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MainDexList产生过程源码分析

2016-06-28 | Comments

0x00 前言

之前的两篇文章分别分析了 MultiDex的编译及Dex过程MultiDex的安装过程

一个讲解了MultiDex的编译及Dex分包过程,我们知道了主dex是由maindexlist.txt决定的。

一个讲解了MultiDex中多个dex是怎么安装到程序中,让程序得以正常运行的。

本文重点讲解maindexlist.txt是怎么产生的。

0x01 源码分析

对于一个使用了MultiDex的Android工程,编译后在/build/intermediates/multi-dex/{variant_path}/路径下面,可以看到如下几个文件。

  • componentClasses.jar
  • components.flags
  • manifest_keep.txt
  • maindexlist.txt

这几个文件决定了主Dex中的该放哪些类。

下面依次对这几个文件的产生过程进行分析。

1.CreateMainDexList

这小节讲的是maindexlist.txt的产生逻辑。

调用顺序为:

(1)/build-system/gradle-core/src/main/groovy/com/android/build/gradle/internal/tasks/multidex/CreateMainDexList.groovy -> output()

(2)/build-system/builder/src/main/java/com/android/builder/core/AndroidBuilder.java -> createMainDexList(allClassesJarFile, jarOfRoots)

(3)/dalvik/dx/src/com/android/multidex/ClassReferenceListBuilder.java -> addRoots(ZipFile jarOfRoots)

源码如下:

//build-system/gradle-core/src/main/groovy/com/android/build/gradle/internal/tasks/multidex/CreateMainDexList.groovy
@Override
void execute(CreateMainDexList createMainDexList) {
    createMainDexList.androidBuilder = scope.globalScope.androidBuilder
    createMainDexList.setVariantName(scope.getVariantConfiguration().getFullName())

    def files = inputFiles
    createMainDexList.allClassesJarFile = files.call().first()
    ConventionMappingHelper.map(createMainDexList, "componentsJarFile") {
        scope.getProguardComponentsJarFile()
    }
    createMainDexList.mainDexListFile = scope.manifestKeepListFile
    createMainDexList.outputFile = scope.getMainDexListFile()
}

@TaskAction
void output() {
    if (getAllClassesJarFile() == null) {
        throw new NullPointerException("No input file")
    }

    // manifest components plus immediate dependencies must be in the main dex.
    File _allClassesJarFile = getAllClassesJarFile()
    Set<String> mainDexClasses = callDx(_allClassesJarFile, getComponentsJarFile())

    // add additional classes specified via a jar file.
    File _includeInMainDexJarFile = getIncludeInMainDexJarFile()
    if (_includeInMainDexJarFile != null) {
        mainDexClasses.addAll(callDx(_allClassesJarFile, _includeInMainDexJarFile))
    }

    if (mainDexListFile != null) {
        Set<String> mainDexList = new HashSet<String>(Files.readLines(mainDexListFile, Charsets.UTF_8))
        mainDexClasses.addAll(mainDexList)
    }

    String fileContent = Joiner.on(System.getProperty("line.separator")).join(mainDexClasses)

    Files.write(fileContent, getOutputFile(), Charsets.UTF_8)
}

CreateMainDexList中涉及到如下几个成员变量:

  • @InputFile allClassesJarFile: /build/intermediates/multi-dex/{variant_path}/allclasses.jar
  • @InputFile componentsJarFile: /build/intermediates/multi-dex/{variant_path}/componentClasses.jar
  • @OutputFile outputFile: /build/intermediates/multi-dex/{variant_path}/maindexlist.txt
  • @InputFile includeInMainDexJarFile: 额外指定的Jar包
  • @InputFile mainDexListFile: /build/intermediates/multi-dex/{variant_path}/manifest_keep.txt

这些参数来源于:

/build-system/gradle-core/src/main/groovy/com/android/build/gradle/internal/scope/VariantScope.java

通过分析componentClasses.jar和额外指定的Jar包includeInMainDexJarFile中的Class,从allClassesJarFile中找出前面Class直接或间接引用到的Class,然后加上manifest_keep.txt中keep住的类一起作为maindexlist.txt的内容。将maindexlist.txt里的Class进行Dex操作就产生了classes.dex。

参考网上一些文章以及变量命名,allClassesJarFile代表的应该是包含了所有class的一个Jar包,路径应该是/build/intermediates/multi-dex/{variant_path}/allclasses.jar,然而我在项目下并没发现该文件。

类引用关系的实现,可参考: /dalvik/dx/src/com/android/multidex/ClassReferenceListBuilder.java中的 addRoots(ZipFile jarOfRoots)

关于componentClasses.jar,我理解的是,产生maindexlist.txt的根jar包(jarOfRoots),就像GC操作的Root一样,关于其产生过程,文章后面进行了分析。

更上一层的调用入口是

/build-system/gradle-core/src/main/groovy/com/android/build/gradle/internal/scope/TaskManager.java -> createPostCompilationTasks()

