1 okhttp总体流程
下图摘抄自网络
图1.1 okHttp总体流程图
2 Request、Response、Call基本概念
-
Request
request主要是对url，请求方法，请求参数，请求头等参数进行初始化，是通过Builder模式进行初始化 -
Response
请求返回给用户的一些参数，如协议，响应码，信息，返回数据等。 -
Call
Call是一个接口，它的实现类是RealCall。RealCall是final类型，是不可被继承的。RealCall主要作用是发送请求、建立拦截器和异步回调。请求方式有同步请求execute和异步请求enqueue。
2.1 OkHttp总体流程解析
- 初始化OkHttpClient对象，可以直接new一个对象，也可以通过Builder方法来build一个对象
- 初始化一个Request对象，Request类主要是对url、请求参数、请求头以及请求方法进行初始化
- 通过okHttpClient.newCall来初始化一个Call对象，newCall方法有个Request参数，该参数是上一步初始化的Request对象
- 然后通过初始化的call对象调用异步请求方法enqueue()或者同步请求方法execute()，如果call调用的是异步请求方法enqueue()，则会调用Dispatcher类的enqueue(AsyncCall)方法，最终会执行AsyncCall的execute()方法。
- 异步方法enquene()和同步方法execute()最终都会调用getResponseWithInspectorChain()方法，该方法会初始化几个拦截器，利用拦截器分层实现缓存、透明压缩、网络 IO 等功能。
- 最后通过Response返回请求的结果信息。
2.2 流程源码
- 初始化OkHttpClient对象，可以直接new一个对象，也可以通过Builder方法来build一个对象
private OkHttpClient(Builder builder) {
this.dispatcher = builder.dispatcher;
this.proxy = builder.proxy;
this.protocols = builder.protocols;
this.connectionSpecs = builder.connectionSpecs;
this.interceptors = Util.immutableList(builder.interceptors);
this.networkInterceptors = Util.immutableList(builder.networkInterceptors);
this.proxySelector = builder.proxySelector;
this.cookieJar = builder.cookieJar;
this.cache = builder.cache;
this.internalCache = builder.internalCache;
this.socketFactory = builder.socketFactory;
boolean isTLS = false;
for (ConnectionSpec spec : connectionSpecs) {
isTLS = isTLS || spec.isTls();
}
if (builder.sslSocketFactory != null || !isTLS) {
this.sslSocketFactory = builder.sslSocketFactory;
this.certificateChainCleaner = builder.certificateChainCleaner;
} else {
X509TrustManager trustManager = systemDefaultTrustManager();
this.sslSocketFactory = systemDefaultSslSocketFactory(trustManager);
this.certificateChainCleaner = CertificateChainCleaner.get(trustManager);
}
this.hostnameVerifier = builder.hostnameVerifier;
this.certificatePinner = builder.certificatePinner.withCertificateChainCleaner(
certificateChainCleaner);
this.proxyAuthenticator = builder.proxyAuthenticator;
this.authenticator = builder.authenticator;
this.connectionPool = builder.connectionPool;
this.dns = builder.dns;
this.followSslRedirects = builder.followSslRedirects;
this.followRedirects = builder.followRedirects;
this.retryOnConnectionFailure = builder.retryOnConnectionFailure;
this.connectTimeout = builder.connectTimeout;
this.readTimeout = builder.readTimeout;
this.writeTimeout = builder.writeTimeout;
}
public OkHttpClient build() {
return new OkHttpClient(this);
}
- 初始化一个Request对象，Request类主要是对url、请求参数、请求头以及请求方法进行初始化
public Request build() {
if (url == null) throw new IllegalStateException("url == null");
return new Request(this);
}
- 通过okHttpClient.newCall来初始化一个Call对象，newCall方法有个Request参数，该参数是上一步初始化的Request对象。执行newCall时会初始化一个RealCall对象，该对象实现了call接口。
@Override public Call newCall(Request request) {
return new RealCall(this, request);
}
- 然后通过初始化的call对象调用异步请求方法enqueue()或者同步请求方法execute()。
（1）如果call调用的是异步请求方法enqueue()，则会调用Dispatcher类的enqueue(AsyncCall)方法，最终会执行AsyncCall的execute()方法。
//RealCall的enqueue方法
void enqueue(Callback responseCallback, boolean forWebSocket) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
client.dispatcher().enqueue(new AsyncCall(responseCallback, forWebSocket));
}
//Dispatcher方法的enqueue方法
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
//executorService()返回的是ExecutorService对象，该对象用的是线程池ThreadPoolExecutor进行初始化
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
//AsyncCall的execute方法
@Override protected void execute() {
boolean signalledCallback = false;
try {
Response response = getResponseWithInterceptorChain(forWebSocket);
if (canceled) {
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 {
responseCallback.onFailure(RealCall.this, e);
}
} finally {
client.dispatcher().finished(this);
}
}
}
（2）使用call调用同步方法execute
@Override protected void execute() {
boolean signalledCallback = false;
try {
Response response = getResponseWithInterceptorChain(forWebSocket);
if (canceled) {
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 {
responseCallback.onFailure(RealCall.this, e);
}
} finally {
client.dispatcher().finished(this);
}
}
由上可得，不管同步还是异步，最终都会调用getResponseWithInterceptorChain(forWebSocket);方法。该方法会初始化几个拦截器，利用拦截器分层实现缓存、透明压缩、网络 IO 等功能。
private 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 (!retryAndFollowUpInterceptor.isForWebSocket()) {
interceptors.addAll(client.networkInterceptors());
}
interceptors.add(new CallServerInterceptor(
retryAndFollowUpInterceptor.isForWebSocket()));
Interceptor.Chain chain = new RealInterceptorChain(
interceptors, null, null, null, 0, originalRequest);
return chain.proceed(originalRequest);
}
- 在配置 OkHttpClient 时设置的 interceptors；
- 负责失败重试以及重定向的 RetryAndFollowUpInterceptor；
- 负责把用户构造的请求转换为发送到服务器的请求、把服务器返回的响应转
- 为用户友好的响应的 BridgeInterceptor；
- 负责读取缓存直接返回、更新缓存的 CacheInterceptor；
- 负责和服务器建立连接的 ConnectInterceptor；
- 配置 OkHttpClient 时设置的 networkInterceptors；
- 负责向服务器发送请求数据、从服务器读取响应数据的CallServerInterceptor。
- 最后通过Response返回请求的结果信息。
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);
}
