由上篇分析了Ok請求的執(zhí)行流程知道辛辨，無論是同步還是異步召娜，最終得到網(wǎng)絡(luò)響應(yīng)玲销，都是通過調(diào)用getResponseWithInterceptorChain() 來獲取的，其內(nèi)部實(shí)現(xiàn)了一條攔截器鏈。下面開始分析源碼內(nèi)部的5個(gè)攔截器的調(diào)用劣欢，以及網(wǎng)絡(luò)數(shù)據(jù)的請求流程。
final class RealCall implements Call {
//構(gòu)造一條攔截器鏈
Response getResponseWithInterceptorChain() throws IOException {
// 構(gòu)建一個(gè)列表來存放所有的攔截器
List<Interceptor> interceptors = new ArrayList<>();
//用戶自定義的攔截器
interceptors.addAll(client.interceptors());
//重定向攔截器
interceptors.add(retryAndFollowUpInterceptor);
//橋接攔截器
interceptors.add(new BridgeInterceptor(client.cookieJar()));
//緩存攔截器
interceptors.add(new CacheInterceptor(client.internalCache()));
//連接攔截器
interceptors.add(new ConnectInterceptor(client));
if (!forWebSocket) {
interceptors.addAll(client.networkInterceptors());
}
//網(wǎng)絡(luò)請求攔截器
interceptors.add(new CallServerInterceptor(forWebSocket));
//根據(jù)列表中的攔截器蜒秤，開始構(gòu)造一條攔截器鏈衅疙。
Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
originalRequest, this, eventListener, client.connectTimeoutMillis(),
client.readTimeoutMillis(), client.writeTimeoutMillis());
//開始整條鏈的調(diào)用
return chain.proceed(originalRequest);
}
用戶可以自定義自己的攔截器，并被首先添加到列表中溅呢，系統(tǒng)內(nèi)部自己實(shí)現(xiàn)了5個(gè)重要的攔截器澡屡，分別是RetryAndFollowUpInterceptor、BridgeInterceptor咐旧、CacheInterceptor驶鹉、ConnectInterceptor和CallServerInterceptor，整個(gè)攔截器鏈正是通過這5個(gè)攔截器串聯(lián)起來的铣墨。我們首先看proceed方法室埋，它接收了我們構(gòu)造的Request對象。
public interface Interceptor {
Response intercept(Chain chain) throws IOException;
interface Chain {
Request request();
Response proceed(Request request) throws IOException;
......
}
}
Interceptor 是攔截器的接口伊约，由子類實(shí)現(xiàn)不同攔截器姚淆。Chain 是其內(nèi)部類，它由RealInterceptorChain屡律，構(gòu)成鏈的節(jié)點(diǎn)腌逢。
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;//鏈節(jié)的角標(biāo)
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;
}
//調(diào)用4參的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");
}
//構(gòu)建下一鏈節(jié)，角標(biāo)加1
RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
writeTimeout);
//從列表取出第一個(gè)攔截器
Interceptor interceptor = interceptors.get(index);
//調(diào)用intercept超埋，將下一鏈節(jié)傳入
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;
}
}
攔截器鏈的整體結(jié)構(gòu)類似鏈表搏讶，RealInterceptorChain相當(dāng)于鏈表節(jié)點(diǎn)對象，封裝了攔截器霍殴，每個(gè)節(jié)點(diǎn)媒惕，由上一個(gè)節(jié)點(diǎn)構(gòu)造而來。假設(shè)我們沒有自定義自己的攔截器来庭，則第一鏈節(jié)會取出RetryAndFollowUpInterceptor妒蔚，并構(gòu)造下一個(gè)節(jié)點(diǎn)RealInterceptorChain，調(diào)用intercept方法月弛，將節(jié)點(diǎn)傳入肴盏。
//重定向攔截器
public final class RetryAndFollowUpInterceptor implements Interceptor {
//失敗重連的最大次數(shù)
private static final int MAX_FOLLOW_UPS = 20;
