最大恢复追逐次数：
private static final int MAX_FOLLOW_UPS = ;
处理的业务:
- 实例化StreamAllocation，初始化一个Socket连接对象，获取到输入／输出流（）基于Okio
- 开启循环，执行下一个调用链（拦截器），等待返回结果（Response）
- 如果发生错误，判断是否继续请求，否：退出
- 检查响应是否符合要求，是：返回
- 关闭响应结果
- 判断是否达到最大限制数，是：退出
- 检查是否有相同连接，是：释放，重建连接
- 重复以上流程
源码
@Override
public Response intercept(Chain chain) throws IOException {
//
Request request = chain.request();
// 1. 初始化一个socket连接对象
streamAllocation = new StreamAllocation(
client.connectionPool(), createAddress(request.url()), callStackTrace); int followUpCount = ;
Response priorResponse = null;
while (true) {
//
if (canceled) {
streamAllocation.release();
throw new IOException("Canceled");
} Response response = null;
boolean releaseConnection = true;
try {
// 2. 执行下一个拦截器，即BridgeInterceptor
response = ((RealInterceptorChain) chain).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.
// 3. 如果有异常，判断是否要恢复
if (!recover(e.getLastConnectException(), 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, 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();
}
// 4. 检查是否符合要求
Request followUp = followUpRequest(response); if (followUp == null) {
if (!forWebSocket) {
streamAllocation.release();
}
// 返回结果
return response;
}
// 5. 不符合，关闭响应流
closeQuietly(response.body());
// 6. 是否超过最大限制
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());
}
// 7. 是否有相同的连接
if (!sameConnection(response, followUp.url())) {
streamAllocation.release();
streamAllocation = new StreamAllocation(
client.connectionPool(), createAddress(followUp.url()), callStackTrace);
} 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;
}
}
初始化连接对象
streamAllocation = new StreamAllocation(
client.connectionPool(), createAddress(request.url()), callStackTrace);
注意：此处还没有真正的去建立连接，只是初始化一个连接对象
继续下一个拦截器
上面一步初始化好后，将继续执行下一个连接器BridgeInterceptor，
// 这里有个很重的信息，即会将初始化好的连接对象传递给下一个拦截器，也是贯穿整个请求的连击对象，
// 上文我们说过，在拦截器执行过程中，RealInterceptorChain的几个属性字段会一步一步赋值
response = ((RealInterceptorChain) chain).proceed(request, streamAllocation, null, null);
抛出异常
如果抛出异常，将判断是否能够继续连接，以下情况不在，重试：
/**
* 不在继续连接的情况：
* 1. 应用层配置不在连接，默认为true
* 2. 请求Request出错不能继续使用
* 3. 是否可以恢复的
* 3.1、协议错误（ProtocolException）
3.2、中断异常（InterruptedIOException）
3.3、SSL握手错误（SSLHandshakeException && CertificateException）
3.4、certificate pinning错误（SSLPeerUnverifiedException）
* 4. 没用更多线路可供选择
*/
private boolean recover(IOException e, boolean requestSendStarted, Request userRequest) {
streamAllocation.streamFailed(e);
// 1. 应用层配置不在连接，默认为true
// The application layer has forbidden retries.
if (!client.retryOnConnectionFailure()) return false; // 2. 请求Request出错不能继续使用
// We can't send the request body again.
if (requestSendStarted && userRequest.body() instanceof UnrepeatableRequestBody) return false; // 是否可以恢复的
// This exception is fatal.
if (!isRecoverable(e, requestSendStarted)) return false; // 4. 没用更多线路可供选择
// No more routes to attempt.
if (!streamAllocation.hasMoreRoutes()) return false; // For failure recovery, use the same route selector with a new connection.
return true;
}