okhttp之源码学习1
2..okhttp源码分析
1.okhttp基本介绍
一.okhttp源码分析
1. 基本使用：
首先是怎么使用，其次是我们使用的功能在内部是如何实现的.跟着本文，过一遍源码。
源码分析：
OkHttpClient client = new OkHttpClient();
String run(String url) throws IOException {
Request request = new Request.Builder().url(url) .build();
Response response = client.newCall(request).execute();
return response.body().string();
}
Request、Response、Call 基本概念
Request： 每一个HTTP请求包含一个URL、一个方法（GET或POST或其他）、一些HTTP头。请求还可能包含一个特定内容类型的数据类的主体部分。
Response：响应是对请求的回复，包含状态码、HTTP头和主体部分。
Call： OkHttp使用Call抽象出一个满足请求的模型，尽管中间可能会有多个请求或响应。执行Call有两种方式，同步或异步
第一步：创建 OkHttpClient对象,进行源码分析：
OkHttpClient client = new OkHttpClient();`
通过okhttp源码分析,直接创建的 OkHttpClient对象并且默认构造builder对象进行初始化
public class OkHttpClient implements Cloneable, Call.Factory, WebSocket.Factory {
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;
......
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;
}
}
第二步：接下来发起 HTTP 请求
Request request = new Request.Builder().url("url").build();
okHttpClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
}
@Override
public void onResponse(Call call, Response response) throws IOException {
}});
第二步：代码流程分析：
Request request = new Request.Builder().url("url").build();
初始化构建者模式和请求对象，并且用URL替换Web套接字URL。
public final class Request {
public Builder() {
this.method = "GET";
this.headers = new Headers.Builder();
}
public Builder url(String url) {
......
// Silently replace web socket URLs with HTTP URLs.
if (url.regionMatches(true, 0, "ws:", 0, 3)) {
url = "http:" + url.substring(3);
} else if (url.regionMatches(true, 0, "wss:", 0, 4)) {
url = "https:" + url.substring(4);
}
HttpUrl parsed = HttpUrl.parse(url);
......
return url(parsed);
}
public Request build() {
......
return new Request(this); }}
第三步：方法解析：
okHttpClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
}
@Override
public void onResponse(Call call, Response response) throws IOException {
}});
源码分析：
public class OkHttpClient implements Cloneable, Call.Factory, WebSocket.Factory {
@Override
public Call newCall(Request request) {
return new RealCall(this, request, false /* for web socket */); }}
RealCall实现了Call.Factory接口创建了一个RealCall的实例，而RealCall是Call接口的实现。
异步请求的执行流程
final class RealCall implements Call {
@Override
public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
client.dispatcher().enqueue(new AsyncCall(responseCallback));}}
由以上源码得知：
1） 检查这个 call 是否已经被执行了，每个 call 只能被执行一次，如果想要一个完全一样的 call，可以利用 call#clone 方法进行克隆。
2）利用 client.dispatcher().enqueue(this) 来进行实际执行，dispatcher 是刚才看到的 OkHttpClient.Builder 的成员之一
3）AsyncCall是RealCall的一个内部类并且继承NamedRunnable，那么首先看NamedRunnable类是什么样的，如下：
public abstract class NamedRunnable implements Runnable {
......
@Override
public final void run() {
......
try {
execute();
}
......
}
protected abstract void execute();
}
可以看到NamedRunnable实现了Runnbale接口并且是个抽象类，其抽象方法是execute()，该方法是在run方法中被调用的，这也就意味着NamedRunnable是一个任务，并且其子类应该实现execute方法。下面再看AsyncCall的实现：
final class AsyncCall extends NamedRunnable {
private final Callback responseCallback;
AsyncCall(Callback responseCallback) {
super("OkHttp %s", redactedUrl());
this.responseCallback = responseCallback;
}
......
final class RealCall implements Call {
@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) {
......
