OKHttp源码分析
半年前阅读了Volley源码，但是现在主流网络请求都是使用OkHttp + Retrofit + RxJava，因此打算好好研究下OkHttp的源码(基于OkHttp3.14.1)，记录一下
一、简单使用
这里只例举基本的Get请求，详细的请看官方文档
val client = OkHttpClient()
fun syncGet(url: String) {
val request = Request.Builder()
.url(url)
.build()
val call = client.newCall(request)
val response = call.execute()
if (response.isSuccessful) {
Log.d(TAG, "请求成功: " + response.body()!!.string())
} else {
Log.d(TAG, "请求失败: " + response.message())
}
}
fun asyncGet(url: String) {
val request = Request.Builder()
.url(url)
.build()
val call = client.newCall(request)
call.enqueue(object : Callback {
override fun onFailure(call: Call, e: IOException) {
Log.d(TAG, "错误: " + e.message)
}
override fun onResponse(call: Call, response: Response) {
if (response.isSuccessful) {
Log.d(TAG, "请求成功: " + response.body()!!.string())
} else {
Log.d(TAG, "请求失败: " + response.message())
}
}
})
}
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由上可知，发送一个基本的get请求需要如下几步
- 创建OkHttpClient实例
- 创建Request实例
- 创建Call实例
- 调用call.execute或者call.enqueue执行同步或者异步请求
下面按照这五步探索下源码
二、OkHttpClient实例的创建
首先看看OkHttpClient的构造器
public OkHttpClient() {
this(new Builder());
}
OkHttpClient(Builder builder) {
// 主要是从builder中取出对应字段进行赋值，忽略
...
}
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其拥有两个构造器不过我们只能直接调用无参的那个，另一个主要给Builder的build方法使用的(典型的建造者模式)，接着看看Builder的构造器
public Builder() {
// 创建异步执行策略
dispatcher = new Dispatcher();
// 默认协议列表Http1.1、Http2.0
protocols = DEFAULT_PROTOCOLS;
// 连接规格，包括TLS(用于https)、CLEARTEXT(未加密用于http)
connectionSpecs = DEFAULT_CONNECTION_SPECS;
// 事件监听，默认没有
eventListenerFactory = EventListener.factory(EventListener.NONE);
// 代理选择器
proxySelector = ProxySelector.getDefault();
// 使用空对象设计模式
if (proxySelector == null) {
proxySelector = new NullProxySelector();
}
// 提供Cookie策略的持久性
cookieJar = CookieJar.NO_COOKIES;
// socket工厂
socketFactory = SocketFactory.getDefault();
// hostname验证器
hostnameVerifier = OkHostnameVerifier.INSTANCE;
// 证书标签
certificatePinner = CertificatePinner.DEFAULT;
// 代理认证
proxyAuthenticator = Authenticator.NONE;
// 认证
authenticator = Authenticator.NONE;
// 连接池
connectionPool = new ConnectionPool();
// dns
dns = Dns.SYSTEM;
// 跟随ssl重定向
followSslRedirects = true;
// 跟随重定向
followRedirects = true;
// 当连接失败时尝试
retryOnConnectionFailure = true;
callTimeout = 0;
// 连接、读取、写超时10秒
connectTimeout = 10_000;
readTimeout = 10_000;
writeTimeout = 10_000;
pingInterval = 0;
}
Builder(OkHttpClient okHttpClient) {
// 从已有的OkHttpClient实例中取出对应的参数赋值给当前实例
...
}
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Builder中的属性到用到时再好好的研究，接着来看看第二步Request实例的创建
三、Request实例的创建
Request实例通过Builder进行创建的，因此首先看看Request.Builder的构造器
public Builder() {
this.method = "GET";
this.headers = new Headers.Builder();
}
Builder(Request request) {
this.url = request.url;
this.method = request.method;
this.body = request.body;
this.tags = request.tags.isEmpty()
? Collections.emptyMap()
: new LinkedHashMap<>(request.tags);
this.headers = request.headers.newBuilder();
}
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其提供了两个构造器，不过我们只能调用无参的那个其内部设置了默认请求方法为GET，并且创建了一个HeaderBuilder实例用于统一管理请求头，第二个构造器用于Request实例中拷贝出对应参数赋值给当前Builder实例，接着看看其url方法和build方法
public Builder url(String url) {
if (url == null) throw new NullPointerException("url == null");
// 默默的将web socket urls替换成http urls
if (url.regionMatches(true, 0, "ws:", 0, 3)) {
url = "http:" + url.substring(3);
} else if (url.regionMatches(true, 0, "wss:", 0, 4)) {
url = "https:" + url.substring(4);
}
return url(HttpUrl.get(url));
}
public Builder url(HttpUrl url) {
if (url == null) throw new NullPointerException("url == null");
this.url = url;
return this;
}
public Request build() {
if (url == null) throw new IllegalStateException("url == null");
return new Request(this);
}
Request(Builder builder) {
this.url = builder.url;
this.method = builder.method;
this.headers = builder.headers.build();
this.body = builder.body;
this.tags = Util.immutableMap(builder.tags);
}
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其中url方法主要是将请求地址封装成HttpUrl实例并赋值给成员url，build方法创建了Request实例。至此第二步结束了接着看看第三步Call实例的创建
四、Call实例的创建
通过调用OkHttpClient实例的newCall()创建Call实例
// OkHttpClient.java
public Call newCall(Request request) {
return RealCall.newRealCall(this, request, false /* for web socket */);
}
// RealCall.java
static RealCall newRealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
RealCall call = new RealCall(client, originalRequest, forWebSocket);
call.transmitter = new Transmitter(client, call);
return call;
}
// Transmitter.java
public Transmitter(OkHttpClient client, Call call) {
this.client = client;
this.connectionPool = Internal.instance.realConnectionPool(client.connectionPool());
this.call = call;
this.eventListener = client.eventListenerFactory().create(call);
// 设置了AsyncTimeout的超时时间默认是0，下文execute方法执行时会用到
this.timeout.timeout(client.callTimeoutMillis(), MILLISECONDS);
}
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newCall方法返回了一个RealCall实例，并且初始化了其transmitter属性(暂时不用管Transmitter的作用)，而在Transmitter构造器中又初始化了connectionPool、eventListener属性，其中Internal.instance在OkHttpClient这个类一加载时就初始化了
// OkHttpClient.java
Internal.instance = new Internal() {
...
