OkHttp自定义重试次数

本文主要应用了OkHttp的Interceptor来实现自定义重试次数

虽然OkHttp自带retryOnConnectionFailure(true)方法可以实现重试，但是不支持自定义重试次数，所以有时并不能满足我们的需求。

#1.自定义重试拦截器：

/**
 * 重试拦截器
 */
public class RetryIntercepter implements Interceptor {

    public int maxRetry;//最大重试次数
    private int retryNum = ;//假如设置为3次重试的话，则最大可能请求4次（默认1次+3次重试）

    public RetryIntercepter(int maxRetry) {
        this.maxRetry = maxRetry;
    }

    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();
        System.out.println("retryNum=" + retryNum);
        Response response = chain.proceed(request);
        while (!response.isSuccessful() && retryNum < maxRetry) {
            retryNum++;
            System.out.println("retryNum=" + retryNum);
            response = chain.proceed(request);
        }
        return response;
    }
}

#2.测试场景类：

 public class RetryTest {
     String mUrl = "https://www.baidu.com/";
     OkHttpClient mClient;

     @Before
     public void setUp() {
         HttpLoggingInterceptor logging = new HttpLoggingInterceptor();
         logging.setLevel(HttpLoggingInterceptor.Level.BODY);

         mClient = new OkHttpClient.Builder()
                 .addInterceptor(new RetryIntercepter())//重试
                 .addInterceptor(logging)//网络日志
                 .addInterceptor(new TestInterceptor())//模拟网络请求
                 .build();
     }

     @Test
     public void testRequest() throws IOException {
         Request request = new Request.Builder()
                 .url(mUrl)
                 .build();
         Response response = mClient.newCall(request).execute();
         System.out.println("onResponse:" + response.body().string());
     }

     class TestInterceptor implements Interceptor {

         @Override
         public Response intercept(Chain chain) throws IOException {
             Request request = chain.request();
             String url = request.url().toString();
             System.out.println("url=" + url);
             Response response = null;
             if (url.equals(mUrl)) {
                 String responseString = "{\"message\":\"我是模拟的数据\"}";//模拟的错误的返回值
                 response = new Response.Builder()
                         .code()
                         .request(request)
                         .protocol(Protocol.HTTP_1_0)
                         .body(ResponseBody.create(MediaType.parse("application/json"), responseString.getBytes()))
                         .addHeader("content-type", "application/json")
                         .build();
             } else {
                 response = chain.proceed(request);
             }
             return response;
         }
     }

 }

#3.输出结果：

 retryNum=
 --> GET https://www.baidu.com/ HTTP/1.1
 --> END GET
 url=https://www.baidu.com/
 <--  null https://www.baidu.com/ (13ms)
 content-type: application/json

 {"message":"我是模拟的数据"}
 <-- END HTTP (-byte body)
 retryNum=
 --> GET https://www.baidu.com/ HTTP/1.1
 --> END GET
 url=https://www.baidu.com/
 <--  null https://www.baidu.com/ (0ms)
 content-type: application/json

 {"message":"我是模拟的数据"}
 <-- END HTTP (-byte body)
 retryNum=
 --> GET https://www.baidu.com/ HTTP/1.1
 --> END GET
 url=https://www.baidu.com/
 <--  null https://www.baidu.com/ (0ms)
 content-type: application/json

 {"message":"我是模拟的数据"}
 <-- END HTTP (-byte body)
 retryNum=
 --> GET https://www.baidu.com/ HTTP/1.1
 --> END GET
 url=https://www.baidu.com/
 <--  null https://www.baidu.com/ (0ms)
 content-type: application/json

 {"message":"我是模拟的数据"}
 <-- END HTTP (-byte body)
 onResponse:{"message":"我是模拟的数据"}

#4.结果分析：
>1. 这里我用一个TestInterceptor拦截器拦截掉真实的网络请求，实现response.code的自定义
2. 在RetryIntercepter中，通过response.isSuccessful()来对响应码进行判断，循环调用了多次chain.proceed(request)来实现重试拦截
3. 从输出中可以看到，一共请求了4次（默认1次+重试3次）。

#5.其它实现方式
如果你是使用OkHttp+Retrofit+RxJava，你也可以使用retryWhen操作符：retryWhen(new RetryWithDelay())来实现重试机制

 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).
                                 LogUtil.print("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);
                         }
                     });
         }
 }