responseCallback.onFailure(RealCall.this, e);
} finally {
client.dispatcher().finished(this);
}
}
AsyncCall实现了execute方法，首先是调用getResponseWithInterceptorChain()方法获取响应，然后获取成功后，就调用回调的onReponse方法，如果失败，就调用回调的onFailure方法。最后，调用Dispatcher的finished方法。
关键代码：
responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
和responseCallback.onResponse(RealCall.this, response);
走完这两句代码会进行回调到刚刚我们初始化Okhttp的地方,如下：
okHttpClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
}
@Override
public void onResponse(Call call, Response response) throws IOException {}});
核心重点类Dispatcher线程池介绍：
public final class Dispatcher {
/** 最大并发请求数为64 */
private int maxRequests = 64;
/** 每个主机最大请求数为5 */
private int maxRequestsPerHost = 5;
private ExecutorService executorService;
/** 准备执行的请求 */
private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>();
/** 正在执行的异步请求，包含已经取消但未执行完的请求 */
private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();
/** 正在执行的同步请求，包含已经取消单未执行完的请求 */
private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();
在OkHttp，使用如下构造了单例线程池
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;
}
构造一个线程池ExecutorService：
executorService = new ThreadPoolExecutor(
//corePoolSize 最小并发线程数,如果是0的话，空闲一段时间后所有线程将全部被销毁 0,
//maximumPoolSize: 最大线程数，当任务进来时可以扩充的线程最大值，当大于了这个值就会根据丢弃处理机制来处理
Integer.MAX_VALUE,
//keepAliveTime: 当线程数大于corePoolSize时，多余的空闲线程的最大存活时间
60, //单位秒 TimeUnit.SECONDS,
//工作队列,先进先出 new SynchronousQueue<Runnable>(),
//单个线程的工厂
Util.threadFactory("OkHttp Dispatcher", false));
可以看出，在Okhttp中，构建了一个核心为[0, Integer.MAX_VALUE]的线程池，它不保留任何最小线程数，随时创建更多的线程数，当线程空闲时只能活60秒，它使用了一个不存储元素的阻塞工作队列，一个叫做"OkHttp Dispatcher"的线程工厂。
也就是说，在实际运行中，当收到10个并发请求时，线程池会创建十个线程，当工作完成后，线程池会在60s后相继关闭所有线程。
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
从上述源码分析，如果当前还能执行一个并发请求，则加入 runningAsyncCalls ，立即执行，否则加入 readyAsyncCalls 队列。
Dispatcher线程池总结：
1）调度线程池Disptcher实现了高并发，低阻塞的实现
2）采用Deque作为缓存，先进先出的顺序执行
3）任务在try/finally中调用了finished函数，控制任务队列的执行顺序，而不是采用锁，减少了编码复杂性提高性能
这里是分析OkHttp源码，并不详细讲线程池原理，如对线程池不了解请参考如下链接
点我，线程池原理，在文章性能优化最后有视频对线程池原理讲解
try {
Response response = getResponseWithInterceptorChain();
if (retryAndFollowUpInterceptor.isCanceled()) {
signalledCallback = true;
responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
} else {
signalledCallback = true;
responseCallback.onResponse(RealCall.this, response);
}
} finally {
client.dispatcher().finished(this);
}
当任务执行完成后，无论是否有异常，finally代码段总会被执行，也就是会调用Dispatcher的finished函数
void finished(AsyncCall call) {
finished(runningAsyncCalls, call, true);
}
从上面的代码可以看出，第一个参数传入的是正在运行的异步队列，第三个参数为true，下面再看有是三个参数的finished方法：
private <T> void finished(Deque<T> calls, T call, boolean promoteCalls) {
int runningCallsCount;
Runnable idleCallback;
synchronized (this) {
if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
if (promoteCalls) promoteCalls();
runningCallsCount = runningCallsCount();
idleCallback = this.idleCallback;
}
if (runningCallsCount == 0 && idleCallback != null) {
idleCallback.run();
}
}
打开源码，发现它将正在运行的任务Call从队列runningAsyncCalls中移除后，获取运行数量判断是否进入了Idle状态,接着执行promoteCalls()函数,
下面是promoteCalls()方法：
private void promoteCalls() {
if (runningAsyncCalls.size() >= maxRequests) return; // Already running max capacity.
