Okhttp3源码解析
2024-10-06 10:38:37
首先是Okhttp的使用：
//缓存文件夹
File cacheFile = new File(getExternalCacheDir().toString(), "cache");
//缓存大小为10M
int cacheSize = 10 * 1024 * 1024;
//创建缓存对象
Cache cache = new Cache(cacheFile, cacheSize);
OkHttpClient client = new OkHttpClient
.Builder()
//.addInterceptor(new LoggingInterceptor())//日志拦截器
.cache(cache)
.build();
Request request = new Request.Builder()
.url("http://www.baidu.com")
.build();
client.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
Log.d("OkHttp", "Call Failed:" + e.getMessage());
} @Override
public void onResponse(Call call, Response response) throws IOException {
Log.d("OkHttp", "Call succeeded:" + response.message());
}
});
先来看一下Request包含的有通讯的信息
url：发起通讯的地址
method：通讯方式
public final class Request {
final HttpUrl url;
final String method;
final Headers headers;
final RequestBody body;
final Object tag;
private volatile CacheControl cacheControl; // Lazily initialized.
Request(Builder builder) {
this.url = builder.url;
this.method = builder.method;
this.headers = builder.headers.build();
this.body = builder.body;
this.tag = builder.tag != null ? builder.tag : this;
}
主体流程
下面我们先来摸清这个框架的主干部分，刚开始看的时候，先沿一条线下来，细枝末节先不要太关心：
我们来看看newCall：
client.newCall(request).enqueue(new Callback() {
@Override public Call newCall(Request request) {
return new RealCall(this, request, false /* for web socket */);
}
final class RealCall implements Call {
RealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
final EventListener.Factory eventListenerFactory = client.eventListenerFactory();
this.client = client;
this.originalRequest = originalRequest;
this.forWebSocket = forWebSocket;
this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client, forWebSocket);
// TODO(jwilson): this is unsafe publication and not threadsafe.
this.eventListener = eventListenerFactory.create(this);
}
可以看出：Call是一个接口，而RealCall是Call的一个具体实现。client.newCall(request)里面是生成一个RealCall的实例
Recall同时持有client和request，
所以：
client.newCall(request).enqueue(new Callback() {
实际上执行到的是RealCall的enqueue：
@Override public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
这里的responseCallback就是我们最外层的回调接口，暂时先不管这个。
重点看这行代码：
client.dispatcher().enqueue(new AsyncCall(responseCallback));
dispatcher是client持有的一个调度器，我们找到Dispatcher这个类里面的enqueue方法：
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
可以看出，runningAsyncCalls，这里是线程池里面的概念，先看executorService().execute(call）
来看一下call：
final class AsyncCall extends NamedRunnable {
public abstract class NamedRunnable implements Runnable {
可以看出，AsyncCall是一个Runnable，所以executorService().execute(call）执行的时候，实际上执行的是AsnycCall里面的execute()方法：
@Override protected void execute() {
boolean signalledCallback = false;
try {
Response response = getResponseWithInterceptorChain();
if (retryAndFollowUpInterceptor.isCanceled()) {
signalledCallback = true;
responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
} else {
signalledCallback = true;
responseCallback.onResponse(RealCall.this, response);
}
} catch (IOException e) {
if (signalledCallback) {
// Do not signal the callback twice!
Platform.get().log(INFO, "Callback failure for " + toLoggableString(), e);
} else {
responseCallback.onFailure(RealCall.this, e);
}
} finally {
client.dispatcher().finished(this);
}
}
找到关键的语句：
Response result = getResponseWithInterceptorChain();
这句是这个框架比较核心的思想：拦截器，通过一个个的拦截器，通过递归串联起来：
Response getResponseWithInterceptorChain() throws IOException {
// Build a full stack of interceptors.
