分析的问题
-
Call如何处理同步和异步请求； -
Dispatcher如何管理请求任务； -
OkHttp拦截器链； - 连接池
ConnectionPool。
1. 同步和异步请求
OkHttpClient用内部类Builder的形式进行创建，在请求网络时，通过OkHttpClient类的newCall()方法创建一个Call实例：
/**
* Prepares the {@code request} to be executed at some point in the future.
*/
@Override public Call newCall(Request request) {
return RealCall.newRealCall(this, request, false /* for web socket */);
}
newCall()方法实际上调用了RealCall类的静态方法newRealCall()：
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;
}
Call是一个接口，RealCall是Call的实现类，在静态方法中创建了RealCall实例并返回。
OkHttp使用execute()和enqueue()方法分别执行同步和异步请求。这两个方法也是Call类的抽象方法，并在RealCall类中实现。
-
RealCall类的同步请求方法execute()
@Override public Response execute() throws IOException {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
eventListener.callStart(this);
try {
client.dispatcher().executed(this);
Response result = getResponseWithInterceptorChain();
if (result == null) throw new IOException("Canceled");
return result;
} catch (IOException e) {
eventListener.callFailed(this, e);
throw e;
} finally {
client.dispatcher().finished(this);
}
}
client.dispatcher.executed(this)，把任务转交给了Dispatcher类的executed()方法。
getResponseWithInterceptorChain()，执行拦截器链，其中包括发送数据和响应数据过程，都是在拦截器中进行。
client.dispatcher().finished(this)，任务执行结束时，调用了Dispatcher的finished()方法。
此外，还应该知道同步请求会阻塞当前的线程。
-
RealCall类的异步请求enqueue()
@Override public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
eventListener.callStart(this);
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
异步请求，client.dispatcher().enqueue(new AsyncCall(responseCallback));调用了Dispatcher类的enqueue()方法。
所以，在ReaCall类中，execute()和enqueue()方法执行任务时，都是转交给了Dispatcher类处理。异步和同步此处不一样的地方是，enqueue()方法的入参不是RealCall的实例，而是RealCall的一个内部类AsyncCall的实例，AsyncCall继承自NamedRunnable类，以便提交给线程池执行。
同步请求有executed和finished两个过程，异步请求在这里只看到enqueue()开始执行的方法，那么它有没有对应的结束调用呢？贴上内部类AsyncCall看看。
final class AsyncCall extends NamedRunnable {
private final Callback responseCallback;
AsyncCall(Callback responseCallback) {
super("OkHttp %s", redactedUrl());
this.responseCallback = responseCallback;
}
String host() {
return originalRequest.url().host();
}
Request request() {
return originalRequest;
}
RealCall get() {
return RealCall.this;
}
@Override
protected void execute() {
boolean signalledCallback = false;
try {
Response response = getResponseWithInterceptorChain();
if (retryAndFollowUpInterceptor.isCanceled()) {
signalledCallback = true;
responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
} else {
signalledCallback = true;
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 {
client.dispatcher().finished(this);
}
}
}
其父类NamedRunnable是一个抽象类，它继承自Runnable接口，可以指定执行线程名，AsyncCall实现了NamedRunnable的execute()抽象方法，在里面有client.dispatcher().finished(this)，在这里调用Dispatcher类的finished()结束请求任务。
2. Dispatcher任务管理
Dispatcher是在Builder构建时新建的实例，并引用给了OkHttpClient类的成员变量
以下是Dispatcher类的成员变量：
private int maxRequests = 64;
private int maxRequestsPerHost = 5;
