07.Retrofit 源码分析
前言
由于之前项目搭建的是 MVP 架构，由RxJava + Glide + OKHttp + Retrofit + Dagger 等开源框架组合而成，之前也都是停留在使用层面上，没有深入的研究，最近打算把它们全部攻下。
介绍
Retrofit 跟之前介绍的 OKHttp 都是来自 Square 公司开源的项目，Retrofit 跟 OKHttp 也都属于 HTTP 网络请求框架，既然都是属于网络框架为什么我们都要分析它呢？有使用过 Retrofit 框架的知道，它的底层其实就是基于 OKHttp 来进行网络访问的。按照严格来说我个人认为 Retrofit 是基于 OKHttp 二次封装，目的就是为了使用更加简单明了。
简单使用
下面我们就简单以一个网络请求来举例说明一下，本章重点在于分析 Retrofit 源码，所以如果对使用有不清楚的可以看Retrofit API ，下面就以鸿洋大神 wanandroid 的开放 API :https://wanandroid.com/wxarticle/chapters/json 来进行网络请求:
定义 Retrofit 网络请求接口
public interface APIService {
//按照 Retrofit 要求定义接口 Retrofit + OKHttp 网络访问
@GET("/wxarticle/chapters/json")
Call<JsonObject> getWXarticle();
//按照 Retrofit 要求定义接口 RxJava + Retrofit + OKHttp 网络访问
@GET("/wxarticle/chapters/json")
Observable<JsonObject> getWXarticle();
}
初始化 Retrofit 实例
public static final String API_URL = "https://wanandroid.com";
//1. 配置 OKHttpClient 添加查看 Request / Response 数据拦截器
OkHttpClient okHttpClient = new OkHttpClient.Builder().addInterceptor(new Interceptor() {
@Override
public Response intercept(Chain chain) throws IOException {
//打印请求前的请求数据
Request request = chain.request();
Log.d(TAG, request.toString());
//打印服务端响应数据
Response response = chain.proceed(request);
MediaType mediaType = response.body().contentType();
String content = response.body().string();
Log.d("JSON：", content);
Log.d("MediaType：", mediaType.toString());
return response.newBuilder().
body(ResponseBody.create(mediaType, content)).
build();
}
}).build();
//2. 构建 Retrofit 对象
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(API_URL) //http API
.addConverterFactory(GsonConverterFactory.create()) //配置 GSON 转换
.addCallAdapterFactory(RxJava2CallAdapterFactory.createAsync()) //配置 RxJava ，支持异步访问 create 同步
.client(okHttpClient)//主动配置 OKhttpClient
.build();
//3. 拿到 Retrofit 请求对象
APIService api = retrofit.create(APIService.class);
**Retrofit + OKHttp **
Call<JsonObject> call = api.getWXarticles();
//OKHttp 异步访问网络
call.enqueue(new Callback<JsonObject>() {
@Override
public void onResponse(Call<JsonObject> call, retrofit2.Response<JsonObject> response) {
Log.d(TAG, "Retrofit + OKHttp "+response.body().toString());
}
@Override
public void onFailure(Call<JsonObject> call, Throwable t) {
Log.d(TAG, "Retrofit + OKHttp "+t.getMessage());
}
});
RxJava + Retrofit + OKHttp
Observable<JsonObject> observable = api.getWXarticle();
observable.subscribeOn(Schedulers.io())
.subscribeOn(AndroidSchedulers.mainThread())
.subscribe(new Observer<JsonObject>() {
@Override
public void onSubscribe(Disposable d) {
Log.d(TAG, "RxJava + Retrofit + OKHttp 订阅成功");
}
@Override
public void onNext(JsonObject s) {
Log.d(TAG, "RxJava + Retrofit + OKHttp "+s.toString());
}
@Override
public void onError(Throwable e) {
Log.d(TAG, "RxJava + Retrofit + OKHttp "+e.getMessage());
}
@Override
public void onComplete() {
Log.d(TAG, "RxJava + Retrofit + OKHttp onComplete");
}
});
输出结果:
//请求地址
com.dn_alan.myapplication.MainActivity: https://wanandroid.com/wxarticle/chapters/json
//请求 Request 信息
com.dn_alan.myapplication.MainActivity: Request{method=GET, url=https://wanandroid.com/wxarticle/chapters/json, tags={class retrofit2.Invocation=com.dn_alan.myapplication.APIService.getWXarticles() []}}；
//Rxjava 订阅成功
com.dn_alan.myapplication.MainActivity: RxJava + Retrofit + OKHttp 订阅成功
//RxJava + Retrofit + OKHttp 服务端返回的数据
D/com.dn_alan.myapplication.MainActivity: RxJava + Retrofit + OKHttp {"data":[{"children":[],"courseId":13,"id":408,"name":"鸿....}
//RxJava + Retrofit + OKHttp 网络请求完成
D/com.dn_alan.myapplication.MainActivity: RxJava + Retrofit + OKHttp onComplete
//Retrofit + OKHttp 网络请求完成
D/com.dn_alan.myapplication.MainActivity: Retrofit + OKHttp {"data":[{"children":.....}
通过打印我们能够看出来 RxJava + Retrofit + OKHttp , Retrofit + OKHttp 都请求成功了，通过请求地址 我们发现最后 Retrofit 会拼接在一起的。这样使用是不是非常的爽。如果对 RxJava , OKHttp 源码还不了解的建议看下我之前的文章先复习下，因为本章会涉及到它们源码，这里不会细讲都是初略带过，因为重点是 Retrofit。
下面就是真正开始分析 Retrofit 怎么配合 OKHttp 还有 RxJava 进行网络访问的。
源码分析
Retrofit 类介绍
package retrofit2;
...
