由上篇分析了Ok请求的执行流程知道，无论是同步还是异步，最终得到网络响应，都是通过调用getResponseWithInterceptorChain() 来获取的，其内部实现了一条拦截器链。下面开始分析源码内部的5个拦截器的调用，以及网络数据的请求流程。
final class RealCall implements Call {
//构造一条拦截器链
Response getResponseWithInterceptorChain() throws IOException {
// 构建一个列表来存放所有的拦截器
List<Interceptor> interceptors = new ArrayList<>();
//用户自定义的拦截器
interceptors.addAll(client.interceptors());
//重定向拦截器
interceptors.add(retryAndFollowUpInterceptor);
//桥接拦截器
interceptors.add(new BridgeInterceptor(client.cookieJar()));
//缓存拦截器
interceptors.add(new CacheInterceptor(client.internalCache()));
//连接拦截器
interceptors.add(new ConnectInterceptor(client));
if (!forWebSocket) {
interceptors.addAll(client.networkInterceptors());
}
//网络请求拦截器
interceptors.add(new CallServerInterceptor(forWebSocket));
//根据列表中的拦截器，开始构造一条拦截器链。
Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
originalRequest, this, eventListener, client.connectTimeoutMillis(),
client.readTimeoutMillis(), client.writeTimeoutMillis());
//开始整条链的调用
return chain.proceed(originalRequest);
}
用户可以自定义自己的拦截器，并被首先添加到列表中，系统内部自己实现了5个重要的拦截器，分别是RetryAndFollowUpInterceptor、BridgeInterceptor、CacheInterceptor、ConnectInterceptor和CallServerInterceptor，整个拦截器链正是通过这5个拦截器串联起来的。我们首先看proceed方法，它接收了我们构造的Request对象。
public interface Interceptor {
Response intercept(Chain chain) throws IOException;
interface Chain {
Request request();
Response proceed(Request request) throws IOException;
......
}
}
Interceptor 是拦截器的接口，由子类实现不同拦截器。Chain 是其内部类，它由RealInterceptorChain，构成链的节点。
public final class RealInterceptorChain implements Interceptor.Chain {
private final List<Interceptor> interceptors;
private final StreamAllocation streamAllocation;
private final HttpCodec httpCodec;
private final RealConnection connection;
private final int index;//链节的角标
private final Request request;//保存Request
private final Call call;//保存RealCall
private final EventListener eventListener;
private final int connectTimeout;
private final int readTimeout;
private final int writeTimeout;
private int calls;
public RealInterceptorChain(List<Interceptor> interceptors, StreamAllocation streamAllocation,
HttpCodec httpCodec, RealConnection connection, int index, Request request, Call call,
EventListener eventListener, int connectTimeout, int readTimeout, int writeTimeout) {
this.interceptors = interceptors;
this.connection = connection;
this.streamAllocation = streamAllocation;
this.httpCodec = httpCodec;
this.index = index;
this.request = request;
this.call = call;
this.eventListener = eventListener;
this.connectTimeout = connectTimeout;
this.readTimeout = readTimeout;
this.writeTimeout = writeTimeout;
}
//调用4参的proceed
@Override public Response proceed(Request request) throws IOException {
return proceed(request, streamAllocation, httpCodec, connection);
}
public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
RealConnection connection) throws IOException {
if (index >= interceptors.size()) throw new AssertionError();
calls++;
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 (this.httpCodec != null && calls > 1) {
throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
+ " must call proceed() exactly once");
}
//构建下一链节，角标加1
RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
writeTimeout);
//从列表取出第一个拦截器
Interceptor interceptor = interceptors.get(index);
//调用intercept，将下一链节传入
