很久没有写过博客了,一直认为自己的技术实力不够,怕写了技术博客产生错误,误导了大家,让大家在错误的方向越走越远,不能解决自己的问题,前段时间看了某大佬的关于写作的分享,我决定从今天开始将自己在Android开发路上学习和解决问题的历程记录下来,如果博客中有错误的地方,也欢迎大家指正,我们共同进步共同学习。今天从OKhttp的源码分析开始!
基本的执行流程如下:
OKhttpClient->Request->RealCall->Dispatcher->interceptors(RetryAndFollow->Bridge->Cache->Connect->CallServer)
名词解释:
OkHttpClient client=new OkHttpClient.Builder().readTimeout(5, TimeUnit.SECONDS).build();
Request request=new Request.Builder().url("http://www.baidu.com").build();
Call call = client.newCall(request);
try {
Response response = call.execute();
} catch (IOException e) {
e.printStackTrace();
}
首先我们来看下OkHttpClient实例的创建,OkHttpClient实例是通过创建者模式来创建的,我们来看下其源码
public Builder() {
dispatcher = new Dispatcher();//这里创建了OKhttp的任务调度器对象
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();//这里创建了连接池
dns = Dns.SYSTEM;
followSslRedirects = true;
followRedirects = true;
retryOnConnectionFailure = true;
connectTimeout = 10_000;
readTimeout = 10_000;
writeTimeout = 10_000;
pingInterval = 0;
}
通过上面的代码来看,这个方法里面主要是基本的赋值操作和任务调度器对象和连接池对象的创建,我们继续往下看build方法
public OkHttpClient build() {
return new OkHttpClient(this);
}
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;
···//篇幅原因,这里就将剩下的代码注释啦。
}
在build方法中直接返回了新创建的OkHttpClient对象,将Builder对象传入OkHttpClient中,并在OkHttpClient的构造方法中进行赋值操作,此时,OkHttpClient的实例对象创建完成。
接着我们看下请求对象Request的创建过程:
Request request=new Request.Builder().url("http://www.baidu.com").build();
也和OkHttpClient的创建过程一样,也是使用了创建者模式,我们来看下Builder方法
public Builder() {
this.method = "GET";
this.headers = new Headers.Builder();
}
在这里我们可以看到,默认情况下,请求方式为GET方式,然后创建了header对象,用来存储HTTP的请求头数据,url方法就是设置url地址的,我们就不跳进去看代码了,我们看下build方法
public Request build() {
if (url == null) throw new IllegalStateException("url == null");
return new Request(this);
}
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;
}
在build方法中,进行了url的判空操作,然后将Builder对象传入Request类的构造函数,返回新创建的Request对象
在Request的构造函数中,只是进行简单的赋值操作。此时Request对象也已经创建完成。
接着进行第三步了,创建Call对象
Call call = client.newCall(request);
我们点击newCall方法进去看看Call对象是具体如何创建的
/**
* 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 */);
}
我们可以看到,里面很简单,其实Call对象的真正创建是在RealCall的newRealCall方法里的,我们进去看看
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;
}
private RealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
this.client = client;
this.originalRequest = originalRequest;
this.forWebSocket = forWebSocket;
this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client, forWebSocket);
}
在newRealCall方法中我们看到,RealCall的创建是通过构造函数创建的,我们点进来继续看,里面只是一些简单的赋值操作,但是,请注意,最后一页是我们在前面简介过的重试拦截器RetryAndFollowUpInterceptor的创建。这里我们先不详细的介绍,后面再详细讲解。
在newRealCall方法中的最后一行是创建Call对象的事件监听对象。
到此为止,Call对象创建成功。
我们继续往下看,最后一步,
Response response = call.execute();
调用call的execute()方法,得到我们想要的response对象,我们进入到execute方法中看看里面是如何得到我们要的response对象的。
@Override public Response execute() throws IOException {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
eventListener.callStart(this);
try {
client.dispatcher().executed(this);
Response result = getResponseWithInterceptorChain();
if (result == null) throw new IOException("Canceled");
return result;
} catch (IOException e) {
eventListener.callFailed(this, e);
throw e;
} finally {
client.dispatcher().finished(this);
}
}
我们直接来看关键代码,client.dispatcher().executed(this);,我们看下dispatcher方法,
public Dispatcher dispatcher() {
return dispatcher;
}
可以看到,这里直接返回了之前在构造器中创建的dispatcher对象,我们接着看execute方法,
/** Used by {@code Call#execute} to signal it is in-flight. */
synchronized void executed(RealCall call) {
runningSyncCalls.add(call);
}
这个runningSynCalls是什么鬼呢,我们看下定义位置
/** Ready async calls in the order they'll be run. */
private final Deque readyAsyncCalls = new ArrayDeque<>();
/** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
private final Deque runningAsyncCalls = new ArrayDeque<>();
/** Running synchronous calls. Includes canceled calls that haven't finished yet. */
private final Deque runningSyncCalls = new ArrayDeque<>();
可以看到,这个是一个存放还没有执行完毕的同步任务的队列,我们还看到了另外两个队列readyAsyncCalls、runningAsyncCalls,一个是待执行的异步任务的队列,一个是正在执行的异步任务的队列。这两个实例我们在后面的异步请求中会用到,这里先跳过。
我们回头看下executed方法,这里只是将Call对象添加到同步任务的执行队列中。
回到前面的代码中,我们接着往下看,
Response result = getResponseWithInterceptorChain();