if (readyAsyncCalls.isEmpty()) return; // No ready calls to promote.
for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
AsyncCall call = i.next();
if (runningCallsForHost(call) < maxRequestsPerHost) {
i.remove();
runningAsyncCalls.add(call);
executorService().execute(call);
}
if (runningAsyncCalls.size() >= maxRequests) return; // Reached max capacity.
}
}
主要就是遍历等待队列，并且需要满足同一主机的请求小于maxRequestsPerHost时，就移到运行队列中并交给线程池运行。就主动的把缓存队列向前走了一步，而没有使用互斥锁等复杂编码
核心重点getResponseWithInterceptorChain方法：
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);
return chain.proceed(originalRequest);
}
1）在配置 OkHttpClient 时设置的 interceptors；
2）负责失败重试以及重定向的 RetryAndFollowUpInterceptor；
3）负责把用户构造的请求转换为发送到服务器的请求、把服务器返回的响应转换为用户友好的响应的 BridgeInterceptor；
4）负责读取缓存直接返回、更新缓存的 CacheInterceptor；
5）负责和服务器建立连接的 ConnectInterceptor；
6）配置 OkHttpClient 时设置的networkInterceptors；
7）负责向服务器发送请求数据、从服务器读取响应数据的 CallServerInterceptor。
OkHttp的这种拦截器链采用的是责任链模式，这样的好处是将请求的发送和处理分开，并且可以动态添加中间的处理方实现对请求的处理、短路等操作。从上述源码得知，不管okhttp有多少拦截器最后都会走，如下方法：
Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0, originalRequest);
return chain.proceed(originalRequest);
调用 chain.proceed(originalRequest); 将request传递进来，从拦截器链里拿到返回结果。那么拦截器Interceptor是干嘛的，Chain是干嘛的呢？继续往下看RealInterceptorChain
RealInterceptorChain类：
下面是RealInterceptorChain的定义，该类实现了Chain接口，在getResponseWithInterceptorChain调用时好几个参数都传的null。
public final class RealInterceptorChain implements Interceptor.Chain {
public RealInterceptorChain(List<Interceptor> interceptors, StreamAllocation streamAllocation,
HttpCodec httpCodec, RealConnection connection, int index, Request request) {
this.interceptors = interceptors;
this.connection = connection;
this.streamAllocation = streamAllocation;
this.httpCodec = httpCodec;
this.index = index;
this.request = request;
}
......
@Override
public Response proceed(Request request) throws IOException {
return proceed(request, streamAllocation, httpCodec, connection);
}
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);
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);
......
return response;
}
protected abstract void execute();
}
主要看proceed方法，proceed方法中判断index（此时为0）是否大于或者等于client.interceptors(List )的大小。由于httpStream为null，所以首先创建next拦截器链，主需要把索引置为index+1即可；然后获取第一个拦截器，调用其intercept方法。
Interceptor 代码如下：
public interface Interceptor {
Response intercept(Chain chain) throws IOException;
interface Chain {
Request request();
Response proceed(Request request) throws IOException;
Connection connection();
}
}
BridgeInterceptor
BridgeInterceptor从用户的请求构建网络请求，然后提交给网络，最后从网络响应中提取出用户响应。从最上面的图可以看出，BridgeInterceptor实现了适配的功能。下面是其intercept方法：
public final class BridgeInterceptor implements Interceptor {
......
