Retrofit簡(jiǎn)介
Retrofit是一個(gè)基于OKHttp的RESTful網(wǎng)絡(luò)請(qǐng)求框架镶摘。簡(jiǎn)單來(lái)說(shuō)，Retrofit就是一個(gè)網(wǎng)絡(luò)請(qǐng)求框架的封裝。網(wǎng)絡(luò)請(qǐng)求工作本質(zhì)上是由OkHttp完成床绪，Retrofit僅負(fù)責(zé)網(wǎng)絡(luò)請(qǐng)求接口的封裝。App應(yīng)用程序通過(guò) Retrofit 請(qǐng)求網(wǎng)絡(luò)其弊，實(shí)際上是使用 Retrofit 接口層封裝請(qǐng)求參數(shù)癞己、Header、Url 等信息梭伐，之后由 OkHttp完成網(wǎng)絡(luò)請(qǐng)求工作痹雅，在服務(wù)端返回?cái)?shù)據(jù)之后，OkHttp 將原始的結(jié)果交給 Retrofit糊识，Retrofit根據(jù)用戶的需求對(duì)結(jié)果進(jìn)行解析绩社。
Retrofit使用
請(qǐng)參考這是一份很詳細(xì)的 Retrofit 2.0 使用教程（含實(shí)例講解），簡(jiǎn)單使用如下赂苗，下邊我們會(huì)以該代碼講解Retrofit代碼執(zhí)行流程
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(BASE_URL) //配置baseUrl
.addConverterFactory(GsonConverterFactory.create())
.build();
public interface RetrofitService {
@GET("query")
Call<ResponseBody> getDataFromInternet();
}
RetrofitService retrofitService = retrofit.create(RetrofitService.class);
Call<ResultBean> responseBodyCall = retrofitService.getDataFromInternet();
responseBodyCall.enqueue(new Callback<ResultBean>() {
@Override
public void onResponse(Call<ResultBean> call, Response<ResultBean> response) {
System.out.println("call:" + response.toString());
}
@Override
public void onFailure(Call<ResultBean> call, Throwable t) {
}
});
Retrofit代碼執(zhí)行流程
（1）創(chuàng)建Retrofit實(shí)例铃将。
（2）創(chuàng)建網(wǎng)絡(luò)請(qǐng)求接口實(shí)例并配置網(wǎng)絡(luò)請(qǐng)求參數(shù)。
（3）執(zhí)行定義的接口方法retrofitService.getDataFromInternet()哑梳；
（4）執(zhí)行網(wǎng)絡(luò)請(qǐng)求，并處理服務(wù)器返回?cái)?shù)據(jù)绘盟。
1.創(chuàng)建Retrofit實(shí)例
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(BASE_URL)
.addConverterFactory(GsonConverterFactory.create())
.build();
1.1 Retrofit類如下
public final class Retrofit {
private final Map<Method, ServiceMethod> serviceMethodCache = new LinkedHashMap<>();
private final okhttp3.Call.Factory callFactory;
private final HttpUrl baseUrl;
private final List<Converter.Factory> converterFactories;
private final List<CallAdapter.Factory> adapterFactories;
private final Executor callbackExecutor;
...
}
相關(guān)成員變量說(shuō)明：
serviceMethodCache:網(wǎng)絡(luò)請(qǐng)求配置對(duì)象（對(duì)網(wǎng)絡(luò)請(qǐng)求接口中方法注解進(jìn)行解析后得到的對(duì)象）,存儲(chǔ)網(wǎng)絡(luò)請(qǐng)求相關(guān)的配置鸠真，如網(wǎng)絡(luò)請(qǐng)求的方法悯仙、數(shù)據(jù)轉(zhuǎn)換器、網(wǎng)絡(luò)請(qǐng)求適配器吠卷、網(wǎng)絡(luò)請(qǐng)求工廠锡垄、基地址等
callFactory:網(wǎng)絡(luò)請(qǐng)求器的工廠,生產(chǎn)網(wǎng)絡(luò)請(qǐng)求器，Retrofit是默認(rèn)使用OKHttp祭隔。
baseUrl:網(wǎng)絡(luò)請(qǐng)求的url地址货岭。
converterFactories：數(shù)據(jù)轉(zhuǎn)換器工廠的集合，放置數(shù)據(jù)轉(zhuǎn)換器工廠疾渴，數(shù)據(jù)轉(zhuǎn)換器工廠用來(lái)生產(chǎn)數(shù)據(jù)轉(zhuǎn)換器
adapterFactories：網(wǎng)絡(luò)請(qǐng)求適配器工廠的集合千贯，放置網(wǎng)絡(luò)請(qǐng)求適配器工廠，網(wǎng)絡(luò)請(qǐng)求適配器工廠用來(lái)生產(chǎn)網(wǎng)絡(luò)請(qǐng)求執(zhí)行器的適配器（CallAdapter）搞坝，網(wǎng)絡(luò)請(qǐng)求執(zhí)行器（Call）的適配器將默認(rèn)的網(wǎng)絡(luò)請(qǐng)求執(zhí)行器（OkHttpCall）轉(zhuǎn)換成適合被不同平臺(tái)來(lái)調(diào)用的網(wǎng)絡(luò)請(qǐng)求執(zhí)行器形式搔谴。
callbackExecutor：回調(diào)方法執(zhí)行器，在服務(wù)器返回相關(guān)請(qǐng)求結(jié)果后桩撮，客戶端用來(lái)切換線程（子線程-主線程）
1.2 Retrofit.Builder()方法如下
Retrofit.java
public Builder(){
//調(diào)用Platform.get()方法
this(Platform.get());
}
Platform.java
//將findPlatform()賦給靜態(tài)變量
private static final Platform PLATFORM=findPlatform();
static Platform get(){
return PLATFORM;
}
Platform.java
private static Platform findPlatform() {
try {
//Class.forName(xxx.xx.xx)要求JVM查找并加載指定的類（即JVM會(huì)執(zhí)行該類的靜態(tài)代碼段）
//未找到對(duì)應(yīng)的類敦第，會(huì)直接進(jìn)入catch中，說(shuō)明不是Android平臺(tái)店量。
Class.forName("android.os.Build");
