RxJava retryWhen操作符实现错误重试机制

业务需求

当我们在app里发起网络请求时，可能会因为各种问题导致失败。如何利用RxJava来实现出现错误后重试若干次，并且可以设定重试的时间间隔。

具体实现

网络请求使用Retrofit来做，还是使用上篇博客中的请求用户信息接口

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

下面是请求用户信息接口的逻辑代码

userApi.getUserInfoNoToken()
                        //总共重试3次，重试间隔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

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);
                        }
                    });
        }
    }

如何模拟重试呢？

方法一：把服务器关闭，关闭服务器后，客户端请求接口的必然会报错，看看是不是重试三次。

运行输出：

‘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

上面是重试三次了，但是我们怎么知道，如果在服务器启动后，在接下的重试中请求成功呢？接下来试试方法二。

方法二：先把服务器关闭，当点击按钮请求的同时，启动Tomcat服务器。

运行输出：

‘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

可以发现，在第三次重试的时候，服务器可用了。

github源码下载