@Override public Response intercept(Chain chain) throws IOException {
//從成員變量獲取Request
Request request = chain.request();
RealInterceptorChain realChain = (RealInterceptorChain) chain;
//從成員變量獲取RealCall
Call call = realChain.call();
EventListener eventListener = realChain.eventListener();
//用于服務(wù)端數(shù)據(jù)的傳輸
StreamAllocation streamAllocation = new StreamAllocation(client.connectionPool(),
createAddress(request.url()), call, eventListener, callStackTrace);
this.streamAllocation = streamAllocation;
//重連累計(jì)次數(shù)
int followUpCount = 0;
Response priorResponse = null;
while (true) {
if (canceled) {
streamAllocation.release();
throw new IOException("Canceled");
}
Response response;
boolean releaseConnection = true;
try {
//調(diào)用proceed，取出第二個(gè)攔截器帽衙，和構(gòu)造第三個(gè)節(jié)點(diǎn)
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());
//重連超過20次則斷開連接
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用于和服務(wù)端數(shù)據(jù)傳輸叁鉴，但在這一個(gè)鏈節(jié)不會用到，會在 ConnectInterceptor這一節(jié)使用到佛寿。
proceed的執(zhí)行類似遞歸幌墓，取出了第二個(gè)攔截器并構(gòu)造了第三個(gè)但壮，就是通過這種方式構(gòu)建整條攔截器鏈，由最后的鏈節(jié)獲得Response 響應(yīng)數(shù)據(jù)常侣，回溯返回蜡饵。這一節(jié)如果失敗了，會進(jìn)行循環(huán)重試胳施，超過最大次數(shù)20次溯祸，則釋放資源。
由攔截器列表添加順序知道舞肆，下一個(gè)攔截器為BridgeInterceptor焦辅。
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();
//添加請求頭信息
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());
}
//交由下一個(gè)攔截器去做請求
Response networkResponse = chain.proceed(requestBuilder.build());
//轉(zhuǎn)化成客戶端可以使用的Response
HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());
Response.Builder responseBuilder = networkResponse.newBuilder()
.request(userRequest);
//解壓縮包
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 主要是為用戶的Request請求添加請求頭等信息，轉(zhuǎn)化為標(biāo)準(zhǔn)的網(wǎng)絡(luò)請求椿胯。接收到響應(yīng)數(shù)據(jù)后筷登，解壓或解析成客戶端方便使用的數(shù)據(jù)格式。下一請求環(huán)節(jié)將交由CacheInterceptor哩盲。
OkHttpClient okHttpClient = new OkHttpClient.Builder()
.readTimeout( 5, TimeUnit.SECONDS )
.cache( new Cache( new File( "cache" ),20*1024*1024 ) )//緩存大小
.build();
在構(gòu)建OkHttpClient 時(shí)前方，我們傳入了Cache對象來做緩存設(shè)置，先來看Cache類的實(shí)現(xiàn)廉油。
//緩存類
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;
//內(nèi)部類實(shí)現(xiàn)了InternalCache接口惠险，實(shí)際方法都由Cache 類實(shí)現(xiàn)
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緩存方法
@Nullable CacheRequest put(Response response) {
//獲取請求方式
String requestMethod = response.request().method();
//如果是"POST""PATCH""PUT""DELETE""MOVE"的請求方式，則不緩存
if (HttpMethod.invalidatesCache(response.request().method())) {
try {
remove(response.request());
} catch (IOException ignored) {
// The cache cannot be written.