private @Nullable Runnable idleCallback;
/** Executes calls. Created lazily. */
private @Nullable ExecutorService executorService;
/** Ready async calls in the order they'll be run. */
private final Deque readyAsyncCalls = new ArrayDeque<>();
/** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
private final Deque runningAsyncCalls = new ArrayDeque<>();
/** Running synchronous calls. Includes canceled calls that haven't finished yet. */
private final Deque runningSyncCalls = new ArrayDeque<>();
maxRequests最大请求任务数，64个，maxRequestsPerHost每个主机最大请求任务数，5个。另外还有一个线程池，一个同步请求的队列，一个异步请求的队列，一个备用的异步请求队列。这三个任务队列，都是在Dispatcher的成员中直接创建的，用来存储请求任务。
- 线程池
public synchronized ExecutorService executorService() {
if (executorService == null) {
executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS,
new SynchronousQueue(), Util.threadFactory("OkHttp Dispatcher", false));
}
return executorService;
}
这个线程池，是在要使用的时候创建，核心线程数为0，最大非核心线程数为Integer的最大值，可以认为它"无界"，且闲置回收时间为60s，并使用了一个非存储的阻塞队列，用于新任务和空闲线程的配对，类似newCachedThreadPool()。
- 同步请求任务管理
前面看到执行同步请求，调用Call的execute()同步方法时，调用了Dispatcher的executed()方法和finished()方法，Dispatcher类的这两个方法如下:
/** Used by {@code Call#execute} to signal it is in-flight. */
synchronized void executed(RealCall call) {
runningSyncCalls.add(call);
}
/** Used by {@code Call#execute} to signal completion. */
void finished(RealCall call) {
finished(runningSyncCalls, call, false);
}
private void finished(Deque calls, T call, boolean promoteCalls) {
int runningCallsCount;
Runnable idleCallback;
synchronized (this) {
if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
if (promoteCalls) promoteCalls();
runningCallsCount = runningCallsCount();
idleCallback = this.idleCallback;
}
if (runningCallsCount == 0 && idleCallback != null) {
idleCallback.run();
}
}
发现在Dispatcher中，发起请求时，把请求任务加入到了同步队列中，且对任务数没有限制，请求结束时，会把任务从队列中移除。
为什么同步请求需要队列去管理，作用是什么？请求开始时，先将任务添加到队列，再执行，请求响应后，再将任务从队列中移除。
在整个Dispatcher类中，发现runningSyncCalls这个同步队列，还在另几个地方出现，一个取消所有请求的时候，一个获取所有正在执行的请求集合的时候，还有一个是获取所有正在执行的请求数的时候。
/**
* Cancel all calls currently enqueued or executing. Includes calls executed both {@linkplain
* Call#execute() synchronously} and {@linkplain Call#enqueue asynchronously}.
*/
public synchronized void cancelAll() {
for (AsyncCall call : readyAsyncCalls) {
call.get().cancel();
}
for (AsyncCall call : runningAsyncCalls) {
call.get().cancel();
}
for (RealCall call : runningSyncCalls) {
call.cancel();
}
}
/** Returns a snapshot of the calls currently being executed. */
public synchronized List runningCalls() {
List result = new ArrayList<>();
result.addAll(runningSyncCalls);
for (AsyncCall asyncCall : runningAsyncCalls) {
result.add(asyncCall.get());
}
return Collections.unmodifiableList(result);
}
public synchronized int runningCallsCount() {
return runningAsyncCalls.size() + runningSyncCalls.size();
}
所以通过队列管理同步请求，比直接执行，可以方便地了解所有请求数，以及控制这些请求任务。即使在多线程的应用场景中，因为加了同步锁，依然可以安全地进行管理。
- 异步请求任务管理
