ARouter源码分析上

2021-08-04 本文已影响0人就叫汉堡吧

What is ARouter
```
A framework for assisting in the renovation of Android app componentization
```
官方介绍只有简短的一句话总结，一套协助Android app组件化革新的框架。
Why to use it

即便是组件化，我们其实也可以用startActivity的方式来进行跳转，那ARouter又有何特殊之处呢？
1. 传统的方式，不管是url传参还是bundle传参都较为繁琐，需要把参数先设置到url或者bundle，然后在跳转页通过getIntent方法来获取传参，ARouter把这部分工作封装了起来。通过链式调用设置参数，通过Autowired注解获取参数。
2. 支持组件化，ARouter的组件化在于不需要module间相互依赖就可以互相跳转。
3. 支持interceptor，可以通过interceptor做一些跳转前的逻辑，比如需要登录状态才能访问的页面。
4. 支持依赖注入，通过AOP思想把注解映射成路由类。
5. 支持Instant Run方式编译的apk。
6. 支持MultiDex。
7. 支持业务类Service，通过Route和Autowired注解和Service类联系起来。

How to use it & Why it work

依赖

每一个需要使用ARouter的module下的build.gradle中添加下面配置（可以把这块抽出来，通过apply from: '../xx.gradle'去引用）：

//如果含有kotlin代码，需要添加一下kotlin plugin
apply plugin: 'kotlin-kapt'

//使用ARouter auto-register自动扫描路由信息，非必选，通过gradle注册，性能更优
apply plugin: 'com.alibaba.arouter'

android {
    defaultConfig {
        ...
        javaCompileOptions {
            annotationProcessorOptions {
                arguments = [AROUTER_MODULE_NAME: project.getName()]
            }
        }
    }
}

//使用ARouter auto-register自动扫描路由信息，非必选，通过gradle注册，性能更优
buildscript {
    repositories {
        jcenter()
    }

    dependencies {
        //ARouter auto-register，Replace with the latest versios
        classpath "com.alibaba:arouter-register:?"
    }
}

//如果是包含kotlin类的路由，需要添加下面代码
kapt {
    arguments {
        arg("AROUTER_MODULE_NAME", project.getName())
    }
}

dependencies {
    // Replace with the latest version
    //使用api继承依赖，不需要每个module都添加
    api 'com.alibaba:arouter-api:?'
    //这个不能使用api依赖继承，所以每个module都要添加
    annotationProcessor 'com.alibaba:arouter-compiler:?'
    //如果是kotlin，需要添加kotlin编译jar包
    kapt 'com.alibaba:arouter-compiler:?'
    ...
}

两种加载方式

通过Route、Autowired、Interceptor等ARouter注解修饰的类需要被加载到一些Map中，这些Map被放在Warehouse类中：

class Warehouse {
    // Cache route and metas
    static Map<String, Class<? extends IRouteGroup>> groupsIndex = new HashMap<>();
    static Map<String, RouteMeta> routes = new HashMap<>();

    // Cache provider
    static Map<Class, IProvider> providers = new HashMap<>();
    static Map<String, RouteMeta> providersIndex = new HashMap<>();

    // Cache interceptor
    static Map<Integer, Class<? extends IInterceptor>> interceptorsIndex = new UniqueKeyTreeMap<>("More than one interceptors use same priority [%s]");
    static List<IInterceptor> interceptors = new ArrayList<>();

    static void clear() {
        routes.clear();
        groupsIndex.clear();
        providers.clear();
        providersIndex.clear();
        interceptors.clear();
        interceptorsIndex.clear();
    }
}

加载的方式有两种，一种是通过plugin来利用gradle的构建自动生成加载代码的方式加载，另一种是通过java代码手动扫描出含有这些注解的类，这也是初始化的两种方式，官方提倡使用register-plugin自动生成性能更好。

初始化

class MyApp : MultiDexApplication() {

    override fun onCreate() {
        super.onCreate()
        if(BuildConfig.DEBUG){
            ARouter.openLog()
            ARouter.openDebug()
        }
        ARouter.init(this)
    }
  
    override fun onTerminate() {
        super.onTerminate()
        ARouter.getInstance().destroy()
    }
}

为了app安全考虑，非debug版本下不要输出log和打开debug模式。

看一下ARouter的init方法做了什么：

/**
 * Init, it must be call before used router.
 */
public static void init(Application application) {
    if (!hasInit) {
        logger = _ARouter.logger;
        _ARouter.logger.info(Consts.TAG, "ARouter init start.");
        hasInit = _ARouter.init(application);

        if (hasInit) {
            _ARouter.afterInit();
        }

        _ARouter.logger.info(Consts.TAG, "ARouter init over.");
    }
}

可见，实际的工作都交给了一个叫_Arouter的类去做的，Arouter只是它的包装类。__ARouter的init方法返回hasInit标志是否已成功初始化：

protected static synchronized boolean init(Application application) {
    mContext = application;
    LogisticsCenter.init(mContext, executor);
    logger.info(Consts.TAG, "ARouter init success!");
    hasInit = true;
    mHandler = new Handler(Looper.getMainLooper());

    return true;
}

此处又调用了LogisticsCenter.init方法：

/**
 * LogisticsCenter init, load all metas in memory. Demand initialization
 */
public synchronized static void init(Context context, ThreadPoolExecutor tpe) throws HandlerException {
    mContext = context;
    executor = tpe;

    try {
        long startInit = System.currentTimeMillis();
        //billy.qi modified at 2017-12-06
        //load by plugin first
        loadRouterMap();
        if (registerByPlugin) {
            logger.info(TAG, "Load router map by arouter-auto-register plugin.");
        } else {
            Set<String> routerMap;

            // It will rebuild router map every times when debuggable.
            if (ARouter.debuggable() || PackageUtils.isNewVersion(context)) {
                logger.info(TAG, "Run with debug mode or new install, rebuild router map.");
                // These class was generated by arouter-compiler.
                routerMap = ClassUtils.getFileNameByPackageName(mContext, ROUTE_ROOT_PAKCAGE);
                if (!routerMap.isEmpty()) {
                    context.getSharedPreferences(AROUTER_SP_CACHE_KEY, Context.MODE_PRIVATE).edit().putStringSet(AROUTER_SP_KEY_MAP, routerMap).apply();
                }

                PackageUtils.updateVersion(context);    // Save new version name when router map update finishes.
            } else {
                logger.info(TAG, "Load router map from cache.");
                routerMap = new HashSet<>(context.getSharedPreferences(AROUTER_SP_CACHE_KEY, Context.MODE_PRIVATE).getStringSet(AROUTER_SP_KEY_MAP, new HashSet<String>()));
            }

            logger.info(TAG, "Find router map finished, map size = " + routerMap.size() + ", cost " + (System.currentTimeMillis() - startInit) + " ms.");
            startInit = System.currentTimeMillis();

            for (String className : routerMap) {
                if (className.startsWith(ROUTE_ROOT_PAKCAGE + DOT + SDK_NAME + SEPARATOR + SUFFIX_ROOT)) {
                    // This one of root elements, load root.
                    ((IRouteRoot) (Class.forName(className).getConstructor().newInstance())).loadInto(Warehouse.groupsIndex);
                } else if (className.startsWith(ROUTE_ROOT_PAKCAGE + DOT + SDK_NAME + SEPARATOR + SUFFIX_INTERCEPTORS)) {
                    // Load interceptorMeta
                    ((IInterceptorGroup) (Class.forName(className).getConstructor().newInstance())).loadInto(Warehouse.interceptorsIndex);
                } else if (className.startsWith(ROUTE_ROOT_PAKCAGE + DOT + SDK_NAME + SEPARATOR + SUFFIX_PROVIDERS)) {
                    // Load providerIndex
                    ((IProviderGroup) (Class.forName(className).getConstructor().newInstance())).loadInto(Warehouse.providersIndex);
                }
            }
        }

        logger.info(TAG, "Load root element finished, cost " + (System.currentTimeMillis() - startInit) + " ms.");

        if (Warehouse.groupsIndex.size() == 0) {
            logger.error(TAG, "No mapping files were found, check your configuration please!");
        }

        if (ARouter.debuggable()) {
            logger.debug(TAG, String.format(Locale.getDefault(), "LogisticsCenter has already been loaded, GroupIndex[%d], InterceptorIndex[%d], ProviderIndex[%d]", Warehouse.groupsIndex.size(), Warehouse.interceptorsIndex.size(), Warehouse.providersIndex.size()));
        }
    } catch (Exception e) {
        throw new HandlerException(TAG + "ARouter init logistics center exception! [" + e.getMessage() + "]");
    }
}

