Kotlin 中 OkHttp 使用及解析

build.gradle

dependencies {
    //OkHttp
    implementation 'com.squareup.okhttp3:okhttp:4.9.0'
}

简单使用例子

            val okHttpClient = OkHttpClient.Builder()
                .connectTimeout(Duration.ofSeconds(10))
                .readTimeout(Duration.ofSeconds(10))
                .writeTimeout(Duration.ofSeconds(10))
                .retryOnConnectionFailure(true)
                .build()
            val request = Request.Builder().url(url).build()
            val call = okHttpClient.newCall(request)
            call.enqueue(object : Callback {
                override fun onFailure(call: Call, e: IOException) {
                    Log.e("TAG", "onFailure:${e.message}")
                }

                override fun onResponse(call: Call, response: Response) {
                    Log.d("TAG", "onResponse: ${response.body?.string()}")
                }
            })

1、通过 Builder 模式得到 okHttpClient ，OkHttpClient 包含了对网络请求的全局配置信息，包括链接超时时间、读写超时时间、链接失败重试等配置。

2、通过 Builder 模式得到 request ,Request 包含了本次网络请求的所有请求参数，包括 url、method、headers、body 等。

3、通过 newCall 方法得到 call，Call 就是用于发起请求，可用于执行 **同步请求（execute）、异步请求（enqueue）、取消请求（cancel）**等各种操作。

4、调用 enqueue 方法发起异步请求返回 response ,Response 就包含了此次网络请求的所有返回信息。

5、拿到 Response 对象的 body 并以字符串流的方式进行读取。

一、OkHttpClient

OkHttpClient 使用 Builder模式来完成初始化，其提供了很多配置参数，每个选项都有默认值。

  class Builder constructor() {
    internal var dispatcher: Dispatcher = Dispatcher()
    internal var connectionPool: ConnectionPool = ConnectionPool()
    internal val interceptors: MutableList<Interceptor> = mutableListOf()
    internal val networkInterceptors: MutableList<Interceptor> = mutableListOf()
    internal var eventListenerFactory: EventListener.Factory = EventListener.NONE.asFactory()
    internal var retryOnConnectionFailure = true
    internal var authenticator: Authenticator = Authenticator.NONE
    internal var followRedirects = true
    internal var followSslRedirects = true
    internal var cookieJar: CookieJar = CookieJar.NO_COOKIES
    internal var cache: Cache? = null
    internal var dns: Dns = Dns.SYSTEM
    internal var proxy: Proxy? = null
    internal var proxySelector: ProxySelector? = null
    internal var proxyAuthenticator: Authenticator = Authenticator.NONE
    internal var socketFactory: SocketFactory = SocketFactory.getDefault()
    internal var sslSocketFactoryOrNull: SSLSocketFactory? = null
    internal var x509TrustManagerOrNull: X509TrustManager? = null
    internal var connectionSpecs: List<ConnectionSpec> = DEFAULT_CONNECTION_SPECS
    internal var protocols: List<Protocol> = DEFAULT_PROTOCOLS
    internal var hostnameVerifier: HostnameVerifier = OkHostnameVerifier
    internal var certificatePinner: CertificatePinner = CertificatePinner.DEFAULT
    internal var certificateChainCleaner: CertificateChainCleaner? = null
    internal var callTimeout = 0
    internal var connectTimeout = 10_000
    internal var readTimeout = 10_000
    internal var writeTimeout = 10_000
    internal var pingInterval = 0
    internal var minWebSocketMessageToCompress = RealWebSocket.DEFAULT_MINIMUM_DEFLATE_SIZE
    internal var routeDatabase: RouteDatabase? = null
}

二、Request

Request 包含了网络请求时的所有请求参数，一共包含以下五个。

  open class Builder {
    internal var url: HttpUrl? = null
    internal var method: String
    internal var headers: Headers.Builder
    internal var body: RequestBody? = null

