RealCall.java中获取response的时候需要经过一系列的拦截器，我今天大致看一下里面的代码
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 (!forWebSocket) {
interceptors.addAll(client.networkInterceptors());
}
interceptors.add(new CallServerInterceptor(forWebSocket));
Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
originalRequest, this, eventListener, client.connectTimeoutMillis(),
client.readTimeoutMillis(), client.writeTimeoutMillis());
Response response = chain.proceed(originalRequest);
if (retryAndFollowUpInterceptor.isCanceled()) {
closeQuietly(response);
throw new IOException("Canceled");
}
return response;
}
client.interceptors() 这个拦截器是用户自己定义的，略过
retryAndFollowUpInterceptor 重试与重定向拦截器
@Override 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StreamAllocation对象（包含http请求组件）
StreamAllocation streamAllocation = new StreamAllocation(client.connectionPool(),createAddress(request.url()), call, eventListener, callStackTrace);
this.streamAllocation = streamAllocation;
int followUpCount = 0;
Response priorResponse = null;
while (true) {
if (canceled) {
streamAllocation.release();
throw new IOException("Canceled");
}
Response response;
boolean releaseConnection = true;
try {
response = realChain.proceed(request, streamAllocation, null, null);
releaseConnection = false;
} catch (RouteException e) {
//路由异常，连接未成功，请求还没发出去
if (!recover(e.getLastConnectException(), streamAllocation, false, request)) {
throw e.getFirstConnectException();
}
releaseConnection = false;
continue;
} catch (IOException e) {
// 请求发出去了，但是和服务器通信失败了（socket流正在读写数据的时候断开连接）
boolean requestSendStarted = !(e instanceof ConnectionShutdownException);
if (!recover(e, streamAllocation, requestSendStarted, request)) throw e;
releaseConnection = false;
continue;
} finally {
// 不是前两种失败，直接关闭和清理所有资源
if (releaseConnection) {
streamAllocation.streamFailed(null);
streamAllocation.release();
}
}
if (priorResponse != null) {
response = response.newBuilder()
.priorResponse(priorResponse.newBuilder()
.body(null)
.build())
.build();
}
//重定向
Request followUp;
try {
followUp = followUpRequest(response, streamAllocation.route());
} catch (IOException e) {
streamAllocation.release();
throw e;
}
if (followUp == null) {
streamAllocation.release();
//不需要重定向直接返回response终止循环
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;
}
}
重试与重定向拦截器主要处理Response，可以看到RouteException和IOException都是调用了recover，返回true表示允许重试。
private boolean recover(IOException e, StreamAllocation streamAllocation,
boolean requestSendStarted, Request userRequest) {
streamAllocation.streamFailed(e);
//是否设置了不允许重试（默认允许），则一旦请求失败就不再重试——>全局配置
if (!client.retryOnConnectionFailure()) return false;
//针对某个请求配置是否需要重试 用户自己实现UnrepeatableRequestBody请求体——>单个请求配置
if (requestSendStarted && requestIsUnrepeatable(e, userRequest)) return false;
// 是否属于重试的异常（协议异常、超时异常、证书异常、SSL握手未授权异常）
if (!isRecoverable(e, requestSendStarted)) return false;
// 是否存在更多的路由
if (!streamAllocation.hasMoreRoutes()) return false;
return true;
}
大致流程
重定向
private Request followUpRequest(Response userResponse, Route route) throws IOException {
if (userResponse == null) throw new IllegalStateException();
int responseCode = userResponse.code();
final String method = userResponse.request().method();
switch (responseCode) {
//407 客户端使用了HTTP代理服务器，在请求头中添加"Proxy-Authorization"让代理服务器授权
case HTTP_PROXY_AUTH:
Proxy selectedProxy = route.proxy();
if (selectedProxy.type() != Proxy.Type.HTTP) {
throw new ProtocolException("Received HTTP_PROXY_AUTH (407) code while not using proxy");
}
return client.proxyAuthenticator().authenticate(route, userResponse);
//401 服务器接口需要验证使用者身份，在请求头中添加"Authorization"
case HTTP_UNAUTHORIZED:
return client.authenticator().authenticate(route, userResponse);
case HTTP_PERM_REDIRECT://308 永久重定向
case HTTP_TEMP_REDIRECT://307临时重定向
//如果请求方式不是GET或HEAD，框架不会自动重定向请求
if (!method.equals("GET") && !method.equals("HEAD")) {
return null;
}
// fall-through
case HTTP_MULT_CHOICE:
case HTTP_MOVED_PERM:
case HTTP_MOVED_TEMP:
case HTTP_SEE_OTHER:
//客服端不允许重定向，返回null
if (!client.followRedirects()) return null;
//从响应头取出loaction
String location = userResponse.header("Location");
if (location == null) return null;
//根据location配置新的请求url
HttpUrl url = userResponse.request().url().resolve(location);
// 取不出，返回null 不进行重定向
if (url == null) return null;
//如果重定向在http到https之间切换，检查用户是否允许（默认允许）
boolean sameScheme = url.scheme().equals(userResponse.request().url().scheme());
if (!sameScheme && !client.followSslRedirects()) return null;
Request.Builder requestBuilder = userResponse.request().newBuilder();
//请求不是get与head
if (HttpMethod.permitsRequestBody(method)) {
final boolean maintainBody = HttpMethod.redirectsWithBody(method);
//除了propfind请求之外都改成GET请求
if (HttpMethod.redirectsToGet(method)) {
requestBuilder.method("GET", null);
} else {
RequestBody requestBody = maintainBody ? userResponse.request().body() : null;
requestBuilder.method(method, requestBody);
}
// 不是propfind的请求，把请求头中关于请求体的数据删除
if (!maintainBody) {
requestBuilder.removeHeader("Transfer-Encoding");
requestBuilder.removeHeader("Content-Length");
requestBuilder.removeHeader("Content-Type");
}
}
// 在跨主机重定向时，删除身份验证请求头
if (!sameConnection(userResponse, url)) {
requestBuilder.removeHeader("Authorization");
}
//构建request
return requestBuilder.url(url).build();
case HTTP_CLIENT_TIMEOUT://408 客户端请求超时
// 判断用户是否允许重试
if (!client.retryOnConnectionFailure()) {
return null;
}
if (userResponse.request().body() instanceof UnrepeatableRequestBody) {
return null;
}
//本次重试结果还是408，就放弃，不再重复请求。
if (userResponse.priorResponse() != null
&& userResponse.priorResponse().code() == HTTP_CLIENT_TIMEOUT) {
return null;
}
//如果服务器告诉我们了 Retry-After 多久后重试，那框架不管了。
if (retryAfter(userResponse, 0) > 0) {
return null;
}
return userResponse.request();
case HTTP_UNAVAILABLE://再次请求还是503，就放弃，不再重复请求。
if (userResponse.priorResponse() != null
&& userResponse.priorResponse().code() == HTTP_UNAVAILABLE) {
return null;
}
if (retryAfter(userResponse, Integer.MAX_VALUE) == 0) {
return userResponse.request();
}
return null;
default:
return null;
}
}
RetryAndFollowUpInterceptor是整个责任链中的第一个，首次接触到Request和最后接收Response的角色，它的主要功能是判断是否需要重试与重定向。
重试的前提是出现了RouteException或IOException，会通过recover方法进行判断是否进行重试。
重定向是发生在重试判定后，不满足重试的条件，会进一步调用followUpRequest根据Response的响应码进行重定向操作。
