一个小技巧提升 OkHttp 请求稳定性
OkHttp是可以说是Android开发中，每个项目都必需依赖的网络库，我们可以很便捷高效的处理网络请求，极大的提升了编码效率。但是有时候，我们使用OkHttp也会遇到这样的问题
崩溃的stacktrace
1 2 3 4 5 6 7 8 9 10 11 | E AndroidRuntime: FATAL EXCEPTION: OkHttp Dispatcher E AndroidRuntime: Process: com.example.okhttpexceptionsample, PID: 13564 E AndroidRuntime: java.lang.NullPointerException: blablabla E AndroidRuntime: at com.example.okhttpexceptionsample.MainActivity$createNPEInterceptor$1.intercept(MainActivity.kt:61) E AndroidRuntime: at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:112) E AndroidRuntime: at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:87) E AndroidRuntime: at okhttp3.RealCall.getResponseWithInterceptorChain(RealCall.kt:184) E AndroidRuntime: at okhttp3.RealCall$AsyncCall.run(RealCall.kt:136) E AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167) E AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641) E AndroidRuntime: at java.lang.Thread.run(Thread.java:784) |
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为什么会崩溃
从上面的stacktrace，我们可以分析到，发生了NullPointerException。发生了崩溃。
等等，我记得OkHttp有处理异常的情况呢。
嗯，确实，OkHttp有处理异常的情况，比如发生异常会调用onFailure。比如下面的Callback的内容介绍。
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | interface Callback { /** * Called when the request could not be executed due to cancellation, a connectivity problem or * timeout. Because networks can fail during an exchange, it is possible that the remote server * accepted the request before the failure. */ fun onFailure(call: Call, e: IOException) /** * Called when the HTTP response was successfully returned by the remote server. The callback may * proceed to read the response body with [Response.body]. The response is still live until its * response body is [closed][ResponseBody]. The recipient of the callback may consume the response * body on another thread. * * Note that transport-layer success (receiving a HTTP response code, headers and body) does not * necessarily indicate application-layer success: `response` may still indicate an unhappy HTTP * response code like 404 or 500. */ @Throws(IOException::class) fun onResponse(call: Call, response: Response) } |
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是的，
- OkHttp只处理了IOException的情况，
- NullPointerException不是IOException的子类
所以没有被处理,发生了崩溃。
那么有没有办法解决，让这种崩溃不发生，对用户不进行干扰呢？其实是可以的。
使用Interceptor
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | package com.example.okhttpexceptionsample import okhttp3.Interceptor import okhttp3.Response import java.io.IOException /** * 对于Interceptor的intercept中可能出现的Throwable包裹成IOExceptionWrapper，转成网络请求失败，而不是应用崩溃 */ class SafeGuardInterceptor : Interceptor { override fun intercept(chain: Interceptor.Chain): Response { try { return chain.proceed(chain.request()) } catch (t: Throwable) { throw IOExceptionWrapper("SafeGuarded when requesting ${chain.request().url}", t) } } } /** * 将chain.proceed处理中发生的Throwable包装成IOExceptionWrapper */ class IOExceptionWrapper(message: String?, cause: Throwable?) : IOException(message, cause) |
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上面的代码，我们将任何Throwable的转成IOExceptionWrapper（伪装成IOException），然后添加到OkHttpClient中
1 2 3 4 5 | fun createOKHttpClient(): OkHttpClient { return OkHttpClient.Builder() .addInterceptor(SafeGuardInterceptor()) .build() } |
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当我们再次执行有NPE的代码，日志就发生了改变(不再是崩溃的日志，而是异常的日志)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | W System.err: com.example.okhttpexceptionsample.IOExceptionWrapper: SafeGuarded=blablabla W System.err: at com.example.okhttpexceptionsample.SafeGuardInterceptor.intercept(SafeGuardInterceptor.kt:12) W System.err: at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:112) W System.err: at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:87) W System.err: at okhttp3.RealCall.getResponseWithInterceptorChain(RealCall.kt:184) W System.err: at okhttp3.RealCall$AsyncCall.run(RealCall.kt:136) W System.err: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167) W System.err: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641) W System.err: at java.lang.Thread.run(Thread.java:784) W System.err: Caused by: java.lang.NullPointerException: blablabla W System.err: at com.example.okhttpexceptionsample.MainActivity$createNPEInterceptor$1.intercept(MainActivity.kt:61) W System.err: at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:112) W System.err: at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:87) W System.err: at com.example.okhttpexceptionsample.SafeGuardInterceptor.intercept(SafeGuardInterceptor.kt:10) W System.err: ... 7 more |
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上述需要注意两点
- 添加的是Interceptor,而不是NetworkInterceptor
- 顺序很重要,一定要放在第一个位置
这么做有什么问题
这么做，当然可以明显增强请求的稳定性和应用的崩溃率。但是是不是也有一些问题呢？比如
- 将问题情况吞掉，不利于发现问题呢
是的，确实可能存在上述的问题，但是我们可以利用下面的方式减轻或者解决问题
- 只针对release情况应用SafeGuardInterceptor,这样便于debug情况下更容易发现
- 针对不同的build variants进行配置，便于尽可能的小范围发现问题
- 实行更加智能的动态开启策略。
在软件工程中，很多决定都是trade-off的体现，具体的实施方案大家可以自行平衡选择。