@Override
public RealConnectionPool realConnectionPool(ConnectionPool connectionPool) {
return connectionPool.delegate;
}
...
}
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接着主要看看client.connectionPool方法和eventListenerFactory方法
// OkHttpClient.java
public Builder() {
connectionPool = new ConnectionPool();
}
public final class ConnectionPool {
final RealConnectionPool delegate;
public ConnectionPool() {
this(5, 5, TimeUnit.MINUTES);
}
public ConnectionPool(int maxIdleConnections, long keepAliveDuration, TimeUnit timeUnit) {
this.delegate = new RealConnectionPool(maxIdleConnections, keepAliveDuration, timeUnit);
}
// 返回当前连接池的空闲连接数
public int idleConnectionCount() {
return delegate.idleConnectionCount();
}
// 返回当前连接池的总共连接数
public int connectionCount() {
return delegate.connectionCount();
}
// 关闭移除当前连接池中所有空闲的连接
public void evictAll() {
delegate.evictAll();
}
}
// RealConnectionPool.java
public RealConnectionPool(int maxIdleConnections, long keepAliveDuration, TimeUnit timeUnit) {
this.maxIdleConnections = maxIdleConnections;
this.keepAliveDurationNs = timeUnit.toNanos(keepAliveDuration);
if (keepAliveDuration <= 0) {
throw new IllegalArgumentException("keepAliveDuration <= 0: " + keepAliveDuration);
}
}
public ConnectionPool connectionPool() {
return connectionPool;
}
public Builder() {
eventListenerFactory = EventListener.factory(EventListener.NONE);
}
static EventListener.Factory factory(EventListener listener) {
return call -> listener;
}
public EventListener.Factory eventListenerFactory() {
return eventListenerFactory;
}
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从上源码可以得出其实connectionPool最终实现是RealConnectionPool、eventListener默认是EventListener.NONE，至此RealCall实例也已经创建完毕了，接着进入最重要的一步execute或者enqueue，我们先看看同步的情况
五、call.execute()
我们知道call其实是一个RealCall实例，因此看看其execute方法
public Response execute() throws IOException {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
transmitter.timeoutEnter();
transmitter.callStart();
try {
client.dispatcher().executed(this);
return getResponseWithInterceptorChain();
} finally {
client.dispatcher().finished(this);
}
}
// Transmitter.java
public final class Transmitter {
public Transmitter(OkHttpClient client, Call call) {
this.client = client;
this.connectionPool = Internal.instance.realConnectionPool(client.connectionPool());
this.call = call;
this.eventListener = client.eventListenerFactory().create(call);
// 设置了AsyncTimeout的超时时间默认是0
this.timeout.timeout(client.callTimeoutMillis(), MILLISECONDS);
}
// AsyncTimeout具体实现就不深究了，只需知道当调用了enter方法后如果达到了设置的时间还没调用
// 就会调用timedOut方法，而这里因为默认的callTimeout是0，因此不会超时
private final AsyncTimeout timeout = new AsyncTimeout() {
@Override
protected void timedOut() {
cancel();
}
};
public void timeoutEnter() {
timeout.enter();
}
public void callStart() {
// 创建了一个Throwable记录了当前栈信息
this.callStackTrace = Platform.get().getStackTraceForCloseable("response.body().close()");
// 回调callStart，默认设置的没处理任何事件
eventListener.callStart(call);
}
}
// Dispatcher.java
public final class Dispatcher {
private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();
synchronized void executed(RealCall call) {
runningSyncCalls.add(call);
}
}
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首先会判断一下当前call是否已经被执行过，如果已经被执行过了就会抛出异常，然后开启WatchDog监听Timeout，如果超时就会取消本次请求，接着记录当前的栈信息并回调callStart，然后将当前RealCall实例加入到OkHttpClient实例内dispatcher的一个双端队列中去，接着执行getResponseWithInterceptorChain
Response getResponseWithInterceptorChain() throws IOException {
List<Interceptor> interceptors = new ArrayList<>();
interceptors.addAll(client.interceptors());
interceptors.add(new RetryAndFollowUpInterceptor(client));
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));
// 责任链设计模式
Interceptor.Chain chain = new RealInterceptorChain(interceptors, transmitter, null, 0,
originalRequest, this, client.connectTimeoutMillis(),
client.readTimeoutMillis(), client.writeTimeoutMillis());
boolean calledNoMoreExchanges = false;
try {
Response response = chain.proceed(originalRequest);
if (transmitter.isCanceled()) {
closeQuietly(response);
throw new IOException("Canceled");
}
return response;
} catch (IOException e) {
calledNoMoreExchanges = true;
throw transmitter.noMoreExchanges(e);
} finally {
if (!calledNoMoreExchanges) {
transmitter.noMoreExchanges(null);
}
}
}
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该方法首先将OkHttpClient的所有Interceptor与框架自己的几个Interceptor进行组合，然后创建RealInterceptorChain实例调用其proceed方法获取到Response，因此网络请求的主要逻辑就是在这个proceed方法中
// RealInterceptorChain
public Response proceed(Request request, Transmitter transmitter, @Nullable Exchange exchange)
throws IOException {
// 默认index = 0，如果index超出了拦截器的总长就抛出错误