}
return null;
}
//只緩存get方式
if (!requestMethod.equals("GET")) {
return null;
}
if (HttpHeaders.hasVaryAll(response)) {
return null;
}
//實(shí)際用了DiskLruCache緩存
Entry entry = new Entry(response);
DiskLruCache.Editor editor = null;
try {
editor = cache.edit(key(response.request().url()));
if (editor == null) {
return null;
}
//緩存請求方式和路徑等
entry.writeTo(editor);
//緩存請求body
return new CacheRequestImpl(editor);
} catch (IOException e) {
abortQuietly(editor);
return null;
}
}
//get獲取緩存內(nèi)容方法
Response get(Request request) {
String key = key(request.url());//獲取key
DiskLruCache.Snapshot snapshot;//緩存快照
Entry entry;//緩存Entry
try {
snapshot = cache.get(key);//通過key獲取緩存快照
if (snapshot == null) {
return null;
}
} catch (IOException e) {
return null;
}
try {
entry = new Entry(snapshot.getSource(ENTRY_METADATA));//如果緩存快照存在抒线，那么構(gòu)造Entry
} catch (IOException e) {
Util.closeQuietly(snapshot);
return null;
}
Response response = entry.response(snapshot);//通過快緩存照獲取響應(yīng)體
if (!entry.matches(request, response)) {
Util.closeQuietly(response.body());
return null;
}
return response;
}
}
//緩存內(nèi)部類
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是一個(gè)接口班巩，定義了緩存的各項(xiàng)操作，Cache 定義了一個(gè)匿名內(nèi)部類來實(shí)現(xiàn)緩存的操作嘶炭。
從緩存put/get方法分析可以看出抱慌，內(nèi)部緩存實(shí)現(xiàn)是DiskLruCache緩存，并且只緩存Get請求方式旱物。
CacheRequestImpl類進(jìn)行了緩存封裝，它實(shí)現(xiàn)了CacheRequest 接口卫袒，用來暴露給緩存攔截器進(jìn)行緩存操作宵呛。
public final class CacheInterceptor implements Interceptor {
final InternalCache cache;
public CacheInterceptor(InternalCache cache) {
this.cache = cache;
}
@Override public Response intercept(Chain chain) throws IOException {
//緩存不為null則從緩存獲取
Response cacheCandidate = cache != null
? cache.get(chain.request())
: null;
long now = System.currentTimeMillis();
//是獲取網(wǎng)絡(luò)還是獲取緩存
CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
Request networkRequest = strategy.networkRequest;
Response cacheResponse = strategy.cacheResponse;
//對緩存的名字進(jìn)行次數(shù)累計(jì)
if (cache != null) {
cache.trackResponse(strategy);
}
if (cacheCandidate != null && cacheResponse == null) {
closeQuietly(cacheCandidate.body());
}
// 沒有網(wǎng)絡(luò)，也沒有緩存夕凝，手動構(gòu)造Response宝穗，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();
}
// 沒有網(wǎng)絡(luò)，但有緩存码秉，將緩存數(shù)據(jù)返回
if (networkRequest == null) {
return cacheResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build();
}
Response networkResponse = null;
try {
//交由下一個(gè)環(huán)請求操作
networkResponse = chain.proceed(networkRequest);
} finally {
//關(guān)閉緩存資源
if (networkResponse == null && cacheCandidate != null) {
closeQuietly(cacheCandidate.body());
}
}
// 有網(wǎng)絡(luò)逮矛，這里再次判斷是否要使用緩存
if (cacheResponse != null) {
//狀態(tài)碼304，獲取緩存
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());
}
}
//最終沒有緩存转砖，則構(gòu)造網(wǎng)絡(luò)獲取的數(shù)據(jù)返回
Response response = networkResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build();
if (cache != null) {
if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) {
//將數(shù)據(jù)緩存起來
