版本号：3.13.1
一.基本使用
//1.创建OkHttpClient对象val okHttpClient = OkHttpClient.Builder().readTimeout(5,TimeUnit.SECONDS).build()//2.创建Request对象val request = Request.Builder().url("www.baidu.com").build()//3.通过OkHttpClient将Request封装成Call对象val call = okHttpClient.newCall(request)//通过Call执行请求//同步请求val response = call.execute()
Log.d("okhttp",response.body().toString())//异步请求call.enqueue(object :Callback{ override fun onFailure(call: Call, e: IOException) {
} override fun onResponse(call: Call, response: Response) {
Log.d("okhttp",response.body().toString())
}
})Call可以理解为Request和Response之间的桥梁，Http请求过程中可能有重定向和重试等操作，你的一个简单请求可能会产生多个请求和响应。OkHttp使用Call这一概念对此来建模：不论为了满足你的请求任务，中间做了多少次请求和响应，都算作一个Call。
二.源码分析
1.创建对象源码分析
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().
public Builder() { //任务分发器
dispatcher = new Dispatcher();
protocols = DEFAULT_PROTOCOLS;
connectionSpecs = DEFAULT_CONNECTION_SPECS;
eventListenerFactory = EventListener.factory(EventListener.NONE);
proxySelector = ProxySelector.getDefault(); if (proxySelector == null) {
proxySelector = new NullProxySelector();
}
cookieJar = CookieJar.NO_COOKIES;
socketFactory = SocketFactory.getDefault();
hostnameVerifier = OkHostnameVerifier.INSTANCE;
certificatePinner = CertificatePinner.DEFAULT;
proxyAuthenticator = Authenticator.NONE;
authenticator = Authenticator.NONE; //连接池
connectionPool = new ConnectionPool();
dns = Dns.SYSTEM;
followSslRedirects = true;
followRedirects = true;
retryOnConnectionFailure = true;
callTimeout = 0; //java7以后在数字中可以使用下划线，只是增加阅读性，没其他作用
connectTimeout = 10_000;
readTimeout = 10_000;
writeTimeout = 10_000;
pingInterval = 0;
}Request.Builder()
public Builder() { this.method = "GET"; this.headers = new Headers.Builder();
}build()方法，都是在该方法中创建各自的对象，在构造方法中将当前的build对象传入，然后把对应的属性值赋。下面以Request为例：
public Request build() { if (url == null) throw new IllegalStateException("url == null"); return new Request(this);
}//Builder模式Request(Builder builder) {this.url = builder.url;this.method = builder.method;this.headers = builder.headers.build();this.body = builder.body;this.tags = Util.immutableMap(builder.tags);
}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)：
@Override public Call newCall(Request request) { //Call是一个接口，RealCall是它的实现类
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.
//创建RealCall对象，将client和request传入
RealCall call = new RealCall(client, originalRequest, forWebSocket); //设置监听器
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; //重定向拦截器
this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client); this.timeout = new AsyncTimeout() { @Override protected void timedOut() {
cancel();
}
}; this.timeout.timeout(client.callTimeoutMillis(), MILLISECONDS);
}从上面代码中可以看到Call的实现类为RealCall，它持有client和request。
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。
2.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);
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);
}
}public Dispatcher dispatcher() { return dispatcher;
}//dispatcher.executedsynchronized void executed(RealCall call) { //将call加入到同步请求对列中
runningSyncCalls.add(call);
}public final class Dispatcher {
...... //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<>();
......
}同步请求调用
realCall.executed方法，在该方法中调用dispatcher.executed将realCall添加到同步运行对列中runningSyncCalls然后调用getResponseWithInterceptorChain获取响应报文。
3.异步请求： call.enqueue
@Override public void enqueue(Callback responseCallback) { synchronized (this) { //当前的call（创建的call）只能执行一次
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
eventListener.callStart(this); //封装成了AsyncCall，它就是一个Runable
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}void enqueue(AsyncCall call) { synchronized (this) { //添加到就绪对列
readyAsyncCalls.add(call);
......
