new PackageParserException(INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION,
"Failed to read manifest from " + apkPath, e);
} finally {
IoUtils.closeQuietly(parser);
}
}
这个方法内部，在关键代码处，调用了parseBaseApk的重载方法，下面看看这个重载方法：
http://androidxref.com/9.0.0_r3/xref/frameworks/base/core/java/android/content/pm/PackageParser.java
private Package parseBaseApk(String apkPath, Resources res, XmlResourceParser parser, int flags,
String[] outError) throws XmlPullParserException, IOException {
final String splitName;
final String pkgName;
...
final Package pkg = new Package(pkgName);
//关键代码1处
TypedArray sa = res.obtainAttributes(parser,
com.android.internal.R.styleable.AndroidManifest);
pkg.mVersionCode = sa.getInteger(
com.android.internal.R.styleable.AndroidManifest_versionCode, 0);
pkg.mVersionCodeMajor = sa.getInteger(
com.android.internal.R.styleable.AndroidManifest_versionCodeMajor, 0);
pkg.applicationInfo.setVersionCode(pkg.getLongVersionCode());
pkg.baseRevisionCode = sa.getInteger(
com.android.internal.R.styleable.AndroidManifest_revisionCode, 0);
pkg.mVersionName = sa.getNonConfigurationString(
com.android.internal.R.styleable.AndroidManifest_versionName, 0);
if (pkg.mVersionName != null) {
pkg.mVersionName = pkg.mVersionName.intern();
}
pkg.coreApp = parser.getAttributeBooleanValue(null, "coreApp", false);
pkg.mCompileSdkVersion = sa.getInteger(
com.android.internal.R.styleable.AndroidManifest_compileSdkVersion, 0);
pkg.applicationInfo.compileSdkVersion = pkg.mCompileSdkVersion;
pkg.mCompileSdkVersionCodename = sa.getNonConfigurationString(
com.android.internal.R.styleable.AndroidManifest_compileSdkVersionCodename, 0);
if (pkg.mCompileSdkVersionCodename != null) {
pkg.mCompileSdkVersionCodename = pkg.mCompileSdkVersionCodename.intern();
}
pkg.applicationInfo.compileSdkVersionCodename = pkg.mCompileSdkVersionCodename;
sa.recycle();
//关键代码2
return parseBaseApkCommon(pkg, null, res, parser, flags, outError);
}
在这个方法中，从资源中提取自定义属性集,接着用TypedArray读取APK的AndroidManifest中的versionCode、revisionCode和versionName的值赋值给Package的对应的属性。在关键代码2处，调用parseBaseApkCommon方法来将来解析manifest文件中的permission,user-sdk,application，feature-group等标签，并调用parseBaseApplication方法，对Application标签进行。下面看看这个方法的具体实现：
http://androidxref.com/9.0.0_r3/xref/frameworks/base/core/java/android/content/pm/PackageParser.java
private boolean parseBaseApplication(Package owner, Resources res,
XmlResourceParser parser, int flags, String[] outError)
throws XmlPullParserException, IOException {
final ApplicationInfo ai = owner.applicationInfo;
final String pkgName = owner.applicationInfo.packageName;
TypedArray sa = res.obtainAttributes(parser,
com.android.internal.R.styleable.AndroidManifestApplication);
...
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, flags, outError, cachedArgs, false,
owner.baseHardwareAccelerated);
if (a == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
hasActivityOrder |= (a.order != 0);
owner.activities.add(a);
} else if (tagName.equals("receiver")) {
Activity a = parseActivity(owner, res, parser, flags, outError, cachedArgs,
true, false);
if (a == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
hasReceiverOrder |= (a.order != 0);
owner.receivers.add(a);
} else if (tagName.equals("service")) {
Service s = parseService(owner, res, parser, flags, outError, cachedArgs);
if (s == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
hasServiceOrder |= (s.order != 0);
owner.services.add(s);
} else if (tagName.equals("provider")) {
Provider p = parseProvider(owner, res, parser, flags, outError, cachedArgs);
if (p == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
owner.providers.add(p);
} else if (parser.getName().equals("meta-data")) {
if ((owner.mAppMetaData = parseMetaData(res, parser, owner.mAppMetaData,
outError)) == null) {
mParseError = PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
return false;
}
}
...
