官网给出的示例
OkHttpClient client = new OkHttpClient();
String run(String url) throws IOException {
Request request = new Request.Builder()
.url(url)
.build();
Response response = client.newCall(request).execute();
return response.body().string();
}
整体流程
OKhttp3流程.png
源码分析
不管是同步请求还是异步请求，都必须先创建OkHttpClient和Request对象，上面使用Build模式创建的，下面分别看一下各自的源码：
OkHttpClient.Builder()
使用构造器模式初始化了一些配置信息：支持协议、任务分发器（其内部包含一个线程池，执行异步请求）、连接池(其内部包含一个线程池，维护connection)、连接/读/写超时时长等信息。
public Builder() {
dispatcher = new Dispatcher(); //任务调度器
protocols = DEFAULT_PROTOCOLS; //支持的协议
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(); //连接池
dns = Dns.SYSTEM;
followSslRedirects = true;
followRedirects = true;
retryOnConnectionFailure = true;
connectTimeout = 10_000;//超时时间
readTimeout = 10_000;
writeTimeout = 10_000;
pingInterval = 0;
}
Request.Builder()
指定了请求方式 GET 和请求 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);
}
...
}
不管同步请求还是异步请求，都是调用Call的方法执行的，下面看一下Call对象的创建okHttpClient.newCall(request)：
//Call是一个接口，RealCall是它的实现类
public Call newCall(Request request) {
return RealCall.newRealCall(this, request, false /* for web socket */);
}
static RealCall newRealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket){
//创建RealCall对象，将client和request传入
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;
//错误、重定向拦截器,默认情况下是第一个拦截器
this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client, forWebSocket);
}
上面创建对象的源码已经分析完了，下面就看一下具体请求的方法。
同步请求call.execute()
@Override
public Response execute() throws IOException {
synchronized (this) {
//同一个请求执行执行一遍，否则跑出异常
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
......
//当执行的请求开始的时候，回调监听中的方法
eventListener.callStart(this);
try {
//真正的请求是dispatcher.executed
client.dispatcher().executed(this);
//获取响应内容,后面分析 ①
Response result = getResponseWithInterceptorChain();
if (result == null) throw new IOException("Canceled");
return result;
}
......
finally {
//执行完成以后从对列中移除请求
client.dispatcher().finished(this);
}
}
dispatcher.executed
public final class Dispatcher {
private int maxRequests = 64; //最大请求数量
private int maxRequestsPerHost = 5; //每台主机最大的请求数量
@Nullable
private Runnable idleCallback;
@Nullable
private ExecutorService executorService; //线程池
//异步就绪对列
private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>();
//异步执行对列
private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();
//同步执行对列
private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();
/** 这个线程池没有核心线程，线程数量没有限制，空闲60s就会回收*/
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;
}
//dispatcher.executedsynchronized
void executed(RealCall call) {
//将call加入到同步请求对列中
runningSyncCalls.add(call);
}
}
异步请求call.enqueue
public void enqueue(Callback responseCallback) {
synchronized (this) {
//每个请求只能之执行一次
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
eventListener.callStart(this);
//封装成了AsyncCall，本质就是一个Runable
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
dispatcher().enqueue
synchronized void enqueue(AsyncCall call) {
//正在执行的任务数量小于最大值（64），并且此任务所属主机的正在执行任务小于最大值（5）
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
现在回头看看 AsyncCall ，它继承自 NamedRunnable，而 NamedRunnable实现了 Runnable 接口，它的作用有2个：
- 采用模板方法的设计模式，让子类将具体的操作放在 execute()方法中;
- 给线程指定一个名字，比如传入模块名称，方便监控线程的活动状态；
NamedRunnable
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 {
//采用模板方法让子类将具体的操作放到此execute()方法
execute();
} finally {
Thread.currentThread().setName(oldName);
}
}
protected abstract void execute();
}
AsyncCall
final class AsyncCall extends NamedRunnable {
//省略...
@Override protected void execute() {
boolean signalledCallback = false;
try {
//获得响应内容 ①
Response response = getResponseWithInterceptorChain();
if (retryAndFollowUpInterceptor.isCanceled()) {
//这个标记为主要是避免异常时2次回调
signalledCallback = true;
//回调Callback告知失败
responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
} else {
signalledCallback = true;
//回调Callback，将响应内容传回去
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 {
//不管请求成功与否，都进行finished()操作
client.dispatcher().finished(this);//②
}
}
}
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) {
//从正在执行的队列中将其移除
if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
if (promoteCalls) promoteCalls(); //推动下一个任务的执行
runningCallsCount = runningCallsCount();//同步+异步的正在执行任务数量
idleCallback = this.idleCallback;
}
//如果没有正在执行的任务，且idleCallback不为null，则回调通知空闲了
if (runningCallsCount == 0 && idleCallback != null) {
idleCallback.run();
}
}
promoteCalls()
private void promoteCalls() {
if (runningAsyncCalls.size() >= maxRequests) return; // Already running max capacity.
if (readyAsyncCalls.isEmpty()) return; // No ready calls to promote.
