本文基于okhttp3.9x
使用方式
OkHttpClient client = new OkHttpClient(); // 创建okhttp对象
String run(String url) throws IOException {
Request request = new Request.Builder()
.url(url)
.build();
try (Response response = client.newCall(request).execute()) {
return response.body().string();
}
}
可以看出这块用到了建造者模式.第一步创建OKHttpClient对象,然后创建Request,最后发起请求并获取请求结果Response.
类结构
public class OkHttpClient implements Cloneable, Call.Factory, WebSocket.Factory {
...
}
- Cloneable 表示可以克隆的
- Call.Factory 接口类,创建一个新的请求包含,newCall方法
- WebSocket.Factory 接口类,创建一个新的web sockect,包含newWebSocket方法
构造方法
final Dispatcher dispatcher;
final @Nullable Proxy proxy;
final List protocols;
final List connectionSpecs;
final List interceptors;
final List networkInterceptors;
final EventListener.Factory eventListenerFactory;
final ProxySelector proxySelector;
final CookieJar cookieJar;
final @Nullable Cache cache;
final @Nullable InternalCache internalCache;
final SocketFactory socketFactory;
final @Nullable SSLSocketFactory sslSocketFactory;
final @Nullable CertificateChainCleaner certificateChainCleaner;
final HostnameVerifier hostnameVerifier;
final CertificatePinner certificatePinner;
final Authenticator proxyAuthenticator;
final Authenticator authenticator;
final ConnectionPool connectionPool;
final Dns dns;
final boolean followSslRedirects;
final boolean followRedirects;
final boolean retryOnConnectionFailure;
final int connectTimeout;
final int readTimeout;
final int writeTimeout;
final int pingInterval;
public OkHttpClient() {
this(new Builder());
}
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.eventListenerFactory = builder.eventListenerFactory;
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;
this.pingInterval = builder.pingInterval;
if (interceptors.contains(null)) {
throw new IllegalStateException("Null interceptor: " + interceptors);
}
if (networkInterceptors.contains(null)) {
throw new IllegalStateException("Null network interceptor: " + networkInterceptors);
}
}
可以看到有两个构造方法，在构造方法中会初始化一个Builder对象（建造者模式），在Builder中设置了OkHttp的属性，比如超时设置、拦截器等。
接下来是Request对象
Request(Builder builder) {
this.url = builder.url;
this.method = builder.method;
this.headers = builder.headers.build();
this.body = builder.body;
this.tag = builder.tag != null ? builder.tag : this;
}
可以看到Request对象也是通过建造者模式创建的，在这里配置了请求url，请求头等信息。
/**
* Prepares the {@code request} to be executed at some point in the future.
*/
@Override public Call newCall(Request request) {
return RealCall.newRealCall(this, request, false /* for web socket */);
}
private RealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
this.client = client;
this.originalRequest = originalRequest;
this.forWebSocket = forWebSocket;
this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client, forWebSocket);
}
static RealCall newRealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
// Safely publish the Call instance to the EventListener.
RealCall call = new RealCall(client, originalRequest, forWebSocket);
call.eventListener = client.eventListenerFactory().create(call);
return call;
}
然后调用了newCall方法创建了RealCall实例,然后通过RealCall发起请求,RealCall.newRealCall,RealCall是Call接口的实现类.异步请求调用了RealCall的enqueue()方法.
@Override public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
eventListener.callStart(this);
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
这里实际上调用了Dispatcher的enqueue方法
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
这里的enqueue方法是个同步方法.首先判断队列是否已满小于maxRequest=64,并且相同host的请求小于maxRequestsPerHost=5,队列不满则开始在线程池中执行请求AsyncCall,AsyncCall继承了NamedRunnable抽象类,而NamedRunnable继承了Runnable接口,在run方法中调用了excute()方法.
/**NamedRunnable中的方法**/
@Override protected void execute() {
boolean signalledCallback = false;
try {
Response response = getResponseWithInterceptorChain();
if (retryAndFollowUpInterceptor.isCanceled()) {
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 {
eventListener.callFailed(RealCall.this, e);
responseCallback.onFailure(RealCall.this, e);
}
} finally {
client.dispatcher().finished(this);
}
}
这里就开始了OkHttp核心的请求部分,在OkHttp中使用了责任链模式处理这一部分请求. getResponseWithInterceptorChain()方法
Response getResponseWithInterceptorChain() throws IOException {
// Build a full stack of interceptors.
