Multidex记录三：源码解析
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Multidex记录一：介绍和使用
Multidex记录二：缺陷&解决
Multidex记录三：源码解析
记录Multidex源码解析
为什么要用记录呢，因为我从开始接触Android时我们的项目就在65535的边缘。不久Google就出了multidex的解决方案。我们也已经接入multidex好多年，但我自己还没有接入，知其然而不知其所以然。出了问题只能自己找源码来分析。前两篇文章 Multidex记录一：介绍和使用 和 Multidex记录二：缺陷&解决 分别讲述了怎么接入和接入时遇到的问题，本博文只是对multidex源码学习过程中的分析和理解的记录。
关于Multidex的相关知识点前两章已经讲的差不多了，这篇文章只分析Multidex的安装。
流程图
源码分析
我们先来看看MultiDex的安装日志：
I/MultiDex: VM with version 1.6.0 does not have multidex support
Installing application
MultiDexExtractor.load(/data/app/com.xxx.xxx-1.apk, false, )
I/MultiDex: Blocking on lock /data/data/com.xxx.xxx/code_cache/secondary-dexes/MultiDex.lock
/data/data/com.xxx.xxx/code_cache/secondary-dexes/MultiDex.lock locked
Detected that extraction must be performed.
I/MultiDex: Extraction is needed for file /data/data/com.xxx.xxx/code_cache/secondary-dexes/com.xxx.xxx-1.apk.classes2.zip
Extracting /data/data/com.xxx.xxx/code_cache/secondary-dexes/tmp-com.xxx.xxx-1.apk.classes1415547735.zip
I/MultiDex: Renaming to /data/data/com.xxx.xxx/code_cache/secondary-dexes/com.xxx.xxx-1.apk.classes2.zip
Extraction succeeded - length /data/data/com.xxx.xxx/code_cache/secondary-dexes/com.xxx.xxx-1.apk.classes2.zip: 4238720 - crc: 2971858359
Extraction is needed for file /data/data/com.xxx.xxx/code_cache/secondary-dexes/com.xxx.xxx-1.apk.classes3.zip
Extracting /data/data/com.xxx.xxx/code_cache/secondary-dexes/tmp-com.xxx.xxx-1.apk.classes-1615165740.zip
I/MultiDex: Renaming to /data/data/com.xxx.xxx/code_cache/secondary-dexes/com.xxx.xxx-1.apk.classes3.zip
Extraction succeeded - length /data/data/com.xxx.xxx/code_cache/secondary-dexes/com.xxx.xxx-1.apk.classes3.zip: 3106018 - crc: 3138243730
Extraction is needed for file /data/data/com.xxx.xxx/code_cache/secondary-dexes/com.xxx.xxx-1.apk.classes4.zip
Extracting /data/data/com.xxx.xxx/code_cache/secondary-dexes/tmp-com.xxx.xxx-1.apk.classes-469912688.zip
I/MultiDex: Renaming to /data/data/com.xxx.xxx/code_cache/secondary-dexes/com.xxx.xxx-1.apk.classes4.zip
Extraction succeeded - length /data/data/com.xxx.xxx/code_cache/secondary-dexes/com.xxx.xxx-1.apk.classes4.zip: 2163715 - crc: 1148318293
load found 3 secondary dex files
I/MultiDex: install done
第二次启动时的日志：
I/MultiDex: VM with version 1.6.0 does not have multidex support
Installing application
MultiDexExtractor.load(/data/app/com.xxx.xxx-1.apk, false, )
Blocking on lock /data/data/com.xxx.xxx/code_cache/secondary-dexes/MultiDex.lock
/data/data/com.xxx.xxx/code_cache/secondary-dexes/MultiDex.lock locked
I/MultiDex: loading existing secondary dex files
load found 3 secondary dex files
install done
初始化信息
public final class MultiDex {