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 通過獲取緩存和網(wǎng)絡(luò)請求兩種策略進(jìn)行比對须鼎，來決定是采用緩存數(shù)據(jù)還是網(wǎng)絡(luò)數(shù)據(jù)鲸伴，并在最后將數(shù)據(jù)緩存起來，以便下次獲取晋控。
如果當(dāng)前網(wǎng)絡(luò)沒有問題汞窗，下個(gè)攔截器將通過連接復(fù)用的方式，獲取到一個(gè)網(wǎng)絡(luò)連接RealConnection 赡译，以供最后一個(gè)攔截器做網(wǎng)絡(luò)請求仲吏，獲取連接的攔截器為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中創(chuàng)建
StreamAllocation streamAllocation = realChain.streamAllocation();
boolean doExtensiveHealthChecks = !request.method().equals("GET");
//HttpCodec為一個(gè)接口蝌焚，對應(yīng)HttpCodec1和HttpCodec2裹唆，即1.0和2.0,主要用于編碼request和解碼response。并且和服務(wù)端建立了連接
HttpCodec httpCodec = streamAllocation.newStream(client, chain, doExtensiveHealthChecks);
RealConnection connection = streamAllocation.connection();
//傳遞給CallServerInterceptor攔截器
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;//連接池
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 {
//獲得連接類只洒，用于網(wǎng)絡(luò)連接
RealConnection resultConnection = findHealthyConnection(connectTimeout, readTimeout,
writeTimeout, pingIntervalMillis, connectionRetryEnabled, doExtensiveHealthChecks);
//獲得編解碼器
HttpCodec resultCodec = resultConnection.newCodec(client, chain, this);
synchronized (connectionPool) {
codec = resultCodec;
return resultCodec;
}
} catch (IOException e) {
throw new RouteException(e);
}
}
//獲取連接器
private RealConnection findHealthyConnection(int connectTimeout, int readTimeout,
int writeTimeout, int pingIntervalMillis, boolean connectionRetryEnabled,
boolean doExtensiveHealthChecks) throws IOException {
//死循環(huán)查找
while (true) {
RealConnection candidate = findConnection(connectTimeout, readTimeout, writeTimeout,
pingIntervalMillis, connectionRetryEnabled);
//如果successCount 為0许帐，說明可用，結(jié)束循環(huán)
synchronized (connectionPool) {
if (candidate.successCount == 0) {
return candidate;
}
}
//如果這個(gè)連接無效(比如流沒關(guān)閉)红碑，則回收舞吭，尋找下一個(gè)
if (!candidate.isHealthy(doExtensiveHealthChecks)) {
noNewStreams();
continue;
}
return candidate;
}
}
}
//獲取一個(gè)RealConnection 鏈接
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");
//看是否能復(fù)用connection
releasedConnection = this.connection;
toClose = releaseIfNoNewStreams();
if (this.connection != null) {
result = this.connection;
releasedConnection = null;
}
if (!reportedAcquired) {
releasedConnection = null;
}
//不能復(fù)用說明為null，從池里獲取新的
if (result == null) {
// 假設(shè)連接池中可用的析珊，第一次嘗試獲取一個(gè)
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為true羡鸥，說明第一次嘗試找到了
if (foundPooledConnection) {
eventListener.connectionAcquired(call, result);
}
//成功獲取則返回
if (result != null) {
return result;
}
//不能復(fù)用，連接池也沒有忠寻，則下面將獲取一個(gè)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) {
//獲取新的路由惧浴，并第二次嘗試從池中獲取
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;
}
}
}
//新建一個(gè)鏈接
if (!foundPooledConnection) {
if (selectedRoute == null) {
selectedRoute = routeSelection.next();
}
route = selectedRoute;
refusedStreamCount = 0;
//構(gòu)建新的RealConnection
result = new RealConnection(connectionPool, selectedRoute);
acquire(result, false);
}
}
// foundPooledConnection為true，說明第二次嘗試找到了