@Override
public Response intercept(Chain chain) throws IOException {
Request userRequest = chain.request();
Request.Builder requestBuilder = userRequest.newBuilder();
RequestBody body = userRequest.body();
//如果存在请求主体部分，那么需要添加Content-Type、Content-Length首部
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");
}
// 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());
}
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);
responseBuilder.body(new RealResponseBody(strippedHeaders, Okio.buffer(responseBody)));
}
return responseBuilder.build();
}
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();
}
}
从上面的代码可以看出，首先获取原请求，然后在请求中添加头，比如Host、Connection、Accept-Encoding参数等，然后根据看是否需要填充Cookie，在对原始请求做出处理后，使用chain的procced方法得到响应，接下来对响应做处理得到用户响应，最后返回响应。接下来再看下一个拦截器ConnectInterceptor的处理。
public final class ConnectInterceptor implements Interceptor {
......
@Override
public Response intercept(Chain chain) throws IOException {
RealInterceptorChain realChain = (RealInterceptorChain) chain;
Request request = realChain.request();
StreamAllocation streamAllocation = realChain.streamAllocation();
// We need the network to satisfy this request. Possibly for validating a conditional GET.
boolean doExtensiveHealthChecks = !request.method().equals("GET");
HttpCodec httpCodec = streamAllocation.newStream(client, doExtensiveHealthChecks);
RealConnection connection = streamAllocation.connection();
return realChain.proceed(request, streamAllocation, httpCodec, connection);
}
}
实际上建立连接就是创建了一个 HttpCodec 对象，它利用Okio对Socket的读写操作进行封装，Okio以后有机会再进行分析，现在让我们对它们保持一个简单地认识：它对 java.io 和 java.nio 进行了封装，让我们更便捷高效的进行 IO 操作。
CallServerInterceptor：
CallServerInterceptor是拦截器链中最后一个拦截器，负责将网络请求提交给服务器。它的intercept方法实现如下：
@Override
public Response intercept(Chain chain) throws IOException {
RealInterceptorChain realChain = (RealInterceptorChain) chain;
HttpCodec httpCodec = realChain.httpStream();
StreamAllocation streamAllocation = realChain.streamAllocation();
RealConnection connection = (RealConnection) realChain.connection();
Request request = realChain.request();
long sentRequestMillis = System.currentTimeMillis();
httpCodec.writeRequestHeaders(request);
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"))) {
httpCodec.flushRequest();
responseBuilder = httpCodec.readResponseHeaders(true);
}
if (responseBuilder == null) {
// Write the request body if the "Expect: 100-continue" expectation was met.
Sink requestBodyOut = httpCodec.createRequestBody(request, request.body().contentLength());
BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);
request.body().writeTo(bufferedRequestBody);
bufferedRequestBody.close();
} else if (!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.
streamAllocation.noNewStreams();
}
}
httpCodec.finishRequest();
if (responseBuilder == null) {
responseBuilder = httpCodec.readResponseHeaders(false);
}
Response response = responseBuilder
.request(request)
.handshake(streamAllocation.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
int code = response.code();
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(httpCodec.openResponseBody(response))
.build();
}
if ("close".equalsIgnoreCase(response.request().header("Connection"))
|| "close".equalsIgnoreCase(response.header("Connection"))) {
streamAllocation.noNewStreams();
}
if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
throw new ProtocolException(
"HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());
}
return response;
}
从上面的代码中可以看出，首先获取HttpStream对象，然后调用writeRequestHeaders方法写入请求的头部，然后判断是否需要写入请求的body部分，最后调用finishRequest()方法将所有数据刷新给底层的Socket，接下来尝试调用readResponseHeaders()方法读取响应的头部，
然后再调用openResponseBody()方法得到响应的body部分，最后返回响应。
二. okhttp基本介绍
Retrofit，OkHttp，Okio Square 安卓平台网络层三板斧源码学习
基于 okhttp 3.9.0 版本 okhttp github 地址
使用方式
OkHttpClient client = new OkHttpClient();
String run(String url) throws IOException {
Request request = new Request.Builder().url(url).build();
Response response = client.newCall(request).execute();
return response.body().string();
}
1. 构造一个 OkHttpClient
2. 构造一个 Request
3. 调用 OkHttpClient.newCall(Request request) 获得一个 Call 对象
4. 执行 Call.execute() 获得 Response 对象
5. 通过 Response.body() 获得 ResponseBody 对象
OkHttpClient 创建 http 请求源码分析。
OkHttpClient 和 OkHttpClient.Builder
OkHttpClient 对象的创建使用了『建造者模式』
public Builder() {
dispatcher = new Dispatcher();
protocols = DEFAULT_PROTOCOLS;
connectionSpecs = DEFAULT_CONNECTION_SPECS;
eventListenerFactory = EventListener.factory(EventListener.NONE);
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;
pingInterval = 0;
}
OkHttpClient.Builder 主要用来设置超时时间、代理、缓存、拦截器等。
然后调用
public OkHttpClient build() {
return new OkHttpClient(this);
}
创建 OkHttpClient
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;
……
}
Request 和 Request.Builder
Request 同样也是使用『建造者模式』
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;
}
Request 主要为了设置 url 、请求方法（GET、POST等）、headers、请求体。
其中有个 tag 比较特殊。
/**
* Attaches {@code tag} to the request. It can be used later to cancel the request. If the tag
* is unspecified or null, the request is canceled by using the request itself as the tag.