public final class Retrofit {
....//省略代码
Retrofit(okhttp3.Call.Factory callFactory, HttpUrl baseUrl,
List<Converter.Factory> converterFactories, List<CallAdapter.Factory> callAdapterFactories,
@Nullable Executor callbackExecutor, boolean validateEagerly) {
this.callFactory = callFactory; //配置的 OKhttp
this.baseUrl = baseUrl;//配置的 Http 地址
this.converterFactories = converterFactories; // 配置的转换功能 比如 GSON,
this.callAdapterFactories = callAdapterFactories; // 配置的 RxJava
this.callbackExecutor = callbackExecutor;
this.validateEagerly = validateEagerly;
}
@SuppressWarnings("unchecked") // Single-interface proxy creation guarded by parameter safety.
public <T> T create(final Class<T> service) {
....//动态代理主要代码 后面讲解
}
....//省略部分代码
public static final class Builder {
private final Platform platform;
private @Nullable okhttp3.Call.Factory callFactory;
private @Nullable HttpUrl baseUrl;
private final List<Converter.Factory> converterFactories = new ArrayList<>();
private final List<CallAdapter.Factory> callAdapterFactories = new ArrayList<>();
private @Nullable Executor callbackExecutor;
private boolean validateEagerly;
Builder(Platform platform) {
this.platform = platform;
}
public Builder() {
this(Platform.get());
}
....//省略部分代码
/**
*
*
* 构建 OKHttpClient
*/
public Builder client(OkHttpClient client) {
return callFactory(checkNotNull(client, "client == null"));
}
/**
*
* 构建 OKHttpClient call
*/
public Builder callFactory(okhttp3.Call.Factory factory) {
this.callFactory = checkNotNull(factory, "factory == null");
return this;
}
/**
* Set the API base URL.
*
* @see #baseUrl(HttpUrl) 构建 URL
*/
public Builder baseUrl(String baseUrl) {
checkNotNull(baseUrl, "baseUrl == null");
return baseUrl(HttpUrl.get(baseUrl));
}
/** 构建 GSON */
public Builder addConverterFactory(Converter.Factory factory) {
converterFactories.add(checkNotNull(factory, "factory == null"));
return this;
}
/**
* 构建 RXJava {@link Call}.
*/
public Builder addCallAdapterFactory(CallAdapter.Factory factory) {
callAdapterFactories.add(checkNotNull(factory, "factory == null"));
return this;
}
public Retrofit build() {
// url
if (baseUrl == null) {
throw new IllegalStateException("Base URL required.");
}
//拿到 OKHttpClient
okhttp3.Call.Factory callFactory = this.callFactory;
if (callFactory == null) {
callFactory = new OkHttpClient();
}
Executor callbackExecutor = this.callbackExecutor;
if (callbackExecutor == null) {
callbackExecutor = platform.defaultCallbackExecutor();
}
// 初始化一个容器
List<CallAdapter.Factory> callAdapterFactories = new ArrayList<>(this.callAdapterFactories);
//添加了一个默认的 DefaultCallAdapterFactory 用于进行协助 OKHttp 网络请求
callAdapterFactories.addAll(platform.defaultCallAdapterFactories(callbackExecutor));
// 初始化默认数据转换器
List<Converter.Factory> converterFactories = new ArrayList<>(
1 + this.converterFactories.size() + platform.defaultConverterFactoriesSize());
converterFactories.add(new BuiltInConverters());
converterFactories.addAll(this.converterFactories);
converterFactories.addAll(platform.defaultConverterFactories());
//构建 Retrofit 对象
return new Retrofit(callFactory, baseUrl, unmodifiableList(converterFactories),
unmodifiableList(callAdapterFactories), callbackExecutor, validateEagerly);
}
}
}
根据 Retrofit 内部代码实现，我们可以知道主要做了 2 件事儿
- create 动态代理执行定义的注解接口函数(内部具体实现我们下一小节细讲)
- 构建一些比如适配 RxJava ，转换 GSON ,网络请求 OKHTTP 配置等等。
下面分析 retrofit create 可以说是核心方法了。
Retrofit create 动态代理实现
public <T> T create(final Class<T> service) {
//1. 检查 service
Utils.validateServiceInterface(service);
if (validateEagerly) {
eagerlyValidateMethods(service);
}
//执行动态代理
return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class<?>[] { service },
new InvocationHandler() {
private final Platform platform = Platform.get();