if (Build.VERSION.SDK_INT != 0) {
//如果是Android平臺(tái)芜果，就創(chuàng)建并返回一個(gè)Android對(duì)象
return new Platform.Android();
}
} catch (ClassNotFoundException ignored) {
}
try {
//確認(rèn)是否是Java平臺(tái)
Class.forName("java.util.Optional");
return new Platform.Java8();
} catch (ClassNotFoundException ignored) {
}
try {
//確認(rèn)是否是IOS平臺(tái)
Class.forName("org.robovm.apple.foundation.NSObject");
return new Platform.IOS();
} catch (ClassNotFoundException ignored) {
}
return new Platform();
}
Platform.java
static class Android extends Platform {
@Override public Executor defaultCallbackExecutor() {
return new Platform.Android.MainThreadExecutor();
}
@Override CallAdapter.Factory defaultCallAdapterFactory(Executor callbackExecutor) {
//默認(rèn)的網(wǎng)絡(luò)請(qǐng)求適配器工廠,該默認(rèn)工廠生產(chǎn)的 adapter 會(huì)使得Call在異步調(diào)用時(shí)在指定的 Executor 上執(zhí)行回調(diào)
return new ExecutorCallAdapterFactory(callbackExecutor);
}
//回調(diào)方法執(zhí)行器,將服務(wù)器返回結(jié)果給客戶端時(shí)，進(jìn)行線程切換
static class MainThreadExecutor implements Executor {
//Looper.getMainLooper()獲取Android主線程Looper
private final Handler handler = new Handler(Looper.getMainLooper());
@Override public void execute(Runnable r) {
//通過(guò)主線程Handler將網(wǎng)絡(luò)請(qǐng)求回調(diào)切換到主線程中融师。
handler.post(r);
}
}
}
Retrofit.java
Builder(Platform platform) {
this.platform = platform;
//將默認(rèn)的數(shù)據(jù)轉(zhuǎn)換器BuiltInConverters()對(duì)象添加到數(shù)據(jù)轉(zhuǎn)換器工廠（converterFactories）
converterFactories.add(new BuiltInConverters());
}
至此右钾，Retrofit.Builder()方法設(shè)置了如下參數(shù)，平臺(tái)類型對(duì)象Android诬滩，網(wǎng)絡(luò)請(qǐng)求適配器工廠ExecutorCallAdapterFactory霹粥，數(shù)據(jù)轉(zhuǎn)換器工廠BuiltInConverters，回調(diào)執(zhí)行器MainThreadExecutor疼鸟。這里只是設(shè)置了默認(rèn)值后控。
1.3 new Retrofit.Builder().baseUrl(url)方法
baseUrl（）用于配置Retrofit類的網(wǎng)絡(luò)請(qǐng)求url地址
并且判斷url參數(shù)是不是以"/"結(jié)尾。
1.4 new Retrofit.Builder().baseUrl(url).addConverterFactory(GsonConverterFactory.create())方法
GsonConverterFactory.create()方法創(chuàng)建了一個(gè)含有Gson對(duì)象實(shí)例的GsonConverterFactory空镜，addConverterFactory(GsonConverterFactory.create())方法將上面創(chuàng)建的GsonConverterFactory放入到converterFactories數(shù)組中浩淘，至此，converterFactories中已經(jīng)有默認(rèn)的數(shù)據(jù)轉(zhuǎn)換器BuiltInConverters()和GsonConverterFactory對(duì)象實(shí)例吴攒。
1.5 new Retrofit.Builder().baseUrl(url).addConverterFactory(GsonConverterFactory.create(gson)).build()方法
其中build（）方法如下
Retrofit.java
public retrofit2.Retrofit build() {
if (baseUrl == null) {
throw new IllegalStateException("Base URL required.");
}
//配置網(wǎng)絡(luò)請(qǐng)求執(zhí)行器,默認(rèn)的網(wǎng)絡(luò)請(qǐng)求執(zhí)行器就是OKHttp,所以Retrofit網(wǎng)絡(luò)請(qǐng)求工作本質(zhì)上還是由OKHttp完成的张抄。
okhttp3.Call.Factory callFactory = this.callFactory;
if (callFactory == null) {
callFactory = new OkHttpClient();
}
//配置回調(diào)方法執(zhí)行器
Executor callbackExecutor = this.callbackExecutor;
if (callbackExecutor == null) {
//如果沒(méi)指定，則默認(rèn)使用Platform檢測(cè)環(huán)境時(shí)的默認(rèn)callbackExecutor,
//即步驟1.2節(jié)中Android平臺(tái)的默認(rèn)回調(diào)方法執(zhí)行器MainThreadExecutor
callbackExecutor = platform.defaultCallbackExecutor();
}
//配置網(wǎng)絡(luò)請(qǐng)求適配器工廠
List<CallAdapter.Factory> adapterFactories = new ArrayList<>(this.adapterFactories);
//向該集合中添加步驟1.2中創(chuàng)建的Android平臺(tái)默認(rèn)網(wǎng)絡(luò)請(qǐng)求適配器工廠ExecutorCallAdapterFactory洼怔。
adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));
//converterFactories在步驟1.2中已經(jīng)添加數(shù)據(jù)轉(zhuǎn)換器工廠BuiltInConverters署惯，
//在步驟1.4中添加GsonConverterFactory對(duì)象實(shí)例