首先调用了loadRouterMap()方法来试图通过arouter-auto-register plugin加载route信息：

/**
 * arouter-auto-register plugin will generate code inside this method
 * call this method to register all Routers, Interceptors and Providers
 * @author billy.qi <a href="mailto:qiyilike@163.com">Contact me.</a>
 * @since 2017-12-06
 */
private static void loadRouterMap() {
    registerByPlugin = false;
    //auto generate register code by gradle plugin: arouter-auto-register
    // looks like below:
    // registerRouteRoot(new ARouter..Root..modulejava());
    // registerRouteRoot(new ARouter..Root..modulekotlin());
}

这个方法里什么也没有，因为这里要交给plugin去注册，默认设置为不通过plugin注册，通过注释可以得知，plugin会把加载逻辑代码动态的生成在这个方法里，至于怎样生成的另起篇文章总结。

下载arouter-register的source包查看:

class RouteMethodVisitor extends MethodVisitor {

    RouteMethodVisitor(int api, MethodVisitor mv) {
        super(api, mv)
    }

    @Override
    void visitInsn(int opcode) {
        //generate code before return
        if ((opcode >= Opcodes.IRETURN && opcode <= Opcodes.RETURN)) {
            extension.classList.each { name ->
                name = name.replaceAll("/", ".")
                mv.visitLdcInsn(name)//类名
                // generate invoke register method into LogisticsCenter.loadRouterMap()
                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)
    }
}

mv.visitMethodInsn方法就是注入加载代码的地方，采用循环的方式来加载每一个类。ScanSetting.GENERATE_TO_CLASS_NAME是：

/**
 * The register code is generated into this class
 */
static final String GENERATE_TO_CLASS_NAME = 'com/alibaba/android/arouter/core/LogisticsCenter'

ScanSetting.REGISTER_METHOD_NAME是：

/**
 * register method name in class: {@link #GENERATE_TO_CLASS_NAME}
 */
static final String REGISTER_METHOD_NAME = 'register'

在arouter-api的jar包中找到LogisticsCenter的register方法：

/**
 * register by class name
 * Sacrificing a bit of efficiency to solve
 * the problem that the main dex file size is too large
 * @author billy.qi <a href="mailto:qiyilike@163.com">Contact me.</a>
 * @param className class name
 */
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);
        }
    }
}

三个方法分别是注册Root（页面）、Interceptor、IProvider（Service）的逻辑：

/**
 * method for arouter-auto-register plugin to register Routers
 * @param routeRoot IRouteRoot implementation class in the package: com.alibaba.android.arouter.core.routers
 * @author billy.qi <a href="mailto:qiyilike@163.com">Contact me.</a>
 * @since 2017-12-06
 */
private static void registerRouteRoot(IRouteRoot routeRoot) {
    markRegisteredByPlugin();
    if (routeRoot != null) {
        routeRoot.loadInto(Warehouse.groupsIndex);
    }
}

/**
 * method for arouter-auto-register plugin to register Interceptors
 * @param interceptorGroup IInterceptorGroup implementation class in the package: com.alibaba.android.arouter.core.routers
 * @author billy.qi <a href="mailto:qiyilike@163.com">Contact me.</a>
 * @since 2017-12-06
 */
private static void registerInterceptor(IInterceptorGroup interceptorGroup) {
    markRegisteredByPlugin();
    if (interceptorGroup != null) {
        interceptorGroup.loadInto(Warehouse.interceptorsIndex);
    }
}

/**
 * method for arouter-auto-register plugin to register Providers
 * @param providerGroup IProviderGroup implementation class in the package: com.alibaba.android.arouter.core.routers
 * @author billy.qi <a href="mailto:qiyilike@163.com">Contact me.</a>
 * @since 2017-12-06
 */
private static void registerProvider(IProviderGroup providerGroup) {
    markRegisteredByPlugin();
    if (providerGroup != null) {
        providerGroup.loadInto(Warehouse.providersIndex);
    }
}

markRegisteredByPlugin是修改registerByPlugin标志位：

/**
 * mark already registered by arouter-auto-register plugin
 * @author billy.qi <a href="mailto:qiyilike@163.com">Contact me.</a>
 * @since 2017-12-06
 */
private static void markRegisteredByPlugin() {
    if (!registerByPlugin) {
        registerByPlugin = true;
    }
}

可以看到，对于不同类型的route类分别保存到Warehouse中对应的Map中，注意这里添加的只是类，不是跳转的所有信息。

回到init方法，判断registerByPlugin是否为true来决定是否手动加载，如果没有设置register-plugin，则会走到else分支，这里就是手动代码检索路由信息的地方：

if (ARouter.debuggable() || PackageUtils.isNewVersion(context))判断如果是debug模式或者是新版本更新的话就重新检索路由信息，核心代码就是ClassUtils.getFileNameByPackageName(mContext, ROUTE_ROOT_PAKCAGE)，ROUTE_ROOT_PACKAGE是：

public static final String ROUTE_ROOT_PAKCAGE = "com.alibaba.android.arouter.routes";

public static Set<String> getFileNameByPackageName(Context context, final String packageName) throws PackageManager.NameNotFoundException, IOException, InterruptedException {
    final Set<String> classNames = new HashSet<>();

    List<String> paths = getSourcePaths(context);
    final CountDownLatch parserCtl = new CountDownLatch(paths.size());

    for (final String path : paths) {
        DefaultPoolExecutor.getInstance().execute(new Runnable() {
            @Override
            public void run() {
                DexFile dexfile = null;

                try {
                    if (path.endsWith(EXTRACTED_SUFFIX)) {
                        //NOT use new DexFile(path), because it will throw "permission error in /data/dalvik-cache"
                        dexfile = DexFile.loadDex(path, path + ".tmp", 0);
                    } else {
                        dexfile = new DexFile(path);
                    }

                    Enumeration<String> dexEntries = dexfile.entries();
                    while (dexEntries.hasMoreElements()) {
                        String className = dexEntries.nextElement();
                        if (className.startsWith(packageName)) {
                            classNames.add(className);
                        }
                    }
                } catch (Throwable ignore) {
                    Log.e("ARouter", "Scan map file in dex files made error.", ignore);
                } finally {
                    if (null != dexfile) {
                        try {
                            dexfile.close();
                        } catch (Throwable ignore) {
                        }
                    }

                    parserCtl.countDown();
                }
            }
        });
    }

    parserCtl.await();

    Log.d(Consts.TAG, "Filter " + classNames.size() + " classes by packageName <" + packageName + ">");
    return classNames;
}

这里的工作就是多线程读取所有的dex文件，逐个判断里面的className，如果className是以com.alibaba.android.arouter.routes开头的则存入classNames集合，最终会返回所有com.alibaba.android.arouter.routes开头的类名。

注意在最前面有一个getSourcePaths方法来获取apk的所有dex文件的位置，然后从这些位置读取dex文件：

 /**
     * get all the dex path
     *
     * @param context the application context
     * @return all the dex path
     * @throws PackageManager.NameNotFoundException
     * @throws IOException
     */
    public static List<String> getSourcePaths(Context context) throws PackageManager.NameNotFoundException, IOException {
        ApplicationInfo applicationInfo = context.getPackageManager().getApplicationInfo(context.getPackageName(), 0);
        File sourceApk = new File(applicationInfo.sourceDir);

        List<String> sourcePaths = new ArrayList<>();
        sourcePaths.add(applicationInfo.sourceDir); //add the default apk path

        //the prefix of extracted file, ie: test.classes
        String extractedFilePrefix = sourceApk.getName() + EXTRACTED_NAME_EXT;

