如对网络知识不熟悉，可跳到最后补一下网络基础
文字总结：
先创建我们的request里面包括我们的Host请求参数等，okhttpClient的.newCall(request)方法生成一个RealCall,RealCall方法是我们的重点，首先执行enqueue方法，RealCall类会调用一个Dispatcher的线程池类，把我们一个异步Call传给Dispatcher线程池，我们Dispatcher类首先判断一下真正执行的任务的数量<64，真在执行host的是否<5，然后把我们的异步Call调用线程池中执行，而异步Call的run()方法最终还是调用RealCall的execute方法，execute方法还是调用的一个得到响应的getResponseWithInterceptorChain()，调用我们的拦截器。
okhttp最基本的请求
添加依赖:
implementation 'com.squareup.okhttp3:okhttp:3.14.5'
//请求客户端
OkHttpClient okHttpClient = new OkHttpClient();
//使用builder模式生成request对象
Request request = new Request.Builder()
.url("https://i0.hdslb.com/bfs/article/2b2d2f26caa0ebf07dbe617be4a5ba919eaa0724.jpg@1320w_742h.webp")
.build();
//请求同步
Response response = okHttpClient.newCall(request).execute();
//请求异步，开启一个子线程，不会阻塞
okHttpClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
}
@Override
public void onResponse(Call call, Response response) throws IOException {
}
});
先看看OkHttp最要的类之一RealCall
#RealCall类
//异步的调用方法，参数callBack是个接口实例，最终还是会调用RealCall的execute()方法
@Override public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
transmitter.callStart();
client.dispatcher().enqueue(new AsyncCall(responseCallback));//把一个异步Call给线程池请求执行，最终还是调用execute方法
}
#线程池类dispatcher的enqueue
synchronized void enqueue(AsyncCall call) {
//判断正在执行的数量<64,正在执行请求Host<5
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call); //线程池执行请求，实际回到RealCall.execure()方法
} else {
readyAsyncCalls.add(call);
}
}
//内部异步Call
final class AsyncCall extends NamedRunnable {
@Override protected void execute() {
boolean signalledCallback = false;
transmitter.timeoutEnter();
try {
Response response = getResponseWithInterceptorChain();
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);
}
}
}
public abstract class NamedRunnable implements Runnable {
......
@Override
public final void run() {
try {
execute();//在线程池执行的时候，又回到RealCall.execute方法
}
protected abstract void execute();
}
//主要作用是调用得到响应的getResponseWithInterceptorChain()方法
@Override public Response execute() throws IOException {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
try {
client.dispatcher().executed(this); //加到同步请求的队列
return getResponseWithInterceptorChain();//调用拦截器
} finally {
client.dispatcher().finished(this); //通知dispatcher任务执行完了。
}
}
1.创建客户端okhttpClient源码:
OkHttpClient okHttpClient = new OkHttpClient();
public class OkHttpClient implements Cloneable, Call.Factory, WebSocket.Factory {
public OkHttpClient() {
this(new Builder());
}
//Builder.builder()方法调用这个构造函数并把builder传进来
OkHttpClient(Builder builder) {
this.dispatcher = builder.dispatcher;
this.proxy = builder.proxy;
...
}
public static final class Builder {
public Builder() {
dispatcher = new Dispatcher();
protocols = DEFAULT_PROTOCOLS;
connectionSpecs = DEFAULT_CONNECTION_SPECS;
proxySelector = ProxySelector.getDefault();
cookieJar = CookieJar.NO_COOKIES;
socketFactory = SocketFactory.getDefault();
hostnameVerifier = OkHostnameVerifier.INSTANCE;
certificatePinner = CertificatePinner.DEFAULT;
proxyAuthenticator = Authenticator.NONE;
authenticator = Authenticator.NONE;
connectionPool = new ConnectionPool();
dns = Dns.SYSTEM;
followSslRedirects = true;
followRedirects = true;
retryOnConnectionFailure = true;
connectTimeout = 10_000;
readTimeout = 10_000;
writeTimeout = 10_000;
}
public OkHttpClient build() {
return new OkHttpClient(this);
}
}
}
2.建立Request（http报文）
Request：包括：请求地址url,请求方法method，请求头head，请求数据requestBody,标志位tag
Request request = new Request.Builder().url("url").build();
public final class Request {
final HttpUrl url;
final String method;
final Headers headers;
final @Nullable RequestBody body;
final Map<Class<?>, Object> tags;
private volatile @Nullable CacheControl cacheControl; // Lazily initialized.