List<Converter.Factory> converterFactories = new ArrayList<>(this.converterFactories);
//最終返回一個(gè)Retrofit的對(duì)象，并傳入上述已經(jīng)配置好的成員變量
return new retrofit2.Retrofit(callFactory, baseUrl, converterFactories, adapterFactories,
callbackExecutor, validateEagerly);
}
至此,已成功成功創(chuàng)建了Retrofit的實(shí)例镣隶。Retrofit已配置以下參數(shù)极谊，平臺(tái)類型對(duì)象Android诡右，網(wǎng)絡(luò)請(qǐng)求的url地址，網(wǎng)絡(luò)請(qǐng)求執(zhí)行器OkHttpClient轻猖，網(wǎng)絡(luò)請(qǐng)求適配器工廠的集合（已添加ExecutorCallAdapterFactory）帆吻，數(shù)據(jù)轉(zhuǎn)換器工廠集合（已添加BuiltInConverters()和GsonConverterFactory對(duì)象實(shí)例），回調(diào)方法執(zhí)行器（Android平臺(tái)的默認(rèn)回調(diào)方法執(zhí)行器MainThreadExecutor）咙边。
2.創(chuàng)建網(wǎng)絡(luò)請(qǐng)求接口實(shí)例并配置網(wǎng)絡(luò)請(qǐng)求參數(shù)
（1）定義接收網(wǎng)絡(luò)數(shù)據(jù)的類ResultBean
（2）定義網(wǎng)絡(luò)請(qǐng)求的接口類RetrofitService
（3）使用Retrofit.create（）方法創(chuàng)建網(wǎng)絡(luò)請(qǐng)求接口實(shí)例retrofit.create(RetrofitService.class)
步驟一猜煮、二可以參考這是一份很詳細(xì)的 Retrofit 2.0 使用教程（含實(shí)例講解）
2.1 Retrofit.create（）方法創(chuàng)建網(wǎng)絡(luò)請(qǐng)求接口的實(shí)例代碼
public <T> T create(final Class<T> service) {
// 創(chuàng)建了網(wǎng)絡(luò)請(qǐng)求接口的動(dòng)態(tài)代理對(duì)象，即通過(guò)動(dòng)態(tài)代理創(chuàng)建網(wǎng)絡(luò)請(qǐng)求接口的實(shí)例
// return (T) roxy.newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler invocationHandler)
// 可以解讀為：getProxyClass(loader, interfaces) .getConstructor(InvocationHandler.class).newInstance(invocationHandler);
// 即通過(guò)動(dòng)態(tài)生成的代理類败许，調(diào)用interfaces接口的方法實(shí)際上是通過(guò)調(diào)用InvocationHandler對(duì)象的invoke（）來(lái)完成指定的功能
return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class<?>[] { service },
new InvocationHandler() {
private final Platform platform = Platform.get();
@Override public Object invoke(Object proxy, Method method, Object... args)
throws Throwable {
// If the method is a method from Object then defer to normal invocation.
if (method.getDeclaringClass() == Object.class) {
return method.invoke(this, args);
}
if (platform.isDefaultMethod(method)) {
return platform.invokeDefaultMethod(method, service, proxy, args);
}
ServiceMethod serviceMethod = loadServiceMethod(method);
OkHttpCall okHttpCall = new OkHttpCall<>(serviceMethod, args);
return serviceMethod.callAdapter.adapt(okHttpCall);
}
});
}
通過(guò)代理模式中的動(dòng)態(tài)代理模式王带，動(dòng)態(tài)生成網(wǎng)絡(luò)請(qǐng)求接口的代理類，并將代理類的實(shí)例創(chuàng)建交給InvocationHandler類作為具體的實(shí)現(xiàn)檐束，并最終返回一個(gè)動(dòng)態(tài)代理對(duì)象辫秧。當(dāng)執(zhí)行定義的網(wǎng)絡(luò)請(qǐng)求接口方法時(shí)會(huì)進(jìn)行攔截，相關(guān)調(diào)用都會(huì)集中轉(zhuǎn)發(fā)到 InvocationHandler#invoke（）中被丧。
3.執(zhí)行定義的接口方法retrofitService.getDataFromInternet()
retrofitService對(duì)象實(shí)際上是動(dòng)態(tài)代理對(duì)象Proxy.newProxyInstance（）盟戏，并不是真正的網(wǎng)絡(luò)請(qǐng)求接口創(chuàng)建的對(duì)象，當(dāng)retrofitService對(duì)象調(diào)用getDataFromInternet（）時(shí)會(huì)被動(dòng)態(tài)代理對(duì)象Proxy.newProxyInstance（）攔截甥桂，然后調(diào)用自身的InvocationHandler # invoke（）柿究，invoke(Object proxy, Method method, Object... args)會(huì)傳入3個(gè)參數(shù)：Object proxy:（代理對(duì)象）、Method method（調(diào)用的getDataFromInternet()）黄选，Object... args（方法的參數(shù)蝇摸，即getDataFromInternet（）中的），然后執(zhí)行InvocationHandler#invoke方法办陷，代碼如下：
Proxy.newProxyInstance(service.getClassLoader(), new Class<?>[] { service },
new InvocationHandler() {
private final Platform platform = Platform.get();
@Override public Object invoke(Object proxy, Method method, Object... args)
throws Throwable {
// If the method is a method from Object then defer to normal invocation.