static final String TAG = "MultiDex";
//老版本dex文件存放路径
private static final String OLD_SECONDARY_FOLDER_NAME = "secondary-dexes";
//dex文件存放路径 code_cache/secondary-dexes
private static final String SECONDARY_FOLDER_NAME;
//Multidex最高支持的版本，大于20Android系统已支持
private static final int MAX_SUPPORTED_SDK_VERSION = 20;
//Multidex最低支持的版本
private static final int MIN_SDK_VERSION = 4;
//vm的版本信息
private static final int VM_WITH_MULTIDEX_VERSION_MAJOR = 2;
private static final int VM_WITH_MULTIDEX_VERSION_MINOR = 1;
//apk路径
private static final Set<String> installedApk;
//是否支持Multidex
private static final boolean IS_VM_MULTIDEX_CAPABLE;
static {
//SECONDARY_FOLDER_NAME=code_cache/secondary-dexes
SECONDARY_FOLDER_NAME = "code_cache" + File.separator + "secondary-dexes";
installedApk = new HashSet();
//VM是否已经支持自动Multidex
IS_VM_MULTIDEX_CAPABLE = isVMMultidexCapable(System.getProperty("java.vm.version"));
}
Multidex安装
public static void install(Context context) {
//VM是否已经支持自动Multidex
if (IS_VM_MULTIDEX_CAPABLE) {
Log.i("MultiDex", "VM has multidex support, MultiDex support library is disabled.");
} else if (VERSION.SDK_INT < 4) {
//Multidex最低支持的版本
throw new RuntimeException("Multi dex installation failed. SDK " + VERSION.SDK_INT + " is unsupported. Min SDK version is " + 4 + ".");
} else {
try {
/***部分代码省略***/
//多线程锁
synchronized(installedApk) {
//apkPath = data/data/com.xxx.xxx/
String apkPath = applicationInfo.sourceDir;
if (installedApk.contains(apkPath)) {
return;
}
installedApk.add(apkPath);
/***部分代码省略***/
//清除 /data/data/com.xxx.xxx/files/secondary-dexes 目录下的文件
try {
clearOldDexDir(context);
} catch (Throwable var8) {
Log.w("MultiDex", "Something went wrong when trying to clear old MultiDex extraction, continuing without cleaning.", var8);
}
//data/data/com.xxx.xxx/code_cache/secondary-dexes
File dexDir = new File(applicationInfo.dataDir, SECONDARY_FOLDER_NAME);
//解压apk，获得dex的zip文件列表
List<File> files = MultiDexExtractor.load(context, applicationInfo, dexDir, false);
//校验zip文件
if (checkValidZipFiles(files)) {
//安装dex文件
installSecondaryDexes(loader, dexDir, files);
} else {
//校验失败，重新执行解压（解压失败直接抛出异常）和安装
Log.w("MultiDex", "Files were not valid zip files. Forcing a reload.");
files = MultiDexExtractor.load(context, applicationInfo, dexDir, true);
if (!checkValidZipFiles(files)) {
throw new RuntimeException("Zip files were not valid.");
}
installSecondaryDexes(loader, dexDir, files);
}
}
}
/***部分代码省略***/
}
}
Multidex获取dex文件
加载dex文件
/**
* @param context
* @param applicationInfo
* @param dexDir /data/data/com.xxx.xxx/code_cache/secondary-dexes/
* @param forceReload 是否强制重新加载
* @return 包含dex的zip文件列表
* @throws IOException
* if an error occurs when writing the file.