List<Interceptor> interceptors = new ArrayList<>();
interceptors.addAll(client.interceptors());
interceptors.add(retryAndFollowUpInterceptor);
interceptors.add(new BridgeInterceptor(client.cookieJar()));
interceptors.add(new CacheInterceptor(client.internalCache()));
interceptors.add(new ConnectInterceptor(client));
if (!forWebSocket) {
interceptors.addAll(client.networkInterceptors());
}
interceptors.add(new CallServerInterceptor(forWebSocket));
Interceptor.Chain chain = new RealInterceptorChain(
interceptors, null, null, null, 0, originalRequest);
return chain.proceed(originalRequest);
}
首先是interceptors.addAll(client.interceptors())，这里面的intterceptors是哪里来的呢，从代码可以看出是由client来的，其实就是我们初始化client的时候，由用户
添加的new OkHttpClient.Builder().addInterceptor(new LoggingInterceptor()).build();这里面的LoggingInterceptor就是我们用户自己定义的interceptor，从上面的代码
我们可以看到interceptors是一个list，说明client的addInterceptor可以添加多个。
我们看client的interceptors，是分为两种类型的， addInterceptor()和addNetworkInterceptor() ，通过 addInterceptor() 方法添加的拦截器是放在最前面的。通过 addNetworkInterceptor() 方法添加的网络拦截器，则是在非 WebSocket 请求时，添加在 ConnectInterceptor 和 CallServerInterceptor 之间的。这两个的区别，可以看
这里：https://blog.csdn.net/qq_38219041/article/details/72935142?utm_source=blogxgwz1
addInterceptor() 添加应用拦截器
● 不需要担心中间过程的响应,如重定向和重试.
● 总是只调用一次,即使HTTP响应是从缓存中获取.
● 观察应用程序的初衷. 不关心OkHttp注入的头信息如: If-None-Match.
● 允许短路而不调用 Chain.proceed(),即中止调用.
● 允许重试,使 Chain.proceed()调用多次.
addNetworkInterceptor() 添加网络拦截器
● 能够操作中间过程的响应,如重定向和重试.
● 当网络短路而返回缓存响应时不被调用.
● 只观察在网络上传输的数据.
● 携带请求来访问连接.
接下来的重点是这句话：
Interceptor.Chain chain = new RealInterceptorChain(
interceptors, null, null, null, 0, originalRequest);
return chain.proceed(originalRequest);
interceptors的循环调用就在这里面了，那我们看一下这里面是如何实现的：
public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
RealConnection connection) throws IOException {
if (index >= interceptors.size()) throw new AssertionError(); calls++; // If we already have a stream, confirm that the incoming request will use it.
if (this.httpCodec != null && !this.connection.supportsUrl(request.url())) {
throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
+ " must retain the same host and port");
} // If we already have a stream, confirm that this is the only call to chain.proceed().
if (this.httpCodec != null && calls > 1) {
throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
+ " must call proceed() exactly once");
} // Call the next interceptor in the chain.
RealInterceptorChain next = new RealInterceptorChain(
interceptors, streamAllocation, httpCodec, connection, index + 1, request);
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next); // Confirm that the next interceptor made its required call to chain.proceed().
if (httpCodec != null && index + 1 < interceptors.size() && next.calls != 1) {
throw new IllegalStateException("network interceptor " + interceptor
+ " must call proceed() exactly once");
} // Confirm that the intercepted response isn't null.
if (response == null) {
throw new NullPointerException("interceptor " + interceptor + " returned null");
} return response;
}
可以看到，RealInterceptorChain的参数index第一次传进来的时候为0，来看porceed这个方法里面，重点是下面这句话：
// Call the next interceptor in the chain.
RealInterceptorChain next = new RealInterceptorChain(
interceptors, streamAllocation, httpCodec, connection, index + 1, request);
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);
这里先new一个RealInterceptorChain，index为在原来的基础上+1，然后从前面的interceptors这个list里面，根据index取出相对应的一个interceptor，然后这个RealInterceptorChain作为一个参数传进interceptor.intercept
这时候我们就要回过头去看一下，说了这么久的interceptor到底是什么：
interceptors.add(new BridgeInterceptor(client.cookieJar()));
public final class BridgeInterceptor implements Interceptor {
public interface Interceptor {
Response intercept(Chain chain) throws IOException;
interface Chain {
Request request();
Response proceed(Request request) throws IOException;
Connection connection();
}
}
interceptort定义一个接口，各个具体的拦截器实现这个接口，我们用户自己定义的拦截器也都是实现这个接口，
前面提到的：
Response response = interceptor.intercept(next);
其实就是每个具体拦截器的方法intercept：
@Override public Response intercept(Chain chain) throws IOException {
Request userRequest = chain.request();
Request.Builder requestBuilder = userRequest.newBuilder();
RequestBody body = userRequest.body();
if (body != null) {
MediaType contentType = body.contentType();
if (contentType != null) {
requestBuilder.header("Content-Type", contentType.toString());
}
long contentLength = body.contentLength();
if (contentLength != -1) {
requestBuilder.header("Content-Length", Long.toString(contentLength));
requestBuilder.removeHeader("Transfer-Encoding");
} else {
requestBuilder.header("Transfer-Encoding", "chunked");
requestBuilder.removeHeader("Content-Length");
}
}
if (userRequest.header("Host") == null) {
requestBuilder.header("Host", hostHeader(userRequest.url(), false));
}
if (userRequest.header("Connection") == null) {
requestBuilder.header("Connection", "Keep-Alive");
}
// If we add an "Accept-Encoding: gzip" header field we're responsible for also decompressing
// the transfer stream.