if (index >= interceptors.size()) throw new AssertionError();
calls++;
// 这里刚才传入的exchange为null
if (this.exchange != null && !this.exchange.connection().supportsUrl(request.url())) {
throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
+ " must retain the same host and port");
}
// 同上
if (this.exchange != null && calls > 1) {
throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
+ " must call proceed() exactly once");
}
// 又创建了一个RealInterceptorChain实例，不过其index在原来基础上加了1
RealInterceptorChain next = new RealInterceptorChain(interceptors, transmitter, exchange,
index + 1, request, call, connectTimeout, readTimeout, writeTimeout);
// 取出一个Interceptor实例调用其intercept方法
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);
if (exchange != null && index + 1 < interceptors.size() && next.calls != 1) {
throw new IllegalStateException("network interceptor " + interceptor
+ " must call proceed() exactly once");
}
// 如果Interceptor返回了null那么抛出NPE
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;
}
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该方法内部主要从interceptors中取出index位置上的一个Interceptor实例，然后创建一个index=index+1的RealInterceptorChain实例next，最后调用Interceptor实例的interceptor方法将next传入，获取到Response返回，那么网络请求重点其实在interceptor.intercept方法内，而默认index等于0，我们的OkHttpClient自己又没有设置Interceptor，于是会调用到RetryAndFollowUpInterceptor(负责失败重试以及重定向)实例的intercept方法
public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
RealInterceptorChain realChain = (RealInterceptorChain) chain;
Transmitter transmitter = realChain.transmitter();
int followUpCount = 0;
Response priorResponse = null;
while (true) {
transmitter.prepareToConnect(request);
if (transmitter.isCanceled()) {
throw new IOException("Canceled");
}
Response response;
boolean success = false;
try {
response = realChain.proceed(request, transmitter, null);
// 表示请求成功但是可能是一个重定向响应
success = true;
} catch (RouteException e) {
// 尝试通过路由连接失败请求将不会发送，判断是否需要进行重试
if (!recover(e.getLastConnectException(), transmitter, false, request)) {
throw e.getFirstConnectException();
}
continue;
} catch (IOException e) {
// 试图与服务器通信失败，请求可能已经发送，判断是否需要进行重试
boolean requestSendStarted = !(e instanceof ConnectionShutdownException);
if (!recover(e, transmitter, requestSendStarted, request)) throw e;
continue;
} finally {
// 如果请求没有成功则释放资源
if (!success) {
transmitter.exchangeDoneDueToException();
}
}
// 如果上个响应存在(表示上个响应是一个重定向响应，其不会拥有响应体)，构建一个新的Response实例
// 将上个响应赋值给priorResponse属性
if (priorResponse != null) {
response = response.newBuilder()
.priorResponse(priorResponse.newBuilder()
.body(null)
.build())
.build();
}
// 暂时不理解这个exchange是干什么用的？？
Exchange exchange = Internal.instance.exchange(response);
Route route = exchange != null ? exchange.connection().route() : null;
// 根据响应头判断是否是重定向，如果是就会新建一个Request实例返回
Request followUp = followUpRequest(response, route);
// 如果followUp为空也就是没有重定向那么直接返回响应
if (followUp == null) {
if (exchange != null && exchange.isDuplex()) {
transmitter.timeoutEarlyExit();
}
return response;
}
RequestBody followUpBody = followUp.body();
// 如果限制只发送一次，那也直接返回响应
if (followUpBody != null && followUpBody.isOneShot()) {
return response;
}
closeQuietly(response.body());
if (transmitter.hasExchange()) {
exchange.detachWithViolence();
}
// 重定向请求太多了，就抛出异常
if (++followUpCount > MAX_FOLLOW_UPS) {
throw new ProtocolException("Too many follow-up requests: " + followUpCount);
}
// 赋值新建的请求，保存上一个响应，最终的响应会包含所有前面重定向的响应
request = followUp;
priorResponse = response;
}
}
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RetryAndFollowUpInterceptor主要做的就是重试以及处理重定向，内部会调用realChain.proceed调用下层Interceptor实例的intercept方法，当下层Interceptor抛出异常会判断是否有重试的必要 ，当下层返回了一个Response，其会根据该Response判断是否为重定向响应，如果是就会创建新建一个Request实例，再次请求获取到新的Response实例后将原先的Response赋值给其priorResponse属性，以此循环直到请求成功(不再重定向)、超出最大重定向数、抛出不可重试的异常。然后看看BridgeInterceptor
public final class BridgeInterceptor implements Interceptor {
private final CookieJar cookieJar;
// 这里的CookieJar就是OkHttpClient的CookieJar，默认是一个空实现
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();
// 如果有请求体，并且请求头如果没有Content-Type、Content-length、Host、Connection就加上
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");
}
// 然后如果没有Accept-Encoding请求头并且不是请求部分资源，那么加上Accept-Encoding: gzip
boolean transparentGzip = false;
if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == null) {
transparentGzip = true;
requestBuilder.header("Accept-Encoding", "gzip");
}
// 从cookieJar中取出Cookie列表
List<Cookie> cookies = cookieJar.loadForRequest(userRequest.url());
if (!cookies.isEmpty()) {
requestBuilder.header("Cookie", cookieHeader(cookies));
}
// 没有UserAgrent就添加为okhttp/3.14.1
if (userRequest.header("User-Agent") == null) {
requestBuilder.header("User-Agent", Version.userAgent());
