OkHttp是一个精巧的网络请求库，有如下特性:
1)支持http2，对一台机器的所有请求共享同一个socket
2)内置连接池，支持连接复用，减少延迟
3)支持透明的gzip压缩响应体
4)通过缓存避免重复的请求
5)请求失败时自动重试主机的其他ip，自动重定向
6)好用的API
其本身就是一个很强大的库，再加上Retrofit2、Picasso的这一套组合拳，使其愈发的受到开发者的关注。本篇博客，我将对Okhttp3进行分析（源码基于Okhttp3.4）。
如何引入Okhttp3？
配置Okhttp3非常简单，只需要在Android Studio 的gradle进行如下的配置：
compile ‘com.squareup.okhttp3:okhttp:3.4.1′
* 1
添加网络权限：
<uses-permission android:name=”android.permission.INTERNET”/>
* 1
Okhttp3的基本使用
okHttp的get请求
okHttp的一般使用如下，okHttp默认使用的就是get请求
String url = “http://write.blog.csdn.net/postlist/0/0/enabled/1”;
mHttpClient = new OkHttpClient();
Request request = new Request.Builder().url(url).build();
okhttp3.Response response = null;
try {
response = mHttpClient.newCall(request).execute();
String json = response.body().string();
Log.d(“okHttp”,json);
} catch (IOException e) {
e.printStackTrace();
}
}
我们试着将数据在logcat进行打印，发现会报错，原因就是不能在主线程中进行耗时的操作

说明mHttpClient.newCall(request).execute()是同步的，那有没有异步的方法呢，答案是肯定的,就是mHttpClient.newCall(request).enqueue()方法，里面需要new一个callback我们对代码进行修改，如下
public void requestBlog() {
String url = “http://write.blog.csdn.net/postlist/0/0/enabled/1”;
mHttpClient = new OkHttpClient();
Request request = new Request.Builder().url(url).build();
/* okhttp3.Response response = null;*/
/*response = mHttpClient.newCall(request).execute();*/
mHttpClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
}
@Override
public void onResponse(Call call, Response response) throws IOException {
String json = response.body().string();
Log.d(“okHttp”, json);
}
});
}

Okhttp的POST请求
POST提交Json数据
private void postJson() throws IOException {
String url = “http://write.blog.csdn.net/postlist/0/0/enabled/1”;
String json = “haha”;
OkHttpClient client = new OkHttpClient();
RequestBody body = RequestBody.create(JSON, json);
Request request = new Request.Builder()
.url(url)
.post(body)
.build();
client.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
}
@Override
public void onResponse(Call call, Response response) throws IOException {
Log.d(TAG, response.body().string());
}
});
}
POST提交键值对
很多时候我们会需要通过POST方式把键值对数据传送到服务器。 OkHttp提供了很方便的方式来做这件事情。
private void post(String url, String json) throws IOException {
OkHttpClient client = new OkHttpClient();
RequestBody formBody = new FormBody.Builder()
.add(“name”, “liming”)
.add(“school”, “beida”)
.build();
Request request = new Request.Builder()
.url(url)
.post(formBody)
.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 {
String str = response.body().string();
Log.i(TAG, str);
}
});
}
异步上传文件
上传文件本身也是一个POST请求
定义上传文件类型
public static final MediaType MEDIA_TYPE_MARKDOWN
= MediaType.parse(“text/x-markdown; charset=utf-8”);
* 1
* 2
将文件上传到服务器上：
private void postFile() {
OkHttpClient mOkHttpClient = new OkHttpClient();
File file = new File(“/sdcard/demo.txt”);
Request request = new Request.Builder()
.url(“https://api.github.com/markdown/raw”)
.post(RequestBody.create(MEDIA_TYPE_MARKDOWN, file))
.build();
mOkHttpClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
}
@Override
public void onResponse(Call call, Response response) throws IOException {
Log.i(TAG, response.body().string());
}
});
}
添加如下权限：
<uses-permission android:name=”android.permission.READ_EXTERNAL_STORAGE”/>
<uses-permission android:name=”android.permission.WRITE_EXTERNAL_STORAGE”/>
提取响应头
典型的HTTP头 像是一个 Map
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
Request request = new Request.Builder()
.url(“https://api.github.com/repos/square/okhttp/issues”)
.header(“User-Agent”, “OkHttp Headers.java”)
.addHeader(“Accept”, “application/json; q=0.5”)
.addHeader(“Accept”, “application/vnd.github.v3+json”)
.build();
Response response = client.newCall(request).execute();
if (!response.isSuccessful()) throw new IOException(“Unexpected code ” + response);
System.out.println(“Server: ” + response.header(“Server”));
System.out.println(“Date: ” + response.header(“Date”));
System.out.println(“Vary: ” + response.headers(“Vary”));
}
Post方式提交String
使用HTTP POST提交请求到服务。这个例子提交了一个markdown文档到web服务，以HTML方式渲染markdown。因为整个请求体都在内存中，因此避免使用此api提交大文档（大于1MB）。
private void postString() throws IOException {
OkHttpClient client = new OkHttpClient();
String postBody = “”
+ “Releases\n”
+ “——–\n”
+ “\n”
