在OkHttp3中，其靈活性很大程度上體現在可以 intercept 其任意一個環節，而這個優勢便是okhttp3整個請求響應架構體系的精髓所在，先放出一張主框架請求流程圖，接着再分析源碼。
String url = "http://wwww.baidu.com";
OkHttpClient okHttpClient = new OkHttpClient();
final Request request = new Request.Builder()
.url(url)
.build();
Call call = okHttpClient.newCall(request);
call.enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
Log.d(TAG, "onFailure: ");
}
@Override
public void onResponse(Call call, Response response) throws IOException {
Log.d(TAG, "onResponse: " + response.body().string());
}
});
這大概是一個最簡單的一個例子了，在new OkHttpClient()內部使用構造器模式初始化了一些配置信息：支持協議、任務分發器（其內部包含一個線程池，執行異步請求）、連接池(其內部包含一個線程池，維護connection)、連接/讀/寫超時時長等信息。
public Builder() {
dispatcher = new Dispatcher(); //任務調度器
protocols = DEFAULT_PROTOCOLS; //支持的協議
connectionSpecs = DEFAULT_CONNECTION_SPECS;
eventListenerFactory = EventListener.factory(EventListener.NONE);
proxySelector = ProxySelector.getDefault();
cookieJar = CookieJar.NO_COOKIES;
socketFactory = SocketFactory.getDefault();
hostnameVerifier = OkHostnameVerifier.INSTANCE;
certificatePinner = CertificatePinner.DEFAULT;
proxyAuthenticator = Authenticator.NONE;
authenticator = Authenticator.NONE;
connectionPool = new ConnectionPool(); //連接池
dns = Dns.SYSTEM;
followSslRedirects = true;
followRedirects = true;
retryOnConnectionFailure = true;
connectTimeout = 10_000;//超時時間
readTimeout = 10_000;
writeTimeout = 10_000;
pingInterval = 0;
}
第一行創建了一個Dispatcher任務調度器，它定義了三個雙向任務隊列，兩個異步隊列：準備執行的請求隊列 readyAsyncCalls、正在運行的請求隊列 runningAsyncCalls；一個正在運行的同步請求隊列 runningSyncCalls；
public final class Dispatcher {
private int maxRequests = 64; //最大請求數量
private int maxRequestsPerHost = 5; //每臺主機最大的請求數量
private @Nullable Runnable idleCallback;
/** Executes calls. Created lazily. */
private @Nullable ExecutorService executorService; //線程池
/** Ready async calls in the order they'll be run. */
private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>();
/** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();
/** Running synchronous calls. Includes canceled calls that haven't finished yet. */
private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();
/** 這個線程池沒有核心線程，線程數量沒有限制，空閒60s就會回收*/
public synchronized ExecutorService executorService() {
if (executorService == null) {
executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp Dispatcher", false));
}
return executorService;
}
}
另外還有一個線程池 executorService ，這個線程池跟Android中的CachedThreadPool非常類似，這種類型的線程池，適用於大量的耗時較短的異步任務。下一篇文章 將對OkHttp框架中的線程池做一個總結。
接下來接着看Request的構造，這個例子Request比較簡單，指定了請求方式 GET 和請求 url
public static class Builder {
HttpUrl url;
String method;
Headers.Builder headers;
RequestBody body;
Object tag;
public Builder() {
this.method = "GET";
this.headers = new Headers.Builder();
}
public Builder url(HttpUrl url) {
if (url == null) throw new NullPointerException("url == null");
this.url = url;
return this;
}
public Request build() {
if (url == null) throw new IllegalStateException("url == null");
return new Request(this);
}
...
}
緊接着通過 OkHttpClient 和 Request 構造一個 Call對象，它的實現是RealCall
public Call newCall(Request request) {
return RealCall.newRealCall(this, request, false /* for web socket */);
}
static RealCall newRealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket){
// Safely publish the Call instance to the EventListener.