//build()最终调用这个方法
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);
}
//写好默认的方法和头，url给我们写
public static class Builder {
@Nullable HttpUrl url;
String method;
Headers.Builder headers;
@Nullable RequestBody body;
Map<Class<?>, Object> tags = Collections.emptyMap();
public Builder() {
//默认使用get方法
this.method = "GET";
this.headers = new Headers.Builder();
}
Builder(Request request) {
this.url = request.url;
this.method = request.method;
this.body = request.body;
this.tags = request.tags.isEmpty()
? Collections.emptyMap()
: new LinkedHashMap<>(request.tags);
this.headers = request.headers.newBuilder();
}
//请求头部
public Builder header(String name, String value) {
headers.set(name, value);
return this;
}
public Builder addHeader(String name, String value) {
headers.add(name, value);
return this;
}
public Builder method(String method, RequestBody body) {
if (method == null) throw new NullPointerException("method == null");
if (method.length() == 0) throw new IllegalArgumentException("method.length() == 0");
if (body != null && !HttpMethod.permitsRequestBody(method)) {
throw new IllegalArgumentException("method " + method + " must not have a request body.");
}
if (body == null && HttpMethod.requiresRequestBody(method)) {
throw new IllegalArgumentException("method " + method + " must have a request body.");
}
this.method = method;
this.body = body;
return this;
}
public Request build() {
if (url == null) throw new IllegalStateException("url == null");
return new Request(this);
}
}
Dispatcher线程池介绍
public final class Dispatcher {
private int maxRequests = 64;
private int maxRequestsPerHost = 5;
/** Executes calls. Created lazily. */
private ExecutorService executorService;
/** Ready async calls in the order they'll be run. */
private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>();
/** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();
/** Running synchronous calls. Includes canceled calls that haven't finished yet. */
private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();
public Dispatcher() {
}
public synchronized ExecutorService executorService() {
if (executorService == null) {
executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp Dispatcher", false));
}
return executorService;
}
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
synchronized void executed(RealCall call) {
runningSyncCalls.add(call);
}
synchronized void finished(Call call) {
if (!runningSyncCalls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
}
核心重点拦截器方法得到响应
getResponseWithInterceptorChain()：
文字总结拦截器的作用：拦截器可以通过Chain参数拿到上一个的拦截器的request，并通过执行Chain接口的proceed(request)把request传给下一个拦截器并从一个拦截器中拿到response。这是一种责任链的设计模式。
//
public interface Interceptor {
Response intercept(Chain chain) throws IOException;
interface Chain {
Request request();
Response proceed(Request request) throws IOException;
...
}
}
//实现Interceptor.Chain接口的实例
public final class RealInterceptorChain implements Interceptor.Chain {
@Override public Request request() {
return request;
}
@Override public Response proceed(Request request) throws IOException {
return proceed(request, transmitter, exchange);
}
public Response proceed(Request request, Transmitter transmitter, @Nullable Exchange exchange)
throws IOException {
RealInterceptorChain next = new RealInterceptorChain(interceptors, transmitter, exchange,
index + 1, request, call, connectTimeout, readTimeout, writeTimeout);
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);
...