List 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());
return chain.proceed(originalRequest);
}
OKHttp拦截器
上面代码中OKHttp通过各种拦截器处理请求,这里简单介绍下拦截器:
- 自定义拦截器：提供给用户的定制的拦截器。
- 重试拦截器（RetryAndFollowUpInterceptor）：请求在失败的时候重新开始的拦截器。
- 桥接拦截器（BridgeInterceptor）：主要用来构造请求。
- 缓存拦截器（CacheInterceptor）：主要处理HTTP缓存。
- 连接拦截器（ConnectInterceptor）：主要处理HTTP链接。
- 网络请求拦截器（CallServerInterceptor）：负责发起网络请求。
上面代码通过RealInterceptorChain的proceed(request)方法开始执行拦截器.
public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
RealConnection connection) throws IOException {
if (index >= interceptors.size()) throw new AssertionError();
calls++;
//...
// Call the next interceptor in the chain.
RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
writeTimeout);
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);
// ...
return response;
}
重试拦截器—RetryAndFollowUpInterceptor
public Response intercept(Chain chain) throws IOException {
//......
int followUpCount = 0;
Response priorResponse = null;
//通过一个循环来重新尝试请求
while (true) {
if (canceled) {
streamAllocation.release();
throw new IOException("Canceled");
}
Response response;
boolean releaseConnection = true;
try {
//1.调用下一个拦截器
response = realChain.proceed(request, streamAllocation, null, null);
releaseConnection = false;
} catch (RouteException e) {
//......
} catch (IOException e) {
//......
}
//......
//2.检测response是否合法
Request followUp = followUpRequest(response);
if (followUp == null) {
if (!forWebSocket) {
streamAllocation.release();
}
//3.返回response，请求完成
return response;
}
//最多尝试20次
if (++followUpCount > MAX_FOLLOW_UPS) {
streamAllocation.release();
throw new ProtocolException("Too many follow-up requests: " + followUpCount);
}
//4.重新设置请求
request = followUp;
priorResponse = response;
}
}
在这里面我们可以看到请求的重度是一个无限循环来处理的,同时在代码里还限制了请求的次数,最多尝试20次.里面的具体逻辑是:
1.开启循环,继续调用下一个拦截器直到返回结果.
2.通过followUpRequest方法检查response是否合法,检查逻辑是根据HTTP返回码检测(比如402这种),如果followup为null则返回结果,否则进行下一步.
3.重新设置request,设置response(用于接下来重新构造response),执行第一步.
桥接拦截器-BridgeInterceptor
public Response intercept(Chain chain) throws IOException {
Request userRequest = chain.request();
Request.Builder requestBuilder = userRequest.newBuilder();
RequestBody body = userRequest.body();
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");
}
}
if (userRequest.header("Host") == null) {
requestBuilder.header("Host", hostHeader(userRequest.url(), false));
}
if (userRequest.header("Connection") == null) {
requestBuilder.header("Connection", "Keep-Alive");
}
boolean transparentGzip = false;
if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == null) {
transparentGzip = true;
requestBuilder.header("Accept-Encoding", "gzip");
}
List 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());
}
Response networkResponse = chain.proceed(requestBuilder.build());
HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());
Response.Builder responseBuilder = networkResponse.newBuilder()
.request(userRequest);
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();
}
这个的作用是设置请求头的各种参数,比如Content-Type,Connection,User-Agent等.
缓存拦截器-CacheInterceptor
public Response intercept(Chain chain) throws IOException {
Response cacheCandidate = cache != null? cache.get(chain.request()): null;//1.取缓存
long now = System.currentTimeMillis();
CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get(); //2.验证缓存
Request networkRequest = strategy.networkRequest;
Response cacheResponse = strategy.cacheResponse; //获取缓存
if (cache != null) {
cache.trackResponse(strategy);
}
// If we're forbidden from using the network and the cache is insufficient, fail.
//如果我们被禁止使用网络并且缓存不足,失败
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.
//3.直接返回缓存
if (networkRequest == null) {
return cacheResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build();
}
Response networkResponse = null;
try {
//4.没有缓存，执行下一个拦截器
networkResponse = chain.proceed(networkRequest);
}
// If we have a cache response too, then we're doing a conditional get.
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();
// Update the cache after combining headers but before stripping the
// Content-Encoding header (as performed by initContentStream()).
cache.trackConditionalCacheHit();
//5.更新缓存
cache.update(cacheResponse, response);
return response;
} else {
closeQuietly(cacheResponse.body());
}
}
//......
if (cache != null) {
if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) {
// Offer this request to the cache.
