1.OkHttp发起网络请求
可以通过OkHttpClient发起一个网络请求
//创建一个Client，相当于打开一个浏览器
OkHttpClient okHttpClient = new OkHttpClient.Builder().build();
//创建一个请求。
Request request = new Request.Builder()
.url("http://www.baidu.com")
.method("GET",null)
.build();
//调用Client 创建一个Call。
Call call = okHttpClient.newCall(request);
//Call传入一个回调函数，并加入到请求队列。
call.enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
}
@Override
public void onResponse(Call call, Response response) throws IOException {
}
});
}
通过Retrofit发起一个OkHttp请求
Retrofit retrofit = new Retrofit.Builder()
.baseUrl("http://www.baidu.com/")
.build();
NetInterface netInterface = retrofit.create(NetInterface.class);
Call call = netInterface.getPerson();
call.enqueue(new Callback() {
@Override
public void onResponse(Call call, Response response) {
}
@Override
public void onFailure(Call call, Throwable t) {
}
});
以上两种方式都是通过call.enqueue() 把网络请求加入到请求队列的。
这个call是RealCall的一个对象。
public void enqueue(Callback responseCallback) {
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
这里有两个判断条件
runningAsyncCalls.size() < maxRequests如果运行队列数量大于最大数量，
runningCallsForHost(call) < maxRequestsPerHost并且访问同一台服务器的请求数量大于最大数量，请求会放入等待队列，否则加入运行队列，直接执行。
//等待队列 private final DequereadyAsyncCalls = new ArrayDeque<>(); //运行队列 private final Deque runningAsyncCalls = new ArrayDeque<>(); //运行队列数量最大值 private int maxRequests = 64; //访问不同主机的最大数量 private int maxRequestsPerHost = 5;
dispatcher.java
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
接下来看这行代码executorService().execute(call);
executorService()拿到一个线程池实例，
public synchronized ExecutorService executorService() {
if (executorService == null) {
executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS,
new SynchronousQueue(), Util.threadFactory("OkHttp Dispatcher", false));
}
return executorService;
execute(call)执行任务，发起网络请求。
//AsyncCall.java
@Override protected void execute() {
try {
//这个方法去请求网络，会返回Respose
Response response = getResponseWithInterceptorChain();
//请求成功，回调接口
responseCallback.onResponse(RealCall.this, response);
}catch(Exceptrion e){
//失败回调
responseCallback.onFailure(RealCall.this, e);
}finally {
//从当前运行队列中删除这个请求
client.dispatcher().finished(this);
}
}
getResponseWithInterceptorChain()
这行代码，使用了设计模式中的责任链模式。
//这个方法命名：通过拦截器链，获取Response
Response getResponseWithInterceptorChain() throws IOException {
// Build a full stack of interceptors.
List interceptors = new ArrayList<>();
// 这个我们自己定义的拦截器。
interceptors.addAll(client.interceptors());
//重试和重定向拦截器
interceptors.add(retryAndFollowUpInterceptor);
//请求头拦截器
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());
}
//访问拦截器
interceptors.add(new CallServerInterceptor(forWebSocket));
//拦截器责任链
Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
originalRequest, this, eventListener, client.connectTimeoutMillis(),
client.readTimeoutMillis(), client.writeTimeoutMillis());
//执行拦截器集合中的拦截器
return chain.proceed(originalRequest);
}
责任链模式中，链条的上游持有下游对象的引用。这样能够保证在链条上的每一个对象，都能对其符合条件的任务进行处理。
但是在上面的拦截器构成责任链中，是把拦截器，放在了一个集合中。
第一个参数interceptors 是一个拦截器的集合。
第五个参数0是集合的index，RealInterceptorChain就是根据这个索引值+1，
对chain.proceed方法循环调用，进行集合遍历，并执行拦截器中定义的方法的。
这个责任链模式，并没有明确的指定下游对象是什么，而是通过集合index值的变化，动态的指定的。
Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0......)
chain.proceed(originalRequest);
public Response proceed(Request request,...){
//构建一个index+1的拦截器链
RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
connection, index + 1,....);
//拿到当前的拦截器
Interceptor interceptor = interceptors.get(index);
//调用拦截器intercept(next)方法，
//在这个方法中继续调用realChain.proceed(),从而进行循环调用，index索引值再加1.
