一般使用OKHttp的方法：
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder().url(url).build();
Response response = client.newCall(request).execute();
if (response.isSuccessful()) {
return response.body().string();
} else {
throw new IOException("Unexpected code " + response);
}
创建OKHttp
public OkHttpClient() {
this(new Builder());
}
private 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.proxySelector = builder.proxySelector;
this.cookieJar = builder.cookieJar;
this.cache = builder.cache;
this.internalCache = builder.internalCache;
this.socketFactory = builder.socketFactory;
boolean isTLS = false;
for (ConnectionSpec spec : connectionSpecs) {
isTLS = isTLS || spec.isTls();
}
if (builder.sslSocketFactory != null || !isTLS) {
this.sslSocketFactory = builder.sslSocketFactory;
this.certificateChainCleaner = builder.certificateChainCleaner;
} else {
X509TrustManager trustManager = systemDefaultTrustManager();
this.sslSocketFactory = systemDefaultSslSocketFactory(trustManager);
this.certificateChainCleaner = CertificateChainCleaner.get(trustManager);
}
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;
}
public Builder() {
dispatcher = new Dispatcher();
protocols = DEFAULT_PROTOCOLS;
connectionSpecs = DEFAULT_CONNECTION_SPECS;
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;
}
@Override public Call newCall(Request request) {
return new RealCall(this, request, false /* for web socket */);
}
newCall会创建一个RealCall对象。真正执行网络请求是调用它的execute方法：
@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);
}
}
先将Realcall加入到Dispatcher的runningSyncCalls中，主要是记录当前有哪些请求。然后调用getResponseWithInterceptorChain获取response，获取玩response后将realCall从Dispatcher中移除
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);
}
先创建一个Interceptor的列表，然后将列表创建一个RealInterceptorChain，调用chain的proceed方法。
public RealInterceptorChain(List<Interceptor> interceptors, StreamAllocation streamAllocation,
HttpCodec httpCodec, Connection connection, int index, Request request) {
this.interceptors = interceptors;
this.connection = connection; //null
this.streamAllocation = streamAllocation; //null
this.httpCodec = httpCodec; //null
this.index = index; //0
this.request = request;
}
public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
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.httpCodec != 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.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);
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");
}
return response;
}
假设没有用户自定义的Interceports，首先是调用retryAndFollowUpInterceptor的intercept方法，
@Override public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
streamAllocation = new StreamAllocation(
client.connectionPool(), createAddress(request.url()), callStackTrace);
int followUpCount = 0;
Response priorResponse = null;
while (true) {
if (canceled) {
streamAllocation.release();
throw new IOException("Canceled");
}
Response response = null;
boolean releaseConnection = true;
try {
response = ((RealInterceptorChain) chain).proceed(request, streamAllocation, null, null);
releaseConnection = false;
} catch (RouteException e) {
// The attempt to connect via a route failed. The request will not have been sent.
if (!recover(e.getLastConnectException(), true, request)) throw e.getLastConnectException();
releaseConnection = false;
continue;
} catch (IOException e) {
// An attempt to communicate with a server failed. The request may have been sent.
if (!recover(e, false, request)) throw e;
releaseConnection = false;
continue;
} finally {
// We're throwing an unchecked exception. Release any resources.
if (releaseConnection) {
streamAllocation.streamFailed(null);
streamAllocation.release();
}
}
// Attach the prior response if it exists. Such responses never have a body.