return response
}
}
重试拦截器：RetryAndFollowUpInterceptor
文字总结：处理重试的拦截器，会处理一些异常，如果这个异常不是致命的则从返回一个request给下级，如果是致命的则将错误给上级。
再重新生成request时会对状态码进行检查，比如重定向的307，就会从返回的响应中获取新的路径，生成一个新的request给下级重新发起一次请求，如果得到的request为null则返回现在的response给上级。
public final class RetryAndFollowUpInterceptor implements Interceptor {
public RetryAndFollowUpInterceptor(OkHttpClient client) {
this.client = client;
}
@Override public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
RealInterceptorChain realChain = (RealInterceptorChain) chain;
//一个多路复用
Transmitter transmitter = realChain.transmitter();
while (true) {
transmitter.prepareToConnect(request);
if (transmitter.isCanceled()) {
throw new IOException("Canceled");
}
Response response;
boolean success = false;
try {
//在try中执行拿到的response
response = realChain.proceed(request, transmitter, null);
success = true;
} catch (RouteException e) {
//判断是否是致命的异常，如果是则抛出错误给上一级，如果不是则continue下一次请求。
if (!recover(e.getLastConnectException(), transmitter, false, request)) {
throw e.getFirstConnectException();
}
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, transmitter, requestSendStarted, request)) throw e;
continue;
} finally {
// The network call threw an exception. Release any resources.
if (!success) {
transmitter.exchangeDoneDueToException();
}
}
// 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();
}
Exchange exchange = Internal.instance.exchange(response);
Route route = exchange != null ? exchange.connection().route() : null;
//根据下级返回的response，判断状态码，并重新确定request
Request followUp = followUpRequest(response, route);
//如果新的request是null则返回response
if (followUp == null) {
if (exchange != null && exchange.isDuplex()) {
transmitter.timeoutEarlyExit();
}
return response;
}
RequestBody followUpBody = followUp.body();
if (followUpBody != null && followUpBody.isOneShot()) {
return response;
}
closeQuietly(response.body());
if (transmitter.hasExchange()) {
exchange.detachWithViolence();
}
if (++followUpCount > MAX_FOLLOW_UPS) {
throw new ProtocolException("Too many follow-up requests: " + followUpCount);
}
request = followUp;
priorResponse = response;
}
}
}
桥接拦截器：BridgeInterceptor
文字总结：给请求头部做一些通用的设置，判断返回的response是否用到压缩并把它变成GzipSource，和保存cookie。
public final class BridgeInterceptor implements Interceptor {
private final CookieJar cookieJar;
public BridgeInterceptor(CookieJar cookieJar) {
this.cookieJar = cookieJar;
}
@Override public Response intercept(Chain chain) throws IOException {
//得到上一级的request
Request userRequest = chain.request();
Request.Builder requestBuilder = userRequest.newBuilder();
//拿到RequestBody
RequestBody body = userRequest.body();
//根据RequestBody设置一些请求首部的参数
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");
}
}
//判断请求首部参数有无并添加
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());
}
//从下级拿到Response
Response networkResponse = chain.proceed(requestBuilder.build());
HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());
Response.Builder responseBuilder = networkResponse.newBuilder()
.request(userRequest);
//判断是否是gzip压缩，生成GzipSource
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();
}
/** Returns a 'Cookie' HTTP request header with all cookies, like {@code a=b; c=d}. */
private String cookieHeader(List<Cookie> cookies) {
StringBuilder cookieHeader = new StringBuilder();
for (int i = 0, size = cookies.size(); i < size; i++) {
if (i > 0) {
cookieHeader.append("; ");
}
Cookie cookie = cookies.get(i);
cookieHeader.append(cookie.name()).append('=').append(cookie.value());
}
return cookieHeader.toString();
}
}
缓存拦截器：CacheInterceptor
文字总结：缓存拦截器会根据请求的request和拿到的缓存生成一个缓存策略，缓存策略有需要请求的request和缓存response，根据缓存策略的request和response是否为空进行下一步的操作，比如两个都为null就返回504，request为Null则直接返回本地缓存，根据下级返回的response查看是否状态码是否为304。
在缓存可用的情况下，读取本地的缓存的数据，如果没有直接去服务器，如果有首先判断有没有缓存策略，然后判断有没有过期，如果没有过期直接拿缓存，如果过期了需要添加一些之前头部信息如：If-Modified-Since ，这个时候后台有可能会给你返回 304 代表你还是可以拿本地缓存，每次读取到新的响应后做一次缓存。
public final class CacheInterceptor implements Interceptor {
public CacheInterceptor(@Nullable InternalCache cache) {
this.cache = cache;
}
@Override public Response intercept(Chain chain) throws IOException {
//根据请求，判断是否有缓存
Response cacheCandidate = cache != null
? cache.get(chain.request())
: null;
long now = System.currentTimeMillis();
//根据请求和得到的缓存拿到一个缓存策略
CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
Request networkRequest = strategy.networkRequest;
Response cacheResponse = strategy.cacheResponse;
if (cache != null) {
cache.trackResponse(strategy);
}
if (cacheCandidate != null && cacheResponse == null) {
closeQuietly(cacheCandidate.body()); // The cache candidate wasn't applicable. Close it.