Response response = interceptor.intercept(next);
if (httpCodec != null && index + 1 < interceptors.size() && next.calls != 1) {
throw new IllegalStateException("network interceptor " + interceptor
+ " must call proceed() exactly once");
}
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;
}
}
拦截器链的整体结构类似链表，RealInterceptorChain相当于链表节点对象，封装了拦截器，每个节点，由上一个节点构造而来。假设我们没有自定义自己的拦截器，则第一链节会取出RetryAndFollowUpInterceptor，并构造下一个节点RealInterceptorChain，调用intercept方法，将节点传入。
//重定向拦截器
public final class RetryAndFollowUpInterceptor implements Interceptor {
//失败重连的最大次数
private static final int MAX_FOLLOW_UPS = 20;
@Override public Response intercept(Chain chain) throws IOException {
//从成员变量获取Request
Request request = chain.request();
RealInterceptorChain realChain = (RealInterceptorChain) chain;
//从成员变量获取RealCall
Call call = realChain.call();
EventListener eventListener = realChain.eventListener();
//用于服务端数据的传输
StreamAllocation streamAllocation = new StreamAllocation(client.connectionPool(),
createAddress(request.url()), call, eventListener, callStackTrace);
this.streamAllocation = streamAllocation;
//重连累计次数
int followUpCount = 0;
Response priorResponse = null;
while (true) {
if (canceled) {
streamAllocation.release();
throw new IOException("Canceled");
}
Response response;
boolean releaseConnection = true;
try {
//调用proceed，取出第二个拦截器，和构造第三个节点
response = realChain.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(), streamAllocation, false, request)) {
throw e.getFirstConnectException();
}
releaseConnection = false;
continue;
} catch (IOException e) {
// An attempt to communicate with a server failed. The request may have been sent.
boolean requestSendStarted = !(e instanceof ConnectionShutdownException);
if (!recover(e, streamAllocation, requestSendStarted, 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;
try {
followUp = followUpRequest(response, streamAllocation.route());
} catch (IOException e) {
streamAllocation.release();
throw e;
}
if (followUp == null) {
streamAllocation.release();
return response;
}
closeQuietly(response.body());
//重连超过20次则断开连接
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()), call, eventListener, callStackTrace);
this.streamAllocation = streamAllocation;
} 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;
}
}
}
StreamAllocation用于和服务端数据传输，但在这一个链节不会用到，会在 ConnectInterceptor这一节使用到。
proceed的执行类似递归，取出了第二个拦截器并构造了第三个，就是通过这种方式构建整条拦截器链，由最后的链节获得Response 响应数据，回溯返回。这一节如果失败了，会进行循环重试，超过最大次数20次，则释放资源。
由拦截器列表添加顺序知道，下一个拦截器为BridgeInterceptor。
public final class BridgeInterceptor implements Interceptor {
private final CookieJar cookieJar;
public BridgeInterceptor(CookieJar cookieJar) {
this.cookieJar = cookieJar;
}
@Override public Response intercept(Chain chain) throws IOException {
Request userRequest = chain.request();
Request.Builder requestBuilder = userRequest.newBuilder();
RequestBody body = userRequest.body();
//添加请求头信息
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");
}
boolean transparentGzip = false;
if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == 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());
}
//交由下一个拦截器去做请求
Response networkResponse = chain.proceed(requestBuilder.build());
//转化成客户端可以使用的Response
HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());
Response.Builder responseBuilder = networkResponse.newBuilder()
.request(userRequest);