+ ” * zhangfei\n”
+ ” * guanyu\n”
+ ” * liubei\n”;
Request request = new Request.Builder()
.url(“https://api.github.com/markdown/raw”)
.post(RequestBody.create(MEDIA_TYPE_MARKDOWN, postBody))
.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 {
System.out.println(response.body().string());
}
});
}
Post方式提交流
以流的方式POST提交请求体。请求体的内容由流写入产生。这个例子是流直接写入Okio的BufferedSink。你的程序可能会使用OutputStream，你可以使用BufferedSink.outputStream()来获取。
public static final MediaType MEDIA_TYPE_MARKDOWN
= MediaType.parse(“text/x-markdown; charset=utf-8”);
private void postStream() throws IOException {
RequestBody requestBody = new RequestBody() {
@Override
public MediaType contentType() {
return MEDIA_TYPE_MARKDOWN;
}
@Override
public void writeTo(BufferedSink sink) throws IOException {
sink.writeUtf8(“Numbers\n”);
sink.writeUtf8(“——-\n”);
for (int i = 2; i <= 997; i++) {
sink.writeUtf8(String.format(” * %s = %s\n”, i, factor(i)));
}
}
private String factor(int n) {
for (int i = 2; i < n; i++) {
int x = n / i;
if (x * i == n) return factor(x) + ” × ” + i;
}
return Integer.toString(n);
}
};
Request request = new Request.Builder()
.url(“https://api.github.com/markdown/raw”)
.post(requestBody)
.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 {
System.out.println(response.body().string());
}
});
}
Post方式提交表单
private void postForm() {
OkHttpClient client = new OkHttpClient();
RequestBody formBody = new FormBody.Builder()
.add(“search”, “Jurassic Park”)
.build();
Request request = new Request.Builder()
.url(“https://en.wikipedia.org/w/index.php”)
.post(formBody)
.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 {
System.out.println(response.body().string());
}
});
}
Post方式提交分块请求
MultipartBody 可以构建复杂的请求体，与HTML文件上传形式兼容。多块请求体中每块请求都是一个请求体，可以定义自己的请求头。这些请求头可以用来描述这块请求，例如他的Content-Disposition。如果Content-Length和Content-Type可用的话，他们会被自动添加到请求头中。
private static final String IMGUR_CLIENT_ID = “…”;
private static final MediaType MEDIA_TYPE_PNG = MediaType.parse(“image/png”);
private void postMultipartBody() {
OkHttpClient client = new OkHttpClient();
// Use the imgur image upload API as documented at https://api.imgur.com/endpoints/image
MultipartBody body = new MultipartBody.Builder(“AaB03x”)
.setType(MultipartBody.FORM)
.addPart(
Headers.of(“Content-Disposition”, “form-data; name=\”title\””),
RequestBody.create(null, “Square Logo”))
.addPart(
Headers.of(“Content-Disposition”, “form-data; name=\”image\””),
RequestBody.create(MEDIA_TYPE_PNG, new File(“website/static/logo-square.png”)))
.build();
Request request = new Request.Builder()
.header(“Authorization”, “Client-ID ” + IMGUR_CLIENT_ID)
.url(“https://api.imgur.com/3/image”)
.post(body)
.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 {
System.out.println(response.body().string());
}
});
}
响应缓存
为了缓存响应，你需要一个你可以读写的缓存目录，和缓存大小的限制。这个缓存目录应该是私有的，不信任的程序应不能读取缓存内容。
一个缓存目录同时拥有多个缓存访问是错误的。大多数程序只需要调用一次new OkHttpClient()，在第一次调用时配置好缓存，然后其他地方只需要调用这个实例就可以了。否则两个缓存示例互相干扰，破坏响应缓存，而且有可能会导致程序崩溃。
响应缓存使用HTTP头作为配置。你可以在请求头中添加Cache-Control: max-stale=3600 ,OkHttp缓存会支持。你的服务通过响应头确定响应缓存多长时间，例如使用Cache-Control: max-age=9600。
int cacheSize = 10 * 1024 * 1024; // 10 MiB
Cache cache = new Cache(cacheDirectory, cacheSize);
OkHttpClient.Builder builder = new OkHttpClient.Builder();
builder.cache(cache);
OkHttpClient client = builder.build();
Request request = new Request.Builder()
.url(“http://publicobject.com/helloworld.txt”)
.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 {
String response1Body = response.body().string();
System.out.println(“Response 1 response: ” + response);
System.out.println(“Response 1 cache response: ” + response.cacheResponse());
System.out.println(“Response 1 network response: ” + response.networkResponse());
}
});
超时
没有响应时使用超时结束call。没有响应的原因可能是客户点链接问题、服务器可用性问题或者这之间的其他东西。OkHttp支持连接，读取和写入超时。
private void ConfigureTimeouts() {
OkHttpClient.Builder builder = new OkHttpClient.Builder();
OkHttpClient client = builder.build();
client.newBuilder().connectTimeout(10, TimeUnit.SECONDS);
client.newBuilder().readTimeout(10,TimeUnit.SECONDS);
client.newBuilder().writeTimeout(10,TimeUnit.SECONDS);
Request request = new Request.Builder()
.url(“http://httpbin.org/delay/2”) // This URL is served with a 2 second delay.