}
// 如果请求的 networkRequest 是空，缓存的 cacheResponse 是空我就返回 504。 指定该数据只从缓存获取
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();
}
// If we don't need the network, we're done.
if (networkRequest == null) {
//不用请求，直接返回缓存response
return cacheResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build();
}
//否则，把networkRequest重新请求一遍
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());
}
}
// 如果本地的缓存不为空，再次请求得到的response的状态码为304，则复用之前的response给上级
if (cacheResponse != null) {
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();
initContentStream()).
cache.trackConditionalCacheHit();
cache.update(cacheResponse, response);
return response;
} else {
closeQuietly(cacheResponse.body());
}
}
Response response = networkResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build();
if (cache != null) {
if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) {
// Offer this request to the cache.
CacheRequest cacheRequest = cache.put(response);
return cacheWritingResponse(cacheRequest, response);
}
if (HttpMethod.invalidatesCache(networkRequest.method())) {
try {
cache.remove(networkRequest);
} catch (IOException ignored) {
// The cache cannot be written.
}
}
}
return response;
}
}
连接拦截器：ConnectInterceptor
文字总结：
findHealthyConnection() 找一个连接，首先判断有没有健康的，没有就创建（建立Scoket,握手连接），连接缓存。
封装 HttpCodec 里面封装了 okio 的 Source（输入） 和 Sink (输出)，我们通过 HttpCodec 就可以操作 Socket的输入输出，我们就可以像服务器写数据和读取返回数据
public final class ConnectInterceptor implements Interceptor {
public final OkHttpClient client;
public ConnectInterceptor(OkHttpClient client) {
this.client = client;
}
@Override public Response intercept(Chain chain) throws IOException {
RealInterceptorChain realChain = (RealInterceptorChain) chain;
Request request = realChain.request();
Transmitter transmitter = realChain.transmitter();
// We need the network to satisfy this request. Possibly for validating a conditional GET.
boolean doExtensiveHealthChecks = !request.method().equals("GET");
//建立一个多路复用
Exchange exchange = transmitter.newExchange(chain, doExtensiveHealthChecks);
return realChain.proceed(request, transmitter, exchange);
}
}
CallServerInterceptor
文字总结：写数据和读取数据
写头部信息，写body表单信息等等
public final class CallServerInterceptor implements Interceptor {
private final boolean forWebSocket;
public CallServerInterceptor(boolean forWebSocket) {
this.forWebSocket = forWebSocket;
}
@Override public Response intercept(Chain chain) throws IOException {
RealInterceptorChain realChain = (RealInterceptorChain) chain;
Exchange exchange = realChain.exchange();
Request request = realChain.request();
long sentRequestMillis = System.currentTimeMillis();
exchange.writeRequestHeaders(request);
boolean responseHeadersStarted = false;
Response.Builder responseBuilder = null;
if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
// If there's a "Expect: 100-continue" header on the request, wait for a "HTTP/1.1 100
// Continue" response before transmitting the request body. If we don't get that, return
// what we did get (such as a 4xx response) without ever transmitting the request body.
if ("100-continue".equalsIgnoreCase(request.header("Expect"))) {
exchange.flushRequest();
responseHeadersStarted = true;
exchange.responseHeadersStart();
responseBuilder = exchange.readResponseHeaders(true);
}
if (responseBuilder == null) {
if (request.body().isDuplex()) {
// Prepare a duplex body so that the application can send a request body later.
exchange.flushRequest();
BufferedSink bufferedRequestBody = Okio.buffer(
exchange.createRequestBody(request, true));
request.body().writeTo(bufferedRequestBody);
} else {
// Write the request body if the "Expect: 100-continue" expectation was met.
