简单的使用流程
OkHttpClient okhttpclient = new OkhttpClient.Builder()
.readTimeout(READ_TIME_OUT_VALUE, TimeUnit.SECONDS)
.writeTimeout(WRITE_TIME_OUT_VALUE, TimeUnit.SECONDS)
.build();
Request.Builder builder = new Request.Builder();
Request request = builder.url(httpUrl).get().build();
Call call = okhttpclient.newCall(request);
try{
Response response = call.execute();
} catch (IOException e){
//异常处理
}
从newCall出发深入源码
/**
* 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 */);
}
我们继续查看RealCall.newRealCall
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;
}
RealCall是Call的一个实现，Response是call的execute()方法得到的，我们接下来继续跟踪RealCall的execute方法。
@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);
}
}
方法中我们可以看到Response通过getResponseWithInterceptorChain()得到，下面是其源码：
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);
}
经过中间的一系列步骤，最终返回的是chain.proceed(originalRequest)，那我们继续跟踪查看RealInterceptorChain并找到proceed方法的内容：
public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
RealConnection 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.httpCodec != null && !this.connection.supportsUrl(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.httpCodec != 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, httpCodec,
connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
writeTimeout);
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);
// Confirm that the next interceptor made its required call to chain.proceed().
if (httpCodec != 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");
}
if (response.body() == null) {
throw new IllegalStateException(
"interceptor " + interceptor + " returned a response with no body");
}
return response;
}
通过上面的代码，我们发现Response response = interceptor.intercept(next);最终的请求结果是由interceptor.intercept()得到的，我们回想上一个getResponseWithInterceptorChain方法中所添加的一系列Interceptor
我们根据变量或类名称推测建立连接的是ConnectInterceptor，我们查看一下它的具体内容：
/** Opens a connection to the target server and proceeds to the next interceptor. */
/** 打开一个到目标服务器的连接，并进入下一个interceptor.*/
public final class ConnectInterceptor implements Interceptor {
public final OkHttpClient client;
public ConnectInterceptor(OkHttpClient client) {
this.client = client;
}
@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);
}
}
代码中可以看到，OkHttpClient通过RealConnection connection = streamAllocation.connection();建立了一个连接。
我们查看RealConnection类：
public final class RealConnection extends Http2Connection.Listener implements Connection {
private static final String NPE_THROW_WITH_NULL = "throw with null exception";
private static final int MAX_TUNNEL_ATTEMPTS = 21;
private final ConnectionPool connectionPool;
private final Route route;
// The fields below are initialized by connect() and never reassigned.
/** The low-level TCP socket. */
private Socket rawSocket;
/**
* The application layer socket. Either an {@link SSLSocket} layered over {@link #rawSocket}, or
* {@link #rawSocket} itself if this connection does not use SSL.
*/
private Socket socket;
......
}
我们在代码中找到了比较重要的信息Socket，基本可以证明，Okhttp3的底层是Socket实现的。
到这里不妨回忆一下我们所经历的步骤，一切都与RealInterceptorChain有很大的关系，OkhttpClient通过不断地执行它的proceed方法，反复的修饰了我们的网络请求。
经过百度搜索，我发现这样一篇文章Okhttp3源码分析
终于明白了它文章开篇的这个Okhttp请求流程图：
请求流程图
至此，我们了解了Okhttp3的简单实用，以及它的底层是通过Socket实现的，并且认识了它的拦截器链RealInterceptorChain，下一步从异步与多线程入手，再次学习Okhttp3源码。