.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 {
System.out.println(“Response completed: ” + response);
}
});
}
简单封装okHttp框架
新建一个工具类OkHttpUtils
OkHttpClient必须是单例的，所以这里我们需要使用到单例设计模式,私有化构造函数，提供一个方法给外界获取OkHttpUtils实例对象
public class OkHttpUtils {
private static OkHttpUtils mInstance;
private OkHttpClient mHttpClient;
private OkHttpUtils() {
};
public static OkHttpUtils getInstance(){
return mInstance;
}
}
一般网络请求分为get和post请求两种，但无论哪种请求都是需要用到request的，所以我们首先封装一个request,创建一个doRequest方法，在其内先编写mHttpClient.newCall(request).enqueue(new Callback())相关逻辑
public void doRequest(final Request request){
mHttpClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
}
@Override
public void onResponse(Call call, Response response) throws IOException {
}
});
}
我们需要自定义一个callback，BaseCallback,并将其传入request方法中
public class BaseCallback {
}
在OkHttpUtils中编写get和post方法
public void get(String url){
}
public void post(String url,Map<String,Object> param){
}
post方法中构建request对象，这里我们需要创建一个buildRequest方法，用于生成request对象
private Request buildRequest(String url,HttpMethodType methodType,Map<String,Object> params){
return null;
}
这里需要定一个枚举对象HttpMethodType，用于区分是get还是post
enum HttpMethodType{
GET,
POST,
}
buildRequest方法根据HttpMethodType不同有相应的逻辑处理
private Request buildRequest(String url,HttpMethodType methodType,Map<String,Object> params){
Request.Builder builder = new Request.Builder()
.url(url);
if (methodType == HttpMethodType.POST){
builder.post(body);
}
else if(methodType == HttpMethodType.GET){
builder.get();
}
return builder.build();
}
builder.post()方法中需要一个body,所以我们需要创建一个方法builderFormData()方法用于返回RequestBody,这里内部逻辑后面再进行完善
private RequestBody builderFormData(Map<String,Object> params){
return null;
}
于是buildRequest方法变成了这样
private Request buildRequest(String url,HttpMethodType methodType,Map<String,Object> params){
Request.Builder builder = new Request.Builder()
.url(url);
if (methodType == HttpMethodType.POST){
RequestBody body = builderFormData(params);
builder.post(body);
}
else if(methodType == HttpMethodType.GET){
builder.get();
}
return builder.build();
}
get方法进行修改：
public void get(String url,BaseCallback callback){
Request request = buildRequest(url,HttpMethodType.GET,null);
doRequest(request,callback);
}
post方法进行修改：
public void post(String url,Map<String,Object> params,BaseCallback callback){
Request request = buildRequest(url,HttpMethodType.POST,params);
doRequest(request,callback);
}
完善builderFormData()方法
private RequestBody builderFormData(Map<String,String> params){
FormBody.Builder builder = new FormBody.Builder();
if(params!=null){
for(Map.Entry<String,String> entry:params.entrySet()){
builder.add(entry.getKey(),entry.getValue());
}
}
return builder.build();
}
BaseCallback中定义一个抽象方法onBeforeRequest，这样做的理由是我们在加载网络数据成功前，一般都有进度条等显示，这个方法就是用来做这些处理的
public abstract class BaseCallback {
public abstract void onBeforeRequest(Request request);
}
OkHttpUtils的doRequest方法增加如下语句：
baseCallback.onBeforeRequest(request);
* 1
BaseCallback中多定义2个抽象方法
public abstract void onFailure(Request request, Exception e) ;
/**
*请求成功时调用此方法
* @param response
*/
public abstract void onResponse(Response response);
由于Response的状态有多种，比如成功和失败，所以需要onResponse分解为3个抽象方法
/**
*
* 状态码大于200，小于300 时调用此方法
* @param response
* @param t
* @throws
*/
public abstract void onSuccess(Response response,T t) ;
/**
* 状态码400，404，403，500等时调用此方法
* @param response
* @param code
* @param e
*/
public abstract void onError(Response response, int code,Exception e) ;
/**
* Token 验证失败。状态码401,402,403 等时调用此方法
* @param response
* @param code
*/
public abstract void onTokenError(Response response, int code);
response.body.string()方法返回的都是String类型，而我们需要显示的数据其实是对象，所以我们就想抽取出方法，直接返回对象，由于我们不知道对象的类型是什么，所以我们在BaseCallback中使用范型