*/
static List<File> load(Context context, ApplicationInfo applicationInfo, File dexDir, boolean forceReload) throws IOException {
//data/data/com.xxx.xxx/
File sourceApk = new File(applicationInfo.sourceDir);
//apk的循环冗余校验码
long currentCrc = getZipCrc(sourceApk);
List files;
//是否强制执行reload和是否已经解压过apk
if (!forceReload && !isModified(context, sourceApk, currentCrc)) {
try {
//是否已存在zip文件
files = loadExistingExtractions(context, sourceApk, dexDir);
} catch (IOException var9) {
files = performExtractions(sourceApk, dexDir);
putStoredApkInfo(context, getTimeStamp(sourceApk), currentCrc, files.size() + 1);
}
} else {
//获取apk中的classes2.dex并且压缩为zip文件
files = performExtractions(sourceApk, dexDir);
//存储当前apk的信息，作为下次有效缓存的明证
putStoredApkInfo(context, getTimeStamp(sourceApk), currentCrc, files.size() + 1);
}
return files;
}
/**
* @param context
* @param timeStamp apk的最后一次修改时间
* @param crc apk的循环冗余校验码
* @param totalDexNumber apk中一共有几个dex
*/
private static void putStoredApkInfo(Context context, long timeStamp, long crc, int totalDexNumber) {
SharedPreferences prefs = getMultiDexPreferences(context);
Editor edit = prefs.edit();
edit.putLong("timestamp", timeStamp);
edit.putLong("crc", crc);
edit.putInt("dex.number", totalDexNumber);
apply(edit);
}
获取已经存在的dex的压缩包
/**
* @param context
* @param dexDir /data/data/com.xxx.xxx/code_cache/secondary-dexes/
* @param sourceApk data/app/com.xxx.xxx-1.apk
* @return 包含dex的zip文件列表
* @throws IOException
* if an error occurs when writing the file.
*/
private static List<File> loadExistingExtractions(Context context, File sourceApk, File dexDir) throws IOException {
//extractedFilePrefix = com.xxx.xxx.apk.classes
String extractedFilePrefix = sourceApk.getName() + ".classes";
//totalDexNumber=apk中dex的数量
int totalDexNumber = getMultiDexPreferences(context).getInt("dex.number", 1);
List<File> files = new ArrayList(totalDexNumber);
//主dex已经加载过了，加载class2.dex,class3.dex......
for(int secondaryNumber = 2; secondaryNumber <= totalDexNumber; ++secondaryNumber) {
//fileName = com.xxx.xxx.apk.classes2.zip
String fileName = extractedFilePrefix + secondaryNumber + ".zip";
//extractedFile = data/data/com.xxx.xxx/code_cache/secondary-dexes/com.wuba.bangjob-1.apk.classes2.zip
File extractedFile = new File(dexDir, fileName);
if (!extractedFile.isFile()) {
throw new IOException("Missing extracted secondary dex file '" + extractedFile.getPath() + "'");
}
files.add(extractedFile);
//校验zip文件是否完整
if (!verifyZipFile(extractedFile)) {
Log.i("MultiDex", "Invalid zip file: " + extractedFile);
throw new IOException("Invalid ZIP file.");
}
}
return files;
}
生成dex的压缩zip文件
/**
* @param sourceApk data/app/com.xxx.xxx-1.apk
* @param dexDir /data/data/com.xxx.xxx/code_cache/secondary-dexes/
* @return 包含dex的zip文件列表
* @throws IOException
* if an error occurs when writing the file.