BufferedSink bufferedRequestBody = Okio.buffer(
exchange.createRequestBody(request, false));
request.body().writeTo(bufferedRequestBody);
bufferedRequestBody.close();
}
} else {
exchange.noRequestBody();
if (!exchange.connection().isMultiplexed()) {
// If the "Expect: 100-continue" expectation wasn't met, prevent the HTTP/1 connection
// from being reused. Otherwise we're still obligated to transmit the request body to
// leave the connection in a consistent state.
exchange.noNewExchangesOnConnection();
}
}
} else {
exchange.noRequestBody();
}
if (request.body() == null || !request.body().isDuplex()) {
exchange.finishRequest();
}
if (!responseHeadersStarted) {
exchange.responseHeadersStart();
}
if (responseBuilder == null) {
responseBuilder = exchange.readResponseHeaders(false);
}
Response response = responseBuilder
.request(request)
.handshake(exchange.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
int code = response.code();
if (code == 100) {
// server sent a 100-continue even though we did not request one.
// try again to read the actual response
response = exchange.readResponseHeaders(false)
.request(request)
.handshake(exchange.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
code = response.code();
}
exchange.responseHeadersEnd(response);
if (forWebSocket && code == 101) {
// Connection is upgrading, but we need to ensure interceptors see a non-null response body.
response = response.newBuilder()
.body(Util.EMPTY_RESPONSE)
.build();
} else {
response = response.newBuilder()
.body(exchange.openResponseBody(response))
.build();
}
if ("close".equalsIgnoreCase(response.request().header("Connection"))
|| "close".equalsIgnoreCase(response.header("Connection"))) {
exchange.noNewExchangesOnConnection();
}
if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
throw new ProtocolException(
"HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());
}
return response;
}
}
拦截器总结：首先调用retry拦截它可以在传给下级request得到response的过程中对一些非致命的异常进行再一次的请求，对于下级返回的response对状态码进行判断做再次的请求或者给上一级，对于一些致命异常也是返回给上一级。第二个是BridgeInterceptor拦截器，它会对请求的首部做一些通用的设置，并对返回的response进行是否需要压缩的判断返回gzip和保存response的cookie。第三个是cache缓存拦截，会根据请求拿到本地的缓存，并根据请求和本地缓存拿到生成的缓存策略，根据缓存策略的request和response判断是直接返回缓存，还是继续请求，并根据返回的response判断状态码是否继续返回本地缓存。第四connect连接拦截器主要是与服务器建立TCL的握手连接，这里的连接会使用多路复用，就是没有断开连接之前可以有多个请求共享一个连接，端对端是使用socket连接的。第五：CallServer拦截器主要是读写数据。
getResponseWithInterceptorChain得到最上级的resonse响应。
Response getResponseWithInterceptorChain() throws IOException {
// Build a full stack of interceptors.
List<Interceptor> interceptors = new ArrayList<>();
interceptors.addAll(client.interceptors()); //增加自己定义的拦截器
interceptors.add(new RetryAndFollowUpInterceptor(client));//重试拦截器
interceptors.add(new BridgeInterceptor(client.cookieJar()));//桥接拦截器，为请求头部添加数据
interceptors.add(new CacheInterceptor(client.internalCache()));//缓存拦截器，
interceptors.add(new ConnectInterceptor(client));//连接拦截器，负责请求和服务器连接
if (!forWebSocket) {
interceptors.addAll(client.networkInterceptors());
}
interceptors.add(new CallServerInterceptor(forWebSocket));//网络服务端的连接
//最终把拦截器责任链表
Interceptor.Chain chain = new RealInterceptorChain(interceptors, transmitter, null, 0,
originalRequest, this, client.connectTimeoutMillis(),
client.readTimeoutMillis(), client.writeTimeoutMillis());
boolean calledNoMoreExchanges = false;
try {
//reTry拦截器返回的response
Response response = chain.proceed(originalRequest);
if (transmitter.isCanceled()) {
closeQuietly(response);
throw new IOException("Canceled");
}
return response;
} catch (IOException e) {
calledNoMoreExchanges = true;
throw transmitter.noMoreExchanges(e);
} finally {
if (!calledNoMoreExchanges) {
transmitter.noMoreExchanges(null);
}
}
}
RealConnect类
ublic final class RealConnection extends Http2Connection.Listener implements Connection {
private static final String NPE_THROW_WITH_NULL = "throw with null exception";
private static final int MAX_TUNNEL_ATTEMPTS = 21;
public final RealConnectionPool connectionPool;
private final Route route;
// The fields below are initialized by connect() and never reassigned.