}
// 调用下一个Interceptor
Response networkResponse = chain.proceed(requestBuilder.build());
// 使用cookieJar保存cookie
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)) {
// 设置对应的响应头
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");
// 自动进行解压，不过contentLength变成了-1
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();
}
}
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BridgeInterceptor的逻辑很清晰，其做为应用程序代码与网络代码中间的桥梁，首先根据给用户的Request实例创建一个添加了某些请求头的Request实例；其次调用了chain.proceed执行下一个拦截器；最后将下层返回的Response实例构建成用户需要的Response实例，此外上述代码还告诉我们如果想要持久化管理cookie可以实现CookieJar这个接口设置给OkHttpClient，接着继续看看下一层CacheInterceptor
public final class CacheInterceptor implements Interceptor {
// 这个cache就是OkHttpClient里面的internalCache
final InternalCache cache;
public CacheInterceptor(@Nullable InternalCache cache) {
this.cache = cache;
}
@Override
public Response intercept(Chain chain) throws IOException {
// 如果给OkHttpClient设置了InternalCache，那么从里面获取缓存的响应
Response cacheCandidate = cache != null
? cache.get(chain.request())
: null;
long now = System.currentTimeMillis();
// 这个里面主要是根据请求和缓存的响应判断缓存是否命中
CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
Request networkRequest = strategy.networkRequest;
Response cacheResponse = strategy.cacheResponse;
if (cache != null) {
cache.trackResponse(strategy);
}
if (cacheCandidate != null && cacheResponse == null) {
closeQuietly(cacheCandidate.body());
}
// 客户端设置了only-if-cached，表示只使用缓存而缓存又没有命中因此直接构建一个Response返回
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();
}
// 缓存命中，构造一个Response实例并将去掉了body的cacheResponse赋值给该实例的cacheResponse属性
if (networkRequest == null) {
return cacheResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build();
}
Response networkResponse = null;
try {
networkResponse = chain.proceed(networkRequest);
} finally {
// 发生了异常需要将缓存响应体关闭
if (networkResponse == null && cacheCandidate != null) {
closeQuietly(cacheCandidate.body());
}
}
// 如果有缓存响应并且响应码是304，就根据返回的响应和缓存的响应构造一个新的响应并且更新下缓存
if (cacheResponse != null) {
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());
}
}
// 响应码不是304，则构造一个新的Response将cacheResponse、networkResponse分别去掉body赋值给
// cacheResponse和networkResponse
Response response = networkResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build();
if (cache != null) {
if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) {
// 将最终响应放到cache中
CacheRequest cacheRequest = cache.put(response);
return cacheWritingResponse(cacheRequest, response);
}
if (HttpMethod.invalidatesCache(networkRequest.method())) {
try {
cache.remove(networkRequest);
} catch (IOException ignored) {
}
}
}
return response;
}
}
public final class CacheStrategy {
public static class Factory {
public Factory(long nowMillis, Request request, Response cacheResponse) {
this.nowMillis = nowMillis;
this.request = request;
this.cacheResponse = cacheResponse;
// 根据缓存响应头提取出一些缓存有关的信息
if (cacheResponse != null) {
this.sentRequestMillis = cacheResponse.sentRequestAtMillis();
this.receivedResponseMillis = cacheResponse.receivedResponseAtMillis();
Headers headers = cacheResponse.headers();
for (int i = 0, size = headers.size(); i < size; i++) {
String fieldName = headers.name(i);
String value = headers.value(i);
if ("Date".equalsIgnoreCase(fieldName)) {
servedDate = HttpDate.parse(value);
servedDateString = value;
} else if ("Expires".equalsIgnoreCase(fieldName)) {
expires = HttpDate.parse(value);
} else if ("Last-Modified".equalsIgnoreCase(fieldName)) {
lastModified = HttpDate.parse(value);
lastModifiedString = value;
} else if ("ETag".equalsIgnoreCase(fieldName)) {
etag = value;
} else if ("Age".equalsIgnoreCase(fieldName)) {
ageSeconds = HttpHeaders.parseSeconds(value, -1);
}
}
}
}
}
}
public CacheStrategy get() {
CacheStrategy candidate = getCandidate();
if (candidate.networkRequest != null && request.cacheControl().onlyIfCached()) {
// 如果设置了onlyIfCached那么在CacheInterceptor的intercept方法内部会直接构造一个响应码为504的Response
return new CacheStrategy(null, null);
}
return candidate;
}
private CacheStrategy getCandidate() {
// 没有缓存响应就直接创建一个没响应的CacheStrategy实例
if (cacheResponse == null) {
return new CacheStrategy(request, null);
}
// 丢弃缓存响应，如果请求是https并且缺少必要的握手
if (request.isHttps() && cacheResponse.handshake() == null) {
return new CacheStrategy(request, null);
}
// 如果不应该使用缓存也丢弃缓存响应
if (!isCacheable(cacheResponse, request)) {
return new CacheStrategy(request, null);
}
CacheControl requestCaching = request.cacheControl();
// 如果Request包含noCache请求头，或者带上了 If-Modified-Since、If-None-Match两个请求头也丢弃响应
// 应该带上这两个请求头表示客户端在循环服务端资源是否发生变化，没变化会返回304，因此不应该使用缓存
if (requestCaching.noCache() || hasConditions(request)) {
return new CacheStrategy(request, null);
}
