OkHttp自定義重試次數

本文主要應用了OkHttp的Interceptor來實現自定義重試次數

雖然OkHttp自帶retryOnConnectionFailure(true)方法可以實現重試，但是不支持自定義重試次數，所以有時並不能滿足我們的需求。

#1.自定義重試攔截器：

/**
 * 重試攔截器
 */
public class RetryIntercepter implements Interceptor {

    public int maxRetry;//最大重試次數
    private int retryNum = 0;//假如設置為3次重試的話，則最大可能請求4次（預設1次+3次重試）

    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.測試場景類：

 1 public class RetryTest {
 2     String mUrl = "https://www.baidu.com/";
 3     OkHttpClient mClient;
 4 
 5     @Before
 6     public void setUp() {
 7         HttpLoggingInterceptor logging = new HttpLoggingInterceptor();
 8         logging.setLevel(HttpLoggingInterceptor.Level.BODY);
 9 
10         mClient = new OkHttpClient.Builder()
11                 .addInterceptor(new RetryIntercepter(3))//重試
12                 .addInterceptor(logging)//網路日誌
13                 .addInterceptor(new TestInterceptor())//模擬網路請求
14                 .build();
15     }
16 
17     @Test
18     public void testRequest() throws IOException {
19         Request request = new Request.Builder()
20                 .url(mUrl)
21                 .build();
22         Response response = mClient.newCall(request).execute();
23         System.out.println("onResponse:" + response.body().string());
24     }
25 
26     class TestInterceptor implements Interceptor {
27 
28         @Override
29         public Response intercept(Chain chain) throws IOException {
30             Request request = chain.request();
31             String url = request.url().toString();
32             System.out.println("url=" + url);
33             Response response = null;
34             if (url.equals(mUrl)) {
35                 String responseString = "{\"message\":\"我是模擬的數據\"}";//模擬的錯誤的返回值
36                 response = new Response.Builder()
37                         .code(400)
38                         .request(request)
39                         .protocol(Protocol.HTTP_1_0)
40                         .body(ResponseBody.create(MediaType.parse("application/json"), responseString.getBytes()))
41                         .addHeader("content-type", "application/json")
42                         .build();
43             } else {
44                 response = chain.proceed(request);
45             }
46             return response;
47         }
48     }
49 
50 }

#3.輸出結果：

 1 retryNum=0
 2 --> GET https://www.baidu.com/ HTTP/1.1
 3 --> END GET
 4 url=https://www.baidu.com/
 5 <-- 400 null https://www.baidu.com/ (13ms)
 6 content-type: application/json
 7 
 8 {"message":"我是模擬的數據"}
 9 <-- END HTTP (35-byte body)
10 retryNum=1
11 --> GET https://www.baidu.com/ HTTP/1.1
12 --> END GET
13 url=https://www.baidu.com/
14 <-- 400 null https://www.baidu.com/ (0ms)
15 content-type: application/json
16 
17 {"message":"我是模擬的數據"}
18 <-- END HTTP (35-byte body)
19 retryNum=2
20 --> GET https://www.baidu.com/ HTTP/1.1
21 --> END GET
22 url=https://www.baidu.com/
23 <-- 400 null https://www.baidu.com/ (0ms)
24 content-type: application/json
25 
26 {"message":"我是模擬的數據"}
27 <-- END HTTP (35-byte body)
28 retryNum=3
29 --> GET https://www.baidu.com/ HTTP/1.1
30 --> END GET
31 url=https://www.baidu.com/
32 <-- 400 null https://www.baidu.com/ (0ms)
33 content-type: application/json
34 
35 {"message":"我是模擬的數據"}
36 <-- END HTTP (35-byte body)
37 onResponse:{"message":"我是模擬的數據"}

#4.結果分析：
>1. 這裡我用一個TestInterceptor攔截器攔截掉真實的網路請求，實現response.code的自定義
2. 在RetryIntercepter中，通過response.isSuccessful()來對響應碼進行判斷，迴圈調用了多次chain.proceed(request)來實現重試攔截
3. 從輸出中可以看到，一共請求了4次（預設1次+重試3次）。

#5.其它實現方式
如果你是使用OkHttp+Retrofit+RxJava，你也可以使用retryWhen操作符：retryWhen(new RetryWithDelay())來實現重試機制

 1 public class RetryWithDelay implements Func1<Observable<? extends Throwable>, Observable<?>> {
 2 
 3         private final int maxRetries;
 4         private final int retryDelayMillis;
 5         private int retryCount;
 6 
 7         public RetryWithDelay(int maxRetries, int retryDelayMillis) {
 8             this.maxRetries = maxRetries;
 9             this.retryDelayMillis = retryDelayMillis;
10         }
11 
12         @Override
13         public Observable<?> call(Observable<? extends Throwable> attempts) {
14             return attempts
15                     .flatMap(new Func1<Throwable, Observable<?>>() {
16                         @Override
17                         public Observable<?> call(Throwable throwable) {
18                             if (++retryCount <= maxRetries) {
19                                 // When this Observable calls onNext, the original Observable will be retried (i.e. re-subscribed).
20                                 LogUtil.print("get error, it will try after " + retryDelayMillis + " millisecond, retry count " + retryCount);
21                                 return Observable.timer(retryDelayMillis,
22                                         TimeUnit.MILLISECONDS);
23                             }
24                             // Max retries hit. Just pass the error along.
25                             return Observable.error(throwable);
26                         }
27                     });
28         }
29 }