private final Object[] emptyArgs = new Object[0];
@Override public @Nullable Object invoke(Object proxy, Method method,
@Nullable Object[] args) throws Throwable {
// 是否是 Object 类型
if (method.getDeclaringClass() == Object.class) {
return method.invoke(this, args);
}
if (platform.isDefaultMethod(method)) {//一般不会执行这里
return platform.invokeDefaultMethod(method, service, proxy, args);
}
//2. 真正执行定义接口中的具体函数
//2.1 拿到 ServiceMethod 执行内部的 invoke 函数
return loadServiceMethod(method).invoke(args != null ? args : emptyArgs);
}
});
}
对 JAVA 设计模式很熟的应该知道，这里用到了动态代理模式，如果还有对动态代理或者其它设计模式不懂的可以看我以前写的设计模式系列文章 , 先看注释 2 loadServiceMethod 函数
private final Map<Method, ServiceMethod<?>> serviceMethodCache = new ConcurrentHashMap<>();
ServiceMethod<?> loadServiceMethod(Method method) {
//1. 拿到缓存中的 ServiceMethod
ServiceMethod<?> result = serviceMethodCache.get(method);
if (result != null) return result;//1.1 如果存在就返回
//加了一个同步锁
synchronized (serviceMethodCache) {
//在锁里面又获取了一次
result = serviceMethodCache.get(method);
if (result == null) {//如果还是为空
result = ServiceMethod.parseAnnotations(this, method); //开始解析接口上的注解
//解析完成 存入缓存，避免下次再次解析相同的数据
serviceMethodCache.put(method, result);
}
}
return result;
}
通过上面代码我们知道就是从 Map 中拿到 ServiceMethod 对象，如果缓存中没有就进行解析定义 Retrofit 网络请求接口从而构建 ServiceMethod ，这里如果有对 ConcurrentHashMap 不熟悉的推荐看下这篇文章ConcurrentHashMap 解析 。
下面我们看下 ServiceMethod.parseAnnotations
static <T> ServiceMethod<T> parseAnnotations(Retrofit retrofit, Method method) {
//1. 通过 retrofit 实例和 接口中的函数方法拿到一个 Retrofit 请求对象
RequestFactory requestFactory = RequestFactory.parseAnnotations(retrofit, method);
//2. 拿到注解中的返回对象 ：http://loveshisong.cn/%E7%BC%96%E7%A8%8B%E6%8A%80%E6%9C%AF/2016-02-16-Type%E8%AF%A6%E8%A7%A3.html
Type returnType = method.getGenericReturnType();
//内部判断 type
if (Utils.hasUnresolvableType(returnType)) {
...//属于抛一个异常
}
if (returnType == void.class) {
throw methodError(method, "Service methods cannot return void.");
}
//3. 执行 HttpServiceMethod 解析
return HttpServiceMethod.parseAnnotations(retrofit, method, requestFactory);
}
上面代码我们知道主要做了 3 件事儿
- 拿到请求对象
- 判断调用接口中函数的返回值类型
- 执行解析动作
我们来看下 RequestFactory.parseAnnotations(retrofit, method) 内部实现
//定义为 final 不能为继承
final class RequestFactory {
static RequestFactory parseAnnotations(Retrofit retrofit, Method method) {
return new Builder(retrofit, method).build();
}
static final class Builder {
....//省略部分代码
Builder(Retrofit retrofit, Method method) {
this.retrofit = retrofit; //拿到 retrofit 对象
this.method = method; //拿到调动的方法
this.methodAnnotations = method.getAnnotations();//获取方法上面的所有注解
this.parameterTypes = method.getGenericParameterTypes();//获取所有参数类型
this.parameterAnnotationsArray = method.getParameterAnnotations();//获取参数中定义的注解
}
RequestFactory build() {
for (Annotation annotation : methodAnnotations) {
//1. 解析方法上的注解
parseMethodAnnotation(annotation);
}
...//省略属性判断
//拿到参数注解的数量，遍历做一些处理
int parameterCount = parameterAnnotationsArray.length;
parameterHandlers = new ParameterHandler<?>[parameterCount];
for (int p = 0, lastParameter = parameterCount - 1; p < parameterCount; p++) {
parameterHandlers[p] =
parseParameter(p, parameterTypes[p], parameterAnnotationsArray[p], p == lastParameter);
}
...//省略属性判断
//2 . 实例化一个 RequestFactory 对象
return new RequestFactory(this);
}
}
我们先来看下 parseMethodAnnotation
private void parseMethodAnnotation(Annotation annotation) {
if (annotation instanceof DELETE) {
parseHttpMethodAndPath("DELETE", ((DELETE) annotation).value(), false);
} else if (annotation instanceof GET) {
parseHttpMethodAndPath("GET", ((GET) annotation).value(), false);
} else if (annotation instanceof HEAD) {
parseHttpMethodAndPath("HEAD", ((HEAD) annotation).value(), false);
} else if (annotation instanceof PATCH) {