//解压缩包
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);
String contentType = networkResponse.header("Content-Type");
responseBuilder.body(new RealResponseBody(contentType, -1L, Okio.buffer(responseBody)));
}
return responseBuilder.build();
}
private String cookieHeader(List<Cookie> cookies) {
StringBuilder cookieHeader = new StringBuilder();
for (int i = 0, size = cookies.size(); i < size; i++) {
if (i > 0) {
cookieHeader.append("; ");
}
Cookie cookie = cookies.get(i);
cookieHeader.append(cookie.name()).append('=').append(cookie.value());
}
return cookieHeader.toString();
}
}
BridgeInterceptor 主要是为用户的Request请求添加请求头等信息，转化为标准的网络请求。接收到响应数据后，解压或解析成客户端方便使用的数据格式。下一请求环节将交由CacheInterceptor。
OkHttpClient okHttpClient = new OkHttpClient.Builder()
.readTimeout( 5, TimeUnit.SECONDS )
.cache( new Cache( new File( "cache" ),20*1024*1024 ) )//缓存大小
.build();
在构建OkHttpClient 时，我们传入了Cache对象来做缓存设置，先来看Cache类的实现。
//缓存类
public final class Cache implements Closeable, Flushable {
private static final int VERSION = 201105;
private static final int ENTRY_METADATA = 0;
private static final int ENTRY_BODY = 1;
private static final int ENTRY_COUNT = 2;
//内部类实现了InternalCache接口，实际方法都由Cache 类实现
final InternalCache internalCache = new InternalCache() {
@Override public Response get(Request request) throws IOException {
return Cache.this.get(request);
}
@Override public CacheRequest put(Response response) throws IOException {
return Cache.this.put(response);
}
@Override public void remove(Request request) throws IOException {
Cache.this.remove(request);
}
@Override public void update(Response cached, Response network) {
Cache.this.update(cached, network);
}
@Override public void trackConditionalCacheHit() {
Cache.this.trackConditionalCacheHit();
}
@Override public void trackResponse(CacheStrategy cacheStrategy) {
Cache.this.trackResponse(cacheStrategy);
}
};
//put缓存方法
@Nullable CacheRequest put(Response response) {
//获取请求方式
String requestMethod = response.request().method();
//如果是"POST""PATCH""PUT""DELETE""MOVE"的请求方式，则不缓存
if (HttpMethod.invalidatesCache(response.request().method())) {
try {
remove(response.request());
} catch (IOException ignored) {
// The cache cannot be written.
}
return null;
}
//只缓存get方式
if (!requestMethod.equals("GET")) {
return null;
}
if (HttpHeaders.hasVaryAll(response)) {
return null;
}
//实际用了DiskLruCache缓存
Entry entry = new Entry(response);
DiskLruCache.Editor editor = null;
try {
editor = cache.edit(key(response.request().url()));
if (editor == null) {
return null;
}
//缓存请求方式和路径等
entry.writeTo(editor);
//缓存请求body
return new CacheRequestImpl(editor);
} catch (IOException e) {
abortQuietly(editor);
return null;
}
}
//get获取缓存内容方法
Response get(Request request) {
String key = key(request.url());//获取key
DiskLruCache.Snapshot snapshot;//缓存快照
Entry entry;//缓存Entry
try {
snapshot = cache.get(key);//通过key获取缓存快照
if (snapshot == null) {
return null;
}
} catch (IOException e) {
return null;
}
try {
entry = new Entry(snapshot.getSource(ENTRY_METADATA));//如果缓存快照存在，那么构造Entry
} catch (IOException e) {
Util.closeQuietly(snapshot);
return null;
}
Response response = entry.response(snapshot);//通过快缓存照获取响应体
if (!entry.matches(request, response)) {
Util.closeQuietly(response.body());
return null;
}
return response;
}
}
//缓存内部类
private final class CacheRequestImpl implements CacheRequest {