    /** A mutable map of tags, or an immutable empty map if we don't have any. */
    internal var tags: MutableMap<Class<*>, Any> = mutableMapOf()
}

三、Call

当调用 okHttpClient.newCall(request) 时就会得到一个 call 对象。

  /** Prepares the [request] to be executed at some point in the future. */
  override fun newCall(request: Request): Call = RealCall(this, request, forWebSocket = false)

call 是一个接口，我们可以将其看做是网络请求的启动器，可用于同步请求异步请求，但重复发起多次请求的话会抛出异常。

interface Call : Cloneable {
  /** Returns the original request that initiated this call. */
  fun request(): Request

  /**
   * Invokes the request immediately, and blocks until the response can be processed or is in error.
   *
   * To avoid leaking resources callers should close the [Response] which in turn will close the
   * underlying [ResponseBody].
   *
   * ```
   * // ensure the response (and underlying response body) is closed
   * try (Response response = client.newCall(request).execute()) {
   *   ...
   * }
   * ```
   *
   * The caller may read the response body with the response's [Response.body] method. To avoid
   * leaking resources callers must [close the response body][ResponseBody] or the response.
   *
   * 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 if 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.
   * @throws IllegalStateException when the call has already been executed.
   */
  @Throws(IOException::class)
  fun execute(): Response

  /**
   * Schedules the request to be executed at some point in the future.
   *
   * The [dispatcher][OkHttpClient.dispatcher] defines when the request will run: usually
   * immediately unless there are several other requests currently being executed.
   *
   * This client will later call back `responseCallback` with either an HTTP response or a failure
   * exception.
   *
   * @throws IllegalStateException when the call has already been executed.
   */
  fun enqueue(responseCallback: Callback)

  /** Cancels the request, if possible. Requests that are already complete cannot be canceled. */
  fun cancel()

  /**
   * Returns true if this call has been either [executed][execute] or [enqueued][enqueue]. It is an
   * error to execute a call more than once.
   */
  fun isExecuted(): Boolean

  fun isCanceled(): Boolean

  /**
   * Returns a timeout that spans the entire call: resolving DNS, connecting, writing the request
   * body, server processing, and reading the response body. If the call requires redirects or
   * retries all must complete within one timeout period.
   *
   * Configure the client's default timeout with [OkHttpClient.Builder.callTimeout].
   */
  fun timeout(): Timeout

  /**
   * Create a new, identical call to this one which can be enqueued or executed even if this call
   * has already been.
   */
  public override fun clone(): Call

  fun interface Factory {
    fun newCall(request: Request): Call
  }
}

ReallCall 是 Call 接口的唯一实现类

当调用 execute 方法发起同步请求时，

1、判断是否重复请求。

2、时间记录。

3、将自身加入到 dispatcher 中，并在请求结束时从 dispatcher 中移除自身。

4、通过 getResponseWithInterceptorChain 方法得到 response 对象。

override fun execute(): Response {
    check(executed.compareAndSet(false, true)) { "Already Executed" }

    timeout.enter()
    callStart()
    try {
      client.dispatcher.executed(this)
      return getResponseWithInterceptorChain()
    } finally {
      client.dispatcher.finished(this)
    }
  }

四、Dispatcher

Dispatcher 是一个调度器，用于对全局的网络请求进行缓存调度，其包含一下几个成员变量。

var maxRequests = 64

var maxRequestsPerHost = 5

/** Ready async calls in the order they'll be run. */
private val readyAsyncCalls = ArrayDeque<AsyncCall>()

/** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
private val runningAsyncCalls = ArrayDeque<AsyncCall>()

/** Running synchronous calls. Includes canceled calls that haven't finished yet. */
private val runningSyncCalls = ArrayDeque<RealCall>()