parseHttpMethodAndPath("PATCH", ((PATCH) annotation).value(), true);
} else if (annotation instanceof POST) {
parseHttpMethodAndPath("POST", ((POST) annotation).value(), true);
} else if (annotation instanceof PUT) {
parseHttpMethodAndPath("PUT", ((PUT) annotation).value(), true);
} else if (annotation instanceof OPTIONS) {
parseHttpMethodAndPath("OPTIONS", ((OPTIONS) annotation).value(), false);
} else if (annotation instanceof HTTP) {
HTTP http = (HTTP) annotation;
parseHttpMethodAndPath(http.method(), http.path(), http.hasBody());
} else if (annotation instanceof retrofit2.http.Headers) {
String[] headersToParse = ((retrofit2.http.Headers) annotation).value();
if (headersToParse.length == 0) {
throw methodError(method, "@Headers annotation is empty.");
}
headers = parseHeaders(headersToParse);
} else if (annotation instanceof Multipart) {
if (isFormEncoded) {
throw methodError(method, "Only one encoding annotation is allowed.");
}
isMultipart = true;
} else if (annotation instanceof FormUrlEncoded) {
if (isMultipart) {
throw methodError(method, "Only one encoding annotation is allowed.");
}
isFormEncoded = true;
}
}
这里不用注释都知道干嘛了吧，就是拿到当前函数上是否有请求的注解比如 GET,POST，.... ，我们看一下内部实现
private void parseHttpMethodAndPath(String httpMethod, String value, boolean hasBody) {
if (this.httpMethod != null) {
throw methodError(method, "Only one HTTP method is allowed. Found: %s and %s.",
this.httpMethod, httpMethod);
}
this.httpMethod = httpMethod;
this.hasBody = hasBody;
if (value.isEmpty()) {
return;
}
// Get the relative URL path and existing query string, if present.
int question = value.indexOf('?');
if (question != -1 && question < value.length() - 1) {
// Ensure the query string does not have any named parameters.
String queryParams = value.substring(question + 1);
Matcher queryParamMatcher = PARAM_URL_REGEX.matcher(queryParams);
if (queryParamMatcher.find()) {
throw methodError(method, "URL query string \"%s\" must not have replace block. "
+ "For dynamic query parameters use @Query.", queryParams);
}
}
this.relativeUrl = value;
this.relativeUrlParamNames = parsePathParameters(value);
}
内部就是做一些请求链接的预处理，和最后一行代码是对注解中的数据做一些处理返回一个 set 集合。
现在回到 ServiceMethod 类中 的 HttpServiceMethod.parseAnnotations(retrofit, method, requestFactory);
static <ResponseT, ReturnT> HttpServiceMethod<ResponseT, ReturnT> parseAnnotations(
Retrofit retrofit, Method method, RequestFactory requestFactory) {
boolean isKotlinSuspendFunction = requestFactory.isKotlinSuspendFunction; //是否支持 Kotlin
boolean continuationWantsResponse = false;
boolean continuationBodyNullable = false;
//拿到当前网络请求函数中的所有注解
Annotation[] annotations = method.getAnnotations();
Type adapterType;
if (isKotlinSuspendFunction) { //暂时没有支持 所有先不管内部实现
...//
} else {
//返回接口中注解的返回类型
adapterType = method.getGenericReturnType();
}
//1. 创建 createCallAdapter 就是返回的是 RxJava 被观察者对象或者是 OKHttp 的 默认 DefaultCallAdapterFactory 对象，根据注解返回值来判断
CallAdapter<ResponseT, ReturnT> callAdapter =
createCallAdapter(retrofit, method, adapterType, annotations);
Type responseType = callAdapter.responseType();
if (responseType == okhttp3.Response.class) {
throw methodError(method, "'"
+ getRawType(responseType).getName()
+ "' is not a valid response body type. Did you mean ResponseBody?");
}
....//省略判断
//2. 创建一个数据响应转换 返回 GSON
Converter<ResponseBody, ResponseT> responseConverter =
createResponseConverter(retrofit, method, responseType);
//3. 拿到 OKHttp call Factory
okhttp3.Call.Factory callFactory = retrofit.callFactory;
if (!isKotlinSuspendFunction) {
//4. 创建一个 callAdapted
return new CallAdapted<>(requestFactory, callFactory, responseConverter, callAdapter);
} else if (continuationWantsResponse) {
//noinspection unchecked Kotlin compiler guarantees ReturnT to be Object.