CacheControl responseCaching = cacheResponse.cacheControl();
long ageMillis = cacheResponseAge();
long freshMillis = computeFreshnessLifetime();
if (requestCaching.maxAgeSeconds() != -1) {
freshMillis = Math.min(freshMillis, SECONDS.toMillis(requestCaching.maxAgeSeconds()));
}
long minFreshMillis = 0;
if (requestCaching.minFreshSeconds() != -1) {
minFreshMillis = SECONDS.toMillis(requestCaching.minFreshSeconds());
}
long maxStaleMillis = 0;
if (!responseCaching.mustRevalidate() && requestCaching.maxStaleSeconds() != -1) {
maxStaleMillis = SECONDS.toMillis(requestCaching.maxStaleSeconds());
}
// 根据时间判断是否缓存命中，不知道具体是怎么判断的？
if (!responseCaching.noCache() && ageMillis + minFreshMillis < freshMillis + maxStaleMillis) {
Response.Builder builder = cacheResponse.newBuilder();
if (ageMillis + minFreshMillis >= freshMillis) {
builder.addHeader("Warning", "110 HttpURLConnection /"Response is stale/"");
}
long oneDayMillis = 24 * 60 * 60 * 1000L;
if (ageMillis > oneDayMillis && isFreshnessLifetimeHeuristic()) {
builder.addHeader("Warning", "113 HttpURLConnection /"Heuristic expiration/"");
}
return new CacheStrategy(null, builder.build());
}
// 添加If-None-Match、If-Modified-Since请求头
String conditionName;
String conditionValue;
if (etag != null) {
conditionName = "If-None-Match";
conditionValue = etag;
} else if (lastModified != null) {
conditionName = "If-Modified-Since";
conditionValue = lastModifiedString;
} else if (servedDate != null) {
conditionName = "If-Modified-Since";
conditionValue = servedDateString;
} else {
return new CacheStrategy(request, null);
}
Headers.Builder conditionalRequestHeaders = request.headers().newBuilder();
Internal.instance.addLenient(conditionalRequestHeaders, conditionName, conditionValue);
Request conditionalRequest = request.newBuilder()
.headers(conditionalRequestHeaders.build())
.build();
return new CacheStrategy(conditionalRequest, cacheResponse);
}
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CacheInterceptor的主要功能就是从InternalCache中取出保存的响应，然后根据请求和缓存的响应判断缓存是否命中，命中就会直接构建一个新的响应返回，如果没命中(由于响应过期)，则会根据缓存响应的ETag、LastModify等响应头去构造当前的请求头，这样当服务器判断资源没变化时可以直接返回304，框架也只需要更新下缓存的响应头就可以直接返回了。OkHttp为我们提供了一个Cache类(内部使用DiskLruCache实现)如果我们需要能够缓存只需要进行如下设置.
val client = OkHttpClient.Builder().cache(Cache(cacheFile, 50 * 1000)).build() 复制代码
接着看看下一个拦截器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();
Transmitter transmitter = realChain.transmitter();
boolean doExtensiveHealthChecks = !request.method().equals("GET");
Exchange exchange = transmitter.newExchange(chain, doExtensiveHealthChecks);
return realChain.proceed(request, transmitter, exchange);
}
}
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ConnectIntercept代码很少，但是做的事情很多，其会先去ConnectionPoll中寻找是否有合适的RealConnection，如果没有找到会去请求dns服务器获取目标IP再将目标IP封装成一个Route实例然后创建一个RealConnection接着创建Socket实例并发起连接如果是Https请求还会发起握手，校验证书，接着构建Http1ExchangeCodec实例，最后再去构建Exchange实例，接着再看看CallServerInterceptor
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;
Exchange exchange = realChain.exchange();
// 根据Request生成对应的字节数组并且写入到Buffer中
Request request = realChain.request();
long sentRequestMillis = System.currentTimeMillis();
exchange.writeRequestHeaders(request);
boolean responseHeadersStarted = false;
Response.Builder responseBuilder = null;
// 如果请求包含请求体，写入请求体
if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
if ("100-continue".equalsIgnoreCase(request.header("Expect"))) {
exchange.flushRequest();
responseHeadersStarted = true;
exchange.responseHeadersStart();
responseBuilder = exchange.readResponseHeaders(true);
}
if (responseBuilder == null) {
if (request.body().isDuplex()) {
exchange.flushRequest();
BufferedSink bufferedRequestBody = Okio.buffer(
exchange.createRequestBody(request, true));
request.body().writeTo(bufferedRequestBody);
} else {
BufferedSink bufferedRequestBody = Okio.buffer(
exchange.createRequestBody(request, false));
request.body().writeTo(bufferedRequestBody);
bufferedRequestBody.close();
}
} else {
exchange.noRequestBody();
if (!exchange.connection().isMultiplexed()) {
exchange.noNewExchangesOnConnection();
}
}
} else {
exchange.noRequestBody();
}
if (request.body() == null || !request.body().isDuplex()) {
// 将Buffer中的数据写给服务端
exchange.finishRequest();
}
if (!responseHeadersStarted) {
exchange.responseHeadersStart();
}
if (responseBuilder == null) {
// 获取响应头
responseBuilder = exchange.readResponseHeaders(false);
}
Response response = responseBuilder
.request(request)
.handshake(exchange.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
int code = response.code();
if (code == 100) {
response = exchange.readResponseHeaders(false)
.request(request)