if (priorResponse != null) {
response = response.newBuilder()
.priorResponse(priorResponse.newBuilder()
.body(null)
.build())
.build();
}
Request followUp = followUpRequest(response);
if (followUp == null) {
if (!forWebSocket) {
streamAllocation.release();
}
return response;
}
closeQuietly(response.body());
if (++followUpCount > MAX_FOLLOW_UPS) {
streamAllocation.release();
throw new ProtocolException("Too many follow-up requests: " + followUpCount);
}
if (followUp.body() instanceof UnrepeatableRequestBody) {
streamAllocation.release();
throw new HttpRetryException("Cannot retry streamed HTTP body", response.code());
}
if (!sameConnection(response, followUp.url())) {
streamAllocation.release();
streamAllocation = new StreamAllocation(
client.connectionPool(), createAddress(followUp.url()), callStackTrace);
} else if (streamAllocation.codec() != null) {
throw new IllegalStateException("Closing the body of " + response
+ " didn't close its backing stream. Bad interceptor?");
}
request = followUp;
priorResponse = response;
}
}
先创建一个StreamAllocation，然后调用chain.proceed处理下一个interceptor，然后根据是否有异常进行重试或者，重定向。如果请求成功就返回response
看看StreamAllocation的构造函数
public StreamAllocation(ConnectionPool connectionPool, Address address, Object callStackTrace) {
this.connectionPool = connectionPool;
this.address = address;
this.routeSelector = new RouteSelector(address, routeDatabase());
this.callStackTrace = callStackTrace;
}
StreamAllocation主要是用于连接重用的
This class coordinates the relationship between three entities:
Connections: physical socket connections to remote servers. These are potentially slow to establish so it is necessary to be able to cancel a connection currently being connected.
Streams: logical HTTP request/response pairs that are layered on connections. Each connection has its own allocation limit, which defines how many concurrent streams that connection can carry. HTTP/1.x connections can carry 1 stream at a time, SPDY and HTTP/2 typically carry multiple.
Calls: a logical sequence of streams, typically an initial request and its follow up requests. We prefer to keep all streams of a single call on the same connection for better behavior and locality.
接下来调用BridgeInterceptor的intercept
@Override public Response intercept(Chain chain) throws IOException {
Request userRequest = chain.request();
Request.Builder requestBuilder = userRequest.newBuilder();
RequestBody body = userRequest.body();
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) {
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();
}
在这里面是在请求之前加了一些请求头，在收到response后如果content-encoding是gzip，则做gzip的解码。
然后是CacheInterceptor，主要看cache中有没有网络响应。
然后是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, doExtensiveHealthChecks);
RealConnection connection = streamAllocation.connection();
return realChain.proceed(request, streamAllocation, httpCodec, connection);
}
在这里调用streamAllocation将这个stream分配到connection上，然后生成一个HttpCodec，如果是http2.0，则分配Http2Codec，如果是1.1则分配Http1Codec
StreamAllocation.newStream
public HttpCodec 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);
HttpCodec resultCodec;
if (resultConnection.http2Connection != null) {
resultCodec = new Http2Codec(client, this, resultConnection.http2Connection);
} else {
resultConnection.socket().setSoTimeout(readTimeout);
resultConnection.source.timeout().timeout(readTimeout, MILLISECONDS);
resultConnection.sink.timeout().timeout(writeTimeout, MILLISECONDS);
resultCodec = new Http1Codec(
client, this, resultConnection.source, resultConnection.sink);
}
synchronized (connectionPool) {
codec = resultCodec;
return resultCodec;
}
} catch (IOException e) {
throw new RouteException(e);
}
}
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;
}
}
private RealConnection findConnection(int connectTimeout, int readTimeout, int writeTimeout,
boolean connectionRetryEnabled) throws IOException {
Route selectedRoute;
synchronized (connectionPool) {
if (released) throw new IllegalStateException("released");
if (codec != null) throw new IllegalStateException("codec != 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);
synchronized (connectionPool) {
acquire(newConnection);
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;
}
最终调用findConnection找到一个RealConnection。如果这个Call之前已经分配过RealConnection，则直接返回
RealConnection allocatedConnection = this.connection;
if (allocatedConnection != null && !allocatedConnection.noNewStreams) {
return allocatedConnection;
}
如果connectionPool中有符合条件的connection，则返回
RealConnection pooledConnection = Internal.instance.get(connectionPool, address, this);