private final DiskLruCache.Editor editor;
private Sink cacheOut;
private Sink body;
boolean done;
CacheRequestImpl(final DiskLruCache.Editor editor) {
this.editor = editor;
this.cacheOut = editor.newSink(ENTRY_BODY);
this.body = new ForwardingSink(cacheOut) {
@Override public void close() throws IOException {
synchronized (Cache.this) {
if (done) {
return;
}
done = true;
writeSuccessCount++;
}
super.close();
editor.commit();
}
};
}
@Override public void abort() {
synchronized (Cache.this) {
if (done) {
return;
}
done = true;
writeAbortCount++;
}
Util.closeQuietly(cacheOut);
try {
editor.abort();
} catch (IOException ignored) {
}
}
@Override public Sink body() {
return body;
}
}
}
InternalCache是一个接口，定义了缓存的各项操作，Cache 定义了一个匿名内部类来实现缓存的操作。
从缓存put/get方法分析可以看出，内部缓存实现是DiskLruCache缓存，并且只缓存Get请求方式。
CacheRequestImpl类进行了缓存封装，它实现了CacheRequest 接口，用来暴露给缓存拦截器进行缓存操作。
public final class CacheInterceptor implements Interceptor {
final InternalCache cache;
public CacheInterceptor(InternalCache cache) {
this.cache = cache;
}
@Override public Response intercept(Chain chain) throws IOException {
//缓存不为null则从缓存获取
Response cacheCandidate = cache != null
? cache.get(chain.request())
: null;
long now = System.currentTimeMillis();
//是获取网络还是获取缓存
CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
Request networkRequest = strategy.networkRequest;
Response cacheResponse = strategy.cacheResponse;
//对缓存的名字进行次数累计
if (cache != null) {
cache.trackResponse(strategy);
}
if (cacheCandidate != null && cacheResponse == null) {
closeQuietly(cacheCandidate.body());
}
// 没有网络，也没有缓存，手动构造Response，返回504
if (networkRequest == null && cacheResponse == null) {
return new Response.Builder()
.request(chain.request())
.protocol(Protocol.HTTP_1_1)
.code(504)
.message("Unsatisfiable Request (only-if-cached)")
.body(Util.EMPTY_RESPONSE)
.sentRequestAtMillis(-1L)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
}
// 没有网络，但有缓存，将缓存数据返回
if (networkRequest == null) {
return cacheResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build();
}
Response networkResponse = null;
try {
//交由下一个环请求操作
networkResponse = chain.proceed(networkRequest);
} finally {
//关闭缓存资源
if (networkResponse == null && cacheCandidate != null) {
closeQuietly(cacheCandidate.body());
}
}
// 有网络，这里再次判断是否要使用缓存
if (cacheResponse != null) {
//状态码304，获取缓存
if (networkResponse.code() == HTTP_NOT_MODIFIED) {
Response response = cacheResponse.newBuilder()
.headers(combine(cacheResponse.headers(), networkResponse.headers()))
.sentRequestAtMillis(networkResponse.sentRequestAtMillis())
.receivedResponseAtMillis(networkResponse.receivedResponseAtMillis())
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build();
networkResponse.body().close();
cache.trackConditionalCacheHit();
cache.update(cacheResponse, response);
return response;
} else {
closeQuietly(cacheResponse.body());
}
}
//最终没有缓存，则构造网络获取的数据返回
Response response = networkResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build();
if (cache != null) {
if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) {
//将数据缓存起来
CacheRequest cacheRequest = cache.put(response);
return cacheWritingResponse(cacheRequest, response);
}
if (HttpMethod.invalidatesCache(networkRequest.method())) {
try {
cache.remove(networkRequest);
} catch (IOException ignored) {
// The cache cannot be written.