*/
public Builder tag(Object tag) {
this.tag = tag;
return this;
}
根据注释可以看出 tag 主要用来取消请求。如果发起 POST 请求，需要使用一个 RequestBody
RequestBody主要用来设置不同的 POST 请求内容（字节流、文件、字符串）
分析 Call 对象
client.newCall(request)
OkHttpClient 的 newCall
@Override
public Call newCall(Request request) {
return RealCall.newRealCall(this, request, false /* for web socket */);
}
发现请求代理给了 RealCall
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;
}
看下 RealCall 的构造函数
private RealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
this.client = client;
this.originalRequest = originalRequest;
this.forWebSocket = forWebSocket;
this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client, forWebSocket);
}
获得 Call.execute() 和 Call.enqueue(Callback responseCallback)
Call.execute() 负责同步请求。
Call.enqueue(Callback responseCallback) 负责异步请求。
@Override
public Response execute() throws IOException {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
try {
client.dispatcher().executed(this);
Response result = getResponseWithInterceptorChain();
if (result == null) throw new IOException("Canceled");
return result;
} finally {
client.dispatcher().finished(this);
}
}
@Override
public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
从上面代码可以看出 Call 对象会交给 Dispatcher 对象进行管理。
executed() 方法会把 Call 对象存放在 runningSyncCalls 队列
synchronized void executed(RealCall call) {
runningSyncCalls.add(call);
}
enqueue() 方法会把 Call 对象存放在 runningAsyncCalls 队列，如果队列已满则会被存放在 readyAsyncCalls 队列
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
然后会执行到 getResponseWithInterceptorChain
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());
return chain.proceed(originalRequest);
}
这里可以看到添加了一些列的 Interceptor 对象。这些 intercept 分别负责网络请求、缓存、压缩等功能。
而这些 intercept 组合的方式就是『责任链模式』，而最后一个 CallServerInterceptor 会真正发起网络请求。
1. 首先会创建一个 RealInterceptorChain ，传入所有的 Interceptor，index = 0
2. 然后执行 RealInterceptorChain.proceed(Request request)
3. 再调用 RealInterceptorChain.proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
RealConnection connection)
4. 创建一个新的 RealInterceptorChain ，传入 index 值 +1,对象名称为 next
5. 获取 interceptors 中 index 位置的 Interceptor，调用 Interceptor.intercept(next)
6. 在 interceptors 中添加的各种 Interceptor 的 intercept 中都会如下
public Response intercept(Chain chain) throws IOException {
……
chain.proceed(requestBuilder.build());
// or
realChain.proceed(request, streamAllocation, null, null);
……
}
7. 其中 Chain.proceed() 方法又会重复执行 3、4、5、6 步骤，直到所有的 interceptors 被遍历。
8. 最后添加的 ConnectInterceptor 和 CallServerInterceptor 是发起网络请求的关键
总结以上流程如下
先看 ConnectInterceptor
@Override
public Response intercept(Chain chain) throws IOException {
RealInterceptorChain realChain = (RealInterceptorChain) chain;
Request request = realChain.request();
StreamAllocation streamAllocation = realChain.streamAllocation();
// We need the network to satisfy this request. Possibly for validating a conditional GET.
