ARouter源码解析（二）
前言
前几天对 ARouter 的页面跳转源码进行了分析，趁着今天有空，就讲讲 ARouter 里面的拦截器吧。
ARouter 拦截器的使用方法在这就不多说了，不了解的同学可以去 GitHub 上看看。那就直接进入正题了。
拦截器解析
把视线转移回 ARouter 的 init 方法
public static void init(Application application) {
if (!hasInit) {
logger = _ARouter.logger;
_ARouter.logger.info(Consts.TAG, "ARouter init start.");
hasInit = _ARouter.init(application);
// 如果初始化完成了
if (hasInit) {
_ARouter.afterInit();
}
_ARouter.logger.info(Consts.TAG, "ARouter init over.");
}
}
在 init 中，判断了初始化完成后，调用了 _ARouter.afterInit() 来初始化拦截器，跟进代码去看看。
static void afterInit() {
// Trigger interceptor init, use byName.
interceptorService = (InterceptorService) ARouter.getInstance().build("/arouter/service/interceptor").navigation();
}
发现有个 InterceptorService ，InterceptorService 就是用来控制拦截的服务组件，来看看它的接口是怎么定义的
public interface InterceptorService extends IProvider {
/**
* Do interceptions
*/
void doInterceptions(Postcard postcard, InterceptorCallback callback);
}
之前我们分析过，IProvider 也是可以用 ARouter.getInstance().build("xxx").navigation() 的形式获取的。关键的代码在 LogisticsCenter 的 completion 方法中
/**
* Completion the postcard by route metas
*
* @param postcard Incomplete postcard, should complete by this method.
*/
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) {
// 省略一大串代码
...
} else {
// 省略一大串代码
...
switch (routeMeta.getType()) {
case PROVIDER: // if the route is provider, should find its instance
// Its provider, so it must implement IProvider
Class providerMeta = (Class) 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;
}
}
}
可以看到，如果是 PROVIDER 类型的，就会反射出一个单例对象，并且设置为绿色通道（即不受拦截器的影响）。更详细的代码就不过多介绍了，不理解的同学可以结合着上一篇博客私下回去再看。
所以其实在 afterInit 方法中，只是获取到了 InterceptorService 的实例对象，我们根据上面的 “/arouter/service/interceptor” 可以很轻松的查到，InterceptorService 接口的实现类就是 InterceptorServiceImpl
@Route(path = "/arouter/service/interceptor")
public class InterceptorServiceImpl implements InterceptorService {
private static boolean interceptorHasInit;
private static final Object interceptorInitLock = new Object();
...
@Override
public void init(final Context context) {
LogisticsCenter.executor.execute(new Runnable() {
@Override
public void run() {
if (MapUtils.isNotEmpty(Warehouse.interceptorsIndex)) {
for (Map.Entry> entry : Warehouse.interceptorsIndex.entrySet()) {
Class 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();
}
}
}
});
}
}
我们先来看 InterceptorServiceImpl 的 init 方法。
在 init 方法中，做的主要事情就是遍历所有 IInterceptor class 并创建出对象，调用其 init 方法，完成初始化操作。
初始化完成之后，InterceptorService又是在哪里被使用的呢？
我们在 _ARouter 的 navigation 方法里可以看到它的踪迹：
protected Object navigation(final Context context, final Postcard postcard, final int requestCode, final NavigationCallback callback) {
...
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;
}
如果不是绿色通道的话，就会启动拦截器去进行拦截。
@Override
public void doInterceptions(final Postcard postcard, final InterceptorCallback callback) {
if (null != Warehouse.interceptors && Warehouse.interceptors.size() > 0) {
checkInterceptorsInitStatus();
// 如果拦截器还没有初始化好
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 {
_excute(0, interceptorCounter, postcard);
// 设置超时时间 默认300s
interceptorCounter.await(postcard.getTimeout(), TimeUnit.SECONDS);
if (interceptorCounter.getCount() > 0) { // 如果 count 大于 0 说明是拦截器超时
callback.onInterrupt(new HandlerException("The interceptor processing timed out."));
} else if (null != postcard.getTag()) { // 说明是某个拦截器中断了，导致整个流程中断
callback.onInterrupt(new HandlerException(postcard.getTag().toString()));
} else { // 否则就通过
callback.onContinue(postcard);
}
} catch (Exception e) {
callback.onInterrupt(e);
}
}
});
} else { // 如果没有拦截器 就通过
callback.onContinue(postcard);
}
}
/**
* Excute interceptor
*
* @param index current interceptor index
* @param counter interceptor counter
* @param postcard routeMeta
*/
private static void _excute(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();
// 一个拦截器执行好后，执行下一个
_excute(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.
// 如果其中一个拦截器中断的话，就中断整个流程
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());
// }
}
});
}
}
上面的代码基本上都加了注释了，这里就不再多讲了。
到这里整个 ARouter 拦截器的流程就差不多讲完了，如果还有哪里不懂的地方可以在评论区留言。
再见?