}
}
}
return response;
}
CacheInterceptor 通过获取缓存和网络请求两种策略进行比对，来决定是采用缓存数据还是网络数据，并在最后将数据缓存起来，以便下次获取。
如果当前网络没有问题，下个拦截器将通过连接复用的方式，获取到一个网络连接RealConnection ，以供最后一个拦截器做网络请求，获取连接的拦截器为ConnectInterceptor。
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在RetryAndFollowUpInterceptor中创建
StreamAllocation streamAllocation = realChain.streamAllocation();
boolean doExtensiveHealthChecks = !request.method().equals("GET");
//HttpCodec为一个接口，对应HttpCodec1和HttpCodec2，即1.0和2.0,主要用于编码request和解码response。并且和服务端建立了连接
HttpCodec httpCodec = streamAllocation.newStream(client, chain, doExtensiveHealthChecks);
RealConnection connection = streamAllocation.connection();
//传递给CallServerInterceptor拦截器
return realChain.proceed(request, streamAllocation, httpCodec, connection);
}
}
public final class StreamAllocation {
public final Address address;
private RouteSelector.Selection routeSelection;
private Route route;
private final ConnectionPool connectionPool;//连接池
public final Call call;
public final EventListener eventListener;
private final Object callStackTrace;
private final RouteSelector routeSelector;
private int refusedStreamCount;
private RealConnection connection;
private boolean reportedAcquired;
private boolean released;
private boolean canceled;
private HttpCodec codec;
public StreamAllocation(ConnectionPool connectionPool, Address address, Call call,
EventListener eventListener, Object callStackTrace) {
this.connectionPool = connectionPool;
this.address = address;
this.call = call;
this.eventListener = eventListener;
this.routeSelector = new RouteSelector(address, routeDatabase(), call, eventListener);
this.callStackTrace = callStackTrace;
}
public HttpCodec newStream(OkHttpClient client, Interceptor.Chain chain, boolean doExtensiveHealthChecks) {
int connectTimeout = chain.connectTimeoutMillis();
int readTimeout = chain.readTimeoutMillis();
int writeTimeout = chain.writeTimeoutMillis();
int pingIntervalMillis = client.pingIntervalMillis();
boolean connectionRetryEnabled = client.retryOnConnectionFailure();
try {
//获得连接类，用于网络连接
RealConnection resultConnection = findHealthyConnection(connectTimeout, readTimeout,
writeTimeout, pingIntervalMillis, connectionRetryEnabled, doExtensiveHealthChecks);
//获得编解码器
HttpCodec resultCodec = resultConnection.newCodec(client, chain, this);
synchronized (connectionPool) {
codec = resultCodec;
return resultCodec;
}
} catch (IOException e) {
throw new RouteException(e);
}
}
//获取连接器
private RealConnection findHealthyConnection(int connectTimeout, int readTimeout,
int writeTimeout, int pingIntervalMillis, boolean connectionRetryEnabled,
boolean doExtensiveHealthChecks) throws IOException {
//死循环查找
while (true) {
RealConnection candidate = findConnection(connectTimeout, readTimeout, writeTimeout,
pingIntervalMillis, connectionRetryEnabled);
//如果successCount 为0，说明可用，结束循环
synchronized (connectionPool) {
if (candidate.successCount == 0) {
return candidate;
}
}
//如果这个连接无效(比如流没关闭)，则回收，寻找下一个
if (!candidate.isHealthy(doExtensiveHealthChecks)) {
noNewStreams();
continue;
}
return candidate;
}
}
}
//获取一个RealConnection 链接
private RealConnection findConnection(int connectTimeout, int readTimeout, int writeTimeout,
int pingIntervalMillis, boolean connectionRetryEnabled) throws IOException {
boolean foundPooledConnection = false;
RealConnection result = null;
Route selectedRoute = null;
Connection releasedConnection;
Socket toClose;
synchronized (connectionPool) {