RealCall call = new RealCall(client, originalRequest, forWebSocket);
call.eventListener = client.eventListenerFactory().create(call);
return call;
}
private RealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
this.client = client;
this.originalRequest = originalRequest;
this.forWebSocket = forWebSocket;
this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client, forWebSocket);
}
可以看到在 RealCall 的構造方法中創建了一個RetryAndFollowUpInterceptor，用於處理請求錯誤和重定向等，這是 Okhttp 框架的精髓 interceptor chain 中的一環，默認情況下也是第一個攔截器，除非調用 OkHttpClient.Builder#addInterceptor(Interceptor) 來添加全局的攔截器。關於攔截器鏈的順序參見 RealCall#getResponseWithInterceptorChain() 方法。
RealCall#enqueue(Callback)
public void enqueue(Callback responseCallback) {
synchronized (this) {
//每個請求只能之執行一次
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
eventListener.callStart(this);
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
可以看到，一個 Call 只能執行一次，否則會拋異常，這裏創建了一個 AsyncCall 並將Callback傳入，接着再交給任務分發器 Dispatcher 來進一步處理。
synchronized void enqueue(AsyncCall call) {
//正在執行的任務數量小於最大值（64），並且此任務所屬主機的正在執行任務小於最大值（5）
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
從 Dispatcher#enqueue()方法的策略可以看出，對於請求的入隊做了一些限制，若正在執行的請求數量小於最大值（默認64），並且此請求所屬主機的正在執行任務小於最大值（默認5），就加入正在運行的隊列並通過線程池來執行該任務，否則加入準備執行隊列中。
- 流程圖
現在回頭看看 AsyncCall ，它繼承自 NamedRunnable，而 NamedRunnable實現了 Runnable 接口，它的作用有2個：
① 採用模板方法的設計模式，讓子類將具體的操作放在 execute()方法中;
② 給線程指定一個名字，比如傳入模塊名稱，方便監控線程的活動狀態；
public abstract class NamedRunnable implements Runnable {
protected final String name;
public NamedRunnable(String format, Object... args) {
this.name = Util.format(format, args);
}
@Override public final void run() {
String oldName = Thread.currentThread().getName();
Thread.currentThread().setName(name);
try {
//採用模板方法讓子類將具體的操作放到此execute()方法
execute();
} finally {
Thread.currentThread().setName(oldName);
}
}
protected abstract void execute();
}
final class AsyncCall extends NamedRunnable {
//省略...
@Override protected void execute() {
boolean signalledCallback = false;
try {
//調用 getResponseWithInterceptorChain()獲得響應內容
Response response = getResponseWithInterceptorChain(); //①
if (retryAndFollowUpInterceptor.isCanceled()) {
//這個標記爲主要是避免異常時2次回調
signalledCallback = true;
//回調Callback告知失敗
responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
} else {
signalledCallback = true;
//回調Callback，將響應內容傳回去
responseCallback.onResponse(RealCall.this, response);
}
} catch (IOException e) {
if (signalledCallback) {
// Do not signal the callback twice!
Platform.get().log(INFO, "Callback failure for " + toLoggableString(), e);
} else {
eventListener.callFailed(RealCall.this, e);
responseCallback.onFailure(RealCall.this, e);
}
} finally {
//不管請求成功與否，都進行finished()操作
client.dispatcher().finished(this);//②
}
}
}
先看註釋②的行finally塊中執行的 client.dispatcher().finished(this)
void finished(AsyncCall call) {
finished(runningAsyncCalls, call, true);
}
private <T> void finished(Deque<T> calls, T call, boolean promoteCalls) {
int runningCallsCount;
Runnable idleCallback;
synchronized (this) {
//從正在執行的隊列中將其移除
if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
if (promoteCalls) promoteCalls(); //推動下一個任務的執行
runningCallsCount = runningCallsCount();//同步+異步的正在執行任務數量
idleCallback = this.idleCallback;
}
//如果沒有正在執行的任務，且idleCallback不爲null，則回調通知空閒了
if (runningCallsCount == 0 && idleCallback != null) {
idleCallback.run();
}
}
其中promoteCalls()爲推動下一個任務執行，其實它做的也很簡單，就是在條件滿足的情況下，將 readyAsyncCalls 中的任務移動到 runningAsyncCalls中，並交給線程池來執行，以下是它的實現。
private void promoteCalls() {
if (runningAsyncCalls.size() >= maxRequests) return; // Already running max capacity.
if (readyAsyncCalls.isEmpty()) return; // No ready calls to promote.