//        如果VM已经支持了MultiDex，就不要去Secondary Folder加载 Classesx.zip了，那里已经么有了
//        通过是否存在sp中的multidex.version是不准确的，因为从低版本升级上来的用户，是包含这个sp配置的
        if (!isVMMultidexCapable()) {
            //the total dex numbers
            int totalDexNumber = getMultiDexPreferences(context).getInt(KEY_DEX_NUMBER, 1);
            File dexDir = new File(applicationInfo.dataDir, SECONDARY_FOLDER_NAME);

            for (int secondaryNumber = 2; secondaryNumber <= totalDexNumber; secondaryNumber++) {
                //for each dex file, ie: test.classes2.zip, test.classes3.zip...
                String fileName = extractedFilePrefix + secondaryNumber + EXTRACTED_SUFFIX;
                File extractedFile = new File(dexDir, fileName);
                if (extractedFile.isFile()) {
                    sourcePaths.add(extractedFile.getAbsolutePath());
                    //we ignore the verify zip part
                } else {
                    throw new IOException("Missing extracted secondary dex file '" + extractedFile.getPath() + "'");
                }
            }
        }

        if (ARouter.debuggable()) { // Search instant run support only debuggable
            sourcePaths.addAll(tryLoadInstantRunDexFile(applicationInfo));
        }
        return sourcePaths;
    }

isVMMultidexCapable判断是否JVM支持MultiDex了，就是判断JVM的版本（2.1之后的支持）：

/**
 * Identifies if the current VM has a native support for multidex, meaning there is no need for
 * additional installation by this library.
 *
 * @return true if the VM handles multidex
 */
private static boolean isVMMultidexCapable() {
    boolean isMultidexCapable = false;
    String vmName = null;

    try {
        if (isYunOS()) {    // YunOS需要特殊判断
            vmName = "'YunOS'";
            isMultidexCapable = Integer.valueOf(System.getProperty("ro.build.version.sdk")) >= 21;
        } else {    // 非YunOS原生Android
            vmName = "'Android'";
            String versionString = System.getProperty("java.vm.version");
            if (versionString != null) {
                Matcher matcher = Pattern.compile("(\\d+)\\.(\\d+)(\\.\\d+)?").matcher(versionString);
                if (matcher.matches()) {
                    try {
                        int major = Integer.parseInt(matcher.group(1));
                        int minor = Integer.parseInt(matcher.group(2));
                        isMultidexCapable = (major > VM_WITH_MULTIDEX_VERSION_MAJOR)
                                || ((major == VM_WITH_MULTIDEX_VERSION_MAJOR)
                                && (minor >= VM_WITH_MULTIDEX_VERSION_MINOR));
                    } catch (NumberFormatException ignore) {
                        // let isMultidexCapable be false
                    }
                }
            }
        }
    } catch (Exception ignore) {

    }

    Log.i(Consts.TAG, "VM with name " + vmName + (isMultidexCapable ? " has multidex support" : " does not have multidex support"));
    return isMultidexCapable;
}

取到routeMap之后会把它存到SP中，最后遍历routeMap，根据前缀Root、Interceptors、Providers的不同分别存入Warehouse中的对应xxxIndex的map中，这一步和自动加载是一样的。

至此，初始化工作就完成了。

路由名称注意

Route注解指定的路由path中格式为/groupName/elseName...，至少含有两个‘/’且groupName不能为空。因为ARouter会自动生成以groupName为后缀的类，可以在build的generated包下找到。

arouter-api:xxx的这个jar包下的routes包中有三个已经存在的类：

ARouter$$Group$$arouter：

public class ARouter$$Group$$arouter implements IRouteGroup {
    public ARouter$$Group$$arouter() {
    }

    public void loadInto(Map<String, RouteMeta> atlas) {
        atlas.put("/arouter/service/autowired", RouteMeta.build(RouteType.PROVIDER, AutowiredServiceImpl.class, "/arouter/service/autowired", "arouter", (Map)null, -1, -2147483648));
        atlas.put("/arouter/service/interceptor", RouteMeta.build(RouteType.PROVIDER, InterceptorServiceImpl.class, "/arouter/service/interceptor", "arouter", (Map)null, -1, -2147483648));
    }
}

ARouter$$Providers$$arouterapi:

public class ARouter$$Providers$$arouterapi implements IProviderGroup {
    public ARouter$$Providers$$arouterapi() {
    }

    public void loadInto(Map<String, RouteMeta> providers) {
        providers.put("com.alibaba.android.arouter.facade.service.AutowiredService", RouteMeta.build(RouteType.PROVIDER, AutowiredServiceImpl.class, "/arouter/service/autowired", "arouter", (Map)null, -1, -2147483648));
        providers.put("com.alibaba.android.arouter.facade.service.InterceptorService", RouteMeta.build(RouteType.PROVIDER, InterceptorServiceImpl.class, "/arouter/service/interceptor", "arouter", (Map)null, -1, -2147483648));
    }
}

ARouter$$Root$$arouterapi：

public class ARouter$$Root$$arouterapi implements IRouteRoot {
    public ARouter$$Root$$arouterapi() {
    }

    public void loadInto(Map<String, Class<? extends IRouteGroup>> routes) {
        routes.put("arouter", arouter.class);
    }
}

在build中还会自动生成ARouter$$Providers$$moduleName、ARouter$$Root$$moduleName，moduleName是模块的名字。以module是app为例，ARouter$$Root$$app为：

public class ARouter$$Root$$app implements IRouteRoot {
  @Override
  public void loadInto(Map<String, Class<? extends IRouteGroup>> routes) {
    routes.put("john", ARouter$$Group$$john.class);
    routes.put("rxseriers", ARouter$$Group$$rxseriers.class);
  }
}

前面分析的初始化中会调用到loadInto方法，这里就会把ARouter$$Group$$john.class和ARouter$$Group$$rxseriers.class保存到Warehouse.groupsIndex中。

而Route注解生成的类的类名格式为ARouter$$Group$$groupName，知道了这些之后，我们可以得出结论，路由中的groupName不能是“arouter”，倘若相同，自动生成的class名就会和routes包下的默认存在的class同名，那么routes.put("arouter", ARouter$$Group$$john.class)传入的class就会被routes中的同名class替代，从而导致找不到自定义的路由类的问题。

跳转

Example：

ARouter.getInstance().build(Const.LOGIN_ACTIVITY_PATH).withString("name","John").navigation()

通过单例模式获取ARouter实例：

public static ARouter getInstance() {
    if (!hasInit) {
        throw new InitException("ARouter::Init::Invoke init(context) first!");
    } else {
        if (instance == null) {
            synchronized (ARouter.class) {
                if (instance == null) {
                    instance = new ARouter();
                }
            }
        }
        return instance;
    }
}

可以看到实例化之前必须先初始化。

build有多个重载方法：

/**
 * Build postcard by path and default group
 */
protected Postcard build(String path) {
    if (TextUtils.isEmpty(path)) {
        throw new HandlerException(Consts.TAG + "Parameter is invalid!");
    } else {
        PathReplaceService pService = ARouter.getInstance().navigation(PathReplaceService.class);
        if (null != pService) {
            path = pService.forString(path);
        }
        return build(path, extractGroup(path), true);
    }
}

/**
 * Build postcard by uri
 */
protected Postcard build(Uri uri) {
    if (null == uri || TextUtils.isEmpty(uri.toString())) {
        throw new HandlerException(Consts.TAG + "Parameter invalid!");
    } else {
        PathReplaceService pService = ARouter.getInstance().navigation(PathReplaceService.class);
        if (null != pService) {
            uri = pService.forUri(uri);
        }
        return new Postcard(uri.getPath(), extractGroup(uri.getPath()), uri, null);
    }
}

/**
 * Build postcard by path and group
 */
protected Postcard build(String path, String group, Boolean afterReplace) {
    if (TextUtils.isEmpty(path) || TextUtils.isEmpty(group)) {
        throw new HandlerException(Consts.TAG + "Parameter is invalid!");
    } else {
        if (!afterReplace) {
            PathReplaceService pService = ARouter.getInstance().navigation(PathReplaceService.class);
            if (null != pService) {
                path = pService.forString(path);
            }
        }
        return new Postcard(path, group);
    }
}

}

其实就是两种方式，一个参数是String类型的path，这就是Route注解的path属性的值，另一个参数是Uri类型，这种形式最终使用的是Uri的path值，无论哪种形式，都必须是/groupName/???的格式，extractGroup方法决定了这样：

