OkHttp的基本使用
String url = "http://wwww.baidu.com";
//(1)创建一个OKhttpClient
OkHttpClient okHttpClient = new OkHttpClient();
//(2)创建一个Request
final Request request = new Request.Builder()
.url(url)
.build();
//(3)okHttpClient 调用newCall()方法 创建一个Call对象
Call call = okHttpClient.newCall(request);
//(4)call调用enqueue()方法,这次请求Call添加到任务队列，并通过CallBack接收返回结果。
call.enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
Log.d(TAG, "onFailure: ");
}
@Override
public void onResponse(Call call, Response response) throws IOException {
Log.d(TAG, "onResponse: " + response.body().string());
}
});
- 在OkHttp3中，每一个请求任务都封装为一个Call，其实现为RealCall。
- 而所有的策略几乎都可以通过OkHttpClient传入
- 所有全局策略与数据，除了存储在允许上层访问的OkHttpClient实例以外，还有一部分是存储在只允许包可见的Internal.instance中（如连接池、路由黑名单等)
- OkHttp中用户可传入的interceptor分为两类，一类是全局interceptor，该类interceptor在请求开始之前最早被调用，另外一类为非网页请求的networkInterceptor，这类interceptor只有在非网页请求中会被调用，并且是在组装完成请求之后，真正发起请求之前被调用(这块具体可以参看RealCall#getResponseWithInterceptorChain()方法)
- 整个请求过程通过RealInterceptorChain#proceed来连接，在每个interceptor中调用下一个interceptor来完成整个请求流程，并且在回到当前interceptor后完成响应处理
- 在异步请求中，我们通过Callback来获得简单清晰的请求回调(onFailure、onResponse)
- 在OkHttpClient中，我们可以传入EventListener的工厂方法，为每一个请求创建一个EventListener，来接收非常细的事件回调
一、OKHttp3 原理介绍
1、okHttp中大量使用了Builder设置模式
如
OkHttpClient.Builder
Request.Builder
Builder机制的优势是 可以规避大量参数构造方法不灵活的缺点，和set方法不能保证对象的合法性问题。并且Builder采用链式调用，使用方便灵活。
2、Request 类
Request类其实是一个数据承载类，主要承载网络请求的参数信息，代表着一个网络请求。如method(get 或post),HttpUrl(scheme、host、port),headers 和RequestBody
public final class Request {
final HttpUrl url;
final String method;
final Headers headers;
final @Nullable 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;
}
}
3、OkHttpClient 类,也是一个载体类，一个工具箱。它承载http请求相关的策略参数、拦截器、调度分发器、超时时间、连接池等。
public class OkHttpClient implements Cloneable, Call.Factory, WebSocket.Factory {
final Dispatcher dispatcher;
final @Nullable Proxy proxy;
final List<Protocol> protocols;
final List<ConnectionSpec> connectionSpecs;
final List<Interceptor> interceptors;
final List<Interceptor> networkInterceptors;
final EventListener.Factory eventListenerFactory;
final ProxySelector proxySelector;
final CookieJar cookieJar;
final @Nullable Cache cache;
final @Nullable InternalCache internalCache;
final SocketFactory socketFactory;
final @Nullable SSLSocketFactory sslSocketFactory;
final @Nullable CertificateChainCleaner certificateChainCleaner;
final HostnameVerifier hostnameVerifier;
final CertificatePinner certificatePinner;
final Authenticator proxyAuthenticator;
final Authenticator authenticator;
final ConnectionPool connectionPool;
final Dns dns;
final boolean followSslRedirects;
final boolean followRedirects;
final boolean retryOnConnectionFailure;
final int connectTimeout;
final int readTimeout;
final int writeTimeout;
final int pingInterval;
}
OkHttpClient 继承自Call.Factory，实现了newCall()方法
interface Factory {
Call newCall(Request request);
}
@Override public Call newCall(Request request) {
return RealCall.newRealCall(this, request, false /* for web socket */);
}
RealCall类中newRealCall（）
static RealCall newRealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
// Safely publish the Call instance to the EventListener.