public abstract class BaseCallback<T>
* 1
BaseCallback中需要将泛型转换为Type，所以要声明Type类型
public Type mType;
* 1
BaseCallback中需要如下一段代码，将泛型T转换为Type类型
static Type getSuperclassTypeParameter(Class<?> subclass)
{
Type superclass = subclass.getGenericSuperclass();
if (superclass instanceof Class)
{
throw new RuntimeException(“Missing type parameter.”);
}
ParameterizedType parameterized = (ParameterizedType) superclass;
return $Gson$Types.canonicalize(parameterized.getActualTypeArguments()[0]);
}
在BaseCallback的构造函数中进行mType进行赋值
public BaseCallback()
{
mType = getSuperclassTypeParameter(getClass());
}
OkHttpUtils中doRequest方法的onFailure与onResponse方法会相应的去调用baseCallback的方法
mHttpClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
baseCallback.onFailure(request,e);
}
@Override
public void onResponse(Call call, Response response) throws IOException {
if(response.isSuccessful()) {
baseCallback.onSuccess(response,null);
}else {
baseCallback.onError(response,response.code(),null);
}
/*mGson.fromJson(response.body().string(),baseCallback.mType);*/
}
});
onResponse方法中成功的情况又有区分，根据mType的类型不同有相应的处理逻辑，同时还要考虑Gson解析错误的情况
@Override
public void onResponse(Call call, Response response) throws IOException {
if(response.isSuccessful()) {
String resultStr = response.body().string();
if (baseCallback.mType == String.class){
baseCallback.onSuccess(response,resultStr);
}
else {
try {
Object obj = mGson.fromJson(resultStr, baseCallback.mType);
baseCallback.onSuccess(response,obj);
}
catch (com.google.gson.JsonParseException e){ // Json解析的错误
baseCallback.onError(response,response.code(),e);
}
}
}else {
baseCallback.onError(response,response.code(),null);
}
}
构造函数中进行一些全局变量的初始化的操作，还有一些超时的设计
private OkHttpUtils() {
mHttpClient = new OkHttpClient();
OkHttpClient.Builder builder = mHttpClient.newBuilder();
builder.connectTimeout(10, TimeUnit.SECONDS);
builder.readTimeout(10,TimeUnit.SECONDS);
builder.writeTimeout(30,TimeUnit.SECONDS);
mGson = new Gson();
};
静态代码块初始化OkHttpUtils对象
static {
mInstance = new OkHttpUtils();
}
在okHttpUtils内，需要创建handler进行UI界面的更新操作，创建callbackSuccess方法
private void callbackSuccess(final BaseCallback callback , final Response response, final Object obj ){
mHandler.post(new Runnable() {
@Override
public void run() {
callback.onSuccess(response, obj);
}
});
}
doRequest方法的onResponse方法也进行相应的改写
if (baseCallback.mType == String.class){
/*baseCallback.onSuccess(response,resultStr);*/
callbackSuccess(baseCallback,response,resultStr);
}
创建callbackError方法
private void callbackError(final BaseCallback callback, final Response response, final Exception e) {
mHandler.post(new Runnable() {
@Override
public void run() {
callback.onError(response, response.code(), e);
}
});
}
将doRequest方法的onResponse方法中的baseCallback.onError(response,response.code(),e);替换为callbackError(baseCallback,response,e);方法
@Override
public void onResponse(Call call, Response response) throws IOException {
if(response.isSuccessful()) {
String resultStr = response.body().string();
if (baseCallback.mType == String.class){
/*baseCallback.onSuccess(response,resultStr);*/
callbackSuccess(baseCallback,response,resultStr);
}
else {
try {
Object obj = mGson.fromJson(resultStr, baseCallback.mType);
/*baseCallback.onSuccess(response,obj);*/
callbackSuccess(baseCallback,response,obj);
}
catch (com.google.gson.JsonParseException e){ // Json解析的错误
/*baseCallback.onError(response,response.code(),e);*/
callbackError(baseCallback,response,e);
}
}
}else {
callbackError(baseCallback,response,null);
/*baseCallback.onError(response,response.code(),null);*/
}
}
至此，我们的封装基本完成。
OkHttp3源码分析
请求处理分析
当我们要请求网络的时候我们需要用OkHttpClient.newCall(request)进行execute或者enqueue操作，当我们调用newCall时：
/**
* Prepares the {@code request} to be executed at some point in the future.