/**
 * Extract the default group from path.
 */
private String extractGroup(String path) {
    if (TextUtils.isEmpty(path) || !path.startsWith("/")) {
        throw new HandlerException(Consts.TAG + "Extract the default group failed, the path must be start with '/' and contain more than 2 '/'!");
    }

    try {
        String defaultGroup = path.substring(1, path.indexOf("/", 1));
        if (TextUtils.isEmpty(defaultGroup)) {
            throw new HandlerException(Consts.TAG + "Extract the default group failed! There's nothing between 2 '/'!");
        } else {
            return defaultGroup;
        }
    } catch (Exception e) {
        logger.warning(Consts.TAG, "Failed to extract default group! " + e.getMessage());
        return null;
}

所以build之后得到了一个Postcard(明信片)对象，接下来是调用它的navigation方法。

navigation方法同样有多个重载方法，所有可传参数有：Activity mContext, int requestCode, NavigationCallback callback。mContext若不传就是构建时传入的application上下文，requestCode是用以forResult方式打开Activity的需求，可以传一个callback以自定义处理一些特殊情况。

最终会调用到_ARouter的navigation方法中：

protected Object navigation(final Context context, final Postcard postcard, final int requestCode, final NavigationCallback callback) {
    PretreatmentService pretreatmentService = ARouter.getInstance().navigation(PretreatmentService.class);
    if (null != pretreatmentService && !pretreatmentService.onPretreatment(context, postcard)) {
        // Pretreatment failed, navigation canceled.
        return null;
    }

    try {
        LogisticsCenter.completion(postcard);
    } catch (NoRouteFoundException ex) {
        logger.warning(Consts.TAG, ex.getMessage());

        if (debuggable()) {
            // Show friendly tips for user.
            runInMainThread(new Runnable() {
                @Override
                public void run() {
                    Toast.makeText(mContext, "There's no route matched!\n" +
                            " Path = [" + postcard.getPath() + "]\n" +
                            " Group = [" + postcard.getGroup() + "]", Toast.LENGTH_LONG).show();
                }
            });
        }

        if (null != callback) {
            callback.onLost(postcard);
        } else {
            // No callback for this invoke, then we use the global degrade service.
            DegradeService degradeService = ARouter.getInstance().navigation(DegradeService.class);
            if (null != degradeService) {
                degradeService.onLost(context, postcard);
            }
        }

        return null;
    }

    if (null != callback) {
        callback.onFound(postcard);
    }

    if (!postcard.isGreenChannel()) {   // It must be run in async thread, maybe interceptor cost too mush time made ANR.
        interceptorService.doInterceptions(postcard, new InterceptorCallback() {
            /**
             * Continue process
             *
             * @param postcard route meta
             */
            @Override
            public void onContinue(Postcard postcard) {
                _navigation(context, postcard, requestCode, callback);
            }

            /**
             * Interrupt process, pipeline will be destory when this method called.
             *
             * @param exception Reson of interrupt.
             */
            @Override
            public void onInterrupt(Throwable exception) {
                if (null != callback) {
                    callback.onInterrupt(postcard);
                }

                logger.info(Consts.TAG, "Navigation failed, termination by interceptor : " + exception.getMessage());
            }
        });
    } else {
        return _navigation(context, postcard, requestCode, callback);
    }

    return null;
}

这里只看核心代码，LogisticsCenter.completion(postcard)用于完善和检查Postcard的必要信息，暂时先不看，先看方法最终的逻辑：

private Object _navigation(final Context context, final Postcard postcard, final int requestCode, final NavigationCallback callback) {
    final Context currentContext = null == context ? mContext : context;

    switch (postcard.getType()) {
        case ACTIVITY:
            // Build intent
            final Intent intent = new Intent(currentContext, postcard.getDestination());
            intent.putExtras(postcard.getExtras());

            // Set flags.
            int flags = postcard.getFlags();
            if (-1 != flags) {
                intent.setFlags(flags);
            } else if (!(currentContext instanceof Activity)) {    // Non activity, need less one flag.
                intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            }

            // Set Actions
            String action = postcard.getAction();
            if (!TextUtils.isEmpty(action)) {
                intent.setAction(action);
            }

            // Navigation in main looper.
            runInMainThread(new Runnable() {
                @Override
                public void run() {
                    startActivity(requestCode, currentContext, intent, postcard, callback);
                }
            });

            break;
        case PROVIDER:
            return postcard.getProvider();
        case BOARDCAST:
        case CONTENT_PROVIDER:
        case FRAGMENT:
            Class fragmentMeta = postcard.getDestination();
            try {
                Object instance = fragmentMeta.getConstructor().newInstance();
                if (instance instanceof Fragment) {
                    ((Fragment) instance).setArguments(postcard.getExtras());
                } else if (instance instanceof android.support.v4.app.Fragment) {
                    ((android.support.v4.app.Fragment) instance).setArguments(postcard.getExtras());
                }

                return instance;
            } catch (Exception ex) {
                logger.error(Consts.TAG, "Fetch fragment instance error, " + TextUtils.formatStackTrace(ex.getStackTrace()));
            }
        case METHOD:
        case SERVICE:
        default:
            return null;
    }

    return null;
}

/**
 * Start activity
 *
 * @see ActivityCompat
 */
private void startActivity(int requestCode, Context currentContext, Intent intent, Postcard postcard, NavigationCallback callback) {
    if (requestCode >= 0) {  // Need start for result
        if (currentContext instanceof Activity) {
            ActivityCompat.startActivityForResult((Activity) currentContext, intent, requestCode, postcard.getOptionsBundle());
        } else {
            logger.warning(Consts.TAG, "Must use [navigation(activity, ...)] to support [startActivityForResult]");
        }
    } else {
        ActivityCompat.startActivity(currentContext, intent, postcard.getOptionsBundle());
    }

    if ((-1 != postcard.getEnterAnim() && -1 != postcard.getExitAnim()) && currentContext instanceof Activity) {    // Old version.
        ((Activity) currentContext).overridePendingTransition(postcard.getEnterAnim(), postcard.getExitAnim());
    }

    if (null != callback) { // Navigation over.
        callback.onArrival(postcard);
    }
}

可以看到，最底层也是调用了startActvity或startActivityForResult（requestCode大于0且context是Activity）来处理回调，动画和NavigationCallback的处理也是在这里。

回过头来我们看一下LogisticsCenter.completion(postcard)方法，它只在navigation方法里面最开始调用：

public synchronized static void completion(Postcard postcard) {
    if (null == postcard) {
        throw new NoRouteFoundException(TAG + "No postcard!");
    }

    RouteMeta routeMeta = Warehouse.routes.get(postcard.getPath());
    if (null == routeMeta) {    // Maybe its does't exist, or didn't load.
        Class<? extends IRouteGroup> groupMeta = Warehouse.groupsIndex.get(postcard.getGroup());  // Load route meta.
        if (null == groupMeta) {
            throw new NoRouteFoundException(TAG + "There is no route match the path [" + postcard.getPath() + "], in group [" + postcard.getGroup() + "]");
        } else {
            // Load route and cache it into memory, then delete from metas.
            try {
                if (ARouter.debuggable()) {
                    logger.debug(TAG, String.format(Locale.getDefault(), "The group [%s] starts loading, trigger by [%s]", postcard.getGroup(), postcard.getPath()));
                }

                IRouteGroup iGroupInstance = groupMeta.getConstructor().newInstance();
                iGroupInstance.loadInto(Warehouse.routes);
                Warehouse.groupsIndex.remove(postcard.getGroup());

                if (ARouter.debuggable()) {
                    logger.debug(TAG, String.format(Locale.getDefault(), "The group [%s] has already been loaded, trigger by [%s]", postcard.getGroup(), postcard.getPath()));
                }
            } catch (Exception e) {
                throw new HandlerException(TAG + "Fatal exception when loading group meta. [" + e.getMessage() + "]");
            }

            completion(postcard);   // Reload
        }
    } else {
        postcard.setDestination(routeMeta.getDestination());
        postcard.setType(routeMeta.getType());
        postcard.setPriority(routeMeta.getPriority());
        postcard.setExtra(routeMeta.getExtra());

        Uri rawUri = postcard.getUri();
        if (null != rawUri) {   // Try to set params into bundle.
            Map<String, String> resultMap = TextUtils.splitQueryParameters(rawUri);
            Map<String, Integer> paramsType = routeMeta.getParamsType();

            if (MapUtils.isNotEmpty(paramsType)) {
                // Set value by its type, just for params which annotation by @Param
                for (Map.Entry<String, Integer> params : paramsType.entrySet()) {
                    setValue(postcard,
                            params.getValue(),
                            params.getKey(),
                            resultMap.get(params.getKey()));
                }

