根据OkHttp源码阅读，对源码进行分析。
OkHttp 从了解到放弃
源码解析
使用入口
OkHttp 进行网络请求有同步，异步两种方式。
//异步调用
//1.拿到okHttpClient对象,可以设置连接超时等
OkHttpClient okHttpClient=new OkHttpClient();
//2.构造Request请求对象，可以增加头addHeader等
Request.Builder builder = new Request.Builder();
//url()中可以放入网址
Request request = builder.
get().
url("http://publicobject.com/helloworld.txt")
.build();
//3.将Request封装为Call
Call call = okHttpClient.newCall(request);
//4.执行call
//方法一Response response=call.execute();//汇抛出IO异常，同步方法
//方法二,异步方法，放到队列中,处于子线程中，无法更新UI
call.enqueue(new Callback() {
//请求时失败时调用
@Override
public void onFailure(Call call, IOException e) {
}
//请求成功时调用
@Override
public void onResponse(Call call, Response response) throws IOException {
//处于子线程中，能够进行大文件下载，但是无法更新UI
}
});
// 同步调用
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
Request request = new Request.Builder()
.url("http://publicobject.com/helloworld.txt")
.build();
Response response = client.newCall(request).execute();
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
Headers responseHeaders = response.headers();
for (int i = 0; i < responseHeaders.size(); i++) {
System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
}
System.out.println(response.body().string());
}
同步调用和异步调用的区别是异步调用使用的是enqueue函数，而同步调用则是execute函数。
OkHttp 通过 Builder 构建模式构建 Request 对象。Request 类用来存储请求url, post还是get请求，以及http请求中的header 和 body。
构造好 Request 对象后通过 newCall 函数来构造一个 Call 对象，然后通过这个 Call 对象来进行网络请求操作。
@Override 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);
this.timeout = new AsyncTimeout() {
@Override protected void timedOut() {
cancel();
}
};
this.timeout.timeout(client.callTimeoutMillis(), MILLISECONDS);
}
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);
this.timeout = new AsyncTimeout() {
@Override protected void timedOut() {
cancel();
}
};
this.timeout.timeout(client.callTimeoutMillis(), MILLISECONDS);
}
因为 Call 是一个接口，所以实际实现类是 RealCall。实际返回的是一个 RealCall 对象，对象中包含了一个事件监听接口，当在网络请求的过程中会分别触发对应事件函数，例如连接开始，连接结束这些过程。同时，还会生成一个重试和重定向拦截器。
生成了 RealCall 对象后，调用 Call 接口的 enqueue 方法，由 RealCall 实现。
@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));
}
enqueue 方法里面首先触发了事件监听接口的 callStart 方法，表明开始调用请求消息了。然后通过 OkHttpClient 的调度器 dispatcher 将任务加入到队列中，其中 AsyncCall 类是最终继承于 Runable 的。里面重写的 run() 方法之后再介绍。
接着我们来看下调度器 Dispatcher 类的enqueue() 方法。
void enqueue(AsyncCall call) {
synchronized (this) {
readyAsyncCalls.add(call);
}
promoteAndExecute();
}
这里是先将请求任务添加到待请求队列中去， readyAsyncCalls ArrayDeque 类，是一个双向队列。
private boolean promoteAndExecute() {
assert (!Thread.holdsLock(this));
List<AsyncCall> executableCalls = new ArrayList<>();
boolean isRunning;
synchronized (this) {
for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
AsyncCall asyncCall = i.next();
if (runningAsyncCalls.size() >= maxRequests) break; // Max capacity.
if (runningCallsForHost(asyncCall) >= maxRequestsPerHost) continue; // Host max capacity.
i.remove();
executableCalls.add(asyncCall);
runningAsyncCalls.add(asyncCall);
}
isRunning = runningCallsCount() > 0;
}
for (int i = 0, size = executableCalls.size(); i < size; i++) {
AsyncCall asyncCall = executableCalls.get(i);
asyncCall.executeOn(executorService());
}
return isRunning;
}
promoteAndExecute 方法中对待请求队列使用迭代器进行遍历，这里规定了同一时刻运行的所有请求任务不能超过 maxRequests 64个请求，同一主机的请求不能超过 maxRequestsPerHost 5个。然后将请求从待请求队列中移除，添加到正在执行请求队列中。紧接着遍历这些请求调用executeOn()方法，在线程池中执行网络请求。
这里先看下使用的线程池的参数，也即 executorService()中的线程池。
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;
}
线程池参数，核心线程数量为0，最大线程数为 Max 最大值，空闲线程存活时间为60秒，任务队列采用的是 SynchronousQueue。这样设计的好处是，由于 SynchronousQueue 无法存储数据，所以当任务被添加进来时会立刻创建新线程执行请求任务，因此OkHttp 具备高并发的特点。同时核心线程池数设计为0是因为保证网络请求结束后核心线程不会一直保留着浪费资源。
了解完线程池设计，接着我们看下 executeOn() 方法是如何执行任务的。 executeOn() 内部执行了线程池的 execute() 方法。也即会执行到之前提到的 AsyncCall 的 run() 方法。其 run() 方法内只执行了一个 execute() 方法。
@Override protected void execute() {
boolean signalledCallback = false;
timeout.enter();
try {
Response response = getResponseWithInterceptorChain();
signalledCallback = true;
responseCallback.onResponse(RealCall.this, response);
} catch (IOException e) {
e = timeoutExit(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);
}
}
这个方法比较关键，里面调用了 getResponseWithInterceptorChain() 方法得到请求的响应 Response。然后通过 callback 触发 response响应方法告知请求方。也即 getResponseWithInterceptorChain()方法内部完成了网络请求。
Response getResponseWithInterceptorChain() throws IOException {
// Build a full stack of interceptors.