//6.保存缓存
CacheRequest cacheRequest = cache.put(response);
return cacheWritingResponse(cacheRequest, response);
}
}
return response;
}
缓存拦截器流程如下:
1.根据请求(以Request为键值)取出缓存;
2.验证缓存是否可用,如果可用则直接取出缓存,否则下一步;
3.继续执行下一个拦截器,直拉返回结果;
4.如果之前有缓存,则更新缓存,否则新增缓存.
缓存拦截器主要的工作就是处理缓存,知道了大致流程后我们接下来分析一下OKhttp是如何管理缓存的.首先我们分析缓存如何获取,在代码中看到是通过cache.get()得到.代码如下:
final InternalCache internalCache = new InternalCache() {
@Override public Response get(Request request) throws IOException {
return Cache.this.get(request);
}
@Override public CacheRequest put(Response response) throws IOException {
return Cache.this.put(response);
}
@Override public void remove(Request request) throws IOException {
Cache.this.remove(request);
}
@Override public void update(Response cached, Response network) {
Cache.this.update(cached, network);
}
@Override public void trackConditionalCacheHit() {
Cache.this.trackConditionalCacheHit();
}
@Override public void trackResponse(CacheStrategy cacheStrategy) {
Cache.this.trackResponse(cacheStrategy);
}
};
可以看到缓存是通过InternalCache管理的,而InternalCache是接口类,但是并没有使用他的实现类,直接使用接口,它是Cache的内部子类,InternalCache又调用了Cache的方法.我们这里分析一下get()方法
@Nullable Response get(Request request) {
String key = key(request.url());
DiskLruCache.Snapshot snapshot;
Entry entry;
try {
snapshot = cache.get(key);
if (snapshot == null) {
return null;
}
} catch (IOException e) {
return null;
}
try {
entry = new Entry(snapshot.getSource(ENTRY_METADATA));
} catch (IOException e) {
Util.closeQuietly(snapshot);
return null;
}
Response response = entry.response(snapshot);
//......
return response;
}
key使用的Request的url进行md5->hex算法(16进制)->再转成utf-8.
可以看到缓存是通过DiskLruCache管理的,接下来我们分析下OKHTTP如何验证缓存.
在上面代码中缓存最终来自于CacheStrategy.看一下代码.
public Factory(long nowMillis, Request request, Response cacheResponse) {
//......
if (cacheResponse != null) {
this.sentRequestMillis = cacheResponse.sentRequestAtMillis();
this.receivedResponseMillis = cacheResponse.receivedResponseAtMillis();
Headers headers = cacheResponse.headers();
for (int i = 0, size = headers.size(); i < size; i++) {
String fieldName = headers.name(i);
String value = headers.value(i);
//这里获取了缓存的时间限制
if ("Date".equalsIgnoreCase(fieldName)) {
servedDate = HttpDate.parse(value);
servedDateString = value;
} else if ("Expires".equalsIgnoreCase(fieldName)) {
expires = HttpDate.parse(value);
} else if ("Last-Modified".equalsIgnoreCase(fieldName)) {
lastModified = HttpDate.parse(value);
lastModifiedString = value;
} else if ("ETag".equalsIgnoreCase(fieldName)) {
etag = value;
} else if ("Age".equalsIgnoreCase(fieldName)) {
ageSeconds = HttpHeaders.parseSeconds(value, -1);
}
}
}
}
public CacheStrategy get() {
CacheStrategy candidate = getCandidate();
if (candidate.networkRequest != null && request.cacheControl().onlyIfCached()) {
// We're forbidden from using the network and the cache is insufficient.
return new CacheStrategy(null, null);
}
return candidate;
}
private CacheStrategy getCandidate() {
//......
long ageMillis = cacheResponseAge();
long freshMillis = computeFreshnessLifetime(); //计算缓存是否过期
//......
return new CacheStrategy(conditionalRequest, cacheResponse);
}
private long computeFreshnessLifetime() {
//判断缓存是否过期
CacheControl responseCaching = cacheResponse.cacheControl();
if (responseCaching.maxAgeSeconds() != -1) {
return SECONDS.toMillis(responseCaching.maxAgeSeconds());
} else if (expires != null) {
long servedMillis = servedDate != null
? servedDate.getTime()
: receivedResponseMillis;
long delta = expires.getTime() - servedMillis;
return delta > 0 ? delta : 0;
} else if (lastModified != null
&& cacheResponse.request().url().query() == null) {
long servedMillis = servedDate != null
? servedDate.getTime()
: sentRequestMillis;
long delta = servedMillis - lastModified.getTime();
return delta > 0 ? (delta / 10) : 0;
}
return 0;
}
我们知道在HTTP中判断缓存是否过期的依据就是根据请求头的字段来判断比如Last-Modified,expires(不同的HTTP版本有不同的字段表示).在OKHTTP中也是根据这些依据.