*/
@Override public Call newCall(Request request) {
return new RealCall(this, request);
}
实际返回的是一个RealCall类，我们调用enqueue异步请求网络实际上是调用了RealCall的enqueue方法：
@Override public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) throw new IllegalStateException(“Already Executed”);
executed = true;
}
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
最终的请求是dispatcher来完成的。
Dispatcher任务调度
Dispatcher的本质是异步请求的管理器，控制最大请求并发数和单个主机的最大并发数，并持有一个线程池负责执行异步请求。对同步的请求只是用作统计。他是如何做到控制并发呢，其实原理就在上面的2个execute代码里面,真正网络请求执行前后会调用executed和finished方法，而对于AsyncCall的finished方法后，会根据当前并发数目选择是否执行队列中等待的AsyncCall。并且如果修改Dispatcher的maxRequests或者maxRequestsPerHost也会触发这个过程。
Dispatcher主要用于控制并发的请求，它主要维护了以下变量：
/** 最大并发请求数*/
private int maxRequests = 64;
/** 每个主机最大请求数*/
private int maxRequestsPerHost = 5;
/** 消费者线程池 */
private ExecutorService executorService;
/** 将要运行的异步请求队列 */
private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>();
/**正在运行的异步请求队列 */
private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();
/** 正在运行的同步请求队列 */
private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();
构造函数
public Dispatcher(ExecutorService executorService) {
this.executorService = executorService;
}
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;
}
Dispatcher有两个构造函数，可以使用自己设定线程池，如果没有设定线程池则会在请求网络前自己创建线程池，这个线程池类似于CachedThreadPool比较适合执行大量的耗时比较少的任务。
异步请求
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
当正在运行的异步请求队列中的数量小于64并且正在运行的请求主机数小于5时则把请求加载到runningAsyncCalls中并在线程池中执行，否则就再入到readyAsyncCalls中进行缓存等待。
AsyncCall
线程池中传进来的参数就是AsyncCall它是RealCall的内部类，内部也实现了execute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 {
responseCallback.onFailure(RealCall.this, e);
}
} finally {
client.dispatcher().finished(this);
}
}
}
首先我们来看看最后一行， 无论这个请求的结果如何都会执行client.dispatcher().finished(this)；
/** Used by {@code AsyncCall#run} to signal completion. */
void finished(AsyncCall call) {
finished(runningAsyncCalls, call, true);
}
/** Used by {@code Call#execute} to signal completion. */
void finished(RealCall call) {
finished(runningSyncCalls, call, false);
}
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();
}
}
finished方法将此次请求从runningAsyncCalls移除后还执行了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.
}
}
可以看到最关键的点就是会从readyAsyncCalls取出下一个请求，并加入runningAsyncCalls中并交由线程池处理。好了让我们再回到上面的AsyncCall的execute方法，我们会发getResponseWithInterceptorChain方法返回了Response，很明显这是在请求网络。
Interceptor拦截器
在回到RealCall中，我们看到无论是execute还是enqueue，真正的Response是通过这个函数getResponseWithInterceptorChain获取的，其他的代码都是用作控制与回调。而这里就是真正请求的入口，也是到了OkHttp的一个很精彩的设计:Interceptor与Chain
看一下RealCall中的getResponseWithInterceptorChain方法
private 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 (!retryAndFollowUpInterceptor.isForWebSocket()) {
interceptors.addAll(client.networkInterceptors());
}
interceptors.add(new CallServerInterceptor(
retryAndFollowUpInterceptor.isForWebSocket()));
Interceptor.Chain chain = new RealInterceptorChain(
interceptors, null, null, null, 0, originalRequest);
return chain.proceed(originalRequest);
}
这也是与旧版本不一致的地方，在3.4.x以前，没有这些内部的这些拦截器，只有用户的拦截器与网络拦截器。而Request和Response是通过HttpEngine来完成的。在RealCall实现了用户拦截器与RetryAndFollowUp的过程，而在HttpEngine内部处理了请求转换、Cookie、Cache、网络拦截器、连接网络的过程。值得一提的是，在旧版是获取到Response后调用网络拦截器的拦截。
而在这里，RealInterceptorChain会递归的创建并以此调用拦截器，去掉诸多异常，简化版代码如下:
public Response proceed(Request request, StreamAllocation streamAllocation, HttpStream httpStream,
Connection connection) throws IOException {
if (index >= interceptors.size()) throw new AssertionError();
calls++;
// If we already have a stream, confirm that the incoming request will use it.
if (this.httpStream != null && !sameConnection(request.url())) {
throw new IllegalStateException(“network interceptor ” + interceptors.get(index – 1)
+ ” must retain the same host and port”);
}
// If we already have a stream, confirm that this is the only call to chain.proceed().
if (this.httpStream != null && calls > 1) {
throw new IllegalStateException(“network interceptor ” + interceptors.get(index – 1)
+ ” must call proceed() exactly once”);
}
// Call the next interceptor in the chain.
RealInterceptorChain next = new RealInterceptorChain(
interceptors, streamAllocation, httpStream, connection, index + 1, request);
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);
// Confirm that the next interceptor made its required call to chain.proceed().
if (httpStream != null && index + 1 < interceptors.size() && next.calls != 1) {
throw new IllegalStateException(“network interceptor ” + interceptor
+ ” must call proceed() exactly once”);
}
// Confirm that the intercepted response isn’t null.