return (HttpServiceMethod<ResponseT, ReturnT>) new SuspendForResponse<>(requestFactory,
callFactory, responseConverter, (CallAdapter<ResponseT, Call<ResponseT>>) callAdapter);
} else {
//noinspection unchecked Kotlin compiler guarantees ReturnT to be Object.
return (HttpServiceMethod<ResponseT, ReturnT>) new SuspendForBody<>(requestFactory,
callFactory, responseConverter, (CallAdapter<ResponseT, Call<ResponseT>>) callAdapter,
continuationBodyNullable);
}
}
上面还是做一些对注解的预处理，处理完之后返回一个 ServiceMethod 对象。
从上面注释 1 我们可以知道这里根据注解解析返回的是一个 RxJava2CallAdapter 对象或者是 Retrofit 中 Builder 中默认的 DefaultCallAdapterFactory
当返回了 ServiceMethod 对象的时候又继续执行了一个 invoke 函数，我们直接看 HttpServiceMethod 的函数，因为它继承于 ServiceMethod
@Override final @Nullable ReturnT invoke(Object[] args) {
Call<ResponseT> call = new OkHttpCall<>(requestFactory, args, callFactory, responseConverter);
return adapt(call, args);
}
protected abstract @Nullable ReturnT adapt(Call<ResponseT> call, Object[] args);
上面拿到 OKHttpCall 然后执行一个 adapt 抽象函数，由于直接解析注解我们知道在其内部实例化的是 CallAdapter 对象，所以找它内部的 adapt 实现
static final class CallAdapted<ResponseT, ReturnT> extends HttpServiceMethod<ResponseT, ReturnT> {
private final CallAdapter<ResponseT, ReturnT> callAdapter;
CallAdapted(RequestFactory requestFactory, okhttp3.Call.Factory callFactory,
Converter<ResponseBody, ResponseT> responseConverter,
CallAdapter<ResponseT, ReturnT> callAdapter) {
super(requestFactory, callFactory, responseConverter);
this.callAdapter = callAdapter;
}
@Override protected ReturnT adapt(Call<ResponseT> call, Object[] args) {
//调用 CallAdapter 的 adapt 函数
return callAdapter.adapt(call);
}
}
到了这里我们可以知道 callAdapter.adapt 分别就目前知道实现了 2 个类，RxJava2CallAdapter,和 DefaultCallAdapterFactory,下面分别分析各自实现的 adapt(Call call) 函数
- RxJava2CallAdapter adapt
final class RxJava2CallAdapter<R> implements CallAdapter<R, Object> {
@Override public Object adapt(Call<R> call) {
//这里的 isAsync 就是配置 RxJava2CallAdapterFactory.createAsync() 内部有一个 布尔记录
//1. 由于我们配置的是异步所以这里返回 CallEnqueueObservable 被观察者对象
Observable<Response<R>> responseObservable = isAsync
? new CallEnqueueObservable<>(call)
: new CallExecuteObservable<>(call);
Observable<?> observable;
//2. 只要请求接口中泛型参数不是 Result 一般情况下执行 isBody 返回 BodyObservable 内部持有一个 CallEnqueueObservable 被观察者对象
if (isResult) {//如果泛型参数是 Result
observable = new ResultObservable<>(responseObservable);
} else if (isBody) {
observable = new BodyObservable<>(responseObservable);
} else {
observable = responseObservable;
}
//这里没有指定所以为空，也是在 RxJava2CallAdapterFactory 配置的时候指定
if (scheduler != null) {
observable = observable.subscribeOn(scheduler);
}
//定义的是否是 Flowable 被观察者
if (isFlowable) {
return observable.toFlowable(BackpressureStrategy.LATEST);
}
//定义的是否是 Single 被观察者
if (isSingle) {
return observable.singleOrError();
}
//定义的是否是 Maybe 被观察者
if (isMaybe) {
return observable.singleElement();
}
//定义的是否是 Completable 被观察者
if (isCompletable) {
return observable.ignoreElements();
}
//如果都不是的话 直接返回 BodyObservable
return RxJavaPlugins.onAssembly(observable);
}
}
到了这里 api.getWXarticle(); 如果定义的是被观察者对象，那么返回的就是 BodyObservable 内部持有一个 CallEnqueueObservable 的被观察者对象。
- DefaultCallAdapterFactory adapt
final class DefaultCallAdapterFactory extends CallAdapter.Factory {
private final @Nullable Executor callbackExecutor;
DefaultCallAdapterFactory(@Nullable Executor callbackExecutor) {
this.callbackExecutor = callbackExecutor;
}
@Override public @Nullable CallAdapter<?, ?> get(
Type returnType, Annotation[] annotations, Retrofit retrofit) {
...//省略部分代码
return new CallAdapter<Object, Call<?>>() {
@Override public Type responseType() {
return responseType;
}
@Override public Call<Object> adapt(Call<Object> call) {
return executor == null
? call
: new ExecutorCallbackCall<>(executor, call);
}
};
}
static final class ExecutorCallbackCall<T> implements Call<T> {
final Executor callbackExecutor;
final Call<T> delegate;
ExecutorCallbackCall(Executor callbackExecutor, Call<T> delegate) {
this.callbackExecutor = callbackExecutor;
this.delegate = delegate;
}
@Override public void enqueue(final Callback<T> callback) {
checkNotNull(callback, "callback == null");
delegate.enqueue(new Callback<T>() {
@Override public void onResponse(Call<T> call, final Response<T> response) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
if (delegate.isCanceled()) {
// Emulate OkHttp's behavior of throwing/delivering an IOException on cancellation.