RealCall call = new RealCall(client, originalRequest, forWebSocket);
call.eventListener = client.eventListenerFactory().create(call);
return call;
}
okHttpClient的newCall方法内部调用的是RealCall的newRealCall()方法，传入okHttpClient对象（一个公共工具箱）和Request对象(什么网络请求)，返回一个RealCalL对象。
4、RealCall 类
RealCall集成自Call接口
public interface Call extends Cloneable {
//返回request请求
Request request();
//同步执行网络请求
Response execute() throws IOException;
//异步执行网路请求
void enqueue(Callback responseCallback);
//取消执行
void cancel();
boolean isExecuted();
boolean isCanceled();
Call clone();
interface Factory {
Call newCall(Request request);
}
RealCall类是网络请求的具体实施类。持有OkhttpClient(大工具箱)，和Request对象(网络请求)
（1）execute() 同步执行网路请求
@Override public Response execute() throws IOException {
synchronized (this) {
//保证仅执行一次
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
eventListener.callStart(this);
try {
//将该Call 添加到分发器中的同步队列中.
client.dispatcher().executed(this);
//网络请求真正执行的地方
Response result = getResponseWithInterceptorChain();
if (result == null) throw new IOException("Canceled");
return result;
} catch (IOException e) {
eventListener.callFailed(this, e);
throw e;
} finally {
// realCall执行完成，尝试将待执异步任务添加到 异步执行队列
client.dispatcher().finished(this);
}
}
（2）enqueue() 异步执行网络请求
realCall.enqueue() 的具体调用过程，如下图
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@Override public void enqueue(Callback responseCallback) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already Executed");
executed = true;
}
captureCallStackTrace();
eventListener.callStart(this);
//将RealCall 封装成一个AsyncCall同时添加到异步执行队列中。
client.dispatcher().enqueue(new AsyncCall(responseCallback));
}
AsyncCall 继承自NamedRunnable类，同时是RealCall的内部类，真正的执行过程位于execute中。
- NamedRunnable 为Runnable 添加了一个名称属性,成为可命名的Runnable,并将run()方法任务 代理到 虚方法execute()方法中
public abstract class NamedRunnable implements Runnable {
protected final String name;
public NamedRunnable(String format, Object... args) {
this.name = Util.format(format, args);
}
@Override public final void run() {
String oldName = Thread.currentThread().getName();
Thread.currentThread().setName(name);
try {
execute();
} finally {
Thread.currentThread().setName(oldName);
}
}
protected abstract void execute();
}
- AsyncCall继承自NamedRunnable,execuate()方法中，通过责任链getResponseWithInterceptorChain()来完成请求操作
final class AsyncCall extends NamedRunnable {
private final Callback responseCallback;
AsyncCall(Callback responseCallback) {
super("OkHttp %s", redactedUrl());
this.responseCallback = responseCallback;
}
String host() {
return originalRequest.url().host();
}
Request request() {
return originalRequest;
}
RealCall get() {
return RealCall.this;
}
@Override protected void execute() {
boolean signalledCallback = false;
try {
//请求执行的代码
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 {
eventListener.callFailed(RealCall.this, e);
responseCallback.onFailure(RealCall.this, e);
}
} finally {
client.dispatcher().finished(this);
}
}
}
（3）网络请求真正被执行的地方
getResponseWithInterceptorChain() 方法
可以看到该方法中天剑了一个Interceptor.Chain 拦截器链，同时添加了很多连接器。
真正的网络请求在CallServerInterceptor 拦截器中处理
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, this, eventListener, client.connectTimeoutMillis(),
client.readTimeoutMillis(), client.writeTimeoutMillis());
return chain.proceed(originalRequest);
}
}
5、 Dispatcher类 负责任务的分发
- Dispatcher 内部持有一个线程池
- 持有两个异步队列readyAsyncCalls(待执行异步任务队列)和runningAsyncCalls（正在执行的异步任务队列）
- 持有一个同步队列：runningSyncCalls（正在执行的同步任务）
public final class Dispatcher {
private int maxRequests = 64;
private int maxRequestsPerHost = 5;
private @Nullable Runnable idleCallback;
/** Executes calls. Created lazily. */
private @Nullable ExecutorService executorService;
/** Ready async calls in the order they'll be run. */
private final Deque<AsyncCall> readyAsyncCalls = new ArrayDeque<>();
/** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
private final Deque<AsyncCall> runningAsyncCalls = new ArrayDeque<>();
/** Running synchronous calls. Includes canceled calls that haven't finished yet. */
private final Deque<RealCall> runningSyncCalls = new ArrayDeque<>();
public Dispatcher(ExecutorService executorService) {
this.executorService = executorService;
}
public Dispatcher() {
}
public synchronized ExecutorService executorService() {
if (executorService == null) {
executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp Dispatcher", false));
}
return executorService;
}
}
队列管理
异步任务入列时，首先会判断 正在执行的异步任务个数是否小于可同时执行的任务个数，若是，则将call添加到runningAsyncCalls队列，同时在线程池中执行该Call任务
若否，说明任务忙，将Call添加到等待执行队列readyAsyncCalls
synchronized void enqueue(AsyncCall call) {
if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
runningAsyncCalls.add(call);
executorService().execute(call);
} else {
readyAsyncCalls.add(call);
}
}
当某个任务执行完成后，都会调用promoteCalls（）,尝试将等待队列中的任务，切换到正在执行队列，并在线程池中执行call任务。
private void promoteCalls() {
if (runningAsyncCalls.size() >= maxRequests) return; // Already running max capacity.