                // Save params name which need auto inject.
                postcard.getExtras().putStringArray(ARouter.AUTO_INJECT, paramsType.keySet().toArray(new String[]{}));
            }

            // Save raw uri
            postcard.withString(ARouter.RAW_URI, rawUri.toString());
        }

        switch (routeMeta.getType()) {
            case PROVIDER:  // if the route is provider, should find its instance
                // Its provider, so it must implement IProvider
                Class<? extends IProvider> providerMeta = (Class<? extends IProvider>) routeMeta.getDestination();
                IProvider instance = Warehouse.providers.get(providerMeta);
                if (null == instance) { // There's no instance of this provider
                    IProvider provider;
                    try {
                        provider = providerMeta.getConstructor().newInstance();
                        provider.init(mContext);
                        Warehouse.providers.put(providerMeta, provider);
                        instance = provider;
                    } catch (Exception e) {
                        throw new HandlerException("Init provider failed! " + e.getMessage());
                    }
                }
                postcard.setProvider(instance);
                postcard.greenChannel();    // Provider should skip all of interceptors
                break;
            case FRAGMENT:
                postcard.greenChannel();    // Fragment needn't interceptors
            default:
                break;
        }
    }
}

还记得之前init的时候已经把自动生成的Root类保存进了Warehouse.groupsIndex了吧，这里首先会从Warehouse.groupsIndex中取RouteMeta，如果没取到说明之前没有跳转过，则从Warehouse.groupsIndex中取得之前存入的class，取到之后调用groupMeta.getConstructor().newInstance()反射生成实例，调用它的loadInto(Warehouse.routes)方法，这里我定义的是@Route(path="/john/")，所以生成的是ARouter$$Group$$john：

/**
 * DO NOT EDIT THIS FILE!!! IT WAS GENERATED BY AROUTER. */
public class ARouter$$Group$$john implements IRouteGroup {
  @Override
  public void loadInto(Map<String, RouteMeta> atlas) {
    atlas.put("/john/", RouteMeta.build(RouteType.ACTIVITY, LoginActivity.class, "/john/", "john", new java.util.HashMap<String, Integer>(){{put("name", 8); put("age", 3); }}, -1, -2147483648));
  }
}

那么loadInto方法就是这里的，做的工作就是把生成的RouteMeta对象保存进Warehouse.routes，后面再次递归调用completion方法，再次进来，Warehouse.routes内就含有了RouteMeta对象。

我们看一下自动生成的RouteMeta都含有什么关键信息。

首先第一个参数RouteType，标志跳转目标的类型:

public enum RouteType {
    ACTIVITY(0, "android.app.Activity"),
    SERVICE(1, "android.app.Service"),
    PROVIDER(2, "com.alibaba.android.arouter.facade.template.IProvider"),
    CONTENT_PROVIDER(-1, "android.app.ContentProvider"),
    BOARDCAST(-1, ""),
    METHOD(-1, ""),
    FRAGMENT(-1, "android.app.Fragment"),
    UNKNOWN(-1, "Unknown route type");

    int id;
    String className;

    public int getId() {
        return id;
    }

    public RouteType setId(int id) {
        this.id = id;
        return this;
    }

    public String getClassName() {
        return className;
    }

    public RouteType setClassName(String className) {
        this.className = className;
        return this;
    }

    RouteType(int id, String className) {
        this.id = id;
        this.className = className;
    }

    public static RouteType parse(String name) {
        for (RouteType routeType : RouteType.values()) {
            if (routeType.getClassName().equals(name)) {
                return routeType;
            }
        }

        return UNKNOWN;
    }
}

第二个参数是Class类型，是跳转目标类。第三个参数是Route定义的path。第四个参数是group。第五个参数是Map，用于保存Autowired参数类型的，value是整型，表示enum.ordinal：

public enum TypeKind {
    // Base type
    BOOLEAN,
    BYTE,
    SHORT,
    INT,
    LONG,
    CHAR,
    FLOAT,
    DOUBLE,

    // Other type
    STRING,
    SERIALIZABLE,
    PARCELABLE,
    OBJECT;
}

通过setValue方法赋值到postcard的mBundle：

private static void setValue(Postcard postcard, Integer typeDef, String key, String value) {
    if (TextUtils.isEmpty(key) || TextUtils.isEmpty(value)) {
        return;
    }

    try {
        if (null != typeDef) {
            if (typeDef == TypeKind.BOOLEAN.ordinal()) {
                postcard.withBoolean(key, Boolean.parseBoolean(value));
            } else if (typeDef == TypeKind.BYTE.ordinal()) {
                postcard.withByte(key, Byte.parseByte(value));
            } else if (typeDef == TypeKind.SHORT.ordinal()) {
                postcard.withShort(key, Short.parseShort(value));
            } else if (typeDef == TypeKind.INT.ordinal()) {
                postcard.withInt(key, Integer.parseInt(value));
            } else if (typeDef == TypeKind.LONG.ordinal()) {
                postcard.withLong(key, Long.parseLong(value));
            } else if (typeDef == TypeKind.FLOAT.ordinal()) {
                postcard.withFloat(key, Float.parseFloat(value));
            } else if (typeDef == TypeKind.DOUBLE.ordinal()) {
                postcard.withDouble(key, Double.parseDouble(value));
            } else if (typeDef == TypeKind.STRING.ordinal()) {
                postcard.withString(key, value);
            } else if (typeDef == TypeKind.PARCELABLE.ordinal()) {
                // TODO : How to description parcelable value with string?
            } else if (typeDef == TypeKind.OBJECT.ordinal()) {
                postcard.withString(key, value);
            } else {    // Compatible compiler sdk 1.0.3, in that version, the string type = 18
                postcard.withString(key, value);
            }
        } else {
            postcard.withString(key, value);
        }
    } catch (Throwable ex) {
        logger.warning(Consts.TAG, "LogisticsCenter setValue failed! " + ex.getMessage());
    }
}

注意这里setValue使用resultMap.get(params.getKey())来尝试获取Uri中的值，就是Uri中‘?’到‘#’(可以没有)之间的‘xx=xx&xx=xx&...’键值对。

第六个参数是priority，设置优先级，通过Route注解的priority属性指定，最后一个参数通过Route注解的extras属性指定。

参数传递

对于基本的类型传递，Postcard中都有对应的方法withXxx()来设置，对于实例化类型，如果实现了Serializable或Parcelable的，可以调用withSerializable和withParcelable方法设置。

而对于自定义的未实现上述接口的则需要调用withObject方法：

public Postcard withObject(@Nullable String key, @Nullable Object value) {
    serializationService = ARouter.getInstance().navigation(SerializationService.class);
    mBundle.putString(key, serializationService.object2Json(value));
    return this;
}

可见需要定义实现自SerializationService的类，譬如：

@Route(path = AppConstant.ARouteService.SERVICE_SERIALIZATION)
public class ModuleSerializationRouteServiceImpl implements SerializationService {

    private Gson gson;
    private GsonBuilder gsonBuilder;

    @Override
    public <T> T json2Object(String input, Class<T> clazz) {
        return null;
    }

    @Override
    public String object2Json(Object instance) {
        return gson.toJson(instance);
    }

    @Override
    public <T> T parseObject(String input, Type clazz) {
        return gson.fromJson(input, clazz);
    }

    @Override
    public void init(Context context) {
        gsonBuilder = new GsonBuilder();
        gsonBuilder.registerTypeAdapter(Class.class, new ClassTypeAdapter());
        gson = gsonBuilder.create();
    }
}

这里的navigation(Class<? extends T> service)是：

protected <T> T navigation(Class<? extends T> service) {
    try {
        Postcard postcard = LogisticsCenter.buildProvider(service.getName());

        // Compatible 1.0.5 compiler sdk.
        // Earlier versions did not use the fully qualified name to get the service
        if (null == postcard) {
            // No service, or this service in old version.
            postcard = LogisticsCenter.buildProvider(service.getSimpleName());
        }

        if (null == postcard) {
            return null;
        }

        LogisticsCenter.completion(postcard);
        return (T) postcard.getProvider();
    } catch (NoRouteFoundException ex) {
        logger.warning(Consts.TAG, ex.getMessage());
        return null;
    }
}

LogisticsCenter.buildProvider从Warehouse.providersIndex中取得provider：

public static Postcard buildProvider(String serviceName) {
    RouteMeta meta = Warehouse.providersIndex.get(serviceName);

    if (null == meta) {
        return null;
    } else {
        return new Postcard(meta.getPath(), meta.getGroup());
    }
}

实例化SerializationService和调用它的init的代码就在completion中的：

switch (routeMeta.getType()) {
    case PROVIDER:  // if the route is provider, should find its instance
        // Its provider, so it must implement IProvider
        Class<? extends IProvider> providerMeta = (Class<? extends IProvider>) routeMeta.getDestination();
        IProvider instance = Warehouse.providers.get(providerMeta);
        if (null == instance) { // There's no instance of this provider
            IProvider provider;
            try {
                provider = providerMeta.getConstructor().newInstance();
                provider.init(mContext);
                Warehouse.providers.put(providerMeta, provider);
                instance = provider;
            } catch (Exception e) {
                throw new HandlerException("Init provider failed! " + e.getMessage());
            }
        }
        postcard.setProvider(instance);
        postcard.greenChannel();    // Provider should skip all of interceptors
        break;
            ...
          
