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在本系列的第一篇中讲过，ARouter 可以通过扫描 dex 文件中 class 的全类名，来加载 compiler 生成的路由类。但这种方式影响性能，并且效率也不高。所以在 ARouter v1.3.0 之后的版本中，加入了自动注册的方式进行路由表的加载，自动注册可以缩短初始化时间，解决应用加固导致无法直接访问 dex 文件从而初始化失败的问题。
那么自动注册到底是什么东东，为什么有这么强大的能力呢？
那么接下来，我们就来分析分析。
预先需要了解的知识点：
自定义 gradle plugin
gradle transform api
使用 asm 实现字节码插桩
arouter-register
================
arouter-register 的入口就在 PluginLaunch
public class PluginLaunch implements Plugin<Project> { @Override
public void apply(Project project) {
def isApp = project.plugins.hasPlugin(AppPlugin) //only application module needs this plugin to generate register code
if (isApp) {
Logger.make(project)
Logger.i('Project enable arouter-register plugin')
def android = project.extensions.getByType(AppExtension)
def transformImpl = new RegisterTransform(project) //init arouter-auto-register settings
ArrayList<ScanSetting> list = new ArrayList<>(3)
list.add(new ScanSetting('IRouteRoot'))
list.add(new ScanSetting('IInterceptorGroup'))
list.add(new ScanSetting('IProviderGroup'))
RegisterTransform.registerList = list //register this plugin
android.registerTransform(transformImpl)
}
}
}从上面的代码可知：
只在 application module （一般都是 app module）生成自动注册的代码；
初始化了自动注册的设置，这样自动注册就知道需要注册 IRouteRoot IInterceptorGroup IProviderGroup 这三者；
注册 RegisterTransform ，字节码插桩将在 RegisterTransform 中完成；
可以看出，重点就在 RegisterTransform 里面。那我们重点就关注下 RegisterTransform 的代码，这里就贴出 transform 方法的源码了。（关于 Transform 的 InputTypes 和 Scopes 知识点在这就不讲了，如有需要了解的同学可以看 Android 热修复使用Gradle Plugin1.5改造Nuwa插件）
class RegisterTransform extends Transform {@Overridevoid transform(Context context, Collection<TransformInput> inputs
, Collection<TransformInput> referencedInputs
, TransformOutputProvider outputProvider
, boolean isIncremental) throws IOException, TransformException, InterruptedException {
Logger.i('Start scan register info in jar file.') long startTime = System.currentTimeMillis() boolean leftSlash = File.separator == '/'
inputs.each { TransformInput input -> // 扫描所有的 jar 文件
input.jarInputs.each { JarInput jarInput ->
String destName = jarInput.name // rename jar files
def hexName = DigestUtils.md5Hex(jarInput.file.absolutePath) if (destName.endsWith(".jar")) {
destName = destName.substring(0, destName.length() - 4)
} // 输入的 jar 文件
File src = jarInput.file // 输出的 jar 文件
File dest = outputProvider.getContentLocation(destName + "_" + hexName, jarInput.contentTypes, jarInput.scopes, Format.JAR) // 扫描 jar 文件，查找实现 IRouteRoot IInterceptorGroup IProviderGroup 接口的类，并且找到 LogisticsCenter 在哪个 jar 文件中
// 不扫描 com.android.support 开头的 jar
if (ScanUtil.shouldProcessPreDexJar(src.absolutePath)) { // ScanUtil.scanJar 的代码就不详细展开了，感兴趣的同学可以自己去看下
ScanUtil.scanJar(src, dest)
}
FileUtils.copyFile(src, dest)
} // 扫描所有的 class 文件，查找实现 IRouteRoot IInterceptorGroup IProviderGroup 接口的类
// 和扫描 jar 做差不多类似的工作。不同的点就是不用再去找 LogisticsCenter 类
input.directoryInputs.each { DirectoryInput directoryInput ->
File dest = outputProvider.getContentLocation(directoryInput.name, directoryInput.contentTypes, directoryInput.scopes, Format.DIRECTORY)
String root = directoryInput.file.absolutePath if (!root.endsWith(File.separator))
root += File.separator
directoryInput.file.eachFileRecurse { File file ->
def path = file.absolutePath.replace(root, '') if (!leftSlash) {
path = path.replaceAll("\\\\", "/")
} // 只处理 com/alibaba/android/arouter/routes/ 开头的 class
if(file.isFile() && ScanUtil.shouldProcessClass(path)){
ScanUtil.scanClass(file)
}
} // copy to dest
FileUtils.copyDirectory(directoryInput.file, dest)
}
}
Logger.i('Scan finish, current cost time ' + (System.currentTimeMillis() - startTime) + "ms") // 这里开始字节码插桩操作