.handshake(exchange.connection().handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
code = response.code();
}
exchange.responseHeadersEnd(response);
if (forWebSocket && code == 101) {
response = response.newBuilder()
.body(Util.EMPTY_RESPONSE)
.build();
} else {
response = response.newBuilder()
.body(exchange.openResponseBody(response))
.build();
}
if ("close".equalsIgnoreCase(response.request().header("Connection"))
|| "close".equalsIgnoreCase(response.header("Connection"))) {
exchange.noNewExchangesOnConnection();
}
if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
throw new ProtocolException(
"HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());
}
return response;
}
}
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CallServerInterceptor真正的进行了网络请求，会根据Request实例构建出Http请求，获取到Http响应后再构建出HttpResponse，网络请求成功后会接着执行前几个Interceptor的剩余代码，这里就不看了。直接回到RealCall.execute()
@Override public Response execute() throws IOException {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
transmitter.timeoutEnter();
transmitter.callStart();
try {
client.dispatcher().executed(this);
return getResponseWithInterceptorChain();
} finally {
client.dispatcher().finished(this);
}
}
void finished(RealCall call) {
finished(runningSyncCalls, call);
}
private <T> void finished(Deque<T> calls, T call) {
Runnable idleCallback;
synchronized (this) {
if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
idleCallback = this.idleCallback;
}
boolean isRunning = promoteAndExecute();
if (!isRunning && idleCallback != null) {
idleCallback.run();
}
}
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可以看出当一次同步请求结束后，会将RealCall中队列中移除，然后启动正在等待的异步请求，如果没有异步请求会回调IdleCallback。接着看看异步请求过程
六、call.enqueue()
enqueue方法用于执行异步请求
public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) {
throw new IllegalStateException("Already Executed");
}
executed = true;
}
transmitter.callStart();
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
复制代码
这里都和execute一样只是最后调用了Dispatcher的enqueue方法，不过传入的是AsyncCall实例
//Dispatcher.java
void enqueue(AsyncCall call) {
synchronized (this) {
// 将call加入到队列中去
readyAsyncCalls.add(call);
if (!call.get().forWebSocket) {
// 刚刚创建的call不是使用webSocket所以进入这里
AsyncCall existingCall = findExistingCallWithHost(call.host());
// 目的只是为了统计每个Host有几个AsyncCall
if (existingCall != null) call.reuseCallsPerHostFrom(existingCall);
}
}
promoteAndExecute();
}
// 从正在执行或者等待执行的call队列中取出host属性为host的AsyncCall实例
private AsyncCall findExistingCallWithHost(String host) {
for (AsyncCall existingCall : runningAsyncCalls) {
if (existingCall.host().equals(host)) return existingCall;
}
for (AsyncCall existingCall : readyAsyncCalls) {
if (existingCall.host().equals(host)) return existingCall;
}
return null;
}
private boolean promoteAndExecute() {
assert (!Thread.holdsLock(this));
List<AsyncCall> executableCalls = new ArrayList<>();
boolean isRunning;
synchronized (this) {
for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
AsyncCall asyncCall = i.next();
// 如果已经达到最大请求数64就停止执行
if (runningAsyncCalls.size() >= maxRequests) break; // Max capacity.
// 如果每个Host达到了最大请求数5个就跳过该call
if (asyncCall.callsPerHost().get() >= maxRequestsPerHost) continue; // Host max capacity.
i.remove();
// 每个端口请求计数加1
asyncCall.callsPerHost().incrementAndGet();
executableCalls.add(asyncCall);
runningAsyncCalls.add(asyncCall);
}
isRunning = runningCallsCount() > 0;
}
for (int i = 0, size = executableCalls.size(); i < size; i++) {
AsyncCall asyncCall = executableCalls.get(i);
// 创建一个线程池，然后执行AsyncCall的execute方法
asyncCall.executeOn(executorService());
}
return isRunning;
}
final class AsyncCall extends NamedRunnable {
private final Callback responseCallback;
private volatile AtomicInteger callsPerHost = new AtomicInteger(0);
AsyncCall(Callback responseCallback) {
super("OkHttp %s", redactedUrl());
this.responseCallback = responseCallback;
}
AtomicInteger callsPerHost() {
return callsPerHost;
}
void reuseCallsPerHostFrom(AsyncCall other) {
this.callsPerHost = other.callsPerHost;
}
String host() {
return originalRequest.url().host();
}
Request request() {
return originalRequest;
}
RealCall get() {
return RealCall.this;
}
void executeOn(ExecutorService executorService) {
assert (!Thread.holdsLock(client.dispatcher()));
boolean success = false;
try {
executorService.execute(this);
success = true;
} catch (RejectedExecutionException e) {
InterruptedIOException ioException = new InterruptedIOException("executor rejected");
ioException.initCause(e);
transmitter.noMoreExchanges(ioException);
responseCallback.onFailure(RealCall.this, ioException);
} finally {
if (!success) {
client.dispatcher().finished(this); // This call is no longer running!