List<Interceptor> 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());
Response response = chain.proceed(originalRequest);
if (retryAndFollowUpInterceptor.isCanceled()) {
closeQuietly(response);
throw new IOException("Canceled");
}
return response;
}
列表中添加了7个 interceptor 拦截器，用户自定义的应用拦截器，用于重定向的重试和重定向拦截器，用于完善请求数据的桥接拦截器，用于缓存请求数据的缓存拦截器，用于进行Socket连接的连接拦截器，以及用户可自行添加的网络拦截器，最后有用于向服务器发送http请求的 CallServerInterceptor 拦截器。通过责任链将拦截器串成一起，根据责任链模式分别触发。
责任链
OkHttp 中的责任链通过 Interceptor.Chain 接口来实现的，具体的实现类为 RealInterceptorChain， 通过调用 proceed() 方法来进行责任链上的任务处理流转。
@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;
}
通过 index 就能获取到拦截器，然后触发拦截器的 intercept() 方法对请求进行对应的拦截处理操作。然后每次调用 proceed() 方法都将 index 进行加1，并重新构造一个 RealInterceptorChain 链对象，这样的话在 proceed() 方法中获取到的就是下一个拦截器，调用下一个拦截器的 intercept() 方法，然后再通过回溯的方式将请求的 Response 逐级向上传递，最终将 response 传给请求调用方。
拦截器
OkHttp 通过接口 Interceptor 设置了不同类型的拦截器。通过责任链分别调用不同拦截器的 intercept() 方法进行触发拦截操作。
应用拦截器
该类型拦截器为用户自定义添加的拦截器，每次请求应用拦截器只会被触发一次。根据用户自定义需求进行添加。
RetryAndFollowUpInterceptor
@Override public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
RealInterceptorChain realChain = (RealInterceptorChain) chain;
Call call = realChain.call();
EventListener eventListener = realChain.eventListener();
StreamAllocation streamAllocation = new StreamAllocation(client.connectionPool(),
createAddress(request.url()), call, eventListener, callStackTrace);
this.streamAllocation = streamAllocation;
int followUpCount = 0;
Response priorResponse = null;
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;
} 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.getFirstConnectException();
}
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();
}
Request followUp;
try {
followUp = followUpRequest(response, streamAllocation.route());
} catch (IOException e) {
streamAllocation.release();
throw e;
}
if (followUp == null) {
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;
}
}
这里通过 StreamAllocation 类将请求的连接对象化了为一个 Connection 对象，以及内部使用了连接池进行管理。然后通过 while(true) 不断尝试，使用 request 去继续责任链上的拦截操作，最终完成一次请求拿到 response。 拿到了 response 通过 followUpRequest() 函数来解析 response 的 Http 返回码，如果返回码不对那么重新构造出一个新的请求 request 对象，拿着这个新请求的 request 对象进行重新去继续责任链上的拦截操作，完成请求。不断请求，直到反正正确的 Http 返回码，完成请求流程。 其中 OkHttp 对请求次数也有限制，重试和重定向的请求次数不得超过 MAX_FOLLOW_UPS 20次。(其中Chrome 是21次， 火狐和curl 及 wget 是20次， Safari 是16次， Http/1.0 要求5次)
BridgeInterceptor
@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<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();
}
桥接拦截器，从代码整体中可以看出，作用主要是补充请求的Header内容以及cookie。补充的 Header 数据包括 content-type 等数据。拦截器补充完 headr 和 cookie 数据后再通过 chain.proceed 交给后续拦截器处理。
CacheInterceptor
@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;
}
CacheInterceptor 通过 DiskLruCache 存储网络请求和响应，当网络请求到了这一拦截器时，会先通过 Request 来获取是否有缓存 Response，有的话直接将缓存 Response 返回，没有的话再继续正常的网络请求流程。
ConnectInterceptor
@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);
}
ConnectInterceptor 开始建立Socket连接。通过ConnectionPool 连接池来缓存复用连接对象 Connection。这样的好处是可以减少TCP握手次数，连接未释放之前针对相同的请求重新利用用来发送数据。类似于浏览器的keep-alive机制。
CallServerInterceptor
这个拦截器是在客户端建立好连接之后的拦截器，主要用来向服务器发送http请求。
@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;
}
从代码中可以看到，httpcodec.writeRequestHeaders()进行写入请求到buffer，通过httpCodec.finishRequest();进行发送。发送请求后再通过httpCodec进行获取响应 response。拿到了response后然后再返回在责任链上的各个拦截器上进行回溯。
设计模式
-
- Builder模式
-
- 工厂模式
-
- 责任链模式
-
- 享元模式
通过 Builder 模式进行构建 OkHttpClient 对象和 Request 及 Response。通过工厂模式来针对不同缓存模式进行构建缓存对象。 通过责任链模式来使请求经历不同的拦截器处理，通过享元模式来进行连接池构建不同的连接Connection对象。