if (released) throw new IllegalStateException("released");
if (codec != null) throw new IllegalStateException("codec != null");
if (canceled) throw new IOException("Canceled");
//看是否能复用connection
releasedConnection = this.connection;
toClose = releaseIfNoNewStreams();
if (this.connection != null) {
result = this.connection;
releasedConnection = null;
}
if (!reportedAcquired) {
releasedConnection = null;
}
//不能复用说明为null，从池里获取新的
if (result == null) {
// 假设连接池中可用的，第一次尝试获取一个
Internal.instance.get(connectionPool, address, this, null);
if (connection != null) {
foundPooledConnection = true;
result = connection;
} else {
selectedRoute = route;
}
}
}
closeQuietly(toClose);
if (releasedConnection != null) {
eventListener.connectionReleased(call, releasedConnection);
}
//foundPooledConnection为true，说明第一次尝试找到了
if (foundPooledConnection) {
eventListener.connectionAcquired(call, result);
}
//成功获取则返回
if (result != null) {
return result;
}
//不能复用，连接池也没有，则下面将获取一个新的路由
boolean newRouteSelection = false;
if (selectedRoute == null && (routeSelection == null || !routeSelection.hasNext())) {
newRouteSelection = true;
routeSelection = routeSelector.next();
}
synchronized (connectionPool) {
if (canceled) throw new IOException("Canceled");
if (newRouteSelection) {
//获取新的路由，并第二次尝试从池中获取
List<Route> routes = routeSelection.getAll();
for (int i = 0, size = routes.size(); i < size; i++) {
Route route = routes.get(i);
Internal.instance.get(connectionPool, address, this, route);
if (connection != null) {
foundPooledConnection = true;
result = connection;
this.route = route;
break;
}
}
}
//新建一个链接
if (!foundPooledConnection) {
if (selectedRoute == null) {
selectedRoute = routeSelection.next();
}
route = selectedRoute;
refusedStreamCount = 0;
//构建新的RealConnection
result = new RealConnection(connectionPool, selectedRoute);
acquire(result, false);
}
}
// foundPooledConnection为true，说明第二次尝试找到了
if (foundPooledConnection) {
eventListener.connectionAcquired(call, result);
return result;
}
// 建立新的连接
result.connect(connectTimeout, readTimeout, writeTimeout, pingIntervalMillis,
connectionRetryEnabled, call, eventListener);
routeDatabase().connected(result.route());
Socket socket = null;
synchronized (connectionPool) {
reportedAcquired = true;
// 将连接放入池中
Internal.instance.put(connectionPool, result);
if (result.isMultiplexed()) {
socket = Internal.instance.deduplicate(connectionPool, address, this);
result = connection;
}
}
closeQuietly(socket);
eventListener.connectionAcquired(call, result);
return result;
}
findConnection获取一个链接做了多次尝试，如下：
1，先判断了当前的连接是否能复用，能复用则返回；
2，不能复用，第一次尝试从连接池获取，获取到了则返回；
3，第一次连接池获取失败，取下一个路由，并第二次尝试从连接池获取，获取到则返回；
4，第二次尝试获取失败，则新建一个链接，并把连接缓存到连接池中。
下面来看下是如何从ConnectionPool 连接池中获取到一个链接，和一个新链接如何缓存到池中的。
public final class ConnectionPool {
//线程池
private static final Executor executor = new ThreadPoolExecutor(0 /* corePoolSize */,
Integer.MAX_VALUE /* maximumPoolSize */, 60L /* keepAliveTime */, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp ConnectionPool", true));
//
private final int maxIdleConnections;
private final long keepAliveDurationNs;
//缓存队列
private final Deque<RealConnection> connections = new ArrayDeque<>();
//从池里获取连接
@Nullable RealConnection get(Address address, StreamAllocation streamAllocation, Route route) {
assert (Thread.holdsLock(this));
//遍历队列判断是否符合条件
for (RealConnection connection : connections) {
//根据地址和路由判断是否可用
if (connection.isEligible(address, route)) {
//如果符合则
streamAllocation.acquire(connection, true);