执行异步请求，调用RealCall的enqueue()方法，调用了Dispatcher的enqueue()和finished()方法：
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
/** Used by {@code AsyncCall#run} to signal completion. */
void finished(AsyncCall call) {
finished(runningAsyncCalls, call, true);
}
private void finished(Deque calls, T call, boolean promoteCalls) {
int runningCallsCount;
Runnable idleCallback;
synchronized (this) {
if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
if (promoteCalls) promoteCalls();
runningCallsCount = runningCallsCount();
idleCallback = this.idleCallback;
}
if (runningCallsCount == 0 && idleCallback != null) {
idleCallback.run();
}
}
异步任务，会先判断异步任务队列大小是否达到限制值64（maxRequests，64），以及每个地址的请求数是否到达限制值5（maxRequestsPerHost，5），都未达到，把Call实例添加到正在执行的异步任务队列中，并调用线程池来执行任务。如果已达到最大任务数限制，则会加入到备用的异步任务队列中，等待执行。线程池的优点是线程复用，但Dispatcher通过请求数限制，把任务加入到备用队列中，等线程空闲时，再从备用队列中取出任务提交给空闲线程执行，避免了大量线程的创建。此外，同步和异步finished()方法都调用了另一个finished(Deque范型方法，在它里面进行任务移除，如果是异步任务，则会通过promoteCalls()方法从备用的异步任务队列中，取出任务添加到正在执行的异步任务队列中，同时交给线程池执行。
3. OkHttp拦截器链
无论是同步请求还是异步请求，都是通过拦截器链进行数据请求和响应的处理。同步和异步任务执行中，都调用了RealCall类中getResponseWithInterceptorChain()方法：
Response getResponseWithInterceptorChain() throws IOException {
// Build a full stack of interceptors.
List interceptors = new ArrayList<>();
interceptors.addAll(client.interceptors());
interceptors.add(retryAndFollowUpInterceptor);
interceptors.add(new BridgeInterceptor(client.cookieJar()));
interceptors.add(new CacheInterceptor(client.internalCache()));
interceptors.add(new ConnectInterceptor(client));
if (!forWebSocket) {
interceptors.addAll(client.networkInterceptors());
}
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);
}
在拦截器的集合中，首先会加入我们自定义的所有应用拦截器，自定义的所有网络拦截器，和OKHttp默认的一些拦截器，ConnectInterceptor中是打开一个和server的连接，添加网络拦截器是在打开和server的连接之后，所以在网络拦截器可以看到连接信息。最后一个CallServerInterceptor拦截器，它才真正和服务器交互数据。在这个方法中，第一次创建了一个RealInterceptorChain实例，index的入参为0，然后调用RealInterceptorChain类的proceed()方法。
@Override 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 {
if (index >= interceptors.size()) throw new AssertionError();
calls++;
// If we already have a stream, confirm that the incoming request will use it.
if (this.httpCodec != null && !this.connection.supportsUrl(request.url())) {
throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
+ " must retain the same host and port");
}
// If we already have a stream, confirm that this is the only call to chain.proceed().
if (this.httpCodec != null && calls > 1) {
throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
+ " must call proceed() exactly once");
}
// 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);
// Confirm that the next interceptor made its required call to chain.proceed().
if (httpCodec != null && index + 1 < interceptors.size() && next.calls != 1) {
throw new IllegalStateException("network interceptor " + interceptor
+ " must call proceed() exactly once");
}
// Confirm that the intercepted response isn't null.