//若條件允許，將readyAsyncCalls中的任務移動到runningAsyncCalls中，並交給線程池執行
for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
AsyncCall call = i.next();
if (runningCallsForHost(call) < maxRequestsPerHost) {
i.remove();
runningAsyncCalls.add(call);
executorService().execute(call);
}
//當runningAsyncCalls滿了，直接退出迭代
if (runningAsyncCalls.size() >= maxRequests) return; // Reached max capacity.
}
}
接下來就回到註釋①處的響應內容的獲取 getResponseWithInterceptorChain()
Response getResponseWithInterceptorChain() throws IOException {
// Build a full stack of interceptors.
List<Interceptor> interceptors = new ArrayList<>(); //這是一個List，是有序的
interceptors.addAll(client.interceptors());//首先添加的是用戶添加的全局攔截器
interceptors.add(retryAndFollowUpInterceptor); //錯誤、重定向攔截器
//橋接攔截器，橋接應用層與網絡層，添加必要的頭、
interceptors.add(new BridgeInterceptor(client.cookieJar()));
//緩存處理，Last-Modified、ETag、DiskLruCache等
interceptors.add(new CacheInterceptor(client.internalCache()));
//連接攔截器
interceptors.add(new ConnectInterceptor(client));
//從這就知道，通過okHttpClient.Builder#addNetworkInterceptor()傳進來的攔截器只對非網頁的請求生效
if (!forWebSocket) {
interceptors.addAll(client.networkInterceptors());
}
//真正訪問服務器的攔截器
interceptors.add(new CallServerInterceptor(forWebSocket));
Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
originalRequest, this, eventListener, client.connectTimeoutMillis(),
client.readTimeoutMillis(), client.writeTimeoutMillis());
return chain.proceed(originalRequest);
}
可以看這塊重點就是 interceptors 這個集合，首先將前面的 client.interceptors() 全部加入其中，還有在創建 RealCall時的 retryAndFollowUpInterceptor加入其中，接着還創建並添加了BridgeInterceptor、CacheInterceptor、ConnectInterceptor、CallServerInterceptor，最後通過RealInterceptorChain#proceed(Request)來執行整個 interceptor chain，可見把這個攔截器鏈搞清楚，整體流程也就明朗了。
RealInterceptorChain#proceed()
public Response proceed(Request request) throws IOException {
return proceed(request, streamAllocation, httpCodec, connection);
}
public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
RealConnection connection) throws IOException {
//省略異常處理...
// Call the next interceptor in the chain.
RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
writeTimeout);
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);
//省略異常處理...
return response;
}
從這段實現可以看出，是按照添加到 interceptors 集合的順序，逐個往下調用攔截器的intercept()方法，所以在前面的攔截器會先被調用。這個例子中自然就是 RetryAndFollowUpInterceptor 了。
public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
RealInterceptorChain realChain = (RealInterceptorChain) chain;
Call call = realChain.call();
EventListener eventListener = realChain.eventListener();
//創建一個StreamAllocation
StreamAllocation streamAllocation = new StreamAllocation(client.connectionPool(),
createAddress(request.url()), call, eventListener, callStackTrace);
this.streamAllocation = streamAllocation;
//統計重定向次數，不能大於20
int followUpCount = 0;
Response priorResponse = null;
while (true) {
if (canceled) {
streamAllocation.release();
throw new IOException("Canceled");
}
Response response;
boolean releaseConnection = true;
try {
//調用下一個interceptor的來獲得響應內容
response = realChain.proceed(request, streamAllocation, null, null);
releaseConnection = false;
} catch (RouteException e) {
// The attempt to connect via a route failed. The request will not have been sent.