if (method.getDeclaringClass() == Object.class) {
return method.invoke(this, args);
}
if (platform.isDefaultMethod(method)) {
return platform.invokeDefaultMethod(method, service, proxy, args);
}
/*讀取網(wǎng)絡(luò)請(qǐng)求接口里的方法貌夕，并根據(jù)前面配置好的屬性配置serviceMethod對(duì)象
serviceMethod存儲(chǔ)網(wǎng)絡(luò)請(qǐng)求所需的信息，如網(wǎng)絡(luò)請(qǐng)求的方法民镜、數(shù)據(jù)轉(zhuǎn)換器啡专、網(wǎng)絡(luò)請(qǐng)求適配器、網(wǎng)絡(luò)請(qǐng)求工廠制圈、基地址等
ServiceMethod中封裝了OKHttp網(wǎng)絡(luò)請(qǐng)求所需的相關(guān)參數(shù)们童。這就是Retrofit將定義的interface轉(zhuǎn)換成網(wǎng)絡(luò)請(qǐng)求對(duì)象的過(guò)程。
*/
ServiceMethod serviceMethod = loadServiceMethod(method);
//根據(jù)配置好的serviceMethod對(duì)象創(chuàng)建okHttpCall對(duì)象,其成員變量中有網(wǎng)絡(luò)請(qǐng)求器實(shí)際對(duì)象RealCall鲸鹦。
OkHttpCall okHttpCall = new OkHttpCall<>(serviceMethod, args);
/*從Retrofit對(duì)象的callAdapterFactories工廠集合獲取callAdapter慧库，如果默認(rèn)使用ExecutorCallAdapterFactory則返回
CallObject(ExecutorCallbackCall),如果設(shè)置RxJavaCallAdapterFactory則返回observable。
最終獲取網(wǎng)絡(luò)請(qǐng)求適配器轉(zhuǎn)換后的網(wǎng)絡(luò)請(qǐng)求器對(duì)象*/
return serviceMethod.callAdapter.adapt(okHttpCall);
}
});
3.1 loadServiceMethod(method)方法
Retrofit.java
/*
通過(guò)反射將定義的標(biāo)注方法解析生成ServiceMethod對(duì)象（表示一個(gè)網(wǎng)絡(luò)請(qǐng)求的封裝對(duì)象）
同時(shí)將ServiceMethod對(duì)象加入LinkedHashMap<Method, ServiceMethod>集合
使用LinkedHashMap集合的好處：lruEntries.values().iterator().next()獲取到的是集合最不經(jīng)常用到的元素馋嗜，提供了一種Lru算法的實(shí)現(xiàn)
*/
ServiceMethod loadServiceMethod(Method method) {
ServiceMethod result;
synchronized (serviceMethodCache) {
result = serviceMethodCache.get(method);
if (result == null) {
result = new ServiceMethod.Builder(this, method).build();
serviceMethodCache.put(method, result);
}
}
return result;
}
ServiceMethod.java
public Builder(Retrofit retrofit, Method method) {
this.retrofit = retrofit;
this.method = method;
// 獲取網(wǎng)絡(luò)請(qǐng)求接口方法里的注釋
this.methodAnnotations = method.getAnnotations();
// 獲取網(wǎng)絡(luò)請(qǐng)求接口方法里的參數(shù)類型
this.parameterTypes = method.getGenericParameterTypes();
//獲取網(wǎng)絡(luò)請(qǐng)求接口方法里的注解內(nèi)容
this.parameterAnnotationsArray = method.getParameterAnnotations();
}
ServiceMethod.java
public ServiceMethod build() {
/*根據(jù)網(wǎng)絡(luò)請(qǐng)求接口方法的返回值和注解類型齐板，從Retrofit對(duì)象中獲取對(duì)應(yīng)的網(wǎng)絡(luò)請(qǐng)求適配器
createCallAdapater方法會(huì)調(diào)用Retrofit.callAdapter（），最終從Retrofit.adapterFactories集合中
返回ExecutorCallAdapterFactory，ExecutorCallAdapterFactory在步驟1.5進(jìn)行配置覆积。
*/
callAdapter = createCallAdapter();
// 根據(jù)網(wǎng)絡(luò)請(qǐng)求接口方法的返回值和注解類型听皿，從Retrofit對(duì)象中獲取該網(wǎng)絡(luò)適配器返回的數(shù)據(jù)類型
responseType = callAdapter.responseType();
/*根據(jù)網(wǎng)絡(luò)請(qǐng)求接口方法的返回值和注解類型，從Retrofit對(duì)象中獲取對(duì)應(yīng)的數(shù)據(jù)轉(zhuǎn)換器
createResponseConverter方法會(huì)調(diào)用Retrofit.responseBodyConverter（）宽档，最終從Retrofit.converterFactories集合中
返回GsonConverterFactory，GsonConverterFactory在步驟1.5進(jìn)行配置庵朝。
*/
responseConverter = createResponseConverter();
/* 解析網(wǎng)絡(luò)請(qǐng)求接口中方法的注解,主要是解析獲取Http請(qǐng)求的方法,
注解包括：DELETE吗冤、GET、POST九府、HEAD椎瘟、PATCH、PUT侄旬、OPTIONS肺蔚、HTTP、retrofit2.http.Headers儡羔、Multipart宣羊、FormUrlEncoded
*/
for (Annotation annotation : methodAnnotations) {
parseMethodAnnotation(annotation);
}
// 獲取當(dāng)前方法的參數(shù)數(shù)量
int parameterCount = parameterAnnotationsArray.length;
parameterHandlers = new ParameterHandler<?>[parameterCount];
for (int p = 0; p < parameterCount; p++) {
Type parameterType = parameterTypes[p];
Annotation[] parameterAnnotations = parameterAnnotationsArray[p];
/*
為方法中的每個(gè)參數(shù)創(chuàng)建一個(gè)ParameterHandler<?>對(duì)象并解析每個(gè)參數(shù)使用的注解類型
該對(duì)象的創(chuàng)建過(guò)程就是對(duì)方法參數(shù)中注解進(jìn)行解析
這里的注解包括：Body、PartMap汰蜘、Part仇冯、FieldMap、Field族操、Header苛坚、QueryMap、Query色难、Path泼舱、Url
*/
parameterHandlers[p] = parseParameter(p, parameterType, parameterAnnotations);
}
return new ServiceMethod<>(this);
}
總結(jié)：
（1）根據(jù)返回值類型和方法標(biāo)注從Retrofit對(duì)象的網(wǎng)絡(luò)請(qǐng)求適配器工廠集合和內(nèi)容轉(zhuǎn)換器工廠集合中分別獲取到該方法對(duì)應(yīng)的網(wǎng)絡(luò)請(qǐng)求適配器和Response內(nèi)容轉(zhuǎn)換器，網(wǎng)絡(luò)請(qǐng)求適配器和內(nèi)容轉(zhuǎn)換器在創(chuàng)建Retrofit實(shí)例已經(jīng)進(jìn)行配置枷莉，具體內(nèi)容請(qǐng)參見(jiàn)步驟1.5相關(guān)內(nèi)容娇昙，在ServiceMethod.build()方法中設(shè)置網(wǎng)絡(luò)請(qǐng)求適配器和內(nèi)容轉(zhuǎn)換器。
（2）根據(jù)方法的標(biāo)注對(duì)ServiceMethod的域進(jìn)行賦值