boolean transparentGzip = false;
if (userRequest.header("Accept-Encoding") == null && 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());
}
Response networkResponse = chain.proceed(requestBuilder.build());
HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());
Response.Builder responseBuilder = networkResponse.newBuilder()
.request(userRequest);
if (transparentGzip
&& "gzip".equalsIgnoreCase(networkResponse.header("Content-Encoding"))
&& HttpHeaders.hasBody(networkResponse)) {
GzipSource responseBody = new GzipSource(networkResponse.body().source());
Headers strippedHeaders = networkResponse.headers().newBuilder()
.removeAll("Content-Encoding")
.removeAll("Content-Length")
.build();
responseBuilder.headers(strippedHeaders);
responseBuilder.body(new RealResponseBody(strippedHeaders, Okio.buffer(responseBody)));
}
return responseBuilder.build();
}
以上代码我们先追踪是如何实现循环调用interceptor，主要是以下这一句：
Response networkResponse = chain.proceed(requestBuilder.build());
看到这里，又调用了chain的proceed，而这个chain就是RealInterceptorChain，又回到了chain的proceed里面：
// Call the next interceptor in the chain.
RealInterceptorChain next = new RealInterceptorChain(
interceptors, streamAllocation, httpCodec, connection, index + 1, request);
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);
通过index再次加1，调用下一个interceptor的intercept；所以拦截器list interceptors并不是通过for循环来获得每一个的拦截器，而是通过前面的index每次+1，然后
通过chain来串连起来。
由上可知，每个拦截器的重点位置就是看里面的intercept方法如何执行的，这里面都包括该拦截器的本身的业务处理以及调用下一个拦截器。
拦截器
BridgeInterceptor：转换应用层request数据为真正的网络请求数据：
先看一下BridgeInterceptor,拦截器我们都是从intercept方法入手：
@Override public Response intercept(Chain chain) throws IOException {
Request userRequest = chain.request();
Request.Builder requestBuilder = userRequest.newBuilder();
RequestBody body = userRequest.body();
if (body != null) {
MediaType contentType = body.contentType();
if (contentType != null) {
requestBuilder.header("Content-Type", contentType.toString());
}
long contentLength = body.contentLength();
if (contentLength != -1) {
requestBuilder.header("Content-Length", Long.toString(contentLength));
requestBuilder.removeHeader("Transfer-Encoding");
} else {
requestBuilder.header("Transfer-Encoding", "chunked");
requestBuilder.removeHeader("Content-Length");
}
}
if (userRequest.header("Host") == null) {
requestBuilder.header("Host", hostHeader(userRequest.url(), false));
}
if (userRequest.header("Connection") == null) {
requestBuilder.header("Connection", "Keep-Alive");
}
// If we add an "Accept-Encoding: gzip" header field we're responsible for also decompressing
// the transfer stream.
boolean transparentGzip = false;
if (userRequest.header("Accept-Encoding") == null && 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());
}
Response networkResponse = chain.proceed(requestBuilder.build());
HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());
Response.Builder responseBuilder = networkResponse.newBuilder()
.request(userRequest);
if (transparentGzip
&& "gzip".equalsIgnoreCase(networkResponse.header("Content-Encoding"))
&& HttpHeaders.hasBody(networkResponse)) {
GzipSource responseBody = new GzipSource(networkResponse.body().source());
Headers strippedHeaders = networkResponse.headers().newBuilder()
.removeAll("Content-Encoding")
.removeAll("Content-Length")
.build();
responseBuilder.headers(strippedHeaders);
responseBuilder.body(new RealResponseBody(strippedHeaders, Okio.buffer(responseBody)));
}
return responseBuilder.build();
}
以上代码中，前半部分，chain.proceed(requestBuilder.build())前面，其实就是将最外层的代码，即用户层面定义的request：
Request request = new Request.Builder() .........