}
}
promoteAndExecute();
}private boolean promoteAndExecute() { assert (!Thread.holdsLock(this));
List<AsyncCall> executableCalls = new ArrayList<>(); boolean isRunning; synchronized (this) { //遍历就绪对列执行任务
for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
AsyncCall asyncCall = i.next(); //如果请求大于最大的请求数 maxRequests = 64，不执行
if (runningAsyncCalls.size() >= maxRequests) break; // Max capacity.
//请求的host不能大于maxRequestsPerHost = 5
if (asyncCall.callsPerHost().get() >= maxRequestsPerHost) continue; // Host max capacity.
i.remove();
asyncCall.callsPerHost().incrementAndGet(); //没有大于最大请求数，添加到执行对列中
executableCalls.add(asyncCall);
runningAsyncCalls.add(asyncCall);
}
isRunning = runningCallsCount() > 0;
} //循环执行对列，执行具体的请求
for (int i = 0, size = executableCalls.size(); i < size; i++) {
AsyncCall asyncCall = executableCalls.get(i); //执行任务，传入线程池
asyncCall.executeOn(executorService());
} return isRunning;
}异步请求的时候，通过
dispatcher.enqueue方法将call（封装成了Runable(AsyncCall,它是RealCall的的内部类)）添加到就绪对列中，然后循环就绪对列，如果现在执行的任务数没有超过最大的请求数（64）就添加到执行对列中，然后执行asyncCall.executeOn(executorService());。
public synchronized ExecutorService executorService() { if (executorService == null) { //最大的线程数为 Integer.MAX_VALUE，上面已经限制最大的请求数为64所以这里的数量不会超过64
executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS, new SynchronousQueue<>(), Util.threadFactory("OkHttp Dispatcher", false));
} return executorService;
}void executeOn(ExecutorService executorService) { assert (!Thread.holdsLock(client.dispatcher())); boolean success = false; try { //执行任务
executorService.execute(this);
success = true;
} catch (RejectedExecutionException e) {
InterruptedIOException ioException = new InterruptedIOException("executor rejected");
ioException.initCause(e);
eventListener.callFailed(RealCall.this, ioException);
responseCallback.onFailure(RealCall.this, ioException);
} finally { if (!success) {
client.dispatcher().finished(this); // This call is no longer running!
}
}
}
executorService.execute(this);就是执行AsyncCall中的run()方法
AsyncCall继承NamedRunnable，没有重写run()方法，直接调用父类的，在父类的run()方法中调用了一个execute();方法，该方法是一个抽象方法，需要子类实现，所以实际执行的是AsyncCall.execute()
public abstract class NamedRunnable implements Runnable {
...... @Override public final void run() {
String oldName = Thread.currentThread().getName();
Thread.currentThread().setName(name); try {
execute();
} finally {
Thread.currentThread().setName(oldName);
}
} protected abstract void execute();
}下面就看一个AsyncCall.execute()，真正执行任务的方法：
//该方法在子线程中执行@Override protected void execute() { boolean signalledCallback = false;
timeout.enter(); try { //获取响应报文
Response response = getResponseWithInterceptorChain(); if (retryAndFollowUpInterceptor.isCanceled()) {
signalledCallback = true;
responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
} else {
signalledCallback = true;
responseCallback.onResponse(RealCall.this, response);
}
}...... finally { //调用finished方法，将该请求从请求对列中移除
client.dispatcher().finished(this);
}
}
}
从上面的代码分析我们可以得出：异步请求流程：