*/
private static List<File> performExtractions(File sourceApk, File dexDir) throws IOException {
//extractedFilePrefix = com.xxx.xxx.apk.classes
String extractedFilePrefix = sourceApk.getName() + ".classes";
//删除data/data/com.xxx.xxx/code_cache/secondary-dexes/目录下的文件
prepareDexDir(dexDir, extractedFilePrefix);
List<File> files = new ArrayList();
ZipFile apk = new ZipFile(sourceApk);
try {
//从class2.dex开始
int secondaryNumber = 2;
for(ZipEntry dexFile = apk.getEntry("classes" + secondaryNumber + ".dex"); dexFile != null; dexFile = apk.getEntry("classes" + secondaryNumber + ".dex")) {
//fileName = com.xxx.xxx.apk.classes2.zip
String fileName = extractedFilePrefix + secondaryNumber + ".zip";
File extractedFile = new File(dexDir, fileName);
files.add(extractedFile);
//最多三次尝试生成dex的zip文件
int numAttempts = 0;
//标识是否生成dex的zip文件
boolean isExtractionSuccessful = false;
while(numAttempts < 3 && !isExtractionSuccessful) {
++numAttempts;
extract(apk, dexFile, extractedFile, extractedFilePrefix);
//校验压缩文件是否完整，否则删除重来
isExtractionSuccessful = verifyZipFile(extractedFile);
if (!isExtractionSuccessful) {
extractedFile.delete();
if (extractedFile.exists()) {
Log.w("MultiDex", "Failed to delete corrupted secondary dex '" + extractedFile.getPath() + "'");
}
}
}
if (!isExtractionSuccessful) {
throw new IOException("Could not create zip file " + extractedFile.getAbsolutePath() + " for secondary dex (" + secondaryNumber + ")");
}
++secondaryNumber;
}
}/***部分代码省略***/
return files;
}
将classes2.dex放入zip文件中
/**
* @param apk apk的压缩包
* @param dexFile apk中的classes2.dex文件
* @param extractTo /data/data/com.xxx.xxx/code_cache/secondary-dexes/com.xxx.xxx.apk.classes2.zip
* @param extractedFilePrefix com.wuba.bangjob-1.apk.classes
* @throws IOException
* if an error occurs when writing the file.
*/
private static void extract(ZipFile apk, ZipEntry dexFile, File extractTo, String extractedFilePrefix) throws IOException, FileNotFoundException {
InputStream in = apk.getInputStream(dexFile);
ZipOutputStream out = null;
///data/data/com.wuba.bangjob/code_cache/secondary-dexes/com.xxx.xxx.apk.classes1415547735.zip
File tmp = File.createTempFile(extractedFilePrefix, ".zip", extractTo.getParentFile());
try {
out = new ZipOutputStream(new BufferedOutputStream(new FileOutputStream(tmp)));
try {
//将classes2.dex进行压缩内容名称为classes.dex
ZipEntry classesDex = new ZipEntry("classes.dex");
classesDex.setTime(dexFile.getTime());
out.putNextEntry(classesDex);
byte[] buffer = new byte[16384];
for(int length = in.read(buffer); length != -1; length = in.read(buffer)) {
out.write(buffer, 0, length);
}
out.closeEntry();
} finally {
out.close();
}
//重命名文件为com.xxx.xxx.apk.classes2.zip
if (!tmp.renameTo(extractTo)) {
throw new IOException("Failed to rename \"" + tmp.getAbsolutePath() + "\" to \"" + extractTo.getAbsolutePath() + "\"");
}
}/***部分代码省略***/
}
dex文件的装载
将含有加载含有dex的压缩包进行夹杂，相关知识点参考：Android类加载之PathClassLoader和DexClassLoader。
为什么需要做版本的区分，就是因为版本见类加载的实现是有些差异的。
/**
* @param loader
* @param dexDir /data/data/xxx.xxx.xxx/code_cache/secondary-dexes/
* @param files dex的压缩zip文件
*/
private static void installSecondaryDexes(ClassLoader loader, File dexDir, List<File> files) throws IllegalArgumentException, IllegalAccessException, NoSuchFieldException, InvocationTargetException, NoSuchMethodException, IOException {
if (!files.isEmpty()) {
if (VERSION.SDK_INT >= 19) {//KitKat(19)
MultiDex.V19.install(loader, files, dexDir);
} else if (VERSION.SDK_INT >= 14) {//IceCreamSandwich(14,15),JellyBean(16,17,18)
MultiDex.V14.install(loader, files, dexDir);