里面的各个参数转为真正的网络请求参数，包括Host、Connect、Accept-Encoding、User-Agent、Cookie等http的头部分头信息，通过：
Response networkResponse = chain.proceed(requestBuilder.build());
将这些信息传入到下一个拦截器去执行，请求阶段这个拦截器的作用已经结束，接下来就是调用：
Response.Builder responseBuilder = networkResponse.newBuilder()
.request(userRequest);
来等待下级拦截器的返回结果。所以拦截器的作用就是，我尽管完成我的那一部分工作，把我得到的请求交给下一个拦截器，中间的过程不用管，我就等待下一个拦截器返回结果，然后再将结果同样返回上一个拦截器。
return responseBuilder.build();
CacheInterceptor：缓存拦截器，从网络还是缓存获取数据：
接下来看一下CacheInterceptor：
@Override public Response intercept(Chain chain) throws IOException {
Response cacheCandidate = cache != null
? cache.get(chain.request())
: null;
long now = System.currentTimeMillis();
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()); // The cache candidate wasn't applicable. Close it.
}
// If we're forbidden from using the network and the cache is insufficient, fail.
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();
}
// If we don't need the network, we're done.
if (networkRequest == null) {
return cacheResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build();
}
Response networkResponse = null;
try {
networkResponse = chain.proceed(networkRequest);
} finally {
// If we're crashing on I/O or otherwise, don't leak the cache body.
if (networkResponse == null && cacheCandidate != null) {
closeQuietly(cacheCandidate.body());
}
}
// If we have a cache response too, then we're doing a conditional get.
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();
// Update the cache after combining headers but before stripping the
// Content-Encoding header (as performed by initContentStream()).
cache.trackConditionalCacheHit();
cache.update(cacheResponse, response);
return response;
} else {
closeQuietly(cacheResponse.body());
}
}
Response response = networkResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build();
if (cache != null) {
if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) {
// Offer this request to the cache.
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;
}
首先是这一句：
Response cacheCandidate = cache != null
? cache.get(chain.request())
: null;
判断本地是否存在缓存，如果存在，直接用，如果不存在，则值为空继续往下，那这个cache又从哪里来呢，其实也是应用层定义的：
//缓存文件夹
File cacheFile = new File(getExternalCacheDir().toString(), "cache");
//缓存大小为10M
int cacheSize = 10 * 1024 * 1024;
Cache cache = new Cache(cacheFile, cacheSize);
OkHttpClient client = new OkHttpClient
.Builder()
//.addInterceptor(new LoggingInterceptor())//日志拦截器
.cache(cache)
这里定义了一个file存储cache，定义了名字、存储路径以及最大缓存容量，那是在哪个地方设置值进去呢：
// If we have a cache response too, then we're doing a conditional get.
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(); // Update the cache after combining headers but before stripping the
// Content-Encoding header (as performed by initContentStream()).
cache.trackConditionalCacheHit();
cache.update(cacheResponse, response);
return response;
} else {
closeQuietly(cacheResponse.body());
}
}
我们先来看HTTP_NOT_MODIFIED看是什么意思：
/**
* HTTP Status-Code 304: Not Modified.
*/
public static final int HTTP_NOT_MODIFIED = 304;
返回这个意思就是，当客户端再次请求数据的时候，这个时间到上次请求的时间段内，服务器的资源数据没有更新，所以对于客户端来说，没必要再次去服务器获取具体数据，直接从本地获取上一次的数据，然后return response。
如果说是网络资源已修改，或者是第一次请求，则使用下一层的网络请求返回response，然后将该response缓存在cache里面供下次的请求使用。
RetryAndFollowUpInterceptor 重试和重定向拦截器
作者：chaychan
链接：http://www.imooc.com/article/details/id/271841
来源：慕课网
作者：chaychan
链接：http://www.imooc.com/article/details/id/271841
来源：慕课网
未完待续。。。
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