boolean doExtensiveHealthChecks = !request.method().equals("GET");
HttpCodec httpCodec = streamAllocation.newStream(client, chain, doExtensiveHealthChecks);
RealConnection connection = streamAllocation.connection();
return realChain.proceed(request, streamAllocation, httpCodec, connection);
}
其中 StreamAllocation 对象由 RetryAndFollowUpInterceptor 创建并传入到『责任链』中。
public Response intercept(Chain chain) throws IOException {
……
streamAllocation = new StreamAllocation(client.connectionPool(), createAddress(request.url()),
call, eventListener, callStackTrace);
……
response = realChain.proceed(request, streamAllocation, null, null);
……
}
}
可以看出 ConnectInterceptor 主要作用就是通过 StreamAllocation 创建了一个 HttpCodec。
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 existingConnection = connection;
RealConnection resultConnection = findHealthyConnection(connectTimeout, readTimeout,
writeTimeout, connectionRetryEnabled, doExtensiveHealthChecks);
HttpCodec resultCodec = resultConnection.newCodec(client, chain, this);
if (existingConnection != connection) {
eventListener.connectionAcquired(call, connection);
}
synchronized (connectionPool) {
codec = resultCodec;
return resultCodec;
}
} catch (IOException e) {
throw new RouteException(e);
}
}
通过上面代码我们可以看出虽然返回的只是一个 HttpCodec 但是还会创建一个 RealConnection 。而 RealConnection 则是负责连接服务器发送请求的类。
findHealthyConnection() 方法会调用 findConnection() 方法
private RealConnection findConnection(int connectTimeout, int readTimeout, int writeTimeout,
boolean connectionRetryEnabled) throws IOException {
……
RealConnection result;
……
// Do TCP + TLS handshakes. This is a blocking operation.
result.connect(
connectTimeout, readTimeout, writeTimeout, connectionRetryEnabled, call, eventListener);
……
}
并且调用 RealConnection 的 connect() 方法进行连接
public void connect(int connectTimeout, int readTimeout, int writeTimeout, boolean connectionRetryEnabled, Call call, EventListener eventListener) {
……
connectSocket(connectTimeout, readTimeout, call, eventListener);
……
}
private void connectSocket(int connectTimeout, int readTimeout, Call call, EventListener eventListener) throws IOException {
Proxy proxy = route.proxy();
Address address = route.address();
rawSocket = proxy.type() == Proxy.Type.DIRECT || proxy.type() == Proxy.Type.HTTP
? address.socketFactory().createSocket()
: new Socket(proxy);
eventListener.connectStart(call, route.socketAddress(), proxy);
rawSocket.setSoTimeout(readTimeout);
try {
Platform.get().connectSocket(rawSocket, route.socketAddress(), connectTimeout);
}
……
try {
source = Okio.buffer(Okio.source(rawSocket));
sink = Okio.buffer(Okio.sink(rawSocket));
} ……
}
这里可以看出 connect() 方法会建立一个 Socket 连接，并把 Socket 的输入/输出流 交包装成 Okio 的 Source 和 Sink 对象。
然后到 CallServerInterceptor 中
public Response intercept(Chain chain) throws IOException {
……
Response.Builder responseBuilder = null;
if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
……
//写入 request body
……
}
httpCodec.finishRequest(); // 通过 Socket OutputStream 发送请求
……
if (responseBuilder == null) {
realChain.eventListener().responseHeadersStart(realChain.call());
responseBuilder = httpCodec.readResponseHeaders(false);
}
Response response = responseBuilder
.request(request)
.handshake(streamAllocation.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
……
return response;
}
总计流程图如下