if (response == null) {
throw new NullPointerException("interceptor " + interceptor + " returned null");
}
if (response.body() == null) {
throw new IllegalStateException(
"interceptor " + interceptor + " returned a response with no body");
}
return response;
}
在RealCall类中getResponseWithInterceptorChain()方法中，创建了RealInterceptorChain对象，为何在proceed()方法内部还会出现RealInterceptorChain对象的创建？
其实他们是两个不同的拦截器链对象，第一个拦截器链对象index为0，执行其proceed()方式时，先准备了下一个拦截器链对象，index为1（通过index+1给定）。当interceptors.get(index)拿到第一个拦截器后，执行第一个拦截器的intercept()方法，把刚创建的第二个链对象传了进去，并执行第二个链对象的proceed()方法。这个时候第二链对象的proceed()里面又会准备一个新的链对象(第三个，index为2)，然后一直重复前面的过程，直到最后一个拦截器的intercept()方法被调用。且拦截器链对象的proceed()方法的返回值是Response类型，所以请求过程的处理是从第一个拦截器到最后一个拦截器，响应过程Response的处理，则是从最后一个到第一个的过程。
为什么在介绍OkHttp的拦截器时，都说应用拦截器只执行一次，而网络拦截器会贯穿整个请求过程，可能执行多次呢？要知道这个答案，还得看看默认拦截器的作用分别是什么。
-
RetryAndFollowUpInterceptor拦截器
再贴一次RealCall类的getResponseWithInterceptorChain方法：
//省略
List interceptors = new ArrayList<>();
interceptors.addAll(client.interceptors());
interceptors.add(retryAndFollowUpInterceptor);
interceptors.add(new BridgeInterceptor(client.cookieJar()));
interceptors.add(new CacheInterceptor(client.internalCache()));
interceptors.add(new ConnectInterceptor(client));
if (!forWebSocket) {
interceptors.addAll(client.networkInterceptors());
}
interceptors.add(new CallServerInterceptor(forWebSocket));
//省略
interceptors.add(retryAndFollowUpInterceptor);，关键是这一行，它是一个请求重试和重定向的拦截器，其intercept()方法的部分内容如下：
//省略
while (true) {
if (canceled) {
streamAllocation.release();
throw new IOException("Canceled");
}
Response response;
boolean releaseConnection = true;
try {
response = realChain.proceed(request, streamAllocation, null, null);
releaseConnection = false;
}
//省略
在这个拦截器里有一个循环，取消请求或者没有重定向的请求了，则退出循环。应用拦截器的添加在RetryAndFollowUpInterceptor之前，所以应用拦截器在整个拦截器链执行过程中只会执行一次，而在RetryAndFollowUpInterceptor之后添加的网络拦截器，以及其他拦截器，则会依情况在循环中执行一次或多次。
-
BridgeInterceptor拦截器
public final class BridgeInterceptor implements Interceptor {
private final CookieJar cookieJar;
public BridgeInterceptor(CookieJar cookieJar) {
this.cookieJar = cookieJar;
}
@Override public Response intercept(Chain chain) throws IOException {
Request userRequest = chain.request();
Request.Builder requestBuilder = userRequest.newBuilder();
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 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();
}
/** Returns a 'Cookie' HTTP request header with all cookies, like {@code a=b; c=d}. */
private String cookieHeader(List cookies) {
StringBuilder cookieHeader = new StringBuilder();
for (int i = 0, size = cookies.size(); i < size; i++) {
if (i > 0) {
cookieHeader.append("; ");
}
Cookie cookie = cookies.get(i);
cookieHeader.append(cookie.name()).append('=').append(cookie.value());
}
return cookieHeader.toString();
}
}
这个拦截器处理了一些默认的通用头，请求头和实体头，而且可以看到，当用户没有对Accept-Encoding请求头设置时，OkHttp默认使用了gzip编码格式对数据进行压缩。同时用户可以通过这个拦截器设置cookies，OkHttp默认是NO_COOKIES。
-
CacheInterceptor拦截器
/** Serves requests from the cache and writes responses to the cache. */
public final class CacheInterceptor implements Interceptor {
//省略
@Override 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 {
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;
}
//省略
}
这个拦截器中会先依据用户或OkHttp的默认设置生成缓存策略。
网络请求和缓存都不可用时，返回504；
网络请求不可用（缓存策略可以将网路请求置null），返回缓存数据。
网络请求可用，获取响应数据，如果和本地缓存比较，发现未修改，生成一个含有缓存Response和网络Response的新Response返回。如果没有缓存，也重新生成一个含有缓存Response和网络Response的新Response返回。有缓存则将新数据写入缓存。
缓存策略
CacheStrategy