2.CreateManifestKeepList

这小节讲的是manifest_keep.txt的产生逻辑。

调用顺序为:

/build-system/gradle-core/src/main/groovy/com/android/build/gradle/internal/tasks/multidex/CreateManifestKeepList.groovy -> execute() -> generateKeepListFromManifest()

源码如下:

@Override
void execute(CreateManifestKeepList manifestKeepListTask) {
        manifestKeepListTask.setVariantName(scope.getVariantConfiguration().getFullName())

        // since all the output have the same manifest, besides the versionCode,
        // we can take any of the output and use that.
        final BaseVariantOutputData output = scope.variantData.outputs.get(0)
        ConventionMappingHelper.map(manifestKeepListTask, "manifest") {
            output.getScope().getManifestOutputFile()
        }

        manifestKeepListTask.proguardFile = scope.variantConfiguration.getMultiDexKeepProguard()
        manifestKeepListTask.outputFile = scope.getManifestKeepListFile();

        //variant.ext.collectMultiDexComponents = manifestKeepListTask
    }
    
@TaskAction
void generateKeepListFromManifest() {
    SAXParser parser = SAXParserFactory.newInstance().newSAXParser()

    Writer out = new BufferedWriter(new FileWriter(getOutputFile()))
    try {
        parser.parse(getManifest(), new ManifestHandler(out))

        // add a couple of rules that cannot be easily parsed from the manifest.
        out.write(
            """-keep public class * extends android.app.backup.BackupAgent {
                <init>();
            }
            -keep public class * extends java.lang.annotation.Annotation {
                *;
            }
        """)

        if (proguardFile != null) {
            out.write(Files.toString(proguardFile, Charsets.UTF_8))
        }
    } finally {
        out.close()
    }
}

private static String DEFAULT_KEEP_SPEC = "{ <init>(); }"
private static Map<String, String> KEEP_SPECS = [
    'application'       : """{
                        <init>();
        void attachBaseContext(android.content.Context);
    }""",
    'activity'          : DEFAULT_KEEP_SPEC,
    'service'           : DEFAULT_KEEP_SPEC,
    'receiver'          : DEFAULT_KEEP_SPEC,
    'provider'          : DEFAULT_KEEP_SPEC,
    'instrumentation'   : DEFAULT_KEEP_SPEC,
]

private class ManifestHandler extends DefaultHandler {
    private Writer out

    ManifestHandler(Writer out) {
        this.out = out
    }

    @Override
    void startElement(String uri, String localName, String qName, Attributes attr) {
        String keepSpec = (String)CreateManifestKeepList.KEEP_SPECS[qName]
        if (keepSpec) {

            boolean keepIt = true
            if (CreateManifestKeepList.this.filter) {
                // for ease of use, turn 'attr' into a simple map
                Map<String, String> attrMap = [:]
                for (int i = 0; i < attr.getLength(); i++) {
                    attrMap[attr.getQName(i)] = attr.getValue(i)
                }
                keepIt = CreateManifestKeepList.this.filter(qName, attrMap)
            }

            if (keepIt) {
                out.write((String)"-keep class ${attr.getValue('android:name')} $keepSpec\n")
            }
        }
    }
}

CreateMainDexList中涉及到如下几个成员变量:

  • @InputFile manifest: /build/intermediates/manifests/full/{variant_path}/AndroidManifest.xml
  • @OutputFile outputFile: /build/intermediates/multi-dex/{variant_path}/manifest_keep.txt
  • @InputFile proguardFile

生成manifest_keep.txt的过程是:

遍历并解析/build/intermediates/manifests/full/{variant_path}/AndroidManifest.xml文件,将其中application, activity, service, receiver, provider和instrumentation等标签对应的组件类添加到manifest_keep.txt文件中。

具体解析规则如下:

对于application,keepSpec为

{
    <init>();
    void attachBaseContext(android.content.Context);
}

对于activity, service, receiver, provider和instrumentation,keepSpec为

{ <init>(); }

遍历/build/intermediates/manifests/full/{variant_path}/AndroidManifest.xml中注册的组件,针对每个组件,解析其对应的attr属性,将属性列表转换成Map形式。然后根据-keep class ${attr.getValue('android:name')} $keepSpec\n格式生成对应的keep语句,以activity为例,其keep语句为-keep class ***package.***Activity.class { <init>(); }\n,依次将keep语句写到manifest_keep.txt中。

此外还需增加下面语句:

-keep public class * extends android.app.backup.BackupAgent {
    <init>();
}
-keep public class * extends java.lang.annotation.Annotation {
    *;
}

因此manifest_keep.txt中的内容为AndroidManifest.xml中注册的Application、四大组件、Instrumentation、BackupAgent和Annotation对应的类。有心的同学可以去Android项目验证下是否确实如此。manifest_keep.txt文件中的类是不能混淆的。