}
...
return true;
}
这个方法内部代码太多，只贴出了四大组件相关的解析代码，在解析到activity这个tag时，就将其转换成Activity，这里的Activity并不是平时开发中的activity,这里的Activity是继承自Component类的，它是PackageParser类的一个静态内部类。PackageParser$Activity类中的ActivityInfo类才是正在的Activity的数据。
http://androidxref.com/9.0.0_r3/xref/frameworks/base/core/java/android/content/pm/PackageParser.java
public final static class Activity extends Component<ActivityIntentInfo>{
public final ActivityInfo info;
...
}
将manifest中的activity标签中的各个属性以及子标签解析成PackageParserActvity,然后将其存储到owner这个对象中，这个owner是PackageParserActvity,然后将其存储到owner这个对象中，这个owner是PackageParserActvity,然后将其存储到owner这个对象中，这个owner是PackageParserPackage类型的对象，下面看看PackageParser$Package类
http://androidxref.com/9.0.0_r3/xref/frameworks/base/core/java/android/content/pm/PackageParser.java
public final static class Package implements Parcelable {
public String packageName;
public String manifestPackageName;
...
public boolean baseHardwareAccelerated;
public ApplicationInfo applicationInfo = new ApplicationInfo();
public final ArrayList<Permission> permissions = new ArrayList<Permission>(0);
public final ArrayList<PermissionGroup> permissionGroups = new ArrayList<PermissionGroup>(0);
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>();
...
}
这个类中，存储了很多的解析manifest文件中的信息，由于代码太多，这里只贴出了部分代码。可以看到，里面有activities，receivers，providers，services这四大组件的信息，都存储到这4个ArrayList集合中了。这样就解析完了base Apk的信息,下面接着看parseClusterPackage方法的关键处3：
http://androidxref.com/9.0.0_r3/xref/frameworks/base/core/java/android/content/pm/PackageParser.java
private Package parseClusterPackage(File packageDir, int flags) throws PackageParserException {
//关键代码1
final PackageLite lite = parseClusterPackageLite(packageDir, 0);
...
try {
final AssetManager assets = assetLoader.getBaseAssetManager();
final File baseApk = new File(lite.baseCodePath);
//关键代码2
final Package pkg = parseBaseApk(baseApk, assets, flags);
if (pkg == null) {
throw new PackageParserException(INSTALL_PARSE_FAILED_NOT_APK,
"Failed to parse base APK: " + baseApk);
}
if (!ArrayUtils.isEmpty(lite.splitNames)) {
final int num = lite.splitNames.length;
pkg.splitNames = lite.splitNames;
pkg.splitCodePaths = lite.splitCodePaths;
pkg.splitRevisionCodes = lite.splitRevisionCodes;
pkg.splitFlags = new int[num];
pkg.splitPrivateFlags = new int[num];
pkg.applicationInfo.splitNames = pkg.splitNames;
pkg.applicationInfo.splitDependencies = splitDependencies;
pkg.applicationInfo.splitClassLoaderNames = new String[num];
for (int i = 0; i < num; i++) {
final AssetManager splitAssets = assetLoader.getSplitAssetManager(i);
//关键代码3
parseSplitApk(pkg, i, splitAssets, flags);
}
}
...
return pkg;
} catch (IOException e) {
throw new PackageParserException(INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION,
"Failed to get path: " + lite.baseCodePath, e);
} finally {
IoUtils.closeQuietly(assetLoader);
}
}
在关键代码3处，调用了parseSplitApk方法对split Apk进行解析，parseSplitApk方法内部又调用其重载方法，这个重载方法内部，又调用了parseSplitApplication方法，对application标签中的四大组件等标签进行解析，并将解析的信息存储到PackageParser$Package类中。由于这个过程和解析baseApk类似，所以这就不再贴出
parseSplitApk这个过程的具体代码。
以上便是PMS中对apk的具体解析过程分析。
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