分析的okhttp版本為

 implementation("com.squareup.okhttp3:okhttp:4.9.1")

RealCall.kt文件中 有一個(gè)函數(shù) fun getResponseWithInterceptorChain():Response 這個(gè)函數(shù)中是攔截器相關(guān)邏輯的開(kāi)始。

  @Throws(IOException::class)
  internal fun getResponseWithInterceptorChain(): Response {
    // 構(gòu)建一個(gè)攔截器可變列表，添加全部攔截器到這個(gè)列表
    val interceptors = mutableListOf<Interceptor>()
    interceptors += client.interceptors //用戶自己定義的攔截器
    //以下全部是okhttp內(nèi)置攔截器  
    interceptors += RetryAndFollowUpInterceptor(client)
    interceptors += BridgeInterceptor(client.cookieJar)
    interceptors += CacheInterceptor(client.cache)
    interceptors += ConnectInterceptor
    if (!forWebSocket) {
      interceptors += client.networkInterceptors
    }
    //真正發(fā)起請(qǐng)求的攔截器
    interceptors += CallServerInterceptor(forWebSocket)

    //構(gòu)建攔截器請(qǐng)求chain,注意此處為起始chain
    val chain = RealInterceptorChain(
        call = this,
        interceptors = interceptors, //全部攔截器列表
        index = 0,//需要處理的攔截器列表的index
        exchange = null,
        request = originalRequest,//起初構(gòu)建的 Request 對(duì)象
        connectTimeoutMillis = client.connectTimeoutMillis,
        readTimeoutMillis = client.readTimeoutMillis,
        writeTimeoutMillis = client.writeTimeoutMillis
    )

    var calledNoMoreExchanges = false
    try {
      //執(zhí)行攔截器
      val response = chain.proceed(originalRequest)
      if (isCanceled()) {
        response.closeQuietly()
        throw IOException("Canceled")
      }
      return response
    } catch (e: IOException) {
      calledNoMoreExchanges = true
      throw noMoreExchanges(e) as Throwable
    } finally {
      if (!calledNoMoreExchanges) {
        noMoreExchanges(null)
      }
    }
  }

通過(guò)RealInterceptorChain的構(gòu)造方法也大致可以推斷出它內(nèi)部所包含的對(duì)象數(shù)據(jù)和方法

//簡(jiǎn)寫(xiě)，偽代碼
class RealInterceptorChain(
    allInterceptor:mutableListOf<Interceptor>,//全部的攔截器
    index:Int//當(dāng)前需要處理攔截器列表哪一個(gè)攔截器的index
    originalRequest:Request//原始的請(qǐng)求提對(duì)象
){
    //執(zhí)行
    fun proceed(r:Request){}
}

看一下proceed()做了什么

 @Throws(IOException::class)
  override fun proceed(request: Request): Response {
    
    //此處省略一部分代碼...
 
    //構(gòu)建下一個(gè)chain (RealInterceptorChain)
    val next = copy(index = index + 1, request = request)
    //取出當(dāng)下攔截器，注意下次這個(gè)index 會(huì)被+1
    val interceptor = interceptors[index]

    //通過(guò)攔截器調(diào)用intercept()并把對(duì)應(yīng)的chain傳入攔截器
    val response = interceptor.intercept(next) ?: throw NullPointerException(
        "interceptor $interceptor returned null")

    //此處省去一部分代碼...
    
    return response //返回響應(yīng)體對(duì)象
  }

現(xiàn)在來(lái)看一張圖

攔截器調(diào)用原理.jpg

這張圖詮釋了攔截器的調(diào)用順序與內(nèi)存對(duì)象關(guān)系，簡(jiǎn)單梳理一下：

真正的調(diào)用是第一個(gè)RealInterceptorChain對(duì)象發(fā)起的，通過(guò)它的proceed()方法，構(gòu)建出一個(gè)Chain對(duì)象，并找到一個(gè)攔截器，把這個(gè)chain對(duì)象傳遞給這個(gè)攔截器，通過(guò)攔截器中的chain再次調(diào)用proceed()重復(fù)上面的動(dòng)作。
直到CallServerInterceptor攔截器為止開(kāi)始返回Response對(duì)象，之后就是攔截器中的chain.proceed(req)后面的調(diào)用被執(zhí)行（遞歸）。

通過(guò)了解了攔截器的實(shí)現(xiàn)機(jī)制，我們?cè)诙x攔截器時(shí)，就可以毫不費(fèi)力了。

比如如下定義的攔截器：

/**
* 緩存策略攔截器
*/
class CacheInterceptor(var day: Int = 7) : Interceptor {
    override fun intercept(chain: Interceptor.Chain): Response {
        var request = chain.request()//獲取RealInterceptorChain中的request對(duì)象
        if (!NetworkUtil.isNetworkAvailable(appContext)) {
            request = request.newBuilder()
                .cacheControl(CacheControl.FORCE_CACHE)
                .build()
        }
        val response = chain.proceed(request)//執(zhí)行RealInterceptorChain中的proceed()繼而達(dá)到調(diào)用下一個(gè)攔截器的目的
        
        //以下都是在CallServerInterceptor攔截器返回后被調(diào)用
        if (!NetworkUtil.isNetworkAvailable(appContext)) {
            val maxAge = 60 * 60
            response.newBuilder()
                .removeHeader("Pragma")
                .header("Cache-Control", "public, max-age=$maxAge")
                .build()
        } else {
            val maxStale = 60 * 60 * 24 * day // tolerate 4-weeks stale
            response.newBuilder()
                .removeHeader("Pragma")
                .header("Cache-Control", "public, only-if-cached, max-stale=$maxStale")
                .build()
        }
        return response
    }
}

我們看到自定義攔截器最關(guān)心的兩個(gè)方法是

var request = chain.request() //就是獲取chain中保存的request對(duì)象
val response = chain.proceed(request) //執(zhí)行下一個(gè)攔截器，直到CallServerInterceptor返回

我們?cè)诤?jiǎn)單看一下CallServerInterceptor

class CallServerInterceptor{
    
  override fun intercept(chain: Interceptor.Chain): Response {
    val realChain = chain as RealInterceptorChain
  
    val request = realChain.request
    val requestBody = request.body
    requestBody.writeTo(bufferedRequestBody) //真正使用request對(duì)象
 
    var response = responseBuilder//真正創(chuàng)建 response 對(duì)象
        .request(request)
        .handshake(exchange.connection.handshake())
        .sentRequestAtMillis(sentRequestMillis)
        .receivedResponseAtMillis(System.currentTimeMillis())
        .build()
   
    return response
  }
}

到此 攔截器分析完畢！