業務需求

當我們在app裡發起網路請求時，可能會因為各種問題導致失敗。如何利用RxJava來實現出現錯誤後重試若干次，並且可以設定重試的時間間隔。

具體實現

網路請求使用Retrofit來做，請求使用者資訊介面

@GET("/userinfo?noToken=1")
    Observable<Response> getUserInfoNoToken();

請求使用者資訊介面的邏輯程式碼

userApi.getUserInfoNoToken()
                        //總共重試3次，重試間隔3000毫秒
                        .retryWhen(new
 
 RetryWithDelay(3, 3000))
                        .observeOn(AndroidSchedulers.mainThread())
                        .subscribeOn(Schedulers.io())
                        .subscribe(new Action1<Response>() {
                            @Override
                            public void call(Response response) {
                                String content = new
 
 String(((TypedByteArray) response.getBody()).getBytes());
                                printLog(tvLogs, "", content);
                            }
                        }, new Action1<Throwable>() {
                            @Override
                            public void call(Throwable throwable) {
                                throwable.printStackTrace();
                            }
                        });
 

RetryWithDelay程式碼：

public class RetryWithDelay implements
            Func1<Observable<? extends Throwable>, Observable<?>> {

        private final int maxRetries;
        private final int retryDelayMillis;
        private int retryCount;

        public RetryWithDelay(int maxRetries, int retryDelayMillis) {
            this.maxRetries = maxRetries;
            this.retryDelayMillis = retryDelayMillis;
        }

        @Override
        public Observable<?> call(Observable<? extends Throwable> attempts) {
            return attempts
                    .flatMap(new Func1<Throwable, Observable<?>>() {
                        @Override
                        public Observable<?> call(Throwable throwable) {
                            if (++retryCount <= maxRetries) {
                                // When this Observable calls onNext, the original Observable will be retried (i.e. re-subscribed).
                                printLog(tvLogs, "", "get error, it will try after " + retryDelayMillis
                                        + " millisecond, retry count " + retryCount);
                                return Observable.timer(retryDelayMillis,
                                        TimeUnit.MILLISECONDS);
                            }
                            // Max retries hit. Just pass the error along.
                            return Observable.error(throwable);
                        }
                    });
        }
    }

如何模擬重試呢？

方法一：把伺服器關閉，關閉伺服器後，客戶端請求介面的必然會報錯，看看是不是重試三次。

執行輸出：

'get error, it will try after 3000 millisecond, retry count 1'
Main Thread:false, Thread Name:Retrofit-Idle

'get error, it will try after 3000 millisecond, retry count 2'
Main Thread:false, Thread Name:Retrofit-Idle

'get error, it will try after 3000 millisecond, retry count 3'
Main Thread:false, Thread Name:Retrofit-Idle

上面是重試三次了，但是我們怎麼知道，如果在伺服器啟動後，在接下的重試中請求成功呢？接下來試試方法二。

方法二：先把伺服器關閉，當點選按鈕請求的同時，啟動Tomcat伺服器。

執行輸出：

'get error, it will try after 3000 millisecond, retry count 1'
Main Thread:false, Thread Name:Retrofit-Idle

'get error, it will try after 3000 millisecond, retry count 2'
Main Thread:false, Thread Name:Retrofit-Idle

'username:chiclaim,age:007'
Main Thread:true, Thread Name:main

可以發現，在第三次重試的時候，伺服器可用了。