if (!recover(e.getLastConnectException(), streamAllocation, false, request)) {
throw e.getLastConnectException();
}
releaseConnection = false;
continue;
} catch (IOException e) {
// An attempt to communicate with a server failed. The request may have been sent.
boolean requestSendStarted = !(e instanceof ConnectionShutdownException);
if (!recover(e, streamAllocation, requestSendStarted, request)) throw e;
releaseConnection = false;
continue;
} finally {
// We're throwing an unchecked exception. Release any resources.
if (releaseConnection) {
streamAllocation.streamFailed(null);
streamAllocation.release();
}
}
// Attach the prior response if it exists. Such responses never have a body.
if (priorResponse != null) {
response = response.newBuilder()
.priorResponse(priorResponse.newBuilder()
.body(null)
.build())
.build();
}
//重定向處理
Request followUp = followUpRequest(response, streamAllocation.route());
if (followUp == null) {
if (!forWebSocket) {
streamAllocation.release();
}
return response;
}
closeQuietly(response.body());
if (++followUpCount > MAX_FOLLOW_UPS) {
streamAllocation.release();
throw new ProtocolException("Too many follow-up requests: " + followUpCount);
}
if (followUp.body() instanceof UnrepeatableRequestBody) {
streamAllocation.release();
throw new HttpRetryException("Cannot retry streamed HTTP body", response.code());
}
if (!sameConnection(response, followUp.url())) {
streamAllocation.release();
streamAllocation = new StreamAllocation(client.connectionPool(),
createAddress(followUp.url()), call, eventListener, callStackTrace);
this.streamAllocation = streamAllocation;
} else if (streamAllocation.codec() != null) {
throw new IllegalStateException("Closing the body of " + response
+ " didn't close its backing stream. Bad interceptor?");
}
request = followUp;
priorResponse = response;
}
}
這個攔截器就如同它的名字retry and followUp，主要負責錯誤處理和重定向等問題，比如路由錯誤、IO異常等。
接下來就到了BridgeInterceptor#intercept()，在這個攔截器中，添加了必要請求頭信息，gzip處理等。
public Response intercept(Chain chain) throws IOException {
Request userRequest = chain.request();
Request.Builder requestBuilder = userRequest.newBuilder();
//從這開始給請求添加了一些請求頭信息
RequestBody body = userRequest.body();
if (body != null) {
MediaType contentType = body.contentType();
if (contentType != null) {
requestBuilder.header("Content-Type", contentType.toString());
}
long contentLength = body.contentLength();
if (contentLength != -1) {
requestBuilder.header("Content-Length", Long.toString(contentLength));
requestBuilder.removeHeader("Transfer-Encoding");
} else {
requestBuilder.header("Transfer-Encoding", "chunked");
requestBuilder.removeHeader("Content-Length");
}
}
if (userRequest.header("Host") == null) {
requestBuilder.header("Host", hostHeader(userRequest.url(), false));
}
if (userRequest.header("Connection") == null) {
requestBuilder.header("Connection", "Keep-Alive");
}
// If we add an "Accept-Encoding: gzip" header field we're responsible for also decompressing
// the transfer stream.