1、maxRequests 同一时间允许并发执行网络请求的最大线程数。

2、maxRequestsPerHost 同一个 host 下的最大同时请求数。

3、readyAsyncCalls 保存当前等待执行的异步任务

4、runningAsyncCalls 保存当前正在执行的异步任务。

5、runningSyncCalls 保存等钱正在执行的同步任务。

五、getResponseWithInterceptorChain

其主要逻辑就是通过拦截器来完成整个网络请求过程。

@Throws(IOException::class)
  internal fun getResponseWithInterceptorChain(): Response {
    // Build a full stack of interceptors.
    val interceptors = mutableListOf<Interceptor>()
    interceptors += client.interceptors
    interceptors += RetryAndFollowUpInterceptor(client)
    interceptors += BridgeInterceptor(client.cookieJar)
    interceptors += CacheInterceptor(client.cache)
    interceptors += ConnectInterceptor
    if (!forWebSocket) {
      interceptors += client.networkInterceptors
    }
    interceptors += CallServerInterceptor(forWebSocket)

    val chain = RealInterceptorChain(
        call = this,
        interceptors = interceptors,
        index = 0,
        exchange = null,
        request = originalRequest,
        connectTimeoutMillis = client.connectTimeoutMillis,
        readTimeoutMillis = client.readTimeoutMillis,
        writeTimeoutMillis = client.writeTimeoutMillis
    )

    var calledNoMoreExchanges = false
    try {
      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)
      }
    }
  }

六、interceptor

interceptor 多个拦截器增加串行调用逻辑

package com.gxx

class Request
class Response

interface Chain {
    fun request(): Request
    fun proceed(request: Request): Response
}

interface Interceptor {
    fun intercept(chain: Chain): Response
}

class RealInterceptorChain(
    private val request: Request,
    private val interceptors: List<Interceptor>,
    private val index: Int
) : Chain {

    private fun copy(index: Int): RealInterceptorChain {
        return RealInterceptorChain(request, interceptors, index)
    }

    override fun request(): Request {
        return request
    }

    override fun proceed(request: Request): Response {
        val next = copy(index + 1)
        val interceptor = interceptors[index]
        return interceptor.intercept(next)
    }
}

class LogInterceptor : Interceptor {
    override fun intercept(chain: Chain): Response {
        val request = chain.request()
        println("LogInterceptor -- getRequest")
        val response = chain.proceed(request)
        println("LogInterceptor ---- getResponse")
        return response
    }
}

class HeaderInterceptor : Interceptor {
    override fun intercept(chain: Chain): Response {
        val request = chain.request()
        println("HeaderInterceptor -- getRequest")
        val response = chain.proceed(request)
        println("HeaderInterceptor ---- getResponse")
        return response
    }
}

class CallServerInterceptor : Interceptor {
    override fun intercept(chain: Chain): Response {
        val request = chain.request()
        println("CallServerInterceptor -- getRequest")
        val response = Response()
        println("CallServerInterceptor ---- getResponse")
        return response
    }
}

fun main() {
    val interceptorList = mutableListOf<Interceptor>()
    interceptorList.add(LogInterceptor())
    interceptorList.add(HeaderInterceptor())
    interceptorList.add(CallServerInterceptor())
    val request = Request()
    val realInterceptorChain = RealInterceptorChain(request, interceptorList, 0)
    val response = realInterceptorChain.proceed(request)
    println("main response")
}

/*
fun main() {
    val interceptorList = mutableListOf<Interceptor>()
    interceptorList.add(LogInterceptor())
    interceptorList.add(HeaderInterceptor())
    val request = Request()
    val realInterceptorChain = RealInterceptorChain(request, interceptorList, 0)
    val response = realInterceptorChain.proceed(request)
    println("main response")
}*/

参考：

https://github.com/leavesCZY/AndroidGuide/blob/master/%E4%B8%BB%E6%B5%81%E5%BC%80%E6%BA%90%E5%BA%93%E6%BA%90%E7%A0%81%E5%88%86%E6%9E%90%EF%BC%8811%EF%BC%89OkHttp%20%E6%BA%90%E7%A0%81%E8%AF%A6%E8%A7%A3.md