}

所以实际上withObject存储的是对象的json字符串。

传参自动注入

传参自然需要获取参数，上面我们知道最终也是通过intent和bundle传递的参数，那么获取的时候当然也可是通过getIntent().getExtras()方法获取参数值。

对于ARouter，这些工作我们还可以通过Autowiredz注解自动完成。

要完成自动注入需要两点，一点是必须在每个需要自动注入的属性上面加Autowired注解，它有三个注解属性，必须要有的是name属性，这个属性的值必须和跳转时传递到bundle的key相同，如果指定了name属性，则字段的名字不必和bundle的key相同，反之则必须相同；第二个是required属性，如果设置为true则表示该Field的值不能为null，否则会crash；最后一个参数是desc，用于描述Field的作用。注意如果是kotlin类，则需要同时加上@JvmField属性，否则不能通过kapt编译。

另一点是需要在使用自动注入的字段的值之前调用ARouter.getInstance().inject(this)方法，否则使用值为null的实例会抛出NullPointerException异常。

下面我们看看，对于这些要求ARouter是怎么通过代码设置的。

首先，含有Autowired注解的类会被自动生成一个名为“类名$$ARouter$$Autowired”的类，那么ARouter.getInstance().inject(this)方法调用了_ARouter的inject方法：

static void inject(Object thiz) {
    AutowiredService autowiredService = ((AutowiredService) ARouter.getInstance().build("/arouter/service/autowired").navigation());
    if (null != autowiredService) {
        autowiredService.autowire(thiz);
    }
}

可见，这里会找到path为/arouter/service/autowired的AutowiredService，那这个接口的实现类在哪里，还记得我们初始化的时候for循环loadInto操作吗，就在那个时候前缀为com.alibaba.android.arouter.routes.ARouter$$Providers的类被存到了Warehouse.providesIndex中，所以jar包arouter-api中的ARouter$$Providers$$arouterapi类自然也被加进去了，所以completion中找到这个类调用它的loadInto方法：

public void loadInto(Map<String, RouteMeta> providers) {
    providers.put("com.alibaba.android.arouter.facade.service.AutowiredService", RouteMeta.build(RouteType.PROVIDER, AutowiredServiceImpl.class, "/arouter/service/autowired", "arouter", (Map)null, -1, -2147483648));
    providers.put("com.alibaba.android.arouter.facade.service.InterceptorService", RouteMeta.build(RouteType.PROVIDER, InterceptorServiceImpl.class, "/arouter/service/interceptor", "arouter", (Map)null, -1, -2147483648));
}

所以path为/arouter/service/autowired的就是AutowiredServiceImpl类，接下来调用它的autowire方法，传入的是被跳转页Activity的实例：

@Override
public void autowire(Object instance) {
    doInject(instance, null);
}

/**
 * Recursive injection
 *
 * @param instance who call me.
 * @param parent   parent of me.
 */
private void doInject(Object instance, Class<?> parent) {
    Class<?> clazz = null == parent ? instance.getClass() : parent;

    ISyringe syringe = getSyringe(clazz);
    if (null != syringe) {
        syringe.inject(instance);
    }

    //这里可见会自动把其父类中的Autowired字段注入
    Class<?> superClazz = clazz.getSuperclass();
    // has parent and its not the class of framework.
    if (null != superClazz && !superClazz.getName().startsWith("android")) {
        doInject(instance, superClazz);
    }
}

来看看getSyringe方法：

private ISyringe getSyringe(Class<?> clazz) {
    String className = clazz.getName();

    try {
        if (!blackList.contains(className)) {
            ISyringe syringeHelper = classCache.get(className);
            if (null == syringeHelper) {  // No cache.
                syringeHelper = (ISyringe) Class.forName(clazz.getName() + SUFFIX_AUTOWIRED).getConstructor().newInstance();
            }
            classCache.put(className, syringeHelper);
            return syringeHelper;
        }
    } catch (Exception e) {
        blackList.add(className);    // This instance need not autowired.
    }

    return null;
}

(ISyringe) Class.forName(clazz.getName() + SUFFIX_AUTOWIRED).getConstructor().newInstance()这行代码就是获取自动生成的名为“类名$$ARouter$$Autowired”的类，这里比如说是LoginActivity类，那么这行代码就会找到LoginActivity$$ARouter$$Autowired：

public class LoginActivity$$ARouter$$Autowired implements ISyringe {
  private SerializationService serializationService;

  @Override
  public void inject(Object target) {
    serializationService = ARouter.getInstance().navigation(SerializationService.class);
    LoginActivity substitute = (LoginActivity)target;
    substitute.name = substitute.getIntent().getExtras() == null ? substitute.name : substitute.getIntent().getExtras().getString("name", substitute.name);
    substitute.howOld = substitute.getIntent().getIntExtra("age", substitute.howOld);
  }
}

可见这个类实现自ISyringe接口，所以调用ISyringe的inject方法就是调用LoginActivity$$ARouter$$Autowired的inject方法，可以看到，这个方法里给这个Activity实例的相关字段赋值，取值来源也是通过getIntent()。

Service Management

// Declaration interface, other components get the service instance through the interface
public interface HelloService extends IProvider {
    String sayHello(String name);
}

@Route(path = "/yourservicegroupname/hello", name = "test service")
public class HelloServiceImpl implements HelloService {

    @Override
    public String sayHello(String name) {
        return "hello, " + name;
    }

    @Override
    public void init(Context context) {

    }
}

结合Autowired就可以实现自动注入，原理同上。

NavigationCallback

如果你需要在路由正常跳转或者没找到时做一些回调处理，那么可以在调用navigation方法时传入一个NavigationCallback对象用于处理：

public interface NavigationCallback {

    /**
     * Callback when find the destination.
     *
     * @param postcard meta
     */
    void onFound(Postcard postcard);

    /**
     * Callback after lose your way.
     *
     * @param postcard meta
     */
    void onLost(Postcard postcard);

    /**
     * Callback after navigation.
     *
     * @param postcard meta
     */
    void onArrival(Postcard postcard);

    /**
     * Callback on interrupt.
     *
     * @param postcard meta
     */
    void onInterrupt(Postcard postcard);
}

DegradeService

对于NoRouteFoundException发生时，你可以通过NavigationCallback来处理，但需要每次navigation都需要指定，如果你需要指定一个全局通用的onLost处理，你可以定义一个类实现DegradeService接口，重写onLost方法，这样所有的navigation发生NoRouteFoundException时都会进入到此方法，因为navigation方法中：

try {
    LogisticsCenter.completion(postcard);
} catch (NoRouteFoundException ex) {
    logger.warning(Consts.TAG, ex.getMessage());

    if (debuggable()) {
        // Show friendly tips for user.
        runInMainThread(new Runnable() {
            @Override
            public void run() {
                Toast.makeText(mContext, "There's no route matched!\n" +
                        " Path = [" + postcard.getPath() + "]\n" +
                        " Group = [" + postcard.getGroup() + "]", Toast.LENGTH_LONG).show();
            }
        });
    }

    if (null != callback) {
        callback.onLost(postcard);
    } else {
        // No callback for this invoke, then we use the global degrade service.
        DegradeService degradeService = ARouter.getInstance().navigation(DegradeService.class);
        if (null != degradeService) {
            degradeService.onLost(context, postcard);
        }
    }

    return null;
}

可见，优先走NavigationCallback的onLost。

Interceptor

navigation方法中，判断postcard.isGreenChannel()是否为false来决定是否需要拦截处理，如果是false，则进行拦截处理：

interceptorService.doInterceptions(postcard, new InterceptorCallback() {
    /**
     * Continue process
     *
     * @param postcard route meta
     */
    @Override
    public void onContinue(Postcard postcard) {
        _navigation(context, postcard, requestCode, callback);
    }