}
}
}
@Override
protected void execute() {
// 在线程池中执行
boolean signalledCallback = false;
transmitter.timeoutEnter();
try {
Response response = getResponseWithInterceptorChain();
signalledCallback = true;
responseCallback.onResponse(RealCall.this, response);
} catch (IOException e) {
if (signalledCallback) {
Platform.get().log(INFO, "Callback failure for " + toLoggableString(), e);
} else {
responseCallback.onFailure(RealCall.this, e);
}
} finally {
// 每个端口请求计数减1
client.dispatcher().finished(this);
}
}
}
复制代码
如果调用了enqueue发送网络请求，那么最终会在线程池中执行AsyncCall的execute方法，其内部实现与同步执行基本类似，注意最后会在子线程中直接调用onResponse，因此我们不能在onResponse里面直接更新UI。我们可以写一个WrapCall将Call进行包装这样就能实现回调在主线程了，代码如下
class WrapCall(private val call: Call) : Call by call {
override fun enqueue(responseCallback: Callback) {
call.enqueue(object : Callback {
override fun onFailure(call: Call, e: IOException) {
handler.post {
responseCallback.onFailure(call, e)
}
}
override fun onResponse(call: Call, response: Response) {
handler.post {
responseCallback.onResponse(call, response)
}
}
})
}
companion object {
private val handler = Handler(Looper.getMainLooper())
}
}
// 外界使用，只要包装下
val call = WrapCall(client.newCall(request))
call.enqueue(object : Callback {
override fun onFailure(call: Call, e: IOException) {
Log.d(TAG, "错误: " + e.message)
}
override fun onResponse(call: Call, response: Response) {
if (response.isSuccessful) {
Log.d(TAG, "请求成功: ${Looper.myLooper() === Looper.getMainLooper()}" + response.body()!!.string())
} else {
Log.d(TAG, "请求失败: ${Looper.myLooper() === Looper.getMainLooper()}" + response.message())
}
}
})
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源码分析到这网络流程基本已经清晰，下面再来看看OkHttp的连接复用。
七、连接复用
连接池的具体实现是RealConnectionPool，每次在ConnectInterceptor的intercepte方法都会尝试着先从连接池中取出一个连接，取不到满足条件的才会新建一个连接
public final class RealConnectionPool {
// 这个线程池是专门用来执行清理线程的
private static final Executor executor = new ThreadPoolExecutor(0 /* corePoolSize */,
Integer.MAX_VALUE /* maximumPoolSize */, 60L /* keepAliveTime */, TimeUnit.SECONDS,
new SynchronousQueue<>(), Util.threadFactory("OkHttp ConnectionPool", true));
// 最大空闲连接数 默认5个
private final int maxIdleConnections;
// 最大保存存活的空闲连接时间 默认5分钟
private final long keepAliveDurationNs;
// 当向连接池中加入一个连接后会执行清理操作，内部会寻找空闲时间最长的连接，如果其空闲时间
// 已经超过了最长时间就会将其关闭，不然就等待指定时间
private final Runnable cleanupRunnable = () -> {
while (true) {
long waitNanos = cleanup(System.nanoTime());
if (waitNanos == -1) return;
if (waitNanos > 0) {
long waitMillis = waitNanos / 1000000L;
waitNanos -= (waitMillis * 1000000L);
synchronized (RealConnectionPool.this) {
try {
RealConnectionPool.this.wait(waitMillis, (int) waitNanos);
} catch (InterruptedException ignored) {
}
}
}
}
};
// 双端队列保存当前OkHttpClient的所有连接
private final Deque<RealConnection> connections = new ArrayDeque<>();
// 记录了失败的路由
final RouteDatabase routeDatabase = new RouteDatabase();
// 清理线程是否正在执行
boolean cleanupRunning;
// 首先创建了一个最大空闲连接为5，最大保存存活时间5分钟的连接池
public RealConnectionPool(int maxIdleConnections, long keepAliveDuration, TimeUnit timeUnit) {
this.maxIdleConnections = maxIdleConnections;
this.keepAliveDurationNs = timeUnit.toNanos(keepAliveDuration);
if (keepAliveDuration <= 0) {
throw new IllegalArgumentException("keepAliveDuration <= 0: " + keepAliveDuration);
}
}
// 获取空闲连接数量
public synchronized int idleConnectionCount() {
int total = 0;
for (RealConnection connection : connections) {
if (connection.transmitters.isEmpty()) total++;
}
return total;
}
// 总共的连接数
public synchronized int connectionCount() {
return connections.size();
}
// Transmitter调用该方法获取连接，内部判断如果连接池有连接满足条件就返回true，不然返回false
boolean transmitterAcquirePooledConnection(Address address, Transmitter transmitter,
@Nullable List<Route> routes, boolean requireMultiplexed) {
assert (Thread.holdsLock(this));
for (RealConnection connection : connections) {
if (requireMultiplexed && !connection.isMultiplexed()) continue;
if (!connection.isEligible(address, routes)) continue;
transmitter.acquireConnectionNoEvents(connection);
return true;
}
return false;
}
// 将一个新建的连接放入到连接池中
void put(RealConnection connection) {
assert (Thread.holdsLock(this));
// 如果清理线程还没运行就开始运行
if (!cleanupRunning) {
cleanupRunning = true;
executor.execute(cleanupRunnable);
}
// 再将连接放入双端队列中去
connections.add(connection);
}
// 当一个连接从执行中变成了空闲时调用，该方法会唤醒清理现场
boolean connectionBecameIdle(RealConnection connection) {
assert (Thread.holdsLock(this));
if (connection.noNewExchanges || maxIdleConnections == 0) {
connections.remove(connection);
return true;
} else {
notifyAll(); // Awake the cleanup thread: we may have exceeded the idle connection limit.
