為了保證客戶端穩定性和網路容錯性，提升使用者體驗，在客戶端建立服務端IP輪詢及重試機制是十分有必要的，本文為我個人經驗總結，希望對你能有參考價值。
app在啟動時會請求一些配置資訊，其中就包括ip的路由表，將這份路由表儲存到本地，至於是sp還是物件持久化抑或是其他方式，可根據實際情況自行選擇。
因為專案網路層由Retrofit+Rxjava+Okhttp實現，Retrofit執行時無法改變baseUrl,即使可以通過反射的方式來改變baseUrl，也無法對已經生成的service物件起作用，而且我的專案中所有service物件都通過Dagger2注入，所以最終使用了這樣一種方式。
url交給UrlManager來管理
public class UrlManager {
public static final String[] HOST_SITE = {"https://xxx/api/",xxx};
public static final String[] HOST_WEB = {"https://xxx/",xxx};
public static final String HOST_SITE_DEBUG = "https://xxx/api/";
public static final String HOST_WEB_DEBUG = "https://xxx/";
public static List<String> list;
public static Random random = new Random();
public static String getHostSite() {
if (BuildConfig.IS_DEBUG) {
return processUrl(HOST_SITE_DEBUG);
} else {
String host = getDynamicHost();
if (!TextUtils.isEmpty(host)) return host;
return HOST_SITE[random.nextInt(HOST_SITE.length)];
}
}
@Nullable
private static String getDynamicHost() {
int index = (int) SPUtils.get(NeutronApplication.getContext(), Constants.URL, 0);
if (list != null && list.size() > 0 && index < list.size())
return list.get(index);
return null;
}
public static String getHostWeb() {
if (BuildConfig.IS_DEBUG) {
return processUrl(HOST_WEB_DEBUG);
} else {
String host = getDynamicHost();
if (!TextUtils.isEmpty(host)) return host;
return HOST_WEB[random.nextInt(HOST_WEB.length)];
}
}
public static void setHosts(List<String> list) {
UrlManager.list = list;
RxHelper.setCounterAttempts(list.size());
}
public static void updateUrlIndex(int i) {
if (list != null && i >= list.size())
i = 0;
SPUtils.put(NeutronApplication.getContext(), Constants.URL, i);
}
public static void updateUrlIndex() {
int o = (int) SPUtils.get(NeutronApplication.getContext(), Constants.URL, 0);
updateUrlIndex(o + 1);
}複製程式碼app啟動時拉取到配置後設定UrlManager中的路由表，然後每次根據索引去路由表動態拿請求地址，那路由索引由誰來控制呢？
因為我將專案中的rxjava抽取了一層RxHelper,所以這件事就交給RxHelper來幹了，可以覆蓋所有的網路請求。
public class RxHelper {
private static final int COUNTER_START = 0;
private static int COUNTER_ATTEMPTS = 3;
public static void setCounterAttempts(int counterAttempts) {
COUNTER_ATTEMPTS = counterAttempts;
}
public static <T> rx.Observable.Transformer<T, T> handleResult() {
return tObservable -> tObservable
.flatMap(RxHelper::createData)
.retryWhen(observable -> observable.compose(zipWithFlatMap()))
.observeOn(AndroidSchedulers.mainThread())
.subscribeOn(Schedulers.io());
}
public static <T> rx.Observable.Transformer<T, T> handleResultWithOutRetryPolicy() {
return tObservable -> tObservable.flatMap(RxHelper::createData)
.observeOn(AndroidSchedulers.mainThread())
.subscribeOn(Schedulers.io());
}
public static <T> Observable.Transformer<T, Long> zipWithFlatMap() {
return observable ->
observable.zipWith(Observable.range(COUNTER_START, COUNTER_ATTEMPTS),
(t, repeatAttempt) -> repeatAttempt)
.flatMap(new Func1<Integer, Observable<Long>>() {
@Override
public Observable<Long> call(Integer repeatAttempt) {
UrlManager.updateUrlIndex(repeatAttempt);
return Observable.timer(repeatAttempt * 200, TimeUnit.MILLISECONDS);
}
});
}
private static <T> Observable<T> createData(final T t) {
return Observable.create(new Observable.OnSubscribe<T>() {
@Override
public void call(Subscriber<? super T> subscriber) {
try {
subscriber.onNext(t);
subscriber.onCompleted();
} catch (Exception e) {
LogUtils.logw("Rxhelper: " + e.toString());
subscriber.onError(e);
}
}
});
}
}複製程式碼這樣在每次請求錯誤時，會遞增路由表索引，繼續下次請求，輪詢的間隔為Observable.timer(repeatAttempt * 200, TimeUnit.MILLISECONDS);
對RxJava的retryWhen不理解的同學請移步對RxJava中.repeatWhen()和.retryWhen()操作符的思考。
之前也說了，retrofit不能修改baseUrl，反射的方式也不適合我的專案，至於利用builder生成新的retrofit物件的方式更不考慮了，那我是怎麼實現執行時修改請求地址的呢？別忘了okhttp是可以新增攔截器的，在OkHttpIntercepter中：
public class OkHttpInterceptor implements Interceptor {
@Override
public Response intercept(Chain chain) throws IOException {
//配置request
Request request = chain.request();
Request.Builder requestBuilder = request.newBuilder();
String url = UrlManager.getHostSite();
Uri parse = Uri.parse(url);
String host = parse.getHost();
HttpUrl httpUrl = request.url().newBuilder().host(host).build();
requestBuilder.url(httpUrl);
Response.Builder responseBuilder = chain.proceed(requestBuilder.build()).newBuilder();
Response response = responseBuilder.build();
return response;
}複製程式碼攔截請求的url,修改其host，這樣整個流程就ok了，http的各種錯誤碼的處理也是可以在攔截器中統一處理的，至於其他健壯性的考慮此處就不做過多闡述了。
有同學問我，如果想處理最後一次error通知怎麼辦呢？可以這樣做，修改過的RxHelper如下：
public class RxHelper {
private static final int COUNTER_START = 0;
private static int COUNTER_ATTEMPTS = 3;
public static void setCounterAttempts(int counterAttempts) {
COUNTER_ATTEMPTS = counterAttempts;
}
public static <T> rx.Observable.Transformer<T, T> handleResult() {
return tObservable -> tObservable
.flatMap(RxHelper::createData)
.retryWhen(error -> delayedRetry(error))
.observeOn(AndroidSchedulers.mainThread())
.subscribeOn(Schedulers.io());
}
//貓膩主要在這個方法
private static Observable<Object> delayedRetry(Observable<? extends Throwable> error) {
return error.zipWith(Observable.range(COUNTER_START, COUNTER_ATTEMPTS + 1),
(i, repeatAttempt) -> repeatAttempt)
.flatMap(o -> {
UrlManager.updateUrlIndex(o);
LogUtils.logw("repeat: " + o);
return o < COUNTER_ATTEMPTS ? Observable.timer(o * 200, TimeUnit.MILLISECONDS)
: error.flatMap(Observable::error);
});
}
public static <T> rx.Observable.Transformer<T, T> handleResultWithOutRetryPolicy() {
return tObservable -> tObservable.flatMap(RxHelper::createData)
.observeOn(AndroidSchedulers.mainThread())
.subscribeOn(Schedulers.io());
}
private static <T> Observable<T> createData(final T t) {
return Observable.create(new Observable.OnSubscribe<T>() {
@Override
public void call(Subscriber<? super T> subscriber) {
try {
subscriber.onNext(t);
subscriber.onCompleted();
} catch (Exception e) {
subscriber.onError(e);
}
}
});
}
}複製程式碼