Response response = interceptor.intercept(next);
}
2.OkHttp的连接器
1）RetryAndFollowUpInterceptor：重试和重定向拦截器
public Response intercept(Chain chain){
while (true) {
Response response;
try {
//创建StreamAllocation对象，这个对象会在连接拦截器中用到
StreamAllocation streamAllocation = new StreamAllocation(client.connectionPool(),
createAddress(request.url()), call, eventListener, callStackTrace);
this.streamAllocation = streamAllocation;
调用责任链下游拦截器
response = realChain.proceed(request, streamAllocation, null, null);
} catch (RouteException e) {
// The attempt to connect via a route failed. The request will not have been sent.
路由异常，请求还没发出去。
这样这个recover(),如果返回的是false，则抛出异常，不再重试
如果返回的是true，则执行下面的continue，进行下一次while循环，进行重试，重新发起网络请求。
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.
请求已经发出去了，但是和服务器连接失败了。
这个recover()返回值的处理逻辑和上面异常一样。
boolean requestSendStarted = !(e instanceof ConnectionShutdownException);
if (!recover(e, streamAllocation, requestSendStarted, request)) throw e;
releaseConnection = false;
continue;
}
} finally {//finally是必定会执行到的，不管上面的catch中执行的是continue还是thow
// We're throwing an unchecked exception. Release any resources.
if (releaseConnection) {
streamAllocation.streamFailed(null);
streamAllocation.release();
}
}
在这个重试拦截器中，okhttp的做法很巧妙。先是在外面有一个while循环，如果发生异常，
会在recover方法中对异常类型进行判断，如果不符合属于重试，则返回false，并thow e，结束while循环。
如果符合重试的条件，则返回true，在上面的catch代码块中执行continue方法，进入下一个while循环。
//如果请求正常，并且返回了response，则会进行重定向的逻辑判断
followUpRequest在这个方法中会根据ResponseCode，状态码进行重定向的判断，
Request followUp;
try {
followUp = followUpRequest(response, streamAllocation.route());
} catch (IOException e) {
streamAllocation.release();
throw e;
}
如果flolowUp 为null，则不需要重定向，直接返回response
if (followUp == null) {
if (!forWebSocket) {
streamAllocation.release();
}
return response;
}
如果flolowUp 不为null，则进行重定向了请求
如果重定向次数超过MAX_FOLLOW_UPS=20次，则抛出异常，结束while循环
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();
//从重定向请求中拿到url，封装一个新的streamAllocation对象，
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?");
}
//将重定向请求赋值给request 进入下一个重定向的请求的while循环，继续走上面的while循环代码
request = followUp;
priorResponse = response;
}
}
//只有这个方法返回值为false都不进行重试。
private boolean recover(IOException e, StreamAllocation streamAllocation,
boolean requestSendStarted, Request userRequest) {
streamAllocation.streamFailed(e);
// The application layer has forbidden retries.
应用层禁止重试。可以通过OkHttpClient进行配置(默认是允许的)
if (!client.retryOnConnectionFailure()) return false;
// We can't send the request body again.
if (requestSendStarted && userRequest.body() instanceof UnrepeatableRequestBody) return false;
// This exception is fatal. 致命的异常
判断是否属于重试的异常
if (!isRecoverable(e, requestSendStarted)) return false;
// No more routes to attempt.
没有更多可以连接的路由线路
if (!streamAllocation.hasMoreRoutes()) return false;
// For failure recovery, use the same route selector with a new connection.
return true;
}
只有这个方法返回false，都不进行重试。
private boolean isRecoverable(IOException e, boolean requestSendStarted) {
// If there was a protocol problem, don't recover.
出现了协议异常，不再重试
if (e instanceof ProtocolException) {
return false;
}
// If there was an interruption don't recover, but if there was a timeout connecting to a route
// we should try the next route (if there is one).
requestSendStarted为false时，并且异常类型为Scoket超时异常，将会进行下一次重试
if (e instanceof InterruptedIOException) {
return e instanceof SocketTimeoutException && !requestSendStarted;
}
// Look for known client-side or negotiation errors that are unlikely to be fixed by trying
// again with a different route.