callback.onFailure(ExecutorCallbackCall.this, new IOException("Canceled"));
} else {
callback.onResponse(ExecutorCallbackCall.this, response);
}
}
});
}
@Override public void onFailure(Call<T> call, final Throwable t) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
callback.onFailure(ExecutorCallbackCall.this, t);
}
});
}
});
}
...//省略部分代码
}
}
可以看到如果我们网络请求接口函数返回值定义的是 Call 的话，那么返回的就是实际返回的就是 ExecutorCallbackCall 对象
本章小结
可以看到 create 函数主要通过动态代理来实现了调用接口中的函数，首先解析注解数据，然后解析函数返回值，最后根据函数返回值创建对应的实现类。
下一小节就实际介绍调用了
Retrofit + OKHttp
通过上一小节我们知道 Call call = api.getWXarticles(); call 其实就是ExecutorCallbackCall 对象，那么根据调用
Call<JsonObject> call = api.getWXarticles();
call.enqueue(new Callback<JsonObject>() {
@Override
public void onResponse(Call<JsonObject> call, retrofit2.Response<JsonObject> response) {
Log.d(TAG, "Retrofit + OKHttp " + response.body().toString());
}
@Override
public void onFailure(Call<JsonObject> call, Throwable t) {
Log.d(TAG, "Retrofit + OKHttp " + t.getMessage());
}
});
我们直接看 ExecutorCallbackCall 的 enqueue 函数
static final class ExecutorCallbackCall<T> implements Call<T> {
final Executor callbackExecutor;
final Call<T> delegate;
ExecutorCallbackCall(Executor callbackExecutor, Call<T> delegate) {
this.callbackExecutor = callbackExecutor;
this.delegate = delegate;
}
@Override public void enqueue(final Callback<T> callback) {
//1. 检查 callBack 是否为空的状态
checkNotNull(callback, "callback == null");
//2. 这里的 delegate 其实就是 OKHttpClient 中的 Call
delegate.enqueue(new Callback<T>() {
@Override public void onResponse(Call<T> call, final Response<T> response) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
if (delegate.isCanceled()) {
// Emulate OkHttp's behavior of throwing/delivering an IOException on cancellation.