在上面的代码中,我们可以看到首先会从缓存中获取请求头字段中的时间数据,然后在构造CacheStrategy判断缓存是否过期,最后决定缓存是否合法.
ConnectInterceptor 连接拦截器
ConnectInterceptor的作用就是建立一个与服务端的连接.
public Response intercept(Chain chain) throws IOException {
RealInterceptorChain realChain = (RealInterceptorChain) chain;
Request request = realChain.request();
StreamAllocation streamAllocation = realChain.streamAllocation();
boolean doExtensiveHealthChecks = !request.method().equals("GET");
HttpCodec httpCodec = streamAllocation.newStream(client, chain, doExtensiveHealthChecks);
RealConnection connection = streamAllocation.connection();
return realChain.proceed(request, streamAllocation, httpCodec, connection);
}
可以看到连接来自于StreamAllocation的newStream方法.
public HttpCodec newStream(
OkHttpClient client, Interceptor.Chain chain, boolean doExtensiveHealthChecks) {
int connectTimeout = chain.connectTimeoutMillis();
int readTimeout = chain.readTimeoutMillis();
int writeTimeout = chain.writeTimeoutMillis();
boolean connectionRetryEnabled = client.retryOnConnectionFailure();
try {
RealConnection resultConnection = findHealthyConnection(connectTimeout, readTimeout,
writeTimeout, connectionRetryEnabled, doExtensiveHealthChecks);
HttpCodec resultCodec = resultConnection.newCodec(client, chain, this);
synchronized (connectionPool) {
codec = resultCodec;
return resultCodec;
}
} catch (IOException e) {
throw new RouteException(e);
}
}
可以在newStream()方法中继续寻找连接.我们继续分析代码可以看到,OKhttp的连接是维护在一个连接池中的
private RealConnection findConnection(int connectTimeout, int readTimeout, int writeTimeout,
boolean connectionRetryEnabled) throws IOException {
boolean foundPooledConnection = false;
RealConnection result = null;
Route selectedRoute = null;
Connection releasedConnection;
Socket toClose;
synchronized (connectionPool) {
if (released) throw new IllegalStateException("released");
if (codec != null) throw new IllegalStateException("codec != null");
if (canceled) throw new IOException("Canceled");
// Attempt to use an already-allocated connection. We need to be careful here because our
// already-allocated connection may have been restricted from creating new streams.
releasedConnection = this.connection;
toClose = releaseIfNoNewStreams();
if (this.connection != null) {
// We had an already-allocated connection and it's good.
result = this.connection;
releasedConnection = null;
}
if (!reportedAcquired) {
// If the connection was never reported acquired, don't report it as released!
releasedConnection = null;
}
if (result == null) {
// Attempt to get a connection from the pool.
Internal.instance.get(connectionPool, address, this, null);
if (connection != null) {
foundPooledConnection = true;
result = connection;
} else {
selectedRoute = route;
}
}
}
closeQuietly(toClose);
if (releasedConnection != null) {
eventListener.connectionReleased(call, releasedConnection);
}
if (foundPooledConnection) {
eventListener.connectionAcquired(call, result);
}
if (result != null) {
// If we found an already-allocated or pooled connection, we're done.
return result;
}
// If we need a route selection, make one. This is a blocking operation.
boolean newRouteSelection = false;
if (selectedRoute == null && (routeSelection == null || !routeSelection.hasNext())) {
newRouteSelection = true;
routeSelection = routeSelector.next();
}
synchronized (connectionPool) {
if (canceled) throw new IOException("Canceled");
if (newRouteSelection) {
// Now that we have a set of IP addresses, make another attempt at getting a connection from
// the pool. This could match due to connection coalescing.