    /**
     * Interrupt process, pipeline will be destory when this method called.
     *
     * @param exception Reson of interrupt.
     */
    @Override
    public void onInterrupt(Throwable exception) {
        if (null != callback) {
            callback.onInterrupt(postcard);
        }

        logger.info(Consts.TAG, "Navigation failed, termination by interceptor : " + exception.getMessage());
    }
});

interceptorService是什么时候实例化的呢？答案还是在初始化里面，init方法里，若成功执行完 _ARouter.init(application)方法则会返回true赋值给hasInit，hasInit为true会执行 _ARouter.afterInit()方法：

static void afterInit() {
    // Trigger interceptor init, use byName.
    interceptorService = (InterceptorService) ARouter.getInstance().build("/arouter/service/interceptor").navigation();
}

同AutowiredService一样，初始化时在ARouter$$Providers$$arouterapi的loadInto中path为/arouter/service/interceptor的InterceptorServiceImpl.class被存进了Warehouse.interceptorsIndex，所以这里afterInit会取到InterceptorServiceImpl.class，它的doInterceptions方法如下：

@Override
public void doInterceptions(final Postcard postcard, final InterceptorCallback callback) {
    if (null != Warehouse.interceptors && Warehouse.interceptors.size() > 0) {

        checkInterceptorsInitStatus();

        if (!interceptorHasInit) {
            callback.onInterrupt(new HandlerException("Interceptors initialization takes too much time."));
            return;
        }

        LogisticsCenter.executor.execute(new Runnable() {
            @Override
            public void run() {
                CancelableCountDownLatch interceptorCounter = new CancelableCountDownLatch(Warehouse.interceptors.size());
                try {
                    _execute(0, interceptorCounter, postcard);
                    interceptorCounter.await(postcard.getTimeout(), TimeUnit.SECONDS);
                    if (interceptorCounter.getCount() > 0) {    // Cancel the navigation this time, if it hasn't return anythings.
                        callback.onInterrupt(new HandlerException("The interceptor processing timed out."));
                    } else if (null != postcard.getTag()) {    // Maybe some exception in the tag.
                        callback.onInterrupt(new HandlerException(postcard.getTag().toString()));
                    } else {
                        callback.onContinue(postcard);
                    }
                } catch (Exception e) {
                    callback.onInterrupt(e);
                }
            }
        });
    } else {
        callback.onContinue(postcard);
    }
}

checkInterceptorsInitStatus():

private static void checkInterceptorsInitStatus() {
    synchronized (interceptorInitLock) {
        while (!interceptorHasInit) {
            try {
                interceptorInitLock.wait(10 * 1000);
            } catch (InterruptedException e) {
                throw new HandlerException(TAG + "Interceptor init cost too much time error! reason = [" + e.getMessage() + "]");
            }
        }
    }
}

只要interceptorHasInit不为true，则会一直阻塞当前线程等待，每10秒重新检查一次，那interceptorHasInit在哪里改变的？还记得在completion里：

switch (routeMeta.getType()) {
    case PROVIDER:  // if the route is provider, should find its instance
        // Its provider, so it must implement IProvider
        Class<? extends IProvider> providerMeta = (Class<? extends IProvider>) routeMeta.getDestination();
        IProvider instance = Warehouse.providers.get(providerMeta);
        if (null == instance) { // There's no instance of this provider
            IProvider provider;
            try {
                provider = providerMeta.getConstructor().newInstance();
                provider.init(mContext);
                Warehouse.providers.put(providerMeta, provider);
                instance = provider;
            } catch (Exception e) {
                throw new HandlerException("Init provider failed! " + e.getMessage());
            }
        }
        postcard.setProvider(instance);
        postcard.greenChannel();    // Provider should skip all of interceptors
        break;
    ...
}

此时是InterceptorServiceImpl，为什么InterceptorServiceImpl的Type是PROVIDER而不是INTERCEPTOR呢？因为ARouter$$Providers$$arouterapi的loadInto存入时设置的就是PROVIDER：

providers.put("com.alibaba.android.arouter.facade.service.InterceptorService", RouteMeta.build(RouteType.PROVIDER, InterceptorServiceImpl.class, "/arouter/service/interceptor", "arouter", (Map)null, -1, -2147483648));

所以provider.init()方法就是InterceptorServiceImpl的init方法：

@Override
public void init(final Context context) {
    LogisticsCenter.executor.execute(new Runnable() {
        @Override
        public void run() {
            if (MapUtils.isNotEmpty(Warehouse.interceptorsIndex)) {
                for (Map.Entry<Integer, Class<? extends IInterceptor>> entry : Warehouse.interceptorsIndex.entrySet()) {
                    Class<? extends IInterceptor> interceptorClass = entry.getValue();
                    try {
                        IInterceptor iInterceptor = interceptorClass.getConstructor().newInstance();
                        iInterceptor.init(context);
                        Warehouse.interceptors.add(iInterceptor);
                    } catch (Exception ex) {
                        throw new HandlerException(TAG + "ARouter init interceptor error! name = [" + interceptorClass.getName() + "], reason = [" + ex.getMessage() + "]");
                    }
                }

                interceptorHasInit = true;

                logger.info(TAG, "ARouter interceptors init over.");

                synchronized (interceptorInitLock) {
                    interceptorInitLock.notifyAll();
                }
            }
        }
    });
}

可以看到，这里会把Warehouse.interceptorsIndex里的所以interceptor都执行init方法，然后设置interceptorHasInit为true，因为这里的init方法是新建线程执行的，所以在执行的同时，completion后面的doInterceptions方法也在异步执行，所以现在可以理解checkInterceptorsInitStatus的意义了，它就是在等init完成，调用interceptorInitLock.notifyAll()结束wait，从而继续往下执行doInterceptions方法，如果因为等待时间太长被系统终止则会抛出InterruptedException异常。

doInterceptions下面的代码就是开启子线程执行_execute方法，interceptorCounter.await同步等待 _executes执行完：

  private static void _execute(final int index, final CancelableCountDownLatch counter, final Postcard postcard) {
        if (index < Warehouse.interceptors.size()) {
            IInterceptor iInterceptor = Warehouse.interceptors.get(index);
            iInterceptor.process(postcard, new InterceptorCallback() {
                @Override
                public void onContinue(Postcard postcard) {
                    // Last interceptor excute over with no exception.
                    counter.countDown();
                    _execute(index + 1, counter, postcard);  // When counter is down, it will be execute continue ,but index bigger than interceptors size, then U know.
                }

                @Override
                public void onInterrupt(Throwable exception) {
                    // Last interceptor excute over with fatal exception.

                    postcard.setTag(null == exception ? new HandlerException("No message.") : exception.getMessage());    // save the exception message for backup.
                    counter.cancel();
                    // Be attention, maybe the thread in callback has been changed,
                    // then the catch block(L207) will be invalid.
                    // The worst is the thread changed to main thread, then the app will be crash, if you throw this exception!
//                    if (!Looper.getMainLooper().equals(Looper.myLooper())) {    // You shouldn't throw the exception if the thread is main thread.
//                        throw new HandlerException(exception.getMessage());
//                    }
                }
            });
        }
    }

这里就是对所有的Interceptor依次执行process方法，假如定义了一个Interceptor：

@Interceptor(priority = 8, name = "test interceptor")
public class TestInterceptor implements IInterceptor {
    @Override
    public void process(Postcard postcard, InterceptorCallback callback) {
        ...
        // No problem! hand over control to the framework
        if(LoginUtils.isLogin()){
                callback.onContinue(postcard);
        }else{
          callback.onInterrupt(new Throwable("The Route needs login first!"));
        }
        