if (response == null) {
throw new NullPointerException(“interceptor ” + interceptor + ” returned null”);
}
return response;
}
Chain与Interceptor会互相递归调用，直到链的尽头。
我们看到，通过职责链模式，清楚地切开了不同的逻辑，每个拦截器完成自己的职责，从而完成用户的网络请求。
大概流程是:
1)先经过用户拦截器
2)RetryAndFollowUpInterceptor负责自动重试和进行必要的重定向
3)BridgeIntercetor负责将用户Request转换成一个实际的网络请求的Request，再调用下层的拦截器获取Response，最后再将网络Response转换成用户的Reponse
4)CacheInterceptor负责控制缓存
5)ConnectInterceptor负责进行连接主机
6)网络拦截器进行拦截
7)CallServerInterceptor是真正和服务器通信，完成http请求
连接与通信
在RetryAndFollowUpInterceptor中,会创建StreamAllocation，然后交给下游的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”);
HttpStream httpStream = streamAllocation.newStream(client, doExtensiveHealthChecks);
RealConnection connection = streamAllocation.connection();
return realChain.proceed(request, streamAllocation, httpStream, connection);
}
这里会创建一个HttpStream，并且取到一个RealConnection，继续交给下游的CallServerInterceptor。
我们跟踪进去看看，StreamAllocation里面做了什么
public HttpStream newStream(OkHttpClient client, boolean doExtensiveHealthChecks) {
int connectTimeout = client.connectTimeoutMillis();
int readTimeout = client.readTimeoutMillis();
int writeTimeout = client.writeTimeoutMillis();
boolean connectionRetryEnabled = client.retryOnConnectionFailure();
try {
RealConnection resultConnection = findHealthyConnection(connectTimeout, readTimeout,
writeTimeout, connectionRetryEnabled, doExtensiveHealthChecks);
HttpStream resultStream;
if (resultConnection.framedConnection != null) {
resultStream = new Http2xStream(client, this, resultConnection.framedConnection);
} else {
resultConnection.socket().setSoTimeout(readTimeout);
resultConnection.source.timeout().timeout(readTimeout, MILLISECONDS);
resultConnection.sink.timeout().timeout(writeTimeout, MILLISECONDS);
resultStream = new Http1xStream(
client, this, resultConnection.source, resultConnection.sink);
}
synchronized (connectionPool) {
stream = resultStream;
return resultStream;
}
} catch (IOException e) {
throw new RouteException(e);
}
}
这里的代码逻辑是这样的，找一个健康的连接，设置超时时间，然后根据协议创建一个HttpStream并返回。
继续跟进去看findHealthyConnection:
private RealConnection findHealthyConnection(int connectTimeout, int readTimeout,
int writeTimeout, boolean connectionRetryEnabled, boolean doExtensiveHealthChecks)
throws IOException {
while (true) {
RealConnection candidate = findConnection(connectTimeout, readTimeout, writeTimeout,
connectionRetryEnabled);
// If this is a brand new connection, we can skip the extensive health checks.
synchronized (connectionPool) {
if (candidate.successCount == 0) {
return candidate;
}
}
// Do a (potentially slow) check to confirm that the pooled connection is still good. If it
// isn’t, take it out of the pool and start again.
if (!candidate.isHealthy(doExtensiveHealthChecks)) {
noNewStreams();
continue;
}
return candidate;
}
}
上面的逻辑也很简单，在findConnection中找一个连接，然后做健康检查，如果不健康就回收，并再次循环，那么真正寻找连接的代码就在findConnection里面了:
/**
* Returns a connection to host a new stream. This prefers the existing connection if it exists,
* then the pool, finally building a new connection.
*/
private RealConnection findConnection(int connectTimeout, int readTimeout, int writeTimeout,
boolean connectionRetryEnabled) throws IOException {
Route selectedRoute;
synchronized (connectionPool) {
if (released) throw new IllegalStateException(“released”);
if (stream != null) throw new IllegalStateException(“stream != null”);
if (canceled) throw new IOException(“Canceled”);
RealConnection allocatedConnection = this.connection;
if (allocatedConnection != null && !allocatedConnection.noNewStreams) {
return allocatedConnection;
}
// Attempt to get a connection from the pool.