List routes = routeSelection.getAll();
for (int i = 0, size = routes.size(); i < size; i++) {
Route route = routes.get(i);
Internal.instance.get(connectionPool, address, this, route);
if (connection != null) {
foundPooledConnection = true;
result = connection;
this.route = route;
break;
}
}
}
if (!foundPooledConnection) {
if (selectedRoute == null) {
selectedRoute = routeSelection.next();
}
// Create a connection and assign it to this allocation immediately. This makes it possible
// for an asynchronous cancel() to interrupt the handshake we're about to do.
route = selectedRoute;
refusedStreamCount = 0;
result = new RealConnection(connectionPool, selectedRoute);
acquire(result, false);
}
}
// If we found a pooled connection on the 2nd time around, we're done.
if (foundPooledConnection) {
eventListener.connectionAcquired(call, result);
return result;
}
// Do TCP + TLS handshakes. This is a blocking operation.
result.connect(
connectTimeout, readTimeout, writeTimeout, connectionRetryEnabled, call, eventListener);
routeDatabase().connected(result.route());
Socket socket = null;
synchronized (connectionPool) {
reportedAcquired = true;
// Pool the connection.
Internal.instance.put(connectionPool, result);
// If another multiplexed connection to the same address was created concurrently, then
// release this connection and acquire that one.
if (result.isMultiplexed()) {
socket = Internal.instance.deduplicate(connectionPool, address, this);
result = connection;
}
}
closeQuietly(socket);
eventListener.connectionAcquired(call, result);
return result;
}
以上是OKHttp获取连接的主要逻辑,方法比较复杂,我们这里总结一下.
1.首先尝试从连接池中获取一个连接,获取连接的参数是地址.如果获取到连接,则返回,否则进行下一步;
2.如果需要选择线程,则继续尝试获取连接.如果获取到连接,则返回,否则进行下一步;
3.创建一个新的连接,然后建立与服务端的TCP连接.
4.将连接加入线程池.
CallServerInterceptor 服务端拦截器
CallServerInterceptor是最后一个拦截器,理所当然这个拦截器负责向服务端发送数据.
public Response intercept(Chain chain) throws IOException {
//......
//写入请求头数据
httpCodec.writeRequestHeaders(request);
realChain.eventListener().requestHeadersEnd(realChain.call(), request);
Response.Builder responseBuilder = null;
if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
//......
if (responseBuilder == null) {
// Write the request body if the "Expect: 100-continue" expectation was met.
realChain.eventListener().requestBodyStart(realChain.call());
long contentLength = request.body().contentLength();
//这里写入请求体
CountingSink requestBodyOut =
new CountingSink(httpCodec.createRequestBody(request, contentLength));
BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);
request.body().writeTo(bufferedRequestBody);
bufferedRequestBody.close();
realChain.eventListener()
.requestBodyEnd(realChain.call(), requestBodyOut.successfulCount);
} else if (!connection.isMultiplexed()) {
streamAllocation.noNewStreams();
}
}
//完成请求
httpCodec.finishRequest();
if (responseBuilder == null) {
//这里请求返回，读取返回请求头
realChain.eventListener().responseHeadersStart(realChain.call());
responseBuilder = httpCodec.readResponseHeaders(false);
}
Response response = responseBuilder
.request(request)
.handshake(streamAllocation.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
realChain.eventListener()
.responseHeadersEnd(realChain.call(), response);
int code = response.code();
if (forWebSocket && code == 101) {
response = response.newBuilder()
.body(Util.EMPTY_RESPONSE)
.build();
} else {
//读取返回内容
response = response.newBuilder()
.body(httpCodec.openResponseBody(response))
.build();
}
//......
return response;
}
可以看到主要是由HttpCodec执行的数据写入以有读取.HttpCodec是一个接口,它实现有两个类,分别是Http1Codec(处理http1.,1请求)和http2Codec(处理Http2)请求.在HttpCodec的实现中主要通过okio与服务端通信 .在上一节的ConnectInterceptor我们知道,Okhttp与服务端建立了一个TCP连接,所以客户端的与服务端的通信是直接通过TCP协议层的,当数据返回时,OKhttp会将数据构造HTTP形式的数据.
OkHttp的工作原理就分析到这里了。在上面的文章中，首先分析了OkHttp在发起请求的准备阶段工作，构造OkHttpClient以及Request，然后通过调度器Dispatcher处理请求任务（请求又分为同步请求和异步请求）。最后通过拦截器处理请求
https://www.jianshu.com/p/7b29b89cd7b5
https://www.jianshu.com/p/310ccf5cbea6
https://blog.csdn.net/programerxiaoer/article/details/97837226