OKHttp 执行拦截器前

getResponseWithInterceptorChain():

Response getResponseWithInterceptorChain() throws IOException {
// Build a full stack of interceptors.
List<Interceptor> interceptors = new ArrayList<>();
interceptors.addAll(client.interceptors()); //由我们能定义的 不是由我们定义成为系统拦截器
interceptors.add(retryAndFollowUpInterceptor);
interceptors.add(new BridgeInterceptor(client.cookieJar()));
interceptors.add(new CacheInterceptor(client.internalCache()));
interceptors.add(new ConnectInterceptor(client));
if (!forWebSocket) {//默认是false
interceptors.addAll(client.networkInterceptors()); //由我们能定义的
}
interceptors.add(new CallServerInterceptor(forWebSocket));
//创建拦截器链 并调用proceed(...)
Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
originalRequest, this, eventListener, client.connectTimeoutMillis(),
client.readTimeoutMillis(), client.writeTimeoutMillis());

return chain.proceed(originalRequest);

}

@Override public Response proceed(Request request) throws IOException {
return proceed(request, streamAllocation, httpCodec, connection); //重载方法
}

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.
// index+1 下次进来时取得下一个拦截器
RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
writeTimeout);
//取出拦截器并执行intercept(...)方法
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);

// Confirm that the next interceptor made its required call to chain.proceed().
确保每个拦截器都调用了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;
}