RealConnection pooledConnection = Internal.instance.get(connectionPool, address, this);
if (pooledConnection != null) {
this.connection = pooledConnection;
return pooledConnection;
}
selectedRoute = route;
}
if (selectedRoute == null) {
selectedRoute = routeSelector.next();
synchronized (connectionPool) {
route = selectedRoute;
refusedStreamCount = 0;
}
}
RealConnection newConnection = new RealConnection(selectedRoute);
acquire(newConnection);
synchronized (connectionPool) {
Internal.instance.put(connectionPool, newConnection);
this.connection = newConnection;
if (canceled) throw new IOException(“Canceled”);
}
newConnection.connect(connectTimeout, readTimeout, writeTimeout, address.connectionSpecs(),
connectionRetryEnabled);
routeDatabase().connected(newConnection.route());
return newConnection;
}
这里大概分成分成3大步:
1)如果当前有连接并且符合要求的话，就直接返回
2)如果线程池能取到一个符合要求的连接的话，就直接返回
3)如果Route为空，从RouteSelector取一个Route，然后新建一个RealConnection，并放入ConnectionPool，随后调用connect，再返回
也就是说不管当前走的是步骤1还是2，一开始一定是从3开始的，也就是在RealConnection的connect中真正完成了socket连接。
connect里面代码比较长，真正要做的就是一件事，如果是https请求并且是http代理，则建立隧道连接，隧道连接请参考RFC2817，否则建立普通连接。
这两者都调用了2个函数:connectSocket(connectTimeout, readTimeout); establishProtocol(readTimeout, writeTimeout, connectionSpecSelector);
但是隧道连接则多了一个代理认证的过程，可能会反复的connectSocket和构造请求。
看一下connectSocket:
private void connectSocket(int connectTimeout, int readTimeout) 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);
rawSocket.setSoTimeout(readTimeout);
try {
Platform.get().connectSocket(rawSocket, route.socketAddress(), connectTimeout);
} catch (ConnectException e) {
throw new ConnectException(“Failed to connect to ” + route.socketAddress());
}
source = Okio.buffer(Okio.source(rawSocket));
sink = Okio.buffer(Okio.sink(rawSocket));
}
就是根据Route来创建socket，在connect，随后将rawSocket的InputStream与OutputStream包装成Source与Sink。这里提一下，OkHttp是依赖Okio的，Okio封装了Java的IO API，如这里的Source与Sink，非常简洁实用。
而establishProtocol里，如果是https则走TLS协议，生成一个SSLSocket，并进行握手和验证，同时如果是HTTP2或者SPDY3的话，则生成一个FrameConnection。这里不再多提，HTTP2和HTTP1.X大相径庭，我们这里主要是分析HTTP1.X的连接，后面有机会我们会单独开篇讲HTTP2。同时TLS相关的话题这里也一并略过，想了解的朋友可以看一看相应的Java API和HTTPS连接的资料。
再回到StreamAllcation.newStream的代码resultStream = new Http1xStream( client, this, resultConnection.source, resultConnection.sink);实质上HttpStream其实就是Request和Response读写Socket的抽象，我们看到Http1xStream取到了Socket输入输出流，随后在CallServerInterceptor可以拿来做读写。
我们看CallServerInterceptor做了什么:
@Override public Response intercept(Chain chain) throws IOException {
HttpStream httpStream = ((RealInterceptorChain) chain).httpStream();
StreamAllocation streamAllocation = ((RealInterceptorChain) chain).streamAllocation();
Request request = chain.request();
long sentRequestMillis = System.currentTimeMillis();
httpStream.writeRequestHeaders(request);
if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
Sink requestBodyOut = httpStream.createRequestBody(request, request.body().contentLength());
BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);
request.body().writeTo(bufferedRequestBody);
bufferedRequestBody.close();
}
httpStream.finishRequest();
Response response = httpStream.readResponseHeaders()
.request(request)
.handshake(streamAllocation.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
if (!forWebSocket || response.code() != 101) {
response = response.newBuilder()
.body(httpStream.openResponseBody(response))
.build();
}
if (“close”.equalsIgnoreCase(response.request().header(“Connection”))
|| “close”.equalsIgnoreCase(response.header(“Connection”))) {
streamAllocation.noNewStreams();
}
int code = response.code();
if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
throw new ProtocolException(
“HTTP ” + code + ” had non-zero Content-Length: ” + response.body().contentLength());
}
return response;
}
CallServerInterceptor顾名思义，就是真正和Server进行通信的地方。这里也是按照HTTP协议，依次写入请求头，还有根据情况决定是否写入请求体。随后读响应头闭构造一个Response。
里面具体是如何实现呢，我们看Http1xStream：
首先是写头:
@Override public void writeRequestHeaders(Request request) throws IOException {
String requestLine = RequestLine.get(
request, streamAllocation.connection().route().proxy().type());
writeRequest(request.headers(), requestLine);
}
构造好请求行，进入writeRequest:
/** Returns bytes of a request header for sending on an HTTP transport. */
public void writeRequest(Headers headers, String requestLine) throws IOException {
if (state != STATE_IDLE) throw new IllegalStateException(“state: ” + state);
sink.writeUtf8(requestLine).writeUtf8(“\r\n”);
for (int i = 0, size = headers.size(); i < size; i++) {
sink.writeUtf8(headers.name(i))
.writeUtf8(“: “)
.writeUtf8(headers.value(i))
.writeUtf8(“\r\n”);
}
sink.writeUtf8(“\r\n”);
state = STATE_OPEN_REQUEST_BODY;
}
这里就一目了然了，就是一行行的写请求行和请求头到sink中
再看readResponse:
/** Parses bytes of a response header from an HTTP transport. */
public Response.Builder readResponse() throws IOException {
if (state != STATE_OPEN_REQUEST_BODY && state != STATE_READ_RESPONSE_HEADERS) {
throw new IllegalStateException(“state: ” + state);
}
try {
while (true) {
StatusLine statusLine = StatusLine.parse(source.readUtf8LineStrict());
Response.Builder responseBuilder = new Response.Builder()
.protocol(statusLine.protocol)
.code(statusLine.code)
.message(statusLine.message)
.headers(readHeaders());
if (statusLine.code != HTTP_CONTINUE) {
state = STATE_OPEN_RESPONSE_BODY;
return responseBuilder;
}
}
} catch (EOFException e) {
// Provide more context if the server ends the stream before sending a response.