return false;
}
}
// 关闭所有的连接
public void evictAll() {
List<RealConnection> evictedConnections = new ArrayList<>();
synchronized (this) {
for (Iterator<RealConnection> i = connections.iterator(); i.hasNext(); ) {
RealConnection connection = i.next();
if (connection.transmitters.isEmpty()) {
connection.noNewExchanges = true;
evictedConnections.add(connection);
i.remove();
}
}
}
for (RealConnection connection : evictedConnections) {
closeQuietly(connection.socket());
}
}
// 如果可以清理的话就关闭Socket返回0，不然返回需要等待的时间
long cleanup(long now) {
int inUseConnectionCount = 0;
int idleConnectionCount = 0;
RealConnection longestIdleConnection = null;
long longestIdleDurationNs = Long.MIN_VALUE;
synchronized (this) {
for (Iterator<RealConnection> i = connections.iterator(); i.hasNext(); ) {
RealConnection connection = i.next();
if (pruneAndGetAllocationCount(connection, now) > 0) {
inUseConnectionCount++;
continue;
}
idleConnectionCount++;
long idleDurationNs = now - connection.idleAtNanos;
if (idleDurationNs > longestIdleDurationNs) {
longestIdleDurationNs = idleDurationNs;
longestIdleConnection = connection;
}
}
if (longestIdleDurationNs >= this.keepAliveDurationNs
|| idleConnectionCount > this.maxIdleConnections) {
connections.remove(longestIdleConnection);
} else if (idleConnectionCount > 0) {
return keepAliveDurationNs - longestIdleDurationNs;
} else if (inUseConnectionCount > 0) {
return keepAliveDurationNs;
} else {
cleanupRunning = false;
return -1;
}
}
closeQuietly(longestIdleConnection.socket());
return 0;
}
private int pruneAndGetAllocationCount(RealConnection connection, long now) {
// 对于Http1.1这个List最多也只有一个元素
List<Reference<Transmitter>> references = connection.transmitters;
for (int i = 0; i < references.size(); ) {
Reference<Transmitter> reference = references.get(i);
if (reference.get() != null) {
i++;
continue;
}
// 发现一个泄露的transmitter，这是一个应用程序的bug
TransmitterReference transmitterRef = (TransmitterReference) reference;
String message = "A connection to " + connection.route().address().url()
+ " was leaked. Did you forget to close a response body?";
Platform.get().logCloseableLeak(message, transmitterRef.callStackTrace);
references.remove(i);
connection.noNewExchanges = true; eviction.
if (references.isEmpty()) {
connection.idleAtNanos = now - keepAliveDurationNs;
return 0;
}
}
return references.size();
}
// 连接失败时调用将失败的Route放入到RouteDatabase中
public void connectFailed(Route failedRoute, IOException failure) {
// Tell the proxy selector when we fail to connect on a fresh connection.
if (failedRoute.proxy().type() != Proxy.Type.DIRECT) {
Address address = failedRoute.address();
address.proxySelector().connectFailed(
address.url().uri(), failedRoute.proxy().address(), failure);
}
routeDatabase.failed(failedRoute);
}
}
复制代码
八、总结
不管是同步请求还是异步请求内部都是经过从上到下5个拦截器才能发起请求，获取到响应后还会经过这5个拦截器然后才将结果返回到外界，典型的责任链模式与Android事件分发差不多
- RetryAndFollowUpInterceptor 用于错误重试，以及重定向
- BridgeInterceptor 用于添加请求头(User-Agent、Connection等等)，收到响应的时候可能会进行GZip解压
- CacheInterceptor 进行缓存管理，默认不带缓存，如果需要缓存可以给OkHttpClient设置cache属性，可以使用OkHttp内置的Cache类
- ConnectInterceptor 进行连接，首先从连接池中取出可以复用的连接，取不到就新建一个然后通过InetAddress获取到域名对于的IP地址，然后创建Socket与服务端进行连接，连接成功后如果是Https请求还会进行握手验证证书操作
- CallServerInterceptor 用于真正的发起请求，从Socket获取的输出流写入请求数据，从输入流中读取到响应数据
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近期评论
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666
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文章和留言都翻到11页了 没有OOM
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朋友，翻页到11页，及以后，会出现OOM，无法访问
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版本号是多少，你可以下载哪个代码仓库，jdk选1.8 直接跑就行
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