如果是一个握手异常，并且证书出现问题，则不能重试
if (e instanceof SSLHandshakeException) {
// If the problem was a CertificateException from the X509TrustManager,
// do not retry.
if (e.getCause() instanceof CertificateException) {
return false;
}
}
2）BridgeInterceptor 桥拦截器：连接服务器的桥梁，主要是在请求头中设置一些参数配置
如：请求内容长度，编码，gzip压缩等。
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());
}
..................
}
在请求头中添加gizp，是否压缩
boolean transparentGzip = false;
if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == null) {
transparentGzip = true;
requestBuilder.header("Accept-Encoding", "gzip");
}
//cookies
List cookies = cookieJar.loadForRequest(userRequest.url());
if (!cookies.isEmpty()) {
requestBuilder.header("Cookie", cookieHeader(cookies));
}
调用责任链中下一个拦截器的方法，网络请求得到的数据封装到networkResponse中
Response networkResponse = chain.proceed(requestBuilder.build());
对cookie进行处理
HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());
如果设置了gzip，则会对networkResponse进行解压缩。
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();
}
3）CacheInterceptor缓存拦截器
public Response intercept(Chain chain){
// this.cache = DiskLruCache.create(fileSystem, directory, 201105, 2, maxSize);
这个缓存在底层使用的是DiskLruCache
//以request为key从缓存中拿到response。
Response cacheCandidate = cache != null
? cache.get(chain.request()): null;
long now = System.currentTimeMillis();
//缓存策略
CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
Request networkRequest = strategy.networkRequest;
Response cacheResponse = strategy.cacheResponse;
// If we're forbidden from using the network and the cache is insufficient, fail.
//如果请求和响应都为null，直接返回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();
}
// If we don't need the network, we're done.
//如果请求为null，缓存不为null，则直接使用缓存。
if (networkRequest == null) {
return cacheResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build();
}
Response networkResponse = null;
try {
//调用责任链下一个拦截器
networkResponse = chain.proceed(networkRequest);
} finally {
}
Response response = networkResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build();
// Offer this request to the cache.
//将响应存入缓存。
CacheRequest cacheRequest = cache.put(response);
}
4）ConnectInterceptor 连接拦截器。当一个请求发出，需要建立连接，然后再通过流进行读写。
public Response intercept(Chain chain) throws IOException {
RealInterceptorChain realChain = (RealInterceptorChain) chain;
Request request = realChain.request();
//在重定向拦截器中创建，
StreamAllocation streamAllocation = realChain.streamAllocation();
boolean doExtensiveHealthChecks = !request.method().equals("GET");
//从连接池中，找到一个可以复用的连接，
HttpCodec httpCodec = streamAllocation.newStream(client, chain, doExtensiveHealthChecks);
// RealConnection 中封装了一个Socket和一个Socket连接池
RealConnection connection = streamAllocation.connection();
//调用下一个拦截器
return realChain.proceed(request, streamAllocation, httpCodec, connection);
}
//遍历连接池
RealConnection get(Address address, StreamAllocation streamAllocation, Route route) {
assert (Thread.holdsLock(this));
for (RealConnection connection : connections) {
if (connection.isEligible(address, route)) {
streamAllocation.acquire(connection, true);
return connection;
}
}
return null;
}
public boolean isEligible(Address address, @Nullable Route route) {
// If this connection is not accepting new streams, we're done.
if (allocations.size() >= allocationLimit || noNewStreams) return false;
// If the non-host fields of the address don't overlap, we're done.
if (!Internal.instance.equalsNonHost(this.route.address(), address)) return false;
// If the host exactly matches, we're done: this connection can carry the address.
从连接池中找到一个连接参数一致且并未占用的连接
if (address.url().host().equals(this.route().address().url().host())) {
return true; // This connection is a perfect match.
}
5）CallServerInterceptor 请求服务器拦截器
/** This is the last interceptor in the chain. It makes a network call to the server. */
这是责任链中最后一个拦截器，这个会去请求服务器。
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();
//将请求头写入缓存
httpCodec.writeRequestHeaders(request);
return response;
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