return connection;
}
}
return null;
}
public final class StreamAllocation {
//保存当前获取到的connection
private RealConnection connection;
public void acquire(RealConnection connection, boolean reportedAcquired) {
assert (Thread.holdsLock(connectionPool));
if (this.connection != null) throw new IllegalStateException();
//将符合条件的connection赋值给成员变量
this.connection = connection;
this.reportedAcquired = reportedAcquired;
//将当前StreamAllocation 添加到RealConnection 的弱引用列表中
connection.allocations.add(new StreamAllocationReference(this, callStackTrace));
}
}
public final class RealConnection extends Http2Connection.Listener implements Connection {
//弱引用列表
public final List<Reference<StreamAllocation>> allocations = new ArrayList<>();
连接池get方法，是通过遍历缓存队列ArrayDeque，根据地址和路由，判断是否有可用的连接，如果找到了，则调用StreamAllocation 的acquire方法，将connection 保存到成员变量中，同时将当前的StreamAllocation 对象封装成弱引用，加入到RealConnection 的成员列表allocations 中。这个列表的个数就是用来判断我们的最大连接数是否超过64个的。
下面看连接池如何缓存新建的RealConnection，即put方法：
public final class ConnectionPool {
//线程池
private static final Executor executor = new ThreadPoolExecutor(0 /* corePoolSize */,
Integer.MAX_VALUE /* maximumPoolSize */, 60L /* keepAliveTime */, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp ConnectionPool", true));
//
private final int maxIdleConnections;
private final long keepAliveDurationNs;
//缓存队列
private final Deque<RealConnection> connections = new ArrayDeque<>();
//缓存RealConnection
void put(RealConnection connection) {
assert (Thread.holdsLock(this));
//标记清除算法来回收RealConnection
if (!cleanupRunning) {
cleanupRunning = true;
executor.execute(cleanupRunnable);
}
//将新的RealConnection 添加到队列中
connections.add(connection);
}
}
//回收线程
private final Runnable cleanupRunnable = new Runnable() {
@Override public void run() {
while (true) {
//与下一次需要清理的间隔时间，cleanup做清除
long waitNanos = cleanup(System.nanoTime());
if (waitNanos == -1) return;
if (waitNanos > 0) {
long waitMillis = waitNanos / 1000000L;
waitNanos -= (waitMillis * 1000000L);
synchronized (ConnectionPool.this) {
try {
//等待waitNanos后再次做清除
ConnectionPool.this.wait(waitMillis, (int) waitNanos);
} catch (InterruptedException ignored) {
}
}
}
}
}
};
//实际做回收的方法
long cleanup(long now) {
//记录活跃的连接数
int inUseConnectionCount = 0;
//记录空闲的连接数
int idleConnectionCount = 0;
//空闲时间最长的连接
RealConnection longestIdleConnection = null;
long longestIdleDurationNs = Long.MIN_VALUE;
// 遍历队列
synchronized (this) {
for (Iterator<RealConnection> i = connections.iterator(); i.hasNext(); ) {
RealConnection connection = i.next();
// 返回0说明连接正在使用，则inUseConnectionCount加1，获取下一个连接
if (pruneAndGetAllocationCount(connection, now) > 0) {
inUseConnectionCount++;
continue;
}
//说明空闲，空闲连接加1
idleConnectionCount++;
// 找出了空闲时间最长的连接，准备移除
long idleDurationNs = now - connection.idleAtNanos;
if (idleDurationNs > longestIdleDurationNs) {
longestIdleDurationNs = idleDurationNs;
longestIdleConnection = connection;
}
}
//如果空闲时间最长的连接的空闲时间超过了5分钟，或是空闲的连接数超过了限制，就移除
if (longestIdleDurationNs >= this.keepAliveDurationNs
|| idleConnectionCount > this.maxIdleConnections) {
//从队列移除
connections.remove(longestIdleConnection);
} else if (idleConnectionCount > 0) {
//如果存在空闲连接但是还没有超过5分钟，就返回剩下的时间，便于下次进行清理
return keepAliveDurationNs - longestIdleDurationNs;
} else if (inUseConnectionCount > 0) {
// 如果没有空闲的连接，那就等5分钟后再尝试清理
return keepAliveDurationNs;
} else {
// 当前没有任何连接，就返回-1，跳出循环
cleanupRunning = false;
return -1;
}
}
closeQuietly(longestIdleConnection.socket());
return 0;
}
//判断当前连接是否正在使用