（3）為每個(gè)方法的參數(shù)的標(biāo)注進(jìn)行解析依沮，獲得一個(gè)ParameterHandler<?>對(duì)象
（4）最終返回ServiceMethod對(duì)象（表示一個(gè)網(wǎng)絡(luò)請(qǐng)求的封裝對(duì)象）涯贞，serviceMethod存儲(chǔ)網(wǎng)絡(luò)請(qǐng)求所需的信息，如網(wǎng)絡(luò)請(qǐng)求的方法危喉、數(shù)據(jù)轉(zhuǎn)換器宋渔、網(wǎng)絡(luò)請(qǐng)求適配器、網(wǎng)絡(luò)請(qǐng)求工廠辜限、基地址等皇拣。
3.2 new OkHttpCall<>(serviceMethod, args)方法
OkHttpCall.java
//根據(jù)第一步配置好的ServiceMethod對(duì)象和輸入的請(qǐng)求參數(shù)創(chuàng)建okHttpCall對(duì)象
final class OkHttpCall<T> implements Call<T> {
private final ServiceMethod<T> serviceMethod;
private final Object[] args;
//rawCall網(wǎng)絡(luò)請(qǐng)求器實(shí)際對(duì)象，最終執(zhí)行網(wǎng)絡(luò)請(qǐng)求
private okhttp3.Call rawCall;
OkHttpCall(ServiceMethod<T> serviceMethod, Object[] args) {
// 傳入了配置好的ServiceMethod對(duì)象和輸入的請(qǐng)求參數(shù)
this.serviceMethod = serviceMethod;
this.args = args;
}
}
3.3 serviceMethod.callAdapter.adapt(okHttpCall)方法
serviceMethod.callAdapter在步驟3.1中ServiceMethod.build()進(jìn)行配置，即ExecutorCallAdapterFactory氧急，下面我們來(lái)看ExecutorCallAdapterFactory.adpat（okHttpCall）方法
ExecutorCallAdapterFactory.java
public <R> Call<R> adapt(Call<R> call) {
//其中callbackExecutor在步驟1.5進(jìn)行設(shè)置颗胡，即Android平臺(tái)的默認(rèn)回調(diào)方法執(zhí)行器MainThreadExecutor
//MainThreadExecutor相關(guān)代碼請(qǐng)參考步驟1.4
return new ExecutorCallAdapterFactory.ExecutorCallbackCall(ExecutorCallAdapterFactory.this.callbackExecutor, call);
}
static final class ExecutorCallbackCall<T> implements Call<T> {
final Executor callbackExecutor;
final Call<T> delegate;
ExecutorCallbackCall(Executor callbackExecutor, Call<T> delegate) {
//callbackExecutor：Android平臺(tái)的默認(rèn)回調(diào)方法執(zhí)行器MainThreadExecutor
this.callbackExecutor = callbackExecutor;
//在步驟3.2中創(chuàng)建的OkHttpCall，其中含有網(wǎng)絡(luò)請(qǐng)求器實(shí)際對(duì)象rawCall;
this.delegate = delegate;
}
@Override public void enqueue(final Callback<T> callback) {
if (callback == null) throw new NullPointerException("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(ExecutorCallAdapterFactory.ExecutorCallbackCall.this, new IOException("Canceled"));
} else {
callback.onResponse(ExecutorCallAdapterFactory.ExecutorCallbackCall.this, response);
}
}
});
}
@Override public void onFailure(Call<T> call, final Throwable t) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
callback.onFailure(ExecutorCallAdapterFactory.ExecutorCallbackCall.this, t);
}
});
}
});
}
@Override public Response<T> execute() throws IOException {
return delegate.execute();
}
}
最終返回一個(gè)ExecutorCallAdapterFactory.ExecutorCallbackCall對(duì)象吩坝。至此毒姨，執(zhí)行定義的接口方法retrofitService.getDataFromInternet()最終返回
ExecutorCallbackCall網(wǎng)絡(luò)請(qǐng)求對(duì)象。
4.執(zhí)行網(wǎng)絡(luò)請(qǐng)求钉寝，并處理服務(wù)器返回?cái)?shù)據(jù)
我們以異步請(qǐng)求為例進(jìn)行說(shuō)明弧呐，同步請(qǐng)求相關(guān)流程類似。
//responseBodyCall即步驟3中返回的ExecutorCallAdapterFactory.ExecutorCallbackCall對(duì)象嵌纲。
Call<ResultBean> responseBodyCall = retrofitService.getDataFromInternet();
responseBodyCall.enqueue(new Callback<ResultBean>() {
@Override
public void onResponse(Call<ResultBean> call, Response<ResultBean> response) {
System.out.println("call:" + response.toString());
}
@Override
public void onFailure(Call<ResultBean> call, Throwable t) {
}
});
responseBodyCall即步驟3中返回的ExecutorCallAdapterFactory.ExecutorCallbackCall對(duì)象俘枫，下面我們來(lái)看ExecutorCallbackCall.enqueue(callback)方法；
static final class ExecutorCallbackCall<T> implements Call<T> {
final Executor callbackExecutor;
final Call<T> delegate;
ExecutorCallbackCall(Executor callbackExecutor, Call<T> delegate) {
//callbackExecutor：Android平臺(tái)的默認(rèn)回調(diào)方法執(zhí)行器MainThreadExecutor
this.callbackExecutor = callbackExecutor;
//在步驟3.2中創(chuàng)建的OkHttpCall逮走，其中含有網(wǎng)絡(luò)請(qǐng)求器實(shí)際對(duì)象rawCall;
this.delegate = delegate;
}
@Override
public void enqueue(final Callback<T> callback) {
if (callback == null) throw new NullPointerException("callback == null");
//delegate是OkHttpCall對(duì)象鸠蚪，會(huì)調(diào)用OkHttpCall.enqueue()方法
delegate.enqueue(new Callback<T>() {
@Override
public void onResponse(Call<T> call, final Response<T> response) {
//通過(guò)回調(diào)方法執(zhí)行器MainThreadExecutor切換線程（子線程-主線程），并執(zhí)行相關(guān)回調(diào)
callbackExecutor.execute(new Runnable() {
@Override public void run() {
if (delegate.isCanceled()) {
// Emulate OkHttp's behavior of throwing/delivering an IOException on cancellation.