if (foundPooledConnection) {
eventListener.connectionAcquired(call, result);
return result;
}
// 建立新的連接
result.connect(connectTimeout, readTimeout, writeTimeout, pingIntervalMillis,
connectionRetryEnabled, call, eventListener);
routeDatabase().connected(result.route());
Socket socket = null;
synchronized (connectionPool) {
reportedAcquired = true;
// 將連接放入池中
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獲取一個(gè)鏈接做了多次嘗試奕剃，如下：
1衷旅，先判斷了當(dāng)前的連接是否能復(fù)用，能復(fù)用則返回纵朋；
2柿顶，不能復(fù)用，第一次嘗試從連接池獲取操软，獲取到了則返回嘁锯；
3，第一次連接池獲取失敗聂薪，取下一個(gè)路由家乘，并第二次嘗試從連接池獲取，獲取到則返回藏澳；
4仁锯，第二次嘗試獲取失敗，則新建一個(gè)鏈接翔悠，并把連接緩存到連接池中业崖。
下面來看下是如何從ConnectionPool 連接池中獲取到一個(gè)鏈接野芒，和一個(gè)新鏈接如何緩存到池中的。
public final class ConnectionPool {
//線程池
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;
//緩存隊(duì)列
private final Deque<RealConnection> connections = new ArrayDeque<>();
//從池里獲取連接
@Nullable RealConnection get(Address address, StreamAllocation streamAllocation, Route route) {
assert (Thread.holdsLock(this));
//遍歷隊(duì)列判斷是否符合條件
for (RealConnection connection : connections) {
//根據(jù)地址和路由判斷是否可用
if (connection.isEligible(address, route)) {
//如果符合則
streamAllocation.acquire(connection, true);
return connection;
}
}
return null;
}
public final class StreamAllocation {
//保存當(dāng)前獲取到的connection
private RealConnection connection;
public void acquire(RealConnection connection, boolean reportedAcquired) {
assert (Thread.holdsLock(connectionPool));
if (this.connection != null) throw new IllegalStateException();
//將符合條件的connection賦值給成員變量
this.connection = connection;
this.reportedAcquired = reportedAcquired;
//將當(dāng)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<>();
連接池get方法腻要，是通過遍歷緩存隊(duì)列ArrayDeque复罐，根據(jù)地址和路由，判斷是否有可用的連接雄家，如果找到了效诅，則調(diào)用StreamAllocation 的acquire方法，將connection 保存到成員變量中趟济，同時(shí)將當(dāng)前的StreamAllocation 對象封裝成弱引用乱投，加入到RealConnection 的成員列表allocations 中。這個(gè)列表的個(gè)數(shù)就是用來判斷我們的最大連接數(shù)是否超過64個(gè)的顷编。
下面看連接池如何緩存新建的RealConnection戚炫，即put方法：
public final class ConnectionPool {
//線程池
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;
//緩存隊(duì)列
private final Deque<RealConnection> connections = new ArrayDeque<>();
//緩存RealConnection
void put(RealConnection connection) {
assert (Thread.holdsLock(this));
//標(biāo)記清除算法來回收RealConnection
if (!cleanupRunning) {
cleanupRunning = true;
executor.execute(cleanupRunnable);
}
//將新的RealConnection 添加到隊(duì)列中
connections.add(connection);
}
}
//回收線程
private final Runnable cleanupRunnable = new Runnable() {
@Override public void run() {
while (true) {
//與下一次需要清理的間隔時(shí)間，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) {
}
}
}
}
}
};
//實(shí)際做回收的方法
long cleanup(long now) {
//記錄活躍的連接數(shù)
int inUseConnectionCount = 0;
//記錄空閑的連接數(shù)
int idleConnectionCount = 0;
//空閑時(shí)間最長的連接
RealConnection longestIdleConnection = null;
long longestIdleDurationNs = Long.MIN_VALUE;
// 遍歷隊(duì)列
synchronized (this) {
for (Iterator<RealConnection> i = connections.iterator(); i.hasNext(); ) {
RealConnection connection = i.next();
// 返回0說明連接正在使用媳纬，則inUseConnectionCount加1双肤，獲取下一個(gè)連接