private int pruneAndGetAllocationCount(RealConnection connection, long now) {
//获取软引用列表
List<Reference<StreamAllocation>> references = connection.allocations;
//遍历
for (int i = 0; i < references.size(); ) {
Reference<StreamAllocation> reference = references.get(i);
//如果存在引用，就说明是活跃连接，就继续看下一个StreamAllocation
if (reference.get() != null) {
i++;
continue;
}
StreamAllocation.StreamAllocationReference streamAllocRef =
(StreamAllocation.StreamAllocationReference) reference;
String message = "A connection to " + connection.route().address().url()
+ " was leaked. Did you forget to close a response body?";
Platform.get().logCloseableLeak(message, streamAllocRef.callStackTrace);
//如果没有引用，就移除
references.remove(i);
connection.noNewStreams = true;
// 如果列表为空，就说明此连接上没有StreamAllocation引用了，就返回0，表示是空闲的连接
if (references.isEmpty()) {
connection.idleAtNanos = now - keepAliveDurationNs;
return 0;
}
}
//遍历结束后，返回引用的数量，说明当前连接是活跃连接
return references.size();
}
}
Ok中支持5个并发socket连接，默认的keepAlive时间为5分钟，也可以在构建OkHttpClient时设置。向连接池添加新的连接前，会线程池来清理空闲的连接。其本质是判断每个连接的引用计数对象StreamAllocation的计数，来回收空闲的连接的。
ConnectInterceptor 拦截器的主要任务就是配合ConnectionPool 连接池，获取到一个RealConnection ，并生成编解码器HttpCodec，传递给下一个拦截器CallServerInterceptor进行网络请求。
public final class CallServerInterceptor implements Interceptor {
private final boolean forWebSocket;
public CallServerInterceptor(boolean forWebSocket) {
this.forWebSocket = forWebSocket;
}
@Override public Response intercept(Chain chain) throws IOException {
RealInterceptorChain realChain = (RealInterceptorChain) chain;
HttpCodec httpCodec = realChain.httpStream();
StreamAllocation streamAllocation = realChain.streamAllocation();
RealConnection connection = (RealConnection) realChain.connection();
Request request = realChain.request();
//发送请求的时间戳
long sentRequestMillis = System.currentTimeMillis();
realChain.eventListener().requestHeadersStart(realChain.call());
//向socket写入头信息
httpCodec.writeRequestHeaders(request);
realChain.eventListener().requestHeadersEnd(realChain.call(), request);
Response.Builder responseBuilder = null;
//如果有body，则向socket写入body信息
if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
if ("100-continue".equalsIgnoreCase(request.header("Expect"))) {
httpCodec.flushRequest();
realChain.eventListener().responseHeadersStart(realChain.call());
responseBuilder = httpCodec.readResponseHeaders(true);
}
if (responseBuilder == null) {
realChain.eventListener().requestBodyStart(realChain.call());
long contentLength = request.body().contentLength();
CountingSink requestBodyOut =
new CountingSink(httpCodec.createRequestBody(request, contentLength));
BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);
request.body().writeTo(bufferedRequestBody);
bufferedRequestBody.close();
realChain.eventListener()
.requestBodyEnd(realChain.call(), requestBodyOut.successfulCount);
} else if (!connection.isMultiplexed()) {
streamAllocation.noNewStreams();
}
}
//完成写入操作
httpCodec.finishRequest();
if (responseBuilder == null) {
realChain.eventListener().responseHeadersStart(realChain.call());
//httpCodec解码读取返回的数据，返回responseBuilder 构建者
responseBuilder = httpCodec.readResponseHeaders(false);
}
//responseBuilder 构建Response
Response response = responseBuilder
.request(request)
.handshake(streamAllocation.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
......
//返回response
return response;
}
CallServerInterceptor 主要任务是，向Socket中写入请求信息，并读取返回的数据。再将Response一层层向前返回，最终返回到RealCall的getResponseWithInterceptorChain方法。
网友评论