callback.onFailure(ExecutorCallAdapterFactory.ExecutorCallbackCall.this, new IOException("Canceled"));
} else {
callback.onResponse(ExecutorCallAdapterFactory.ExecutorCallbackCall.this, response);
}
}
});
}
});
}
@Override public Response<T> execute() throws IOException {
return delegate.execute();
}
}
ExecutorCallbackCall.enqueue(callback)會(huì)調(diào)用OkHttpCall.enqueue()方法
OkHttpCall.java
@Override
public void enqueue(final Callback<T> callback) {
okhttp3.Call call;
Throwable failure;
synchronized (this) {
call = rawCall;
failure = creationFailure;
if (call == null && failure == null) {
try {
//步驟一：創(chuàng)建實(shí)際的網(wǎng)絡(luò)網(wǎng)絡(luò)請(qǐng)求對(duì)象
call = rawCall = createRawCall();
} catch (Throwable t) {
failure = creationFailure = t;
}
}
}
if (failure != null) {
callback.onFailure(this, failure);
return;
}
if (canceled) {
call.cancel();
}
//步驟二：執(zhí)行異步請(qǐng)求
call.enqueue(new okhttp3.Callback() {
@Override public void onResponse(okhttp3.Call call, okhttp3.Response rawResponse)
throws IOException {
Response<T> response;
try {
//步驟三：解析返回?cái)?shù)據(jù)
response = parseResponse(rawResponse);
} catch (Throwable e) {
//步驟四：執(zhí)行請(qǐng)求失敗回調(diào)
callFailure(e);
return;
}
//步驟四：執(zhí)行請(qǐng)求成功回調(diào)
callSuccess(response);
}
private void callFailure(Throwable e) {
try {
callback.onFailure(OkHttpCall.this, e);
} catch (Throwable t) {
t.printStackTrace();
}
}
private void callSuccess(Response<T> response) {
try {
callback.onResponse(OkHttpCall.this, response);
} catch (Throwable t) {
t.printStackTrace();
}
}
});
}
4.1 步驟一：createRawCall()創(chuàng)建實(shí)際的網(wǎng)絡(luò)網(wǎng)絡(luò)請(qǐng)求對(duì)象
OkhttpCall.java
private okhttp3.Call createRawCall() throws IOException {
// 從ServiceMethod的toRequest（）返回一個(gè)Request對(duì)象
Request request = serviceMethod.toRequest(args);
//serviceMethod.callFactory:即OkHttpClient,在步驟1.5中設(shè)置callFactory = new OkHttpClient();
//執(zhí)行OkHttpClient.newCall(request)
okhttp3.Call call = serviceMethod.callFactory.newCall(request);
if (call == null) {
throw new NullPointerException("Call.Factory returned null.");
}
return call;
}
OkHttpClient.java
@Override
public Call newCall(Request request) {
//然后調(diào)用OKHttpClient的newcall方法創(chuàng)建Call對(duì)象（RealCall對(duì)象）师溅，Call是HTTP請(qǐng)求任務(wù)封裝
return new RealCall(this, request);
}
serviceMethod.callFactory:即OkHttpClient在步驟1.5中設(shè)置callFactory = new OkHttpClient();然后調(diào)用然后調(diào)用OKHttpClient的newcall方法創(chuàng)建Call對(duì)象（RealCall對(duì)象）茅信，后續(xù)網(wǎng)絡(luò)請(qǐng)求工作由OkHttp接管。Retrofit網(wǎng)絡(luò)請(qǐng)求的工作本質(zhì)上是OkHttp完成险胰，就是在此處體現(xiàn)的汹押。OkHttp相關(guān)內(nèi)容請(qǐng)參考OkHttp源碼解析。
4.2 執(zhí)行異步請(qǐng)求RealCall.enqueue(callback)方法
RealCall.enqueue（）執(zhí)行流程請(qǐng)參考OkHttp源碼解析
4.3 解析網(wǎng)絡(luò)請(qǐng)求的返回?cái)?shù)據(jù)parseResponse(rawResponse)
OkHttpCall.java
Response<T> parseResponse(okhttp3.Response rawResponse) throws IOException {
ResponseBody rawBody = rawResponse.body();
// Remove the body's source (the only stateful object) so we can pass the response along.
rawResponse = rawResponse.newBuilder()
.body(new OkHttpCall.NoContentResponseBody(rawBody.contentType(), rawBody.contentLength()))
.build();
// 收到返回?cái)?shù)據(jù)后進(jìn)行狀態(tài)碼檢查
int code = rawResponse.code();
if (code < 200 || code >= 300) {
try {
// Buffer the entire body to avoid future I/O.