call.enqueue->realCall.enqueue->dispatcher.enqueue（AsyncCall call）（AsyncCall本质就是一个Runable）在dispatcher.enqueue方法中将call添加到就绪对列中，然后外遍历就绪对列，如果现在运行的任务没有超过最大请求数（64）就会把它加入到运行对列中runningAsyncCalls，然后调用asyncCall.executeOn(executorService())（executorService()方法就是创建一个线程池），在executeOn方法中会执行asyncCall，就是调用它的execute方法。在该方法中真正的去执行任务，该方法是在子线程中执行的。
通过上面的分析我们可以得出大致的请求流程图如下：
请求流程图
不管是同步请求还是异步请求，都调用了dispatcher对应的方法，它里面维护了三个任务对列和一个线程池（用来执行异步请求），dispatcher维护着请求任务的添加和移除。
三.Okhttp中的拦截器
拦截器是Okhttp提供的一种强大的机制，它可以实现网络监听、请求以及响应重写、请求失败重试等功能。
Okhttp的拦截器分为两种：一种是应用拦截器（就是我们自定义的拦截器），另一种就是网络拦截器（是Okhttp内部提供给我们的拦截器，真正的网络请求就是通过这些网络拦截器来实现的）。
从上面的代码分析得出：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。下面看一下该方法的代码：
//RealCall中的方法Response getResponseWithInterceptorChain() throws IOException {
List<Interceptor> interceptors = new ArrayList<>(); //添加自定义的拦截器
interceptors.addAll(client.interceptors()); //添加okhttp提供给我们的网络拦截器
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)); //创建一个拦截器链对象，然后将拦截器集合传入
Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
originalRequest, this, eventListener, client.connectTimeoutMillis(),
client.readTimeoutMillis(), client.writeTimeoutMillis()); return chain.proceed(originalRequest);
}创建好拦截器链以后调用了该对象的chain.proceed(originalRequest)方法。该方法源码如下：
public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
RealConnection connection) throws IOException {
...... //又创建了一个拦截器链对象，注意此时传入的index = index + 1
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。
拦截器处理流程图
1.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。
@Override public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
RealInterceptorChain realChain = (RealInterceptorChain) chain;
Call call = realChain.call();
EventListener eventListener = realChain.eventListener(); //1.创建StreamAllocation 对象，该对象用于分配请求过程中的流
StreamAllocation streamAllocation = new StreamAllocation(client.connectionPool(),
createAddress(request.url()), call, eventListener, callStackTrace); this.streamAllocation = streamAllocation; //重连次数
int followUpCount = 0;
Response priorResponse = null; while (true) {
......
Response response; boolean releaseConnection = true; try { //2.调用RealInterceptorChain的proceed方法进行网络请求
response = realChain.proceed(request, streamAllocation, null, null);
releaseConnection = false;
}...... // 叠加先前的响应
if (priorResponse != null) {
response = response.newBuilder()
.priorResponse(priorResponse.newBuilder()
.body(null)
.build())
.build();
}
Request followUp; try { //根据响应判断是否需要重新请求
followUp = followUpRequest(response, streamAllocation.route());
}...... if (followUp == null) { //不需要重新请求，直接返回response，结束while循环
streamAllocation.release(true); return response;
}
...... //需要重新请求，先判断重新请求的次数是否超过设置的最大值，MAX_FOLLOW_UPS = 20
if (++followUpCount > MAX_FOLLOW_UPS) { //超过最大的重新请求次数，抛出异常
streamAllocation.release(true); throw new ProtocolException("Too many follow-up requests: " + followUpCount);
}
...... //重新请求
if (!sameConnection(response, followUp.url())) {
streamAllocation.release(false);
streamAllocation = new StreamAllocation(client.connectionPool(),
createAddress(followUp.url()), call, eventListener, callStackTrace); this.streamAllocation = streamAllocation;
}......