if (pruneAndGetAllocationCount(connection, now) > 0) {
inUseConnectionCount++;
continue;
}
//說明空閑，空閑連接加1
idleConnectionCount++;
// 找出了空閑時(shí)間最長的連接钮惠，準(zhǔn)備移除
long idleDurationNs = now - connection.idleAtNanos;
if (idleDurationNs > longestIdleDurationNs) {
longestIdleDurationNs = idleDurationNs;
longestIdleConnection = connection;
}
}
//如果空閑時(shí)間最長的連接的空閑時(shí)間超過了5分鐘茅糜，或是空閑的連接數(shù)超過了限制，就移除
if (longestIdleDurationNs >= this.keepAliveDurationNs
|| idleConnectionCount > this.maxIdleConnections) {
//從隊(duì)列移除
connections.remove(longestIdleConnection);
} else if (idleConnectionCount > 0) {
//如果存在空閑連接但是還沒有超過5分鐘素挽，就返回剩下的時(shí)間蔑赘，便于下次進(jìn)行清理
return keepAliveDurationNs - longestIdleDurationNs;
} else if (inUseConnectionCount > 0) {
// 如果沒有空閑的連接，那就等5分鐘后再嘗試清理
return keepAliveDurationNs;
} else {
// 當(dāng)前沒有任何連接预明，就返回-1缩赛，跳出循環(huán)
cleanupRunning = false;
return -1;
}
}
closeQuietly(longestIdleConnection.socket());
return 0;
}
//判斷當(dāng)前連接是否正在使用
private int pruneAndGetAllocationCount(RealConnection connection, long now) {
//獲取軟引用列表
List<Reference<StreamAllocation>> references = connection.allocations;
//遍歷
for (int i = 0; i < references.size(); ) {
Reference<StreamAllocation> reference = references.get(i);
//如果存在引用，就說明是活躍連接撰糠，就繼續(xù)看下一個(gè)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);
//如果沒有引用酥馍，就移除
references.remove(i);
connection.noNewStreams = true;
// 如果列表為空，就說明此連接上沒有StreamAllocation引用了阅酪，就返回0旨袒，表示是空閑的連接
if (references.isEmpty()) {
connection.idleAtNanos = now - keepAliveDurationNs;
return 0;
}
}
//遍歷結(jié)束后，返回引用的數(shù)量遮斥，說明當(dāng)前連接是活躍連接
return references.size();
}
}
Ok中支持5個(gè)并發(fā)socket連接峦失，默認(rèn)的keepAlive時(shí)間為5分鐘扇丛，也可以在構(gòu)建OkHttpClient時(shí)設(shè)置术吗。向連接池添加新的連接前，會線程池來清理空閑的連接较屿。其本質(zhì)是判斷每個(gè)連接的引用計(jì)數(shù)對象StreamAllocation的計(jì)數(shù)隧魄，來回收空閑的連接的。
ConnectInterceptor 攔截器的主要任務(wù)就是配合ConnectionPool 連接池隘蝎，獲取到一個(gè)RealConnection 购啄，并生成編解碼器HttpCodec，傳遞給下一個(gè)攔截器CallServerInterceptor進(jìn)行網(wǎng)絡(luò)請求嘱么。
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();
//發(fā)送請求的時(shí)間戳
long sentRequestMillis = System.currentTimeMillis();
realChain.eventListener().requestHeadersStart(realChain.call());
//向socket寫入頭信息
httpCodec.writeRequestHeaders(request);
realChain.eventListener().requestHeadersEnd(realChain.call(), request);
Response.Builder responseBuilder = null;
//如果有body狮含，則向socket寫入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();
}
}
//完成寫入操作
httpCodec.finishRequest();
if (responseBuilder == null) {
realChain.eventListener().responseHeadersStart(realChain.call());
//httpCodec解碼讀取返回的數(shù)據(jù)，返回responseBuilder 構(gòu)建者
responseBuilder = httpCodec.readResponseHeaders(false);
}
//responseBuilder 構(gòu)建Response
Response response = responseBuilder
.request(request)
.handshake(streamAllocation.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
......
//返回response
return response;
}
CallServerInterceptor 主要任務(wù)是曼振，向Socket中寫入請求信息几迄，并讀取返回的數(shù)據(jù)。再將Response一層層向前返回冰评，最終返回到RealCall的getResponseWithInterceptorChain方法映胁。