ResponseBody bufferedBody = Utils.buffer(rawBody);
return Response.error(bufferedBody, rawResponse);
} finally {
rawBody.close();
}
}
try {
// 等Http請(qǐng)求返回后 & 通過(guò)狀態(tài)碼檢查后起便，將response body傳入ServiceMethod中棚贾，ServiceMethod通過(guò)調(diào)用Converter接口（之前設(shè)置的GsonConverterFactory）將response body轉(zhuǎn)成一個(gè)Java對(duì)象，即解析返回的數(shù)據(jù)
body = serviceMethod.toResponse(catchingBody);
//生成Response類
return Response.success(body, rawResponse);
} catch (RuntimeException e) {
// If the underlying source threw an exception, propagate that rather than indicating it was
// a runtime exception.
catchingBody.throwIfCaught();
throw e;
}
}
其中serviceMethod.toResponse會(huì)調(diào)用responseConverter數(shù)據(jù)轉(zhuǎn)換器（GsonConverterFactory）將服務(wù)器返回?cái)?shù)據(jù)轉(zhuǎn)換為Java對(duì)象榆综。
4.4 執(zhí)行請(qǐng)求成功回調(diào)
private void callSuccess(Response<T> response) {
try {
callback.onResponse(OkHttpCall.this, response);
} catch (Throwable t) {
t.printStackTrace();
}
}
其中callback在ExecutorCallbackCall.enqueue(callback)方法中妙痹，我們?cè)俅位氐紼xecutorCallbackCall.enqueue(callback)方法中
static final class ExecutorCallbackCall<T> implements Call<T> {
final Executor callbackExecutor;
final Call<T> delegate;
ExecutorCallbackCall(Executor callbackExecutor, Call<T> delegate) {
//callbackExecutor：Android平臺(tái)的默認(rèn)回調(diào)方法執(zhí)行器MainThreadExecutor
this.callbackExecutor = callbackExecutor;
//在步驟3.2中創(chuàng)建的OkHttpCall，其中含有網(wǎng)絡(luò)請(qǐng)求器實(shí)際對(duì)象rawCall;
this.delegate = delegate;
}
@Override
public void enqueue(final Callback<T> callback) {
if (callback == null) throw new NullPointerException("callback == null");
//delegate是OkHttpCall對(duì)象鼻疮，會(huì)調(diào)用OkHttpCall.enqueue()方法
delegate.enqueue(new Callback<T>() {
@Override
public void onResponse(Call<T> call, final Response<T> response) {
//執(zhí)行步驟4.4會(huì)回調(diào)該方法怯伊，通過(guò)回調(diào)方法執(zhí)行器MainThreadExecutor切換線程（子線程-主線程），并執(zhí)行相關(guān)回調(diào)
callbackExecutor.execute(new Runnable() {
@Override public void run() {
if (delegate.isCanceled()) {
// Emulate OkHttp's behavior of throwing/delivering an IOException on cancellation.
callback.onFailure(ExecutorCallAdapterFactory.ExecutorCallbackCall.this, new IOException("Canceled"));
} else {
callback.onResponse(ExecutorCallAdapterFactory.ExecutorCallbackCall.this, response);
}
}
});
}
});
}
@Override public Response<T> execute() throws IOException {
return delegate.execute();
}
}
在執(zhí)行callSuccess（）請(qǐng)求成功回調(diào)時(shí)又回到ExecutorCallbackCall.enqueue(callback)方法中判沟，然后執(zhí)行callbackExecutor.execute(new Runnable())方法耿芹，其中callbackExecutor是回調(diào)方法執(zhí)行器MainThreadExecutor，用來(lái)切換線程挪哄，并最終執(zhí)行相關(guān)回調(diào)吧秕。MainThreadExecutor代碼如下：
//回調(diào)方法執(zhí)行器,將服務(wù)器返回結(jié)果給客戶端時(shí)，進(jìn)行線程切換
static class MainThreadExecutor implements Executor {
//Looper.getMainLooper()獲取Android主線程Looper
private final Handler handler = new Handler(Looper.getMainLooper());
@Override public void execute(Runnable r) {
//通過(guò)主線程Handler將網(wǎng)絡(luò)請(qǐng)求回調(diào)切換到主線程中迹炼。
handler.post(r);
}
}
最終回調(diào)到responseBodyCall中的onResponse方法
Call<ResultBean> responseBodyCall = retrofitService.getDataFromInternet();
responseBodyCall.enqueue(new Callback<ResultBean>() {
@Override
public void onResponse(Call<ResultBean> call, Response<ResultBean> response) {
System.out.println("call:" + response.toString());
}
@Override
public void onFailure(Call<ResultBean> call, Throwable t) {
}
});
因?yàn)榛卣{(diào)方法在MainThreadExecutor進(jìn)行了線程切換砸彬，所以onResponse（）方法是在主線程中執(zhí)行颠毙。
從responseBodyCall.enqueue（）網(wǎng)絡(luò)請(qǐng)求開(kāi)始到onResponse（）網(wǎng)絡(luò)結(jié)束的整體流程已經(jīng)講解完畢。
以上是單純使用Retrofit砂碉，不加Rxjava進(jìn)行網(wǎng)絡(luò)請(qǐng)求執(zhí)行流程蛀蜜，下面簡(jiǎn)單介紹使用Retrofit+RxJava進(jìn)行網(wǎng)絡(luò)請(qǐng)求時(shí)代碼執(zhí)行流程。
Retrofit + RxJava網(wǎng)絡(luò)請(qǐng)求代碼如下
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(BASE_URL)
.addCallAdapterFactory(RxJavaCallAdapterFactory.create())
.addConverterFactory(GsonConverterFactory.create())
.build();
public interface RxRetrofitService {
@GET("query")
Observable<ResponseBody> getDataFromInternet();
}
RxRetrofitService rxRetrofitService = retrofit.create(RxRetrofitService.class);
rxRetrofitService.getDataFromInternet().subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Subscriber<ResponseBody>() {
@Override
public void onCompleted() {
}
@Override
public void onError(Throwable e) {
}
@Override
public void onNext(ResponseBody weatherEntity) {
}
});
