作者：小马快跑

我们知道在使用ARouter时，需要在build.config里配置：

annotationProcessor 'com.alibaba:arouter-compiler:1.2.2'

并且知道annotationProcessor用来声明注解解析器，arouter-compiler用来解析ARouter中的各个注解并自动生成class类，那么我们就来看一下到底生成了哪些类：

其生成的5个索引文件有4大类(Group类有2个文件，按Group区分开了)，他们都实现了ARouter中的接口：

至于他们都代表什么，我们后面一一分析。

ARouter初始化

在自定义Application中进行初始化：

// 尽可能早，推荐在Application中初始化
ARouter.init(Application.this);

点进去看一下：

//ARouter.java
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.");
    }
}

哦，ARouter又调用了_ARouter.init(application)去初始化，再点进去：

//_ARouter.java

private volatile static ThreadPoolExecutor executor = DefaultPoolExecutor.getInstance();

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;
}

哦，_ARouter在init初始化方法里除了初始化一些变量和一个handler，又调用了LogisticsCenter.init(mContext, executor), 其中executor是一个线程池, 继续跟到LogisticsCenter里去：

/**
 * LogisticsCenter contains all of the map.
 * 1\. Creates instance when it is first used.
 * 2\. Handler Multi-Module relationship map(*)
 * 3\. Complex logic to solve duplicate group definition
 */

//LogisticsCenter.java
public synchronized static void init(Context context, ThreadPoolExecutor tpe) throws HandlerException {

      Set<String> routerMap;

      //1、遍历“com.alibaba.android.arouter.routes”路径下的类并把其加入到set中
      if (ARouter.debuggable() || PackageUtils.isNewVersion(context)) {
          // 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();
          }
         // Save new version name when router map update finishes.
         PackageUtils.updateVersion(context);    
      } 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>()));
            }

      //2、遍历set，将root、group、provider分类并填充到Warehouse路由表中
      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);
          }
      }
  }
}

LogisticsCenter.init方法比较长，上面只保留了核心代码，ARouter优先使用arouter-auto-register插件去解析并填充Warehouse路由表,忽略这种方式。我们来看上面这种加载方式，PackageUtils.isNewVersion(context)中判断SharedPreferences(后面简称sp)里面是否有存储versionName及versionCode，如果没有或者他们有更新的时候，需要重新加载一次com.alibaba.android.arouter.routes这个路径下的类名并填充到Set中，否则直接从sp中取数据并赋值到Set中去。接着就开始遍历这个Set,并通过Class.forName(className)这种反射方式去实例化类并调用类中的loadInto方法将注解对应的索引信息添加到Warehouse路由表中。画个图来总结一下：

ARouter跳转

ARouter跳转时，直接使用ARouter.getInstance().build("xxx/xxx").navigation()即可完成跳转，那我们就来看一下源码，看看里面都做了什么，首先是build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 = navigation(PathReplaceService.class);
        if (null != pService) {
            path = pService.forString(path);
        }
        return build(path, extractGroup(path));
    }
}

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

三个方法中都有，PathReplaceService pService = ARouter.getInstance().navigation(PathReplaceService.class); 那么这个PathReplaceService是干啥的，点进去看看：

/**
 * Preprocess your path
 */
public interface PathReplaceService extends IProvider {

    /**
     * For normal path.
     *
     * @param path raw path
     */
    String forString(String path);

    /**
     * For uri type.
     *
     * @param uri raw uri
     */
    Uri forUri(Uri uri);
}

看它的介绍就知道了，原来这个类是用来预处理path和uri的，调用方需要实现PathReplaceService就可以做预处理，如果不实现，默认pService==null，那么直接走下面的去初始化Postcard实体类。

接着来看navigation方法，因为build方法返回的是PostCard类，所以调用的是PostCard类的navigation方法，经过一系列跳转，最终来到_ARouter.getInstance().navigation(mContext, postcard, requestCode, callback) ：

protected Object navigation(final Context context, final Postcard postcard, final int requestCode, final NavigationCallback callback) {
    try {
        LogisticsCenter.completion(postcard);
      } catch (NoRouteFoundException ex) {
        logger.warning(Consts.TAG, ex.getMessage());
     }
        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() {

            @Override
            public void onContinue(Postcard postcard) {
                _navigation(context, postcard, requestCode, callback);
            }

            @Override
            public void onInterrupt(Throwable exception) {
                if (null != callback) {
                    callback.onInterrupt(postcard);
                }
            }
        });
    } else {
        return _navigation(context, postcard, requestCode, callback);
    }
    return null;
}

去除了部分无关代码，只保留了核心代码，首先调用了LogisticsCenter.completion方法，我们追进去看看：

//LogisticsCenter.java
/**
 * Completion the postcard by route metas
 *
 * @param postcard Incomplete postcard, should complete by this method.
 */
public synchronized static void completion(Postcard 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 {
                IRouteGroup iGroupInstance = groupMeta.getConstructor().newInstance();
                iGroupInstance.loadInto(Warehouse.routes);
                Warehouse.groupsIndex.remove(postcard.getGroup());

            } 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;
        }
    }
}

这个类很长，但是逻辑还是很清晰的：首先从Warehouse路由表的routes中获取RouteMeta，但是第一次获取的时候为空（因为init时只填充了Warehouse路由表的groupsIndex、interceptorsIndex、providersIndex，还记得吗?），接着从Warehouse.groupsIndex中根据group的名字找到对应的group索引，并将生成的索引类的map数据加载到Warehouse.routes中，然后把Warehouse.groupsIndex中对应的group删除掉，以免重复加载数据，然后调用了completion(postcard)进行重新加载。此时Warehouse.routes已经不为空，根据path获取对应的RouteMeta，就会走到else逻辑中，先是对PostCard设置了一堆属性，最后对IProvider的子类进行了初始化并加载到Warehouse.providers中，同时也设置到PostCard中，并给PROVIDER和FRAGMENT设置了绿色通道(不会被拦截)。总结一下：主要逻辑就是通过Warehouse.groupsIndex找到对应的group并进行加载，实现了分组加载路由表。

我们继续回到navigation方法中往下走，首先通过postcard.isGreenChannel()判断是否会拦截，如果拦截，就会走interceptorService的逻辑(interceptorService是在afeterInit中初始化的)，否则就走到了_navigation逻辑中，那么来看_navigation方法：

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;
}

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 {
        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);
    }
}

哦，原来ARouter跳转Activity最终也是用原生的Intent实现的，如果navigation()不传入context，则使用初始化时Application作为context，如果是FRAGMENT、PROVIDER、CONTENT_PROVIDER、BOARDCAST，通过反射方式初始化并返回即可。

尝试画个图来总结一下navigation：

嗯，到这里ARouter内部的主要流程就分析完了~

ARouter跳转原理：ARouter路由跳转本质上也是通过原生的startActiviy及startActivityForResult来实现的，只不过ARouter通过APT形式将编译期通过解析注解生成的索引加载到Warehouse路由表中，从而制造跳转规则。并且可以在跳转之前设置拦截或过滤。