boolean transparentGzip = false;
if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == null) {
transparentGzip = true;
requestBuilder.header("Accept-Encoding", "gzip");
}
List<Cookie> cookies = cookieJar.loadForRequest(userRequest.url());
if (!cookies.isEmpty()) {
requestBuilder.header("Cookie", cookieHeader(cookies));
}
if (userRequest.header("User-Agent") == null) {
requestBuilder.header("User-Agent", Version.userAgent());
}
Response networkResponse = chain.proceed(requestBuilder.build());
HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());
Response.Builder responseBuilder = networkResponse.newBuilder()
.request(userRequest);
if (transparentGzip
&& "gzip".equalsIgnoreCase(networkResponse.header("Content-Encoding"))
&& HttpHeaders.hasBody(networkResponse)) {
GzipSource responseBody = new GzipSource(networkResponse.body().source());
Headers strippedHeaders = networkResponse.headers().newBuilder()
.removeAll("Content-Encoding")
.removeAll("Content-Length")
.build();
responseBuilder.headers(strippedHeaders);
String contentType = networkResponse.header("Content-Type");
responseBuilder.body(new RealResponseBody(contentType, -1L, Okio.buffer(responseBody)));
}
return responseBuilder.build();
}
這個攔截器處理請求信息、cookie、gzip等，接着往下是 CacheInterceptor
public Response intercept(Chain chain) throws IOException {
Response cacheCandidate = cache != null
? cache.get(chain.request())
: null;
long now = System.currentTimeMillis();
CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
Request networkRequest = strategy.networkRequest;
Response cacheResponse = strategy.cacheResponse;
if (cache != null) {
cache.trackResponse(strategy);
}
if (cacheCandidate != null && cacheResponse == null) {
closeQuietly(cacheCandidate.body()); // The cache candidate wasn't applicable. Close it.
}
// If we're forbidden from using the network and the cache is insufficient, fail.
if (networkRequest == null && cacheResponse == null) {
return new Response.Builder()
.request(chain.request())
.protocol(Protocol.HTTP_1_1)
.code(504)
.message("Unsatisfiable Request (only-if-cached)")
.body(Util.EMPTY_RESPONSE)
.sentRequestAtMillis(-1L)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
}
// If we don't need the network, we're done.
if (networkRequest == null) {
return cacheResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build();
}
Response networkResponse = null;
try {
//調用下一個攔截器進行網絡請求
networkResponse = chain.proceed(networkRequest);
} finally {
// If we're crashing on I/O or otherwise, don't leak the cache body.
if (networkResponse == null && cacheCandidate != null) {
closeQuietly(cacheCandidate.body());
}
}
// If we have a cache response too, then we're doing a conditional get.
if (cacheResponse != null) {
if (networkResponse.code() == HTTP_NOT_MODIFIED) {
Response response = cacheResponse.newBuilder()
.headers(combine(cacheResponse.headers(), networkResponse.headers()))
.sentRequestAtMillis(networkResponse.sentRequestAtMillis())
.receivedResponseAtMillis(networkResponse.receivedResponseAtMillis())
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build();
networkResponse.body().close();
// Update the cache after combining headers but before stripping the
// Content-Encoding header (as performed by initContentStream()).
cache.trackConditionalCacheHit();
cache.update(cacheResponse, response);
return response;
} else {
closeQuietly(cacheResponse.body());
}
}
Response response = networkResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build();
if (cache != null) {
if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) {
// Offer this request to the cache.
CacheRequest cacheRequest = cache.put(response);
return cacheWritingResponse(cacheRequest, response);
}
if (HttpMethod.invalidatesCache(networkRequest.method())) {
try {
cache.remove(networkRequest);
} catch (IOException ignored) {
// The cache cannot be written.
}
}
}
return response;
}
這個攔截器主要工作是做做緩存處理，如果有有緩存並且緩存可用，那就使用緩存，否則進行調用下一個攔截器 ConnectionInterceptor 進行網絡請求，並將響應內容緩存。
public Response intercept(Chain chain) throws IOException {
RealInterceptorChain realChain = (RealInterceptorChain) chain;
Request request = realChain.request();
StreamAllocation streamAllocation = realChain.streamAllocation();
// We need the network to satisfy this request. Possibly for validating a conditional GET.