使用RxJava+Retrofit和僅使用Retrofit區(qū)別主要有：
（1）在步驟3.1 ServiceMethod.build()方法中的callAdapter = createCallAdapter();該處的callAdapter會(huì)返回RxJavaCallAdapterFactory.SimpleCallAdapter對(duì)象增蹭。
（2）步驟3.3 serviceMethod.callAdapter.adapt(okHttpCall)方法會(huì)調(diào)用SimpleCallAdapter.adapter方法
RxJavaCallAdapterFactory.java
static final class SimpleCallAdapter implements CallAdapter<Observable<?>> {
private final Type responseType;
private final Scheduler scheduler;
SimpleCallAdapter(Type responseType, Scheduler scheduler) {
this.responseType = responseType;
this.scheduler = scheduler;
}
@Override
public Type responseType() {
return responseType;
}
@Override
public <R> Observable<R> adapt(Call<R> call) {
//將CallOnSubscribe對(duì)象賦值給CallOnSubscribe變量onSubscribe
//調(diào)用Observable.create方法
Observable<R> observable = Observable.create(new CallOnSubscribe<>(call)) //
.lift(OperatorMapResponseToBodyOrError.<R>instance());
if (scheduler != null) {
return observable.subscribeOn(scheduler);
}
return observable;
}
}
Observable.java
public static <T> Observable<T> create(OnSubscribe<T> f) {
return new Observable<T>(RxJavaHooks.onCreate(f));
}
Observable.java
//將CallOnSubscribe賦值給onSubscribe變量
protected Observable(OnSubscribe<T> f) {
this.onSubscribe = f;
}
（3）執(zhí)行rxRetrofitService.getDataFromInternet().subscribe()方法
Observable.java
public final Subscription subscribe(final Observer<? super T> observer) {
return subscribe(new ObserverSubscriber<T>(observer));
}
Observable.java
public final Subscription subscribe(Subscriber<? super T> subscriber) {
return Observable.subscribe(subscriber, this);
}
static <T> Subscription subscribe(Subscriber<? super T> subscriber, Observable<T> observable) {
try {
//RxJavaHooks.onObservableStart返回observable.onSubscribe對(duì)象滴某，
//onSubscribe對(duì)象即CallOnSubscribe，繼續(xù)執(zhí)行CallOnSubscribe.call方法沪铭；
RxJavaHooks.onObservableStart(observable, observable.onSubscribe).call(subscriber);
return RxJavaHooks.onObservableReturn(subscriber);
} catch (Throwable e) {
...
return Subscriptions.unsubscribed();
}
}
static final class CallOnSubscribe<T> implements Observable.OnSubscribe<Response<T>> {
private final Call<T> originalCall;
CallOnSubscribe(Call<T> originalCall) {
this.originalCall = originalCall;
}
//執(zhí)行rxRetrofitService.getDataFromInternet().subscribe()會(huì)調(diào)用該方法
@Override
public void call(final Subscriber<? super Response<T>> subscriber) {
// Since Call is a one-shot type, clone it for each new subscriber.
Call<T> call = originalCall.clone();
// Wrap the call in a helper which handles both unsubscription and backpressure.
RequestArbiter<T> requestArbiter = new RequestArbiter<>(call, subscriber);
subscriber.add(requestArbiter);
//setProducer方法壮池，setProducer會(huì)調(diào)用RequestArbiter.request方法；
subscriber.setProducer(requestArbiter);
}
}
Subscriber.java
public void setProducer(Producer p) {
long toRequest;
boolean passToSubscriber = false;
synchronized (this) {
toRequest = requested;
producer = p;
if (subscriber != null) {
// middle operator ... we pass through unless a request has been made
if (toRequest == NOT_SET) {
// we pass through to the next producer as nothing has been requested
passToSubscriber = true;
}
}
}
// do after releasing lock
if (passToSubscriber) {
subscriber.setProducer(producer);
} else {
// we execute the request with whatever has been requested (or Long.MAX_VALUE)
if (toRequest == NOT_SET) {
producer.request(Long.MAX_VALUE);
} else {
//調(diào)用RequestArbiter.request方法
producer.request(toRequest);
}
}
}
static final class RequestArbiter<T> extends AtomicBoolean implements Subscription, Producer {
private final Call<T> call;
private final Subscriber<? super Response<T>> subscriber;
RequestArbiter(Call<T> call, Subscriber<? super Response<T>> subscriber) {
this.call = call;
this.subscriber = subscriber;
}
@Override
public void request(long n) {
try {
//執(zhí)行OkHttpCall.execute()方法杀怠，后續(xù)也是創(chuàng)建RealCall,然后調(diào)用OkHttp網(wǎng)絡(luò)請(qǐng)求流程
Response<T> response = call.execute();
if (!subscriber.isUnsubscribed()) {
//回調(diào)相關(guān)方法
subscriber.onNext(response);
}
} catch (Throwable t) {
if (!subscriber.isUnsubscribed()) {
//回調(diào)相關(guān)方法
subscriber.onError(t);
}
return;
}
if (!subscriber.isUnsubscribed()) {
//回調(diào)相關(guān)方法
subscriber.onCompleted();
}
}
}
@Override
public Response<T> execute() throws IOException {
okhttp3.Call call;
synchronized (this) {
if (executed) throw new IllegalStateException("Already