在前面那段代码中，通过cacheCandidate).get()返回了CacheStrategy的实例，里面依据各种情况来决定返回的CacheStrategy对象，以及它的两个重要成员networkRequest和cacheResponse，缓存拦截器中大多数的判断都依赖着这两成员对象，决定如何使用网络和缓存数据。ConnectInterceptor连接拦截器
/** Opens a connection to the target server and proceeds to the next interceptor. */
public final class ConnectInterceptor implements Interceptor {
public final OkHttpClient client;
public ConnectInterceptor(OkHttpClient client) {
this.client = client;
}
@Override 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);
}
}
如果不是GET请求，会先确认一次连接池中到主机的连接是否可用。这个拦截器的作用主要是从连接池获取一个到server的有效连接。
/** This is the last interceptor in the chain. It makes a network call to the server. */
public final class CallServerInterceptor implements Interceptor {
private final boolean forWebSocket;
public CallServerInterceptor(boolean forWebSocket) {
this.forWebSocket = forWebSocket;
}
@Override 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;
}
static final class CountingSink extends ForwardingSink {
long successfulCount;
CountingSink(Sink delegate) {
super(delegate);
}
@Override public void write(Buffer source, long byteCount) throws IOException {
super.write(source, byteCount);
successfulCount += byteCount;
}
}
}
拦截器集合中最后添加的这个拦截器，是真正和server交互数据的地方。
4. 连接池ConnectionPool
在OkHttpClient的Builder类中，connectionPool = new ConnectionPool();创建了一个连接池对象。首先，看一下该类中的成员变量。
/**
* Background threads are used to cleanup expired connections. There will be at most a single
* thread running per connection pool. The thread pool executor permits the pool itself to be
* garbage collected.
*/
private static final Executor executor = new ThreadPoolExecutor(0 /* corePoolSize */,
Integer.MAX_VALUE /* maximumPoolSize */, 60L /* keepAliveTime */, TimeUnit.SECONDS,
new SynchronousQueue(), Util.threadFactory("OkHttp ConnectionPool", true));
/** The maximum number of idle connections for each address. */
private final int maxIdleConnections;
private final long keepAliveDurationNs;
private final Runnable cleanupRunnable = new Runnable() {
@Override public void run() {
while (true) {
long waitNanos = cleanup(System.nanoTime());
if (waitNanos == -1) return;
if (waitNanos > 0) {
long waitMillis = waitNanos / 1000000L;
waitNanos -= (waitMillis * 1000000L);
synchronized (ConnectionPool.this) {
try {
ConnectionPool.this.wait(waitMillis, (int) waitNanos);
} catch (InterruptedException ignored) {
}
}
}
}
}
};
private final Deque connections = new ArrayDeque<>();
final RouteDatabase routeDatabase = new RouteDatabase();
boolean cleanupRunning;
一个线程池，用于清理失效连接，一个阻塞队列，用于管理RealConnection对象的生产和消费，队列中任务对象的数量没有限制。
构造函数
/**
* Create a new connection pool with tuning parameters appropriate for a single-user application.
* The tuning parameters in this pool are subject to change in future OkHttp releases. Currently
* this pool holds up to 5 idle connections which will be evicted after 5 minutes of inactivity.
*/
public ConnectionPool() {
this(5, 5, TimeUnit.MINUTES);
}
public ConnectionPool(int maxIdleConnections, long keepAliveDuration, TimeUnit timeUnit) {
this.maxIdleConnections = maxIdleConnections;
this.keepAliveDurationNs = timeUnit.toNanos(keepAliveDuration);
// Put a floor on the keep alive duration, otherwise cleanup will spin loop.
if (keepAliveDuration <= 0) {
throw new IllegalArgumentException("keepAliveDuration <= 0: " + keepAliveDuration);
}
}
从构造函数中，可以了解，其默认的闲置连接是5个，且每个连接的闲置时长为5分钟。在清理任务时，如果发现闲置连接超过5个，则闲置时间最长的连接会被从阻塞队列中移除。如果一个连接的闲置时间超过5分钟，该连接也会被从阻塞队列中移除。到server连接的复用，可以减少三次握手，四次挥手的过程，提高网络请求的效率。