//以下字段由connect（）初始化，并且从不重新分配。
/** 低级TCP套接字. */
private Socket rawSocket;
private Socket socket;
//通过这个对象握手
private Handshake handshake;
private Protocol protocol; //协议
private Http2Connection http2Connection; //http2.0
private BufferedSource source; //输入流
private BufferedSink sink; //输出流
总结：OkHttp的底层是通过Java的Socket发送HTTP请求与接受响应的(这也好理解，HTTP就是基于TCP协议的)，但是OkHttp实现了连接池的概念，即对于同一主机的多个请求，其实可以公用一个Socket连接，而不是每次发送完HTTP请求就关闭底层的Socket，这样就实现了连接池的概念。而OkHttp对Socket的读写操作使用的OkIo库进行了一层封装。
image.png
http的相关知识
HTTP,FTP,DNS,TCP,UDP,IP
OSI七层协议：应用层、表示层、会话层、传输层、网络层、数据链路层、物理层
五层：应用层、传输层、网络层、数据链路层、物理层
image.png
TCP的三次握手和四次分手
文字总结：
三次握手之后才开始发送数据
客户端先发一条信息给服务端说能听到吗
服务端就发送一条信息并带ACK给客户端说我能听到，你能听到吗
客户端就发送一条信息给服务端说我能听到
四次挥手：
挂了
好的。挂了
好的
image.png
Http报文
请求报文(Qequest)：请求头(首部)+空行+请求数据
响应报文(Response)：响应头(首部)+空行+响应数据
Http首部
image.png
image.png
请求首部
Accept：用户代理可处理的媒体类型
Accept-Charset：优先的字符集
Accept-Language：优先的语言（自然语言）
Accept-Encoding：优先的内容编码
If-Modified-Since：比较资源的更新时间
If-Range：资源未更新时发送实体 Byte 的范围请求
Cookie: 设置Cookie
响应首部
Cache-Control：控制缓存的行为
set-Cookie: 设置Cookie
Location：令客户端重定向至指定 URI
Expires：实体主体过期的日期时间
Last-Modified：资源的最后修改日期时间
Status Code: 响应的状态码
cookie:服务端发过来的信息，在客户端保存并再请求的时候发给服务端，cookie有个过期时间
session:在服务端保存客户端的信息，断开链接时则失效
token:服务端给客户端的一个id身份号码。
Http缓存
cache-Control(缓存策略)：Public、private、no_cache、max_age、no-store(不缓存)
Expires(缓存的过期策略)：指名了缓存数据有效的绝对时间，告诉客户端到了这个时间点（比照客户端时间点）后本地缓存就作废了。
如果缓存过期再去请求服务器时，不一定拿到数据（304）
Http状态码
1xx: Infomational (信息状态码) ，接收的请求正在处理
2xx: Succeed(成功)，请求正常处理完毕,如 200，204
3xx: Redirection(重定向)，需要进行附加操作，一般是没有响应数据返回的，如 304（Not,modified）307
4xx: Client Error (客户端的错误)，服务器无法处理请求，如 404，405
5xx: Server Error (服务端的错误)，服务器处理请求出错，如 500，502
Http和Https的区别
https=http+加密验证
http的缺点：
1.数据没有加密传输，可能被监听
2.不验证通信方的身份容易被伪装
3.无法验证报文的完成性可能被篡改
TLS/SSL协议：
加密：对称加密(AES,DES)+非对称加密(RSA,DSA)
证书：建立连接的速度会被拖慢，TCP 8次握手
Http1.0和Http2.0的区别
http2.0:
1.使用二进制传输不是文本
2.可以多路复用
3.报头使用了压缩
4.让服务器可以主动推送到客户端
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