if (fileContainsInitClass) { // 遍历之前找的 IRouteRoot IInterceptorGroup IProviderGroup
registerList.each { ext ->
Logger.i('Insert register code to file ' + fileContainsInitClass.absolutePath) if (ext.classList.isEmpty()) {
Logger.e("No class implements found for interface:" + ext.interfaceName)
} else {
ext.classList.each {
Logger.i(it)
} // 对 LogisticsCenter.class 做字节码插桩
RegisterCodeGenerator.insertInitCodeTo(ext)
}
}
}
Logger.i("Generate code finish, current cost time: " + (System.currentTimeMillis() - startTime) + "ms")
}
}上面代码的逻辑很清晰，按照之前设置好的 IRouteRoot IInterceptorGroup IProviderGroup 这三个接口，然后扫描整个项目的代码，分别找到这三者各自的实现类，然后加入到集合中。最后在 LogisticsCenter 中实现字节码插桩。
我们来详细看下 RegisterCodeGenerator.insertInitCodeTo(ext) 的代码
static void insertInitCodeTo(ScanSetting registerSetting) { if (registerSetting != null && !registerSetting.classList.isEmpty()) {
RegisterCodeGenerator processor = new RegisterCodeGenerator(registerSetting) // RegisterTransform.fileContainsInitClass 就是包含了 LogisticsCenter.class 的那个 jar 文件
File file = RegisterTransform.fileContainsInitClass if (file.getName().endsWith('.jar')) // 开始处理
processor.insertInitCodeIntoJarFile(file)
}
}插入的操作在 insertInitCodeIntoJarFile 中实现。
private File insertInitCodeIntoJarFile(File jarFile) { if (jarFile) {
def optJar = new File(jarFile.getParent(), jarFile.name + ".opt") if (optJar.exists())
optJar.delete()
def file = new JarFile(jarFile)
Enumeration enumeration = file.entries()
JarOutputStream jarOutputStream = new JarOutputStream(new FileOutputStream(optJar)) // 遍历 jar 文件中的 class
while (enumeration.hasMoreElements()) {
JarEntry jarEntry = (JarEntry) enumeration.nextElement()
String entryName = jarEntry.getName()
ZipEntry zipEntry = new ZipEntry(entryName)
InputStream inputStream = file.getInputStream(jarEntry)
jarOutputStream.putNextEntry(zipEntry) // 如果是 LogisticsCenter.class 的话
if (ScanSetting.GENERATE_TO_CLASS_FILE_NAME == entryName) {
Logger.i('Insert init code to class >> ' + entryName) // 插桩操作
def bytes = referHackWhenInit(inputStream)
jarOutputStream.write(bytes)
} else {
jarOutputStream.write(IOUtils.toByteArray(inputStream))
}
inputStream.close()
jarOutputStream.closeEntry()
}
jarOutputStream.close()
file.close() // 把字节码插桩的 jar 替换掉原来旧的 jar 文件
if (jarFile.exists()) {
jarFile.delete()
}
optJar.renameTo(jarFile)
} return jarFile
}字节码插桩的代码还在 referHackWhenInit 方法中。
//refer hack class when object initprivate byte[] referHackWhenInit(InputStream inputStream) {
ClassReader cr = new ClassReader(inputStream)
ClassWriter cw = new ClassWriter(cr, 0)
ClassVisitor cv = new MyClassVisitor(Opcodes.ASM5, cw)
cr.accept(cv, ClassReader.EXPAND_FRAMES) return cw.toByteArray()
}class MyClassVisitor extends ClassVisitor {
MyClassVisitor(int api, ClassVisitor cv) { super(api, cv)
} void visit(int version, int access, String name, String signature,
String superName, String[] interfaces) { super.visit(version, access, name, signature, superName, interfaces)
} @Override
MethodVisitor visitMethod(int access, String name, String desc,
String signature, String[] exceptions) {
MethodVisitor mv = super.visitMethod(access, name, desc, signature, exceptions) // 对 loadRouterMap 这个方法进行代码插入
if (name == ScanSetting.GENERATE_TO_METHOD_NAME) {
mv = new RouteMethodVisitor(Opcodes.ASM5, mv)
} return mv
}
}class RouteMethodVisitor extends MethodVisitor {
RouteMethodVisitor(int api, MethodVisitor mv) { super(api, mv)
} @Override
void visitInsn(int opcode) { // 插入的代码在 return 之前
if ((opcode >= Opcodes.IRETURN && opcode <= Opcodes.RETURN)) {
extension.classList.each { name ->
name = name.replaceAll("/", ".")