callback.onFailure(ExecutorCallbackCall.this, new IOException("Canceled"));
} else {
callback.onResponse(ExecutorCallbackCall.this, response);
}
}
});
}
@Override public void onFailure(Call<T> call, final Throwable t) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
callback.onFailure(ExecutorCallbackCall.this, t);
}
});
}
});
}
....//省略部分代码
}
根据上面注释 2 我们知道 delegate 就是 通过上层 HttpServiceMethod invoke 函数传进来的
@Override final @Nullable ReturnT invoke(Object[] args) {
Call<ResponseT> call = new OkHttpCall<>(requestFactory, args, callFactory, responseConverter);
return adapt(call, args);
}
没错就是我们熟悉的 OKHttpCall 对象，那么我们直接看 OkHttpCall.enqueue(new Callback
//继承自 OKHttp 中的 Call
final class OkHttpCall<T> implements Call<T> {
@Override public void enqueue(final Callback<T> callback) {
checkNotNull(callback, "callback == null");
//拿到 OKHttp 中的 Call
okhttp3.Call call;
Throwable failure;
synchronized (this) {
if (executed) throw new IllegalStateException("Already executed.");
executed = true;
call = rawCall;
failure = creationFailure;
if (call == null && failure == null) {
try {
//1. 创建一个 RealCall 对象
call = rawCall = createRawCall();
} catch (Throwable t) {
throwIfFatal(t);
failure = creationFailure = t;
}
}
}
if (failure != null) {
callback.onFailure(this, failure);
return;
}
if (canceled) {
call.cancel();
}
//2. 通过 RealCall 对象执行 enqueue 异步网络请求
call.enqueue(new okhttp3.Callback() {
@Override public void onResponse(okhttp3.Call call, okhttp3.Response rawResponse) {
Response<T> response;
try {
response = parseResponse(rawResponse);
} catch (Throwable e) {
throwIfFatal(e);
callFailure(e);
return;
}
try {
callback.onResponse(OkHttpCall.this, response);
} catch (Throwable t) {
throwIfFatal(t);
t.printStackTrace(); // TODO this is not great
}
}
@Override public void onFailure(okhttp3.Call call, IOException e) {
callFailure(e);
}
private void callFailure(Throwable e) {
try {
callback.onFailure(OkHttpCall.this, e);
} catch (Throwable t) {
throwIfFatal(t);
t.printStackTrace(); // TODO this is not great
}
}
});
}
}
这里主要做了 2 件事儿
- 创建 OKHttp call 也就是 RealCall
- 执行 RealCall enqueue 异步函数
我们看一下注释 1 因为 OKHttp 请求还需要 Request 对象，这里我们还没看见所以，继续在找
private okhttp3.Call createRawCall() throws IOException {
//1.
okhttp3.Call call = callFactory.newCall(requestFactory.create(args));
if (call == null) {
throw new NullPointerException("Call.Factory returned null.");
}
return call;
}
通过注释 1 . 我们知道 callFactory.newCall(requestFactory.create(args)) 返回的是 OKHTTP.call 对象，但是熟悉 OKHTTP 的知道 newCall 中需要传入一个 Request 对象
//OKHttpClient.java
@Override public Call newCall(Request request) {
return RealCall.newRealCall(this, request, false /* for web socket */);
}
所以我们直接看 requestFactory.create(args)
//1. 返回一个 Request 对象
okhttp3.Request create(Object[] args) throws IOException {
@SuppressWarnings("unchecked") // It is an error to invoke a method with the wrong arg types.
ParameterHandler<Object>[] handlers = (ParameterHandler<Object>[]) parameterHandlers;
int argumentCount = args.length;
if (argumentCount != handlers.length) {
...//省略抛异常代码
}
//构建一个 Retrofit Request 对象
RequestBuilder requestBuilder = new RequestBuilder(httpMethod, baseUrl, relativeUrl,
headers, contentType, hasBody, isFormEncoded, isMultipart);
if (isKotlinSuspendFunction) {
argumentCount--;
}
List<Object> argumentList = new ArrayList<>(argumentCount);
for (int p = 0; p < argumentCount; p++) {
argumentList.add(args[p]);
handlers[p].apply(requestBuilder, args[p]);
}
//2.
return requestBuilder.get()
.tag(Invocation.class, new Invocation(method, argumentList))
.build();
}
通过上面代码我们知道内部构建了一个 Retrofit 的 Request 对象，最后调用注释 2 代码，我们继续跟
// requestBuilder.get()
Request.Builder get() {
HttpUrl url;
HttpUrl.Builder urlBuilder = this.urlBuilder;
if (urlBuilder != null) { //如果 URL 为空 重新构建一个
url = urlBuilder.build();
} else {
//这里正在把 一个连接完整拼接在一起 "https://wanandroid.com/wxarticle/chapters/json"
url = baseUrl.resolve(relativeUrl);
if (url == null) {
throw new IllegalArgumentException(
"Malformed URL. Base: " + baseUrl + ", Relative: " + relativeUrl);
}
}
//构建请求体
RequestBody body = this.body;
if (body == null) {
// Try to pull from one of the builders.
if (formBuilder != null) {
body = formBuilder.build();
} else if (multipartBuilder != null) {
body = multipartBuilder.build();
} else if (hasBody) {
// Body is absent, make an empty body.