request = followUp;
priorResponse = response;
}
}从RetryAndFollowUpInterceptor.intercept方法得出主要做了以下几件事：
1.创建StreamAllocation对象。
2.调用RealInterceptorChain的
proceed方法进行网络请求，该方法就会调用下一个拦截器的intercept方法，依次调用，获取对应的Response。
intercept方法有些类似递归调用，这里是不同拦截器对象的intercept方法，这样就从上到下形成了一个链。
3.根据异常结果或者响应结果判断是否要进行重新请求。
2.BridgeInterceptor（桥接拦截器）
该拦截器的作用主要就是处理请求和响应
在RetryAndFollowUpInterceptor拦截器中创建StreamAllocation对象以后，就会调用chain.proceed方法进行网络请求，其实就是调用下一个拦截器的intercept方法，RetryAndFollowUpInterceptor的下一个拦截就是BridgeInterceptor，下面看一下它的intercept代码：
@Override public Response intercept(Chain chain) throws IOException {
Request userRequest = chain.request();
Request.Builder requestBuilder = userRequest.newBuilder();
RequestBody body = userRequest.body(); //1.为请求添加一些头信息
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());
} //2.发送网络请求
Response networkResponse = chain.proceed(requestBuilder.build()); //3.解压响应数据，支持`gzip`，所以需要解压
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();
}从BridgeInterceptor.intercept方法得出主要做了以下几件事：
1.将用户构建的Request转化为能够进行网络访问的请求（添加一些头信息，如：
Connection、Accept-Encoding、Host等）。2.将设置好的Request发送网络请求（调用
chan.proceed）。3.将请求返回的Response转化为用户可用的Response（可能使用gzip压缩，需要解压）。
3.CacheInterceptor（缓存拦截器）
该拦截器的作用主要就是处理数据的缓存
在BridgeInterceptor.intercept方法中构建好Request后就发送请求，就会调用CacheInterceptor.intercept方法，该方法的代码为：
@Override public Response intercept(Chain chain) throws IOException { //如果设置了缓存就获取缓存
Response cacheCandidate = cache != null
? cache.get(chain.request())
: null; long now = System.currentTimeMillis(); //获取缓存策略，里面维护着一个networkRequest和cacheResponse
CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
Request networkRequest = strategy.networkRequest;
Response cacheResponse = strategy.cacheResponse; if (cache != null) { //如果有缓存，跟新一下缓存的各项指标，主要是缓存命中率
cache.trackResponse(strategy);
} if (cacheCandidate != null && cacheResponse == null) { //有缓存，但是对应的Response 为null即缓存不符合要求，关闭该缓存
closeQuietly(cacheCandidate.body()); // The cache candidate wasn't applicable. Close it.
} // 如果此时网络不可用，同时网络不可用，抛出一个504的错误
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();
} //网络不可用，但是有缓存，直接返回缓存。
if (networkRequest == null) { return cacheResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build();
} //没有缓存，但是网路可用，发起网络请求
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 (cacheResponse != null) { //如果网络请求返回的状态码为 HTTP_NOT_MODIFIED = 304，从缓存中获取数据
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();
......
}
Response response = networkResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build(); if (cache != null) { //如果请求可以缓存，就将网络请求后的数据添加到缓存
if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) { // Offer this request to the cache.
CacheRequest cacheRequest = cache.put(response); return cacheWritingResponse(cacheRequest, response);
} //如果请求方法缓存无效，从缓存中删除
if (HttpMethod.invalidatesCache(networkRequest.method())) { try {
cache.remove(networkRequest);
} catch (IOException ignored) { // The cache cannot be written.
}
}
} return response;
}@Override public Response intercept(Chain chain) throws IOException { //如果设置了缓存就获取缓存
Response cacheCandidate = cache != null
? cache.get(chain.request())
: null; long now = System.currentTimeMillis(); //获取缓存策略，里面维护着一个networkRequest和cacheResponse
CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
Request networkRequest = strategy.networkRequest;
Response cacheResponse = strategy.cacheResponse; if (cache != null) { //如果有缓存，跟新一下缓存的各项指标，主要是缓存命中率
cache.trackResponse(strategy);
} if (cacheCandidate != null && cacheResponse == null) { //有缓存，但是对应的Response 为null即缓存不符合要求，关闭该缓存
closeQuietly(cacheCandidate.body()); // The cache candidate wasn't applicable. Close it.
} // 如果此时网络不可用，同时缓存不可用，抛出一个504的错误
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();
} //网络不可用，但是有缓存，直接返回缓存。
if (networkRequest == null) { return cacheResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build();
} //没有缓存，但是网路可用，发起网络请求
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 (cacheResponse != null) { //如果网络请求返回的状态码为 HTTP_NOT_MODIFIED = 304，从缓存中获取数据
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();
......
}
Response response = networkResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build(); if (cache != null) { //如果请求可以缓存，就将网络请求后的数据添加到缓存
if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) { // Offer this request to the cache.
CacheRequest cacheRequest = cache.put(response); return cacheWritingResponse(cacheRequest, response);
} //如果请求方法缓存无效，从缓存中删除
if (HttpMethod.invalidatesCache(networkRequest.method())) { try {
cache.remove(networkRequest);
} catch (IOException ignored) { // The cache cannot be written.
}
}
} return response;
}
作者：慕涵盛华
链接：https://www.jianshu.com/p/073893ac22bd
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