boolean doExtensiveHealthChecks = !request.method().equals("GET");
HttpCodec httpCodec = streamAllocation.newStream(client, chain, doExtensiveHealthChecks);
RealConnection connection = streamAllocation.connection();
return realChain.proceed(request, streamAllocation, httpCodec, connection);
}
這個攔截器主要是打開一個到目標服務器的 connection 並調用下一個攔截器 CallServerInterceptor，這是攔截器鏈最後一個攔截器，它向服務器發起真正的網絡請求。
public Response intercept(Chain chain) throws IOException {
RealInterceptorChain realChain = (RealInterceptorChain) chain;
HttpCodec httpCodec = realChain.httpStream();
StreamAllocation streamAllocation = realChain.streamAllocation();
RealConnection connection = (RealConnection) realChain.connection();
Request request = realChain.request();
long sentRequestMillis = System.currentTimeMillis();
realChain.eventListener().requestHeadersStart(realChain.call());
httpCodec.writeRequestHeaders(request);
realChain.eventListener().requestHeadersEnd(realChain.call(), request);
Response.Builder responseBuilder = null;
if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
// If there's a "Expect: 100-continue" header on the request, wait for a "HTTP/1.1 100
// Continue" response before transmitting the request body. If we don't get that, return
// what we did get (such as a 4xx response) without ever transmitting the request body.
if ("100-continue".equalsIgnoreCase(request.header("Expect"))) {
httpCodec.flushRequest();
realChain.eventListener().responseHeadersStart(realChain.call());
responseBuilder = httpCodec.readResponseHeaders(true);
}
if (responseBuilder == null) {
// Write the request body if the "Expect: 100-continue" expectation was met.
realChain.eventListener().requestBodyStart(realChain.call());
long contentLength = request.body().contentLength();
CountingSink requestBodyOut =
new CountingSink(httpCodec.createRequestBody(request, contentLength));
BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);
request.body().writeTo(bufferedRequestBody);
bufferedRequestBody.close();
realChain.eventListener()
.requestBodyEnd(realChain.call(), requestBodyOut.successfulCount);
} else if (!connection.isMultiplexed()) {
// If the "Expect: 100-continue" expectation wasn't met, prevent the HTTP/1 connection
// from being reused. Otherwise we're still obligated to transmit the request body to
// leave the connection in a consistent state.
streamAllocation.noNewStreams();
}
}
httpCodec.finishRequest();
if (responseBuilder == null) {
realChain.eventListener().responseHeadersStart(realChain.call());
responseBuilder = httpCodec.readResponseHeaders(false);
}
Response response = responseBuilder
.request(request)
.handshake(streamAllocation.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
int code = response.code();
if (code == 100) {
// server sent a 100-continue even though we did not request one.
// try again to read the actual response
responseBuilder = httpCodec.readResponseHeaders(false);
response = responseBuilder
.request(request)
.handshake(streamAllocation.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
code = response.code();
}
realChain.eventListener()
.responseHeadersEnd(realChain.call(), response);
if (forWebSocket && code == 101) {
// Connection is upgrading, but we need to ensure interceptors see a non-null response body.
response = response.newBuilder()
.body(Util.EMPTY_RESPONSE)
.build();
} else {
response = response.newBuilder()
.body(httpCodec.openResponseBody(response))
.build();
}
if ("close".equalsIgnoreCase(response.request().header("Connection"))
|| "close".equalsIgnoreCase(response.header("Connection"))) {
streamAllocation.noNewStreams();
}
if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
throw new ProtocolException(
"HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());
}
return response;
}
從上面的請求流程圖可以看出，OkHttp的攔截器鏈可謂是其整個框架的精髓，用戶可傳入的 interceptor 分爲兩類：
①一類是全局的 interceptor，該類 interceptor 在整個攔截器鏈中最早被調用，通過 OkHttpClient.Builder#addInterceptor(Interceptor) 傳入；
②另外一類是非網頁請求的 interceptor ，這類攔截器只會在非網頁請求中被調用，並且是在組裝完請求之後，真正發起網絡請求前被調用，所有的 interceptor 被保存在 List<Interceptor> interceptors 集合中，按照添加順序來逐個調用，具體可參考 RealCall#getResponseWithInterceptorChain() 方法。通過 OkHttpClient.Builder#addNetworkInterceptor(Interceptor) 傳入；
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