if (readyAsyncCalls.isEmpty()) return; // No ready calls to promote.
for (Iterator<AsyncCall> i = readyAsyncCalls.iterator(); i.hasNext(); ) {
AsyncCall call = i.next();
if (runningCallsForHost(call) < maxRequestsPerHost) {
i.remove();
runningAsyncCalls.add(call);
executorService().execute(call);
}
if (runningAsyncCalls.size() >= maxRequests) return; // Reached max capacity.
}
}
/** Used by {@code Call#execute} to signal completion. */
void finished(RealCall call) {
finished(runningSyncCalls, call, false);
}
private <T> void finished(Deque<T> calls, T call, boolean promoteCalls) {
int runningCallsCount;
Runnable idleCallback;
synchronized (this) {
if (!calls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
if (promoteCalls) promoteCalls();
runningCallsCount = runningCallsCount();
idleCallback = this.idleCallback;
}
if (runningCallsCount == 0 && idleCallback != null) {
idleCallback.run();
}
}
二、OKHttp 中拦截器链是其整个框架的精髓
image
用户可传入的 interceptor 分为两类：
- ①一类是全局的 interceptor，该类 interceptor 在整个拦截器链中最早被调用，通过 OkHttpClient.Builder#addInterceptor(Interceptor) 传入；
- ②另外一类是非网页请求的 interceptor ，这类拦截器只会在非网页请求中被调用，并且是在组装完请求之后，真正发起网络请求前被调用，所有的 interceptor 被保存在 List<Interceptor> interceptors 集合中，按照添加顺序来逐个调用。具体可参考 RealCall#getResponseWithInterceptorChain() 方法。通过 OkHttpClient.Builder#addNetworkInterceptor(Interceptor) 传入；
image
1、RetryAndFollowUpInterceptor 负责错误重试
如下面所示,外层是一个while(true)循环,执行完请求之后,由followUpRequest(response, route)判定是应该重试,直到followUp == null 退出循环。
class RetryAndFollowUpInterceptor(private val client: OkHttpClient) : Interceptor {
@Throws(IOException::class)
override fun intercept(chain: Interceptor.Chain): Response {
var request = chain.request()
val realChain = chain as RealInterceptorChain
var followUpCount = 0
var priorResponse: Response? = null
//(1) while 死循环
while (true) {
var response: Response
var success = false
try {
// 执行请求
response = realChain.proceed(request, transmitter, null)
success = true
} catch (e: RouteException) {
// The attempt to connect via a route failed. The request will not have been sent.
if (!recover(e.lastConnectException, transmitter, false, request)) {
throw e.firstConnectException
}
continue
} catch (e: IOException) {
// An attempt to communicate with a server failed. The request may have been sent.
val requestSendStarted = e !is ConnectionShutdownException
if (!recover(e, transmitter, requestSendStarted, request)) throw e
continue
} finally {
// The network call threw an exception. Release any resources.