mv.visitLdcInsn(name)//这里的name就是之前扫描出来的 IRouteRoot IInterceptorGroup IProviderGroup 实现类名
// 生成 LogisticsCenter.register(name) 代码
mv.visitMethodInsn(Opcodes.INVOKESTATIC
, ScanSetting.GENERATE_TO_CLASS_NAME
, ScanSetting.REGISTER_METHOD_NAME
, "(Ljava/lang/String;)V"
, false)
}
} super.visitInsn(opcode)
} @Override
void visitMaxs(int maxStack, int maxLocals) { super.visitMaxs(maxStack + 4, maxLocals)
}
}最终，生成的代码会像下面所示：
private static void loadRouterMap() {
registerByPlugin = false; //auto generate register code by gradle plugin: arouter-auto-register
// looks like below:
register("com.alibaba.android.arouter.routes.ARouter$$Root$$app");
register("com.alibaba.android.arouter.routes.ARouter$$Interceptors$$app");
register("com.alibaba.android.arouter.routes.ARouter$$Group$$arouter");
}那么顺便来跟踪一下 register 方法的代码，看看里面是如何完成路由表注册的。
private static void register(String className) { if (!TextUtils.isEmpty(className)) { try {
Class<?> clazz = Class.forName(className);
Object obj = clazz.getConstructor().newInstance(); if (obj instanceof IRouteRoot) {
registerRouteRoot((IRouteRoot) obj);
} else if (obj instanceof IProviderGroup) {
registerProvider((IProviderGroup) obj);
} else if (obj instanceof IInterceptorGroup) {
registerInterceptor((IInterceptorGroup) obj);
} else {
logger.info(TAG, "register failed, class name: " + className
+ " should implements one of IRouteRoot/IProviderGroup/IInterceptorGroup.");
}
} catch (Exception e) {
logger.error(TAG,"register class error:" + className);
}
}
}// 注册 IRouteRoot 类型private static void registerRouteRoot(IRouteRoot routeRoot) {
markRegisteredByPlugin(); if (routeRoot != null) {
routeRoot.loadInto(Warehouse.groupsIndex);
}
}// 注册 IInterceptorGroup 类型private static void registerInterceptor(IInterceptorGroup interceptorGroup) {
markRegisteredByPlugin(); if (interceptorGroup != null) {
interceptorGroup.loadInto(Warehouse.interceptorsIndex);
}
}// 注册 IProviderGroup 类型private static void registerProvider(IProviderGroup providerGroup) {
markRegisteredByPlugin(); if (providerGroup != null) {
providerGroup.loadInto(Warehouse.providersIndex);
}
}// 标记通过gradle plugin完成自动注册private static void markRegisteredByPlugin() { if (!registerByPlugin) {
registerByPlugin = true;
}
}这样相比之下，自动注册的方式确实比扫描 dex 文件更高效，扫描 dex 文件是在 app 运行时操作的，这样会影响 app 的性能，对用户造成不好的体验。而自动注册是在 build 的时候完成字节码插桩的，对运行时不产生影响。
学了今天这招，以后 compiler 生成的代码需要注册的步骤都可以通过自动注册来完成了，赞一个
番外
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之前看到自动注册这么神奇，所以想看下插入字节码之后 LogisticsCenter 代码的效果，所以反编译了一下 ARouter demo apk，可以看到 LogisticsCenter.smali 的 loadRouterMap 方法：
.method private static loadRouterMap()V .locals 1 .line 64 const/4 v0, 0x0 sput-boolean v0, Lcom/alibaba/android/arouter/core/LogisticsCenter;->registerByPlugin:Z .line 69 const-string v0, "com.alibaba.android.arouter.routes.ARouter$$Root$$modulejava" invoke-static {v0}, Lcom/alibaba/android/arouter/core/LogisticsCenter;->register(Ljava/lang/String;)V const-string v0, "com.alibaba.android.arouter.routes.ARouter$$Root$$modulekotlin" invoke-static {v0}, Lcom/alibaba/android/arouter/core/LogisticsCenter;->register(Ljava/lang/String;)V const-string v0, "com.alibaba.android.arouter.routes.ARouter$$Root$$arouterapi" invoke-static {v0}, Lcom/alibaba/android/arouter/core/LogisticsCenter;->register(Ljava/lang/String;)V const-string v0, "com.alibaba.android.arouter.routes.ARouter$$Root$$app" invoke-static {v0}, Lcom/alibaba/android/arouter/core/LogisticsCenter;->register(Ljava/lang/String;)V const-string v0, "com.alibaba.android.arouter.routes.ARouter$$Interceptors$$modulejava" invoke-static {v0}, Lcom/alibaba/android/arouter/core/LogisticsCenter;->register(Ljava/lang/String;)V const-string v0, "com.alibaba.android.arouter.routes.ARouter$$Interceptors$$app" invoke-static {v0}, Lcom/alibaba/android/arouter/core/LogisticsCenter;->register(Ljava/lang/String;)V const-string v0, "com.alibaba.android.arouter.routes.ARouter$$Providers$$modulejava" invoke-static {v0}, Lcom/alibaba/android/arouter/core/LogisticsCenter;->register(Ljava/lang/String;)V const-string v0, "com.alibaba.android.arouter.routes.ARouter$$Providers$$modulekotlin" invoke-static {v0}, Lcom/alibaba/android/arouter/core/LogisticsCenter;->register(Ljava/lang/String;)V const-string v0, "com.alibaba.android.arouter.routes.ARouter$$Providers$$arouterapi" invoke-static {v0}, Lcom/alibaba/android/arouter/core/LogisticsCenter;->register(Ljava/lang/String;)V const-string v0, "com.alibaba.android.arouter.routes.ARouter$$Providers$$app" invoke-static {v0}, Lcom/alibaba/android/arouter/core/LogisticsCenter;->register(Ljava/lang/String;)V return-void.end method
作者：俞其荣
链接：https://www.jianshu.com/p/8ad636fbfcc6