        // Interrupt routing process
        // callback.onInterrupt(new RuntimeException("Something exception"));      

        // The above two types need to call at least one of them, otherwise it will not continue routing
    }

    @Override
    public void init(Context context) {
        // Interceptor initialization, this method will be called when sdk is initialized, it will only be called once
    }
}

这里模拟了跳转需要登录的逻辑，如果已登录则执行跳转，如果未登录则intertupt。在process中调用callback.onContinue或者callback.onInterrupt方法就会回到_execute中处理。

执行完后判断如果interceptorCounter的getCount大于0说明因Postcard超时时间到期中止，这个超时时间可以设置，默认300秒，如果postcard.getTag()不为null说明有异常产生，若顺利的话会走到callback.onContinue(postcard)，就会回调到_ARouter.navigation方法里doIntercaptions传入的匿名InterceptorCallback对象的onContinue方法，从而执行 _navigation方法执行跳转。

至此，拦截工作就完成了。

Priority

Interceptor的priority在哪设置的？@Interceptor注解修饰的类会被自动创建的ARouter$$Interceptors$$app存进Warehouse.interceptorsIndex中，原理同上：

public class ARouter$$Interceptors$$app implements IInterceptorGroup {
  @Override
  public void loadInto(Map<Integer, Class<? extends IInterceptor>> interceptors) {
    interceptors.put(5, LoginInterceptor.class);
  }
}

因为我创建的Interceptor是：

@Interceptor(name = "LoginInInterceptor" , priority = 5)
class LoginInterceptor : IInterceptor {

所以interceptors.put的参数分别是5和LoginInterceptor.class，5是设置的priority，为什么把priority作为key呢？因为Warehouse的interceptorsIndex是一个UniqueKeyTreeMap，它的put方法：

@Override
public V put(K key, V value) {
    if (containsKey(key)) {
        throw new RuntimeException(String.format(tipText, key));
    } else {
        return super.put(key, value);
    }
}

比其父类多的一个操作是首先判断不能添加重复key值的value。然后调用了父类TreeMap的put方法：

public V put(K key, V value) {
    TreeMapEntry<K,V> t = root;
    if (t == null) {
        compare(key, key); // type (and possibly null) check

        root = new TreeMapEntry<>(key, value, null);
        size = 1;
        modCount++;
        return null;
    }
    int cmp;
    TreeMapEntry<K,V> parent;
    // split comparator and comparable paths
    Comparator<? super K> cpr = comparator;
    if (cpr != null) {
        do {
            parent = t;
            cmp = cpr.compare(key, t.key);
            if (cmp < 0)
                t = t.left;
            else if (cmp > 0)
                t = t.right;
            else
                return t.setValue(value);
        } while (t != null);
    }
    else {
        if (key == null)
            throw new NullPointerException();
        @SuppressWarnings("unchecked")
            Comparable<? super K> k = (Comparable<? super K>) key;
        do {
            parent = t;
            cmp = k.compareTo(t.key);
            if (cmp < 0)
                t = t.left;
            else if (cmp > 0)
                t = t.right;
            else
                return t.setValue(value);
        } while (t != null);
    }
    TreeMapEntry<K,V> e = new TreeMapEntry<>(key, value, parent);
    if (cmp < 0)
        parent.left = e;
    else
        parent.right = e;
    fixAfterInsertion(e);
    size++;
    modCount++;
    return null;
}

可见会按照key值将新元素插入到合适的位置，顺序就是key值越小越靠前，而我们前面看到执行process的时候都是从Warehouse.interceptorsIndex的第0个元素开始，这也就是为什么它文档上写的priority越小优先级越高。

Route注解里面也可以设置priority，但是我发现它好像没有用到，我唯一能想到的就是可以在NavigationCallback或者Interceptor中通过Postcard对象取到它然后根据它的值来做点什么逻辑，同样extra属性也是这样。

Pretreatment Service

在navigation方法的最前面有这样几行代码：

PretreatmentService pretreatmentService = ARouter.getInstance().navigation(PretreatmentService.class);
if (null != pretreatmentService && !pretreatmentService.onPretreatment(context, postcard)) {
    // Pretreatment failed, navigation canceled.
    return null;
}

如果说Interceptor是在找到路由后、跳转之前的处理拦截，那PretreatmentService就是在查找路由之前的处理拦截：

@Route(path = "/xxx/xxx")
public class PretreatmentServiceImpl implements PretreatmentService {
    @Override
    public boolean onPretreatment(Context context, Postcard postcard) {
        // Do something before the navigation, if you need to handle the navigation yourself, the method returns false
    }

    @Override
    public void init(Context context) {

    }
}

官方注释告诉我们，如果你不希望通过ARouter自动跳转的话这里可以返回false，就不会执行查找路由等操作了。

注意，PretreatmentService只能定义一个，因为：

public class ARouter$$Providers$$app implements IProviderGroup {
  @Override
  public void loadInto(Map<String, RouteMeta> providers) {
    providers.put("com.alibaba.android.arouter.facade.service.PretreatmentService", RouteMeta.build(RouteType.PROVIDER, MyPreTreatmentService.class, "/lllSS/myPretreatmentService", "lllSS", null, 1, -2147483648));
    providers.put("com.alibaba.android.arouter.facade.service.PretreatmentService", RouteMeta.build(RouteType.PROVIDER, OtherPretreatmentService.class, "/lllSS/otherPretreatmentService", "lllSS", null, 2, -2147483648));
  }
}

定义多个，key值是一样的，因此只有最后一个会生效。

Rewrite URL

在 _ARouter.build方法里有这样的处理：

PathReplaceService pService = ARouter.getInstance().navigation(PathReplaceService.class);
if (null != pService) {
    //path是String
    path = pService.forString(path);
    //path是Uri
    //path = pService.forUri(path);
}

也就是说出build传入的路由地址还可以通过PathReplaceService的api统一处理。

定义如下：

// Implement the PathReplaceService interface
@Route(path = "/xxx/xxx")
public class PathReplaceServiceImpl implements PathReplaceService {
    /**
    * For normal path.
    *
    * @param path raw path
    */
    String forString(String path) {
        // Custom logic
        return path;
    }

/**
    * For uri type.
    *
    * @param uri raw uri
    */
    Uri forUri(Uri uri) {
        // Custom logic
        return url;
    }
}

同样，定义多个只会以ARouter$$Providers$$moduleName的loadInto里面put的最后一个key为com.alibaba.android.arouter.facade.service.PathReplaceService的为准。

其他API description

// Build a standard route request
ARouter.getInstance().build("/home/main").navigation();

// Build a standard route request, via URI
Uri uri;
ARouter.getInstance().build(uri).navigation();

// Build a standard route request, startActivityForResult
// The first parameter must be Activity and the second parameter is RequestCode
ARouter.getInstance().build("/home/main", "ap").navigation(this, 5);

// Pass Bundle directly
Bundle params = new Bundle();
ARouter.getInstance()
    .build("/home/main")
    .with(params)
    .navigation();

// Set Flag
ARouter.getInstance()
    .build("/home/main")
    .withFlags();
    .navigation();

// For fragment
Fragment fragment = (Fragment) ARouter.getInstance().build("/test/fragment").navigation();
                    
// transfer the object 
ARouter.getInstance()
    .withObject("key", new TestObj("Jack", "Rose"))
    .navigation();

// Think the interface is not enough, you can directly set parameter into Bundle
ARouter.getInstance()
        .build("/home/main")
        .getExtra();

// Transition animation (regular mode)
ARouter.getInstance()
    .build("/test/activity2")
    .withTransition(R.anim.slide_in_bottom, R.anim.slide_out_bottom)
    .navigation(this);

// Transition animation (API16+)
ActivityOptionsCompat compat = ActivityOptionsCompat.
    makeScaleUpAnimation(v, v.getWidth() / 2, v.getHeight() / 2, 0, 0);

// ps. makeSceneTransitionAnimation, When using shared elements, you need to pass in the current Activity in the navigation method

ARouter.getInstance()
    .build("/test/activity2")
    .withOptionsCompat(compat)
    .navigation();
        
// Use green channel (skip all interceptors)
ARouter.getInstance().build("/home/main").greenChannel().navigation();

// Use your own log tool to print logs
ARouter.setLogger();

// Use your custom thread pool
ARouter.setExecutor();