if (!success) {
transmitter.exchangeDoneDueToException()
}
}
val exchange = response.exchange
val route = exchange?.connection()?.route()
//(3) 错误处理,followUp ！= null 则进行重试
val followUp = followUpRequest(response, route)
if (followUp == null) {
if (exchange != null && exchange.isDuplex) {
transmitter.timeoutEarlyExit()
}
return response
}
}
}
2、BridgeInterceptor 主要负责添加某些请求头Headers
class BridgeInterceptor(private val cookieJar: CookieJar) : Interceptor {
@Throws(IOException::class)
override fun intercept(chain: Interceptor.Chain): Response {
val userRequest = chain.request()
val requestBuilder = userRequest.newBuilder()
val body = userRequest.body
if (body != null) {
val contentType = body.contentType()
if (contentType != null) {
requestBuilder.header("Content-Type", contentType.toString())
}
val contentLength = body.contentLength()
if (contentLength != -1L) {
requestBuilder.header("Content-Length", contentLength.toString())
requestBuilder.removeHeader("Transfer-Encoding")
} else {
requestBuilder.header("Transfer-Encoding", "chunked")
requestBuilder.removeHeader("Content-Length")
}
}
if (userRequest.header("Host") == null) {
requestBuilder.header("Host", userRequest.url.toHostHeader())
}
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.
var transparentGzip = false
if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == null) {
transparentGzip = true
requestBuilder.header("Accept-Encoding", "gzip")
}
val cookies = cookieJar.loadForRequest(userRequest.url)
if (cookies.isNotEmpty()) {
requestBuilder.header("Cookie", cookieHeader(cookies))
}
if (userRequest.header("User-Agent") == null) {
requestBuilder.header("User-Agent", userAgent)
}
val networkResponse = chain.proceed(requestBuilder.build())
cookieJar.receiveHeaders(userRequest.url, networkResponse.headers)
val responseBuilder = networkResponse.newBuilder()
.request(userRequest)
...
return responseBuilder.build()
}
3、CacheInterceptor 主要是处理缓存的策略
class CacheInterceptor(internal val cache: Cache?) : Interceptor {
@Throws(IOException::class)
override fun intercept(chain: Interceptor.Chain): Response {
val cacheCandidate = cache?.get(chain.request())
val now = System.currentTimeMillis()
val strategy = CacheStrategy.Factory(now, chain.request(), cacheCandidate).compute()
val networkRequest = strategy.networkRequest
val cacheResponse = strategy.cacheResponse
cache?.trackResponse(strategy)
if (cacheCandidate != null && cacheResponse == null) {
// The cache candidate wasn't applicable. Close it.
cacheCandidate.body?.closeQuietly()
}
//(1)禁止使用网络请求，切无有效的本地缓存，则直接返回失败
// If we're forbidden from using the network and the cache is insufficient, fail.
if (networkRequest == null && cacheResponse == null) {
return Response.Builder()
.request(chain.request())
.protocol(Protocol.HTTP_1_1)
.code(HTTP_GATEWAY_TIMEOUT)
.message("Unsatisfiable Request (only-if-cached)")
.body(EMPTY_RESPONSE)
.sentRequestAtMillis(-1L)
.receivedResponseAtMillis(System.currentTimeMillis())
.build()
}
//(2) 需要要请求网络,则直接返回缓存数据
// If we don't need the network, we're done.
if (networkRequest == null) {
return cacheResponse!!.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build()
}
var networkResponse: Response? = null
try {
//(3) 重新从网络获取
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) {
cacheCandidate.body?.closeQuietly()
}
}
4、ConnectInterceptor 负责建立一个实际的网络链接
object ConnectInterceptor : Interceptor {
@Throws(IOException::class)
override fun intercept(chain: Interceptor.Chain): Response {
val realChain = chain as RealInterceptorChain
val request = realChain.request()
val transmitter = realChain.transmitter()
// We need the network to satisfy this request. Possibly for validating a conditional GET.
val doExtensiveHealthChecks = request.method != "GET"
//(1)生成一个新的Exchange对象。Exchange代表一个网络链接
val exchange = transmitter.newExchange(chain, doExtensiveHealthChecks)
return realChain.proceed(request, transmitter, exchange)
}
}
5、CallServerInterceptor 负责访问服务器
class CallServerInterceptor(private val forWebSocket: Boolean) : Interceptor {
@Throws(IOException::class)
override fun intercept(chain: Interceptor.Chain): Response {
val realChain = chain as RealInterceptorChain
val exchange = realChain.exchange()
val request = realChain.request()
val requestBody = request.body
val sentRequestMillis = System.currentTimeMillis()
exchange.writeRequestHeaders(request)
var responseHeadersStarted = false
var responseBuilder: Response.Builder? = null
if (HttpMethod.permitsRequestBody(request.method) && requestBody != null) {
// If there's a "Expect: 100-continue" header on the request, wait for a "HTTP/1.1 100
// Continue" response before transmitting the request body. If we don't get that, return
// what we did get (such as a 4xx response) without ever transmitting the request body.
