一、okhttp使用简介
1.创建一个OkHttpClient对象
2.创建一个request对象，通过内部类Builder调用生成Request对象
3.创建一个Call对象，调用execute(同步)/enqueue(异步)
4.返回Response对象，对Response对象进行处理
//第一步
private final OkHttpClient client = new OkHttpClient();
//第二步
Request request = new Request.Builder()
.url("http://www.baidu.com").build();
//同步请求
public void okHttpAsycGet() throws IOException {
//第三步
Response response = client.newCall(request).execute();
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}
//异步请求
public void okHttpSyncGet() throws IOException {
//第三步
client.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
e.printStackTrace();
}
@Override
public void onResponse(Call call, Response response) throws IOException {
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}
});
}
二、okhttp代码分析
同步方法代码分析
在client.newCall(request).execute();代码中的newCall方法实现如下：
@Override
public Call newCall(Request request) {
return new RealCall(this, request, false /* for web socket */);
}
newCall()方法会返回一个RealCall对象，RealCall中的execute()方法实现如下：
@Override
public Response execute() throws IOException {
synchronized (this) { //方法检测，execute()只会执行一次
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
try {
client.dispatcher().executed(this); //将RealCall添加到Dispatcher中的同步请求队列中
Response result = getResponseWithInterceptorChain(); //获取Response
if (result == null) throw new IOException("Canceled");
return result; //返回Response
} finally {
client.dispatcher().finished(this); //通知Dispatcher该RealCall已执行完
}
}
其中的获取Response的关键方法getResponseWithInterceptorChain()实现如下：
Response getResponseWithInterceptorChain() throws IOException {
// Build a full stack of interceptors.
List<Interceptor> interceptors = new ArrayList<>(); //拦截器栈
interceptors.addAll(client.interceptors()); //添加client中的所有拦截器
interceptors.add(retryAndFollowUpInterceptor); //失败重试拦截器
interceptors.add(new BridgeInterceptor(client.cookieJar())); //桥接拦截器
interceptors.add(new CacheInterceptor(client.internalCache())); //缓存拦截器
interceptors.add(new ConnectInterceptor(client)); //与服务器进行连接的拦截器
if (!forWebSocket) {
interceptors.addAll(client.networkInterceptors()); //网络拦截器
}
interceptors.add(new CallServerInterceptor(forWebSocket)); //网络服务端连接拦截器
Interceptor.Chain chain = new RealInterceptorChain(
interceptors, null, null, null, 0, originalRequest); //将拦截器栈连成链
return chain.proceed(originalRequest);
}
异步方法代码分析
newCall()方法会返回一个RealCall对象，RealCall中的enqueue()方法实现如下：
@Override
public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
可以看到，方法的最后调用了Dispatcher的enqueue()方法，该方法的具体实现如下：
/** Ready async calls in the order they'll be run. */
private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>(); //准备中的异步队列
/** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>(); //运行中的异步队列
/** Running synchronous calls. Includes canceled calls that haven't finished yet. */
private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>(); //运行中的同步队列
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) { //若当前正在运行的异步队列可容纳新的任务
runningAsyncCalls.add(call); //添加回调方法到正在运行中的异步队列
executorService().execute(call); //使用线程池执行该回调方法
} else {
readyAsyncCalls.add(call); //添加回调方法到准备中的异步方法
}
}