body = RequestBody.create(null, new byte[0]);
}
}
//构建请求数据类型
MediaType contentType = this.contentType;
if (contentType != null) {
if (body != null) {
body = new ContentTypeOverridingRequestBody(body, contentType);
} else {
headersBuilder.add("Content-Type", contentType.toString());
}
}
//构建一个 Request 对象包含 url,headers,body
return requestBuilder
.url(url)
.headers(headersBuilder.build())
.method(method, body);
}
这里 get 函数就是 Retrofit Request - > OKHttp Request 的一个过程。
现在 OKHttp Request ,RealCall 对象都有了 就可以执行对应的异步函数，最后回调给调用层数据了。这里如果对 OKHttp 运行机制不了解的可以看根据 本文章前言 来进行阅读。
RxJava + Retrofit + OKHttp
通过 Retrofit create 小节讲解，我们知道 Observable<JsonObject> observable = api.getWXarticle(); Observable 其实就是 BodyObservable 它的上游是 CallEnqueueObservable 异步观察者对象 对象，那么根据调用
Observable<JsonObject> observable = api.getWXarticle();
//这里的 observable 就是 BodyObservable 内部持有一个上游 CallEnqueueObservable 被观察者
observable.subscribeOn(AndroidSchedulers.mainThread())
.subscribe(new Observer<JsonObject>() {
@Override
public void onSubscribe(Disposable d) {
Log.d(TAG, "RxJava + Retrofit + OKHttp 订阅成功");
}
@Override
public void onNext(JsonObject s) {
Log.d(TAG, "RxJava + Retrofit + OKHttp " + s.toString());
}
@Override
public void onError(Throwable e) {
Log.d(TAG, "RxJava + Retrofit + OKHttp " + e.getMessage());
}
@Override
public void onComplete() {
Log.d(TAG, "RxJava + Retrofit + OKHttp onComplete");
}
});
由于这里返回的是 BodyObservable 被观察者，那么根据执行流程在 ObservableSubscribeOn.subscribeActual 的 s.onSubscribe(parent); 函数中订阅成功。根据 RxJava 订阅成功执行流程可以知道下游会往上游走，最后会回调到 BodyObservable.subscribeActual 函数中，具体实现如下
@Override protected void subscribeActual(Observer<? super T> observer) {
upstream.subscribe(new BodyObserver<T>(observer));
}
根据 RxJava 源码中的调用执行流程这里的 upstream 就是上游 CallEnqueueObservable 异步被观察者对象，也直接看它的 subscribeActual 函数具体实现
//CallEnqueueObservable.java
@Override protected void subscribeActual(Observer<? super Response<T>> observer) {
// 1.
Call<T> call = originalCall.clone();
//2.
CallCallback<T> callback = new CallCallback<>(call, observer);
//3.
observer.onSubscribe(callback);
if (!callback.isDisposed()) {
//4.
call.enqueue(callback);
}
}
总结下上面注解意思
- 拿到 OKhttpCall Call 对象
- 对 call 和 observer 再次包装
- 调用下层观察者对象也就是 BodyObserver
- 最后才是执行 OKHttp 异步网络请求，把封装好的 CallCallback 传给 OKHttpCall 对象
我们直接看 OKHttpCall enqueue 函数具体实现
@Override public void enqueue(final Callback<T> callback) {
checkNotNull(callback, "callback == null");
...//省略部分代码
call.enqueue(new okhttp3.Callback() {
@Override public void onResponse(okhttp3.Call call, okhttp3.Response rawResponse) {
Response<T> response;
try {
response = parseResponse(rawResponse);
} catch (Throwable e) {
throwIfFatal(e);
callFailure(e);
return;
}
try {
callback.onResponse(OkHttpCall.this, response);
} catch (Throwable t) {
throwIfFatal(t);
t.printStackTrace(); // TODO this is not great
}
}
@Override public void onFailure(okhttp3.Call call, IOException e) {
callFailure(e);
}
private void callFailure(Throwable e) {
try {
callback.onFailure(OkHttpCall.this, e);
} catch (Throwable t) {
throwIfFatal(t);
t.printStackTrace(); // TODO this is not great
}
}
});
}
这里看到如果请求成功就直接回调到 OKhttp.callback.onResponse 中然后回调给 CallCallback 的 onResponse 函数，下面是具体实现
@Override public void onResponse(Call<T> call, Response<T> response) {
if (disposed) return;
try {
observer.onNext(response);
if (!disposed) {
terminated = true;
observer.onComplete();
}
} catch (Throwable t) {
Exceptions.throwIfFatal(t);
if (terminated) {
RxJavaPlugins.onError(t);
} else if (!disposed) {
try {
observer.onError(t);
} catch (Throwable inner) {
Exceptions.throwIfFatal(inner);
RxJavaPlugins.onError(new CompositeException(t, inner));
}
}
}
}
通过 observer.onNext(response); 一层传一层最后传递到 ObservableSubscribeOn#SubscribeOnObserver.onNext() 函数中到这里整个请求算是完成了。
总结
到这里 Retrofit 网络请求的源码已经分析完了 ，其中包括 Retrofit + OKHttp ，RxJava + Retrofit + OKHttp 相互之间怎么配合网络请求，也都进行讲解了一遍。建议在学习 Retrofit 网络请求之前，一定要知道 OKHttp 和 RxJava 的基本原理，不然 Retrofit 是看不下去的。
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