IOException exception = new IOException(“unexpected end of stream on ” + streamAllocation);
exception.initCause(e);
throw exception;
}
}
也是一样的，从source中读请求行和请求头
最后看openResponseBody:
@Override public ResponseBody openResponseBody(Response response) throws IOException {
Source source = getTransferStream(response);
return new RealResponseBody(response.headers(), Okio.buffer(source));
}
这里说一下就是根据请求的响应把包裹InputStream的source再次封装，里面做一些控制逻辑，然后再封装成ResponseBody。
例如FiexdLengthSource，就是期望获取到byte的长度是固定的值:
/** An HTTP body with a fixed length specified in advance. */
private class FixedLengthSource extends AbstractSource {
private long bytesRemaining;
public FixedLengthSource(long length) throws IOException {
bytesRemaining = length;
if (bytesRemaining == 0) {
endOfInput(true);
}
}
@Override public long read(Buffer sink, long byteCount) throws IOException {
if (byteCount < 0) throw new IllegalArgumentException(“byteCount < 0: ” + byteCount);
if (closed) throw new IllegalStateException(“closed”);
if (bytesRemaining == 0) return -1;
long read = source.read(sink, Math.min(bytesRemaining, byteCount));
if (read == -1) {
endOfInput(false); // The server didn’t supply the promised content length.
throw new ProtocolException(“unexpected end of stream”);
}
bytesRemaining -= read;
if (bytesRemaining == 0) {
endOfInput(true);
}
return read;
}
@Override public void close() throws IOException {
if (closed) return;
if (bytesRemaining != 0 && !Util.discard(this, DISCARD_STREAM_TIMEOUT_MILLIS, MILLISECONDS)) {
endOfInput(false);
}
closed = true;
}
}
当读完期望的长度时就把这个RealConnection回收，如果少于期望的长度则抛异常。
ConnectionPool
到了OkHttp3时代，ConnectionPool就是每个Client独享的了，我们刚才提到了ConnectionPool，那么他到底是如何运作呢。
ConnectionPool持有一个静态的线程池。
StreamAllocation不管通过什么方式，在获取到RealConnection后，RealConnection会添加一个对StreamAllocation的引用。
在每个RealConnection加入ConnectionPool后，如果当前没有在清理，就会把cleanUpRunnable加入线程池。
cleanUpRunnable里面是一个while(true),一个循环包括:
调用一次cleanUp方法进行清理并返回一个long, 如果是-1则退出，否则调用wait方法等待这个long值的时间
cleanUp代码如下:
ong cleanup(long now) {
int inUseConnectionCount = 0;
int idleConnectionCount = 0;
RealConnection longestIdleConnection = null;
long longestIdleDurationNs = Long.MIN_VALUE;
// Find either a connection to evict, or the time that the next eviction is due.
synchronized (this) {
for (Iterator<RealConnection> i = connections.iterator(); i.hasNext(); ) {
RealConnection connection = i.next();
// If the connection is in use, keep searching.
if (pruneAndGetAllocationCount(connection, now) > 0) {
inUseConnectionCount++;
continue;
}
idleConnectionCount++;
// If the connection is ready to be evicted, we’re done.
long idleDurationNs = now – connection.idleAtNanos;
if (idleDurationNs > longestIdleDurationNs) {
longestIdleDurationNs = idleDurationNs;
longestIdleConnection = connection;
}
}
if (longestIdleDurationNs >= this.keepAliveDurationNs
|| idleConnectionCount > this.maxIdleConnections) {
// We’ve found a connection to evict. Remove it from the list, then close it below (outside
// of the synchronized block).
connections.remove(longestIdleConnection);
} else if (idleConnectionCount > 0) {
// A connection will be ready to evict soon.
return keepAliveDurationNs – longestIdleDurationNs;
} else if (inUseConnectionCount > 0) {
// All connections are in use. It’ll be at least the keep alive duration ’til we run again.
return keepAliveDurationNs;
} else {
// No connections, idle or in use.
cleanupRunning = false;
return -1;
}
}
closeQuietly(longestIdleConnection.socket());
// Cleanup again immediately.
return 0;
}
遍历每一个RealConnection，通过引用数目确定哪些是空闲的，哪些是在使用中，同时找到空闲时间最长的RealConnection。
如果空闲数目超过最大空闲数或者空闲时间超过最大空闲时间，则清理掉这个RealConnection，并返回0，表示需要立刻再次清理
否则如果空闲的数目大于0个，则等待最大空闲时间-已有的最长空闲时间
否则如果使用中的数目大于0，则等待最大空闲时间
否则 返回 -1，并标识退出清除状态
同时如果某个RealConnection空闲后，会进入ConnectionPool.connectionBecameIdle方法,如果不可被复用，则被移除，否则立刻唤醒上面cleanUp的wait，再次清理，因为可能超过了最大空闲数目
这样通过一个静态的线程池，ConnectionPool做到了每个实例定期清理，保证不会超过最大空闲时间和最大空闲数目的策略。
OkHttp3分析就到此结束了。