//若条件允许，将readyAsyncCalls(异步就绪对列)中的任务移动到runningAsyncCalls(异步执行对列)中，并交给线程池执行
for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
AsyncCall call = i.next();
if (runningCallsForHost(call) < maxRequestsPerHost) {
i.remove();
runningAsyncCalls.add(call);
executorService().execute(call);
}
//当runningAsyncCalls(异步执行对列)满了，直接退出迭代
if (runningAsyncCalls.size() >= maxRequests) return; // Reached max capacity.
}
}
不管是同步请求还是异步请求，最终都是通过getResponseWithInterceptorChain()方法来获取Response的，该方法就是构建一个拦截器链。
回到注释带有①标记的 getResponseWithInterceptorChain()
Response getResponseWithInterceptorChain() throws IOException {
// Build a full stack of interceptors.
//这是一个List，是有序的
List<Interceptor> interceptors = new ArrayList<>();
//首先添加的是用户添加的全局拦截器
interceptors.addAll(client.interceptors());
//错误、重定向拦截器，默认是第一个拦截器
interceptors.add(retryAndFollowUpInterceptor);
//桥接拦截器，桥接应用层与网络层，添加必要的头、
interceptors.add(new BridgeInterceptor(client.cookieJar()));
//缓存处理，Last-Modified、ETag、DiskLruCache等
interceptors.add(new CacheInterceptor(client.internalCache()));
//连接拦截器
interceptors.add(new ConnectInterceptor(client));
//从这就知道，通过okHttpClient.Builder#addNetworkInterceptor()传进来的拦截器只对非网页的请求生效
if (!forWebSocket) {
interceptors.addAll(client.networkInterceptors());
}
//真正访问服务器的拦截器
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);
}
Okhttp中的拦截器
chain.proceed(originalRequest)
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 {
......
// Call the next interceptor in the chain.
RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
writeTimeout);
//顺序获取拦截器，然后调用拦截器的intercept方法
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);
......
return response;
}
在chain.proceed方法中调用了interceptor.intercept(next);方法，并将新创建的拦截器链对象传入，此时index为index + 1，这样就构成了依次调用拦截器集合的所用拦截器的intercept方法。在该方法中完成对应的功能以后，调用下一个拦截器的intercept方法，并将处理后的Response返回给上一个拦截器。
RetryAndFollowUpInterceptor（重定向拦截器）
该拦截器的主要作用就是：负责请求的重定向操作以及请求失败后的重试机制。
public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
RealInterceptorChain realChain = (RealInterceptorChain) chain;
Call call = realChain.call();
EventListener eventListener = realChain.eventListener();
//创建一个StreamAllocation
StreamAllocation streamAllocation = new StreamAllocation(client.connectionPool(),
createAddress(request.url()), call, eventListener, callStackTrace);
this.streamAllocation = streamAllocation;
//统计重定向次数，不能大于20
int followUpCount = 0;
Response priorResponse = null;
while (true) {
if (canceled) {
streamAllocation.release();
throw new IOException("Canceled");
}
Response response;
boolean releaseConnection = true;
try {
//调用下一个interceptor的来获得响应内容
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();
}
//重定向处理
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;
}
}
BridgeInterceptor（桥接拦截器）
该拦截器的作用主要就是处理请求和响应,添加了必要请求头信息，gzip处理等。
public Response intercept(Chain chain) throws IOException {
Request userRequest = chain.request();
Request.Builder requestBuilder = userRequest.newBuilder();
//从这开始给请求添加了一些请求头信息
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();
}
CacheInterceptor（缓存拦截器）
该拦截器主要工作是做做缓存处理，如果有有缓存并且缓存可用，那就使用缓存，否则进行调用下一个拦截器 ConnectionInterceptor 进行网络请求，并将响应内容缓存。
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 {
//调用下一个拦截器进行网络请求
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;
}
ConnectionInterceptor （连接拦截器）
该拦截器主要是打开一个到目标服务器的connection
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);
}
CallServerInterceptor
这是拦截器链最后一个拦截器，它向服务器发起真正的网络请求。
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();
// (1)写入请求
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 ("100-continue".equalsIgnoreCase(request.header("Expect"))) {
httpCodec.flushRequest();
realChain.eventListener().responseHeadersStart(realChain.call());
responseBuilder = httpCodec.readResponseHeaders(true);
}
if (responseBuilder == null) {
// (2)如果有请求体，写入请求体，POST 请求
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()) {
streamAllocation.noNewStreams();
}
}
httpCodec.finishRequest();
// (3)请求码判断
int code = response.code();
if (code == 100) {
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) {
response = response.newBuilder()
.body(Util.EMPTY_RESPONSE)
.build();
} else {
// (4) openResponseBody 获取响应体信息
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());
}
// (5)往上级 ConnectInterceptor 返回 Response。
return response;
}
小结
okhttp 的请求实际上就是分解为各个拦截器的动作，各个拦截器按照先后的顺序，依次执行，采用责任链模式，最终完成请求，责任链在请求过程中逐步携带请求的参数信息， 逐步的意思就是来源前面拦截器创建的参数，后面的拦截器依赖前面拦截器的参数，参数由责任链传递过来；此外，在请求结果返回时，责任链中又从后面回溯到前面，依次处理返回结果，就是这样一去一回的过程。