} else {
MultiDex.V4.install(loader, files);
}
}
}
Android类加载之PathClassLoader和DexClassLoader 这篇文章将的是VERSION.SDK_INT >= 19 那么我们先看看第一个case：
private static final class V19 {
private V19() {
}
/**
* @param loader PathClassLoader
* @param additionalClassPathEntries dex压缩包路径
* @param optimizedDirectory opt之后的dex文件目录
*/
private static void install(ClassLoader loader, List<File> additionalClassPathEntries, File optimizedDirectory) throws IllegalArgumentException, IllegalAccessException, NoSuchFieldException, InvocationTargetException, NoSuchMethodException {
//PathClassLoader的DexPathList类型变量pathList
Field pathListField = MultiDex.findField(loader, "pathList");
Object dexPathList = pathListField.get(loader);
ArrayList<IOException> suppressedExceptions = new ArrayList();
//进行dex的opt并合并dex的Element
MultiDex.expandFieldArray(dexPathList, "dexElements", makeDexElements(dexPathList, new ArrayList(additionalClassPathEntries), optimizedDirectory, suppressedExceptions));
//处理异常
if (suppressedExceptions.size() > 0) {
Iterator i$ = suppressedExceptions.iterator();
while(i$.hasNext()) {
IOException e = (IOException)i$.next();
Log.w("MultiDex", "Exception in makeDexElement", e);
}
//一直感觉Google源码这块有些问题，loader应该改为dexPathList。因为dexElementsSuppressedExceptions变量是属于DexPathList的成员
Field suppressedExceptionsField = MultiDex.findField(loader, "dexElementsSuppressedExceptions");
IOException[] dexElementsSuppressedExceptions = (IOException[])((IOException[])suppressedExceptionsField.get(loader));
if (dexElementsSuppressedExceptions == null) {
dexElementsSuppressedExceptions = (IOException[])suppressedExceptions.toArray(new IOException[suppressedExceptions.size()]);
} else {
IOException[] combined = new IOException[suppressedExceptions.size() + dexElementsSuppressedExceptions.length];
suppressedExceptions.toArray(combined);
System.arraycopy(dexElementsSuppressedExceptions, 0, combined, suppressedExceptions.size(), dexElementsSuppressedExceptions.length);
dexElementsSuppressedExceptions = combined;
}
suppressedExceptionsField.set(loader, dexElementsSuppressedExceptions);
}
}
//调用DexPathList的makeDexElements方法进行dex的opt
private static Object[] makeDexElements(Object dexPathList, ArrayList<File> files, File optimizedDirectory, ArrayList<IOException> suppressedExceptions) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {
Method makeDexElements = MultiDex.findMethod(dexPathList, "makeDexElements", ArrayList.class, File.class, ArrayList.class);
return (Object[])((Object[])makeDexElements.invoke(dexPathList, files, optimizedDirectory, suppressedExceptions));
}
}
19 > VERSION.SDK_INT >= 14的处理支持比VERSION.SDK_INT >= 19少了异常处理。是因为DexPathList的makeDexElements方法有了修改。
/**
* VERSION.SDK_INT >= 19
*/
private static Element[] makeDexElements(ArrayList<File> files, File optimizedDirectory,
ArrayList<IOException> suppressedExceptions);
/**
* 19 > VERSION.SDK_INT >= 14
*/
private static Element[] makeDexElements(ArrayList<File> files,File optimizedDirectory);
VERSION_SDK_INT < 14 的情况和前面的都不相同是因为PathClassLoader的是实现就不相同。。。。
/**
* VERSION.SDK_INT == 13
*/
public class PathClassLoader extends ClassLoader {
private final String path;
private final String libPath;
/*
* Parallel arrays for jar/apk files.
*
* (could stuff these into an object and have a single array;
* improves clarity but adds overhead)
*/
private final String[] mPaths;
private final File[] mFiles;
private final ZipFile[] mZips;
private final DexFile[] mDexs;
/***部分代码省略***/
}
apk解压结果预览
文章到这里就全部讲述完啦，若有其他需要交流的可以留言哦！！
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