原来真正得到response对象是在这里,通过getResponseWithInterceptorChain();方法得到的,我们进入到这个方法中看下是如何执行的。
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);
}
return语句之前的代码都是创建拦截器链的操作,拦截器链创建完成后,通过拦截器链的proceed方法得到response对象,我们继续跟进
@Override public Response proceed(Request request) throws IOException {
return proceed(request, streamAllocation, httpCodec, connection);
}
我们可以看到里面又调用了另一个重载的proceed方法,我们跳过去看下,
public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
RealConnection connection) throws IOException {
if (index >= interceptors.size()) throw new AssertionError();
calls++;
···//省略部分代码
// 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);
···//为了简化篇幅,将后面一些判断代码进行省略
return response;
}
我们可以看到中间的代码,这部分代码就是得到拦截器链中的下一个拦截器,然后进行该拦截器的intercept(next)方法操作,在这个方法中,会继续调用拦截器链中的下一个拦截器的intercept(next)方法调用,最后执行到CallServerInterceptor拦截器,从而获取真正的response对象,然后一层层的返回,每返回一层,在当前层的拦截器中进行包装处理,最后返回到这里,再进行返回,从而得到我们要的response对象。拦截器链中的详细执行流程我们后面再详细讲解。
通过上面的代码分析,我们就已经分析完了同步请求的执行流程。下面我们继续看下异步请求流程的源码分析。
我们先来看下如何来执行异步请求
OkHttpClient client = new OkHttpClient.Builder().readTimeout(5, TimeUnit.SECONDS).build();
Request request = new Request.Builder().url("http://www.baidu.com").build();
Call call = client.newCall(request);
call.enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
}
@Override
public void onResponse(Call call, Response response) throws IOException {
}
});
我们可以看到,前面三行代码是和同步请求一致,我们重点来看call的enqueue方法。上面我们讲过,call对象的真正实现是RealCall,那我们就看RealCall中enqueue方法的实现
@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));
}
最后一行,还是OkHttpClient对象获取了任务调度器来执行enqueue方法,并将我们传递进来的Callback对象封装成AsyncCall对象,我们看下Dispatcher中的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);
}
}
可以看到,首先进行判断,如果正在运行的异步任务数量小于指定的数量(64),就将AsyncCall对象添加到正在运行的异步任务队列中,并加入线程池中执行任务,否则就加入到等待运行的异步任务队列中去。如果线程池中线程开始运行了,线程池中的执行对象肯定是一个线程,那就肯定要有run方法的,那么我们就来看下AsyncCall到底是个什么东东。
final class AsyncCall extends NamedRunnable {
private final Callback responseCallback;
AsyncCall(Callback responseCallback) {
super("OkHttp %s", redactedUrl());
this.responseCallback = responseCallback;
}
······//省略部分代码
}
上面代码中我们可以看到,AsyncCall继承了NamedRunnable,我们继续看NamedRunnable是什么,
public abstract class NamedRunnable implements Runnable {
protected final String name;
public NamedRunnable(String format, Object... args) {
this.name = Util.format(format, args);
}
@Override public final void run() {
String oldName = Thread.currentThread().getName();
Thread.currentThread().setName(name);
try {
execute();
} finally {
Thread.currentThread().setName(oldName);
}
}
protected abstract void execute();
}
可以看到,原来NamedRunnable实现了Runnable接口,肯定要执行run方法,那就看下NamedRunnable的run方法,其中最重要的就是execute();这一句了,我们看下execute()方法,咦,是个抽象方法,这个方法是给其子类来实现的,那么我们看下刚刚实现了NamedRunnable类的子类AsyncCall中的executed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);
}
}
我们可以看到熟悉的代码,熟悉的味道,······,额,我们看下这一行
Response response = getResponseWithInterceptorChain();
是不是似曾相识呢,对的,在前面的同步执行流程的源码分析中我们已经见过这个代码了,如果你不记得了,就往前面翻一翻,这里就不再讲解啦。通过这一句,我们得到了我们想要的response对象,那么我们看下下面的代码是做什么的
try···catch代码块中是判断和对callback方法的调用,我们忽略它,来看下finally中的代码,我们知道,finally中的代码是一定会执行到的,我们看下finished方法
void finished(AsyncCall call) {
finished(runningAsyncCalls, call, true);
}
private void finished(Deque 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();
}
}
finished方法调用了重载的另一个finished方法,我们看下,在finished方法中,首先将刚刚执行完的call对象进行移除队列,然后我们看这行代码
if (promoteCalls) promoteCalls();
我们看下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 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.
}
}
头两行代码是判断正在执行的任务队列中的任务数量如果大于或等于指定的最大任务数就返回,或者正在等待的任务数为0也返回,我们来看下for循环中的代码,这里是对等待的任务队列进行遍历,首先取出一个任务,判断是否符合运行条件,如果符合,就将其从等待队列中移除,添加到运行队列中去,并加入线程池执行,最后一行,如果正在运行的任务数量大于等于最大指定任务数,就跳出for循环,我们可以看到,这个promoteCalls方法的作用就是判断正在运行的任务数量,如果数量小于指定的任务数,就从等待的任务队列中取出,添加到正在运行的任务队列中,并加入线程池中运行,那么这里就又可以回到前面分析过的代码,那我们就继续回到前面的finished方法中去,继续往下看,
runningCallsCount = runningCallsCount();
我们来看下这行代码
public synchronized int runningCallsCount() {
return runningAsyncCalls.size() + runningSyncCalls.size();
}
很简单,只是重新计算正在运行的任务数量,现在我们回过头来继续看finished方法中的最后一部分代码
if (runningCallsCount == 0 && idleCallback != null) {
idleCallback.run();
}
这里是判断如果正在执行的任务数量为0,并且空闲回收线程不为null,就执行空闲回收线程的run方法进行回收操作。
好了,到此为止,我们就已经分析完了同步和异步执行流程,下一篇我们来分析okhttp的任务调度核心类Dispatcher