if (responseBuilder == null) {
if (requestBody.isDuplex()) {
// Prepare a duplex body so that the application can send a request body later.
exchange.flushRequest()
val bufferedRequestBody = exchange.createRequestBody(request, true).buffer()
requestBody.writeTo(bufferedRequestBody)
} else {
// Write the request body if the "Expect: 100-continue" expectation was met.
val bufferedRequestBody = exchange.createRequestBody(request, false).buffer()
requestBody.writeTo(bufferedRequestBody)
bufferedRequestBody.close()
}
}
}
if (requestBody == null || !requestBody.isDuplex()) {
exchange.finishRequest()
}
if (!responseHeadersStarted) {
exchange.responseHeadersStart()
}
if (responseBuilder == null) {
responseBuilder = exchange.readResponseHeaders(false)!!
}
var response = responseBuilder
.request(request)
.handshake(exchange.connection()!!.handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build()
var code = response.code
if (code == 100) {
// server sent a 100-continue even though we did not request one.
// try again to read the actual response
response = exchange.readResponseHeaders(false)!!
.request(request)
.handshake(exchange.connection()!!.handshake())
.sentRequestAtMillis(sentRequestMillis)
.receivedResponseAtMillis(System.currentTimeMillis())
.build()
code = response.code
}
exchange.responseHeadersEnd(response)
response = if (forWebSocket && code == 101) {
// Connection is upgrading, but we need to ensure interceptors see a non-null response body.
response.newBuilder()
.body(EMPTY_RESPONSE)
.build()
} else {
response.newBuilder()
.body(exchange.openResponseBody(response))
.build()
}
i
return response
}
}
三、如何实现一个拦截器
1、定义拦截器接口Interceptor 和连接器链Chain
- Interceptor 最主要方法是intercept(),参数为拦截链，返回值为Respone结果。
- Interceptor.Chain 拦截器链最主要的方法为proceed（）参数为Request
public interface Interceptor {
Response intercept(Chain chain) throws IOException;
interface Chain {
Request request();
Response proceed(Request request) throws IOException;
@Nullable Connection connection();
Call call();
}
}
2、实现Interceptor 定义具体的拦截器
实现intercept()方法
- 请求预处理过程:取出原始request ，对原始request请求做相应的处理，生产一个新的Request
- 调用chain.proceed，将新request传递到下一个拦截器进行处理
- 下一个拦截器返回处理结果后，可以对结果进行二次处理，返回给上一个拦截器。
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 {
//（1）取出原始request ，对原始request请求做相应的处理，生产一个新的Request
Request userRequest = chain.request();
Request.Builder requestBuilder = userRequest.newBuilder();
if (userRequest.header("Host") == null) {
requestBuilder.header("Host", hostHeader(userRequest.url(), false));
}
//(2)将新request传递到下一个拦截器进行处理
Response networkResponse = chain.proceed(requestBuilder.build());
//(3)获取到下一个拦截器处理的结果，可以对结果进行一些后处理。然后返回给上一个拦截器。
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);
String contentType = networkResponse.header("Content-Type");
responseBuilder.body(new RealResponseBody(contentType, -1L, Okio.buffer(responseBody)));
}
return responseBuilder.build();
}
3、实现具体的Interceptor.Chain
public final class RealInterceptorChain implements Interceptor.Chain{
//interceptors 数组
private final List<Interceptor> interceptors;
//index指示当前 需要哪个Interceptor 处理Request
private final int index;
//记录当前的request请求
private final Request request;
@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();
//(1)Clone出一个新的RealInterceptorChain,更新原来的requst,index+1,将当前interceptor的下一个拦截器为当前的interceptor。
RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
writeTimeout);
//(2)执行当前interceptor的intercept()方法,将Clone出来的 RealInterceptorChain 作为参数传递给拦截器。
Interceptor interceptor = interceptors.get(index);
Response response = interceptor.intercept(next);
//返回response
return response;
}
}
到此 一个建议的拦截器链 完成。拦截器有很多应用，如Okhttp库，组件化方法CC库都用拦截器实现了其核心接口。
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