if (pooledConnection != null) {
this.connection = pooledConnection;
return pooledConnection;
}
否则看是否有route, 没有的话就从routeSelector中选取一个，然后创建RealConnection，放入ConnectionPool中。注意同一OkhttpClient的所有请求都共享这个ConnectionPool。ConnectionPool最大idle的连接数是5，keepalive最长时间是5分钟，多余的connection会被清理掉。判断connection是不是idle是通过StreamAllocation.aquire和release方法将自己加入到connection的allocations变量中，如果allocation为空，说明没有stream跑在上面。
if (selectedRoute == null) {
selectedRoute = routeSelector.next();
synchronized (connectionPool) {
route = selectedRoute;
refusedStreamCount = 0;
}
}
RealConnection newConnection = new RealConnection(selectedRoute);
调用connection.connect方法
newConnection.connect(connectTimeout, readTimeout, writeTimeout, address.connectionSpecs(),
connectionRetryEnabled);
public void connect(int connectTimeout, int readTimeout, int writeTimeout,
List<ConnectionSpec> connectionSpecs, boolean connectionRetryEnabled) {
if (protocol != null) throw new IllegalStateException("already connected");
RouteException routeException = null;
ConnectionSpecSelector connectionSpecSelector = new ConnectionSpecSelector(connectionSpecs);
if (route.address().sslSocketFactory() == null) {
if (!connectionSpecs.contains(ConnectionSpec.CLEARTEXT)) {
throw new RouteException(new UnknownServiceException(
"CLEARTEXT communication not enabled for client"));
}
String host = route.address().url().host();
if (!Platform.get().isCleartextTrafficPermitted(host)) {
throw new RouteException(new UnknownServiceException(
"CLEARTEXT communication to " + host + " not permitted by network security policy"));
}
}
while (protocol == null) {
try {
if (route.requiresTunnel()) {
buildTunneledConnection(connectTimeout, readTimeout, writeTimeout,
connectionSpecSelector);
} else {
buildConnection(connectTimeout, readTimeout, writeTimeout, connectionSpecSelector);
}
} catch (IOException e) {
closeQuietly(socket);
closeQuietly(rawSocket);
socket = null;
rawSocket = null;
source = null;
sink = null;
handshake = null;
protocol = null;
if (routeException == null) {
routeException = new RouteException(e);
} else {
routeException.addConnectException(e);
}
if (!connectionRetryEnabled || !connectionSpecSelector.connectionFailed(e)) {
throw routeException;
}
}
}
}
如果是http连接，则会调用buildConnection
private void buildConnection(int connectTimeout, int readTimeout, int writeTimeout,
ConnectionSpecSelector connectionSpecSelector) throws IOException {
connectSocket(connectTimeout, readTimeout);
establishProtocol(readTimeout, writeTimeout, connectionSpecSelector);
}
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) {
ConnectException ce = new ConnectException("Failed to connect to " + route.socketAddress());
ce.initCause(e);
throw ce;
}
source = Okio.buffer(Okio.source(rawSocket));
sink = Okio.buffer(Okio.sink(rawSocket));
}
private void establishProtocol(int readTimeout, int writeTimeout,
ConnectionSpecSelector connectionSpecSelector) throws IOException {
if (route.address().sslSocketFactory() != null) {
connectTls(readTimeout, writeTimeout, connectionSpecSelector);
} else {
protocol = Protocol.HTTP_1_1;
socket = rawSocket;
}
if (protocol == Protocol.HTTP_2) {
socket.setSoTimeout(0); // Framed connection timeouts are set per-stream.
Http2Connection http2Connection = new Http2Connection.Builder(true)
.socket(socket, route.address().url().host(), source, sink)
.listener(this)
.build();
http2Connection.start();
// Only assign the framed connection once the preface has been sent successfully.
this.allocationLimit = http2Connection.maxConcurrentStreams();
this.http2Connection = http2Connection;
} else {
this.allocationLimit = 1;
}
}
connectSocket创建socket，然后OKIO创建source和sink，最后source和sink封装在httpCodec里的
最后是CallServerInterceptor
@Override public Response intercept(Chain chain) throws IOException {
HttpCodec httpCodec = ((RealInterceptorChain) chain).httpStream();
StreamAllocation streamAllocation = ((RealInterceptorChain) chain).streamAllocation();
Request request = chain.request();
long sentRequestMillis = System.currentTimeMillis();
httpCodec.writeRequestHeaders(request);
if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
Sink requestBodyOut = httpCodec.createRequestBody(request, request.body().contentLength());
BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);
request.body().writeTo(bufferedRequestBody);
bufferedRequestBody.close();
}
httpCodec.finishRequest();
Response response = httpCodec.readResponseHeaders()
.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;
}
通过HttpCodec来进行真正的通信。
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