3.ProGuard混淆和components.flags

这小节讲的是Proguard混淆和components.flags的产生逻辑。

调用顺序为:

(1)/build-system/gradle-core/src/main/groovy/com/android/build/gradle/internal/TaskManager.java -> createPostCompilationTasks(TaskFactory, VariantScope)

(2)/build-system/gradle-core/src/main/groovy/com/android/build/gradle/tasks/factory/ProGuardTaskConfigAction.java -> execute()

(3)/external/proguard/src/proguard/gradle/ProGuardTask.java -> proguard() -> getConfiguration()

(4)/external/proguard/src/proguard/ProGuard.java

(5)/external/proguard/src/proguard/Configuration.java; /external/proguard/src/proguard/ConfigurationParser.java

源码如下:

//build-system/gradle-core/src/main/groovy/com/android/build/gradle/tasks/factory/ProGuardTaskConfigAction.java
@Override
public void execute(ProGuardTask proguardComponentsTask) {
    proguardComponentsTask.dontobfuscate();
    proguardComponentsTask.dontoptimize();
    proguardComponentsTask.dontpreverify();
    proguardComponentsTask.dontwarn();
    proguardComponentsTask.forceprocessing();

    try {
        proguardComponentsTask.configuration(scope.getManifestKeepListFile());

        proguardComponentsTask.libraryjars(new Callable<File>() {
            @Override
            public File call() throws Exception {
                Preconditions.checkNotNull(
                        scope.getGlobalScope().getAndroidBuilder().getTargetInfo());
                File shrinkedAndroid = new File(
                        scope.getGlobalScope().getAndroidBuilder().getTargetInfo()
                                .getBuildTools()
                                .getLocation(),
                        "lib" + File.separatorChar + "shrinkedAndroid.jar");

                // TODO remove in 1.0
                // STOPSHIP
                if (!shrinkedAndroid.isFile()) {
                    shrinkedAndroid = new File(
                            scope.getGlobalScope().getAndroidBuilder().getTargetInfo()
                                    .getBuildTools().getLocation(),
                            "multidex" + File.separatorChar + "shrinkedAndroid.jar");
                }

                return shrinkedAndroid;
            }
        });

        proguardComponentsTask.injars(new Callable<File>() {
            @Override
            public File call() throws Exception {
                return inputFiles.call().iterator().next();
            }
        });

        proguardComponentsTask.outjars(scope.getProguardComponentsJarFile());

        proguardComponentsTask.printconfiguration(
                scope.getGlobalScope().getBuildDir() + "/" + FD_INTERMEDIATES
                        + "/multi-dex/" + scope.getVariantConfiguration().getDirName()
                        + "/components.flags");
    } catch (ParseException e) {
        throw new RuntimeException(e);
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}

//external/proguard/src/proguard/gradle/ProGuardTask.java
@TaskAction
public void proguard()
throws ParseException, IOException
{
    // Let the logging manager capture the standard output and errors from
    // ProGuard.
    LoggingManager loggingManager = getLogging();
    loggingManager.captureStandardOutput(LogLevel.INFO);
    loggingManager.captureStandardError(LogLevel.WARN);

    // Run ProGuard with the collected configuration.
    new ProGuard(getConfiguration()).execute();

}

针对混淆ProGuard,先进行如下配置:

  • 添加dontobfuscate
  • 添加dontoptimize
  • 添加dontpreverify
  • 添加dontwarn
  • 添加forceprocessing
  • 添加配置文件manifest_keep.txt
  • 添加libraryjars: 如/Users/wangxinghe/Library/Android/sdk/build-tools/23.0.1/lib/shrinkedAndroid.jar
  • 添加injars: /build/intermediates/transforms/jarMerging/{variant_path}/jars/1/1f/combined.jar
  • 添加outjars: /build/intermediates/multi-dex/{variant_path}/componentClasses.jar
  • 添加配置输出文件printConfiguration: /build/intermediates/multi-dex/{variant_path}/components.flags

然后调用/external/proguard/src/proguard/gradle/ProGuardTask.java->getConfiguration()方法,通过/external/proguard/src/proguard/ConfigurationParser.java解析以上配置,得到/external/proguard/src/proguard/Configuration.java实例。

然后调用/external/proguard/src/proguard/ProGuard.java->execute()方法,根据上面得到的Configuration实例配置,进行具体的ProGuard操作,同时将相关配置写到/build/intermediates/multi-dex/{variant_path}/components.flags文件中。

关于componentClasses.jar的生成,根据components.flags文件的描述,我个人理解的是,是由manifest_keep.txt文件和通过JarMergingTask任务生成的combined.jar文件产生的。至于combined.jar怎么产生的,根据前两篇文章关于jar的ZipEntry源码分析经验,将combined.jar扩展名改为.zip并解压后,发现是一个所有类及R合并后的class集合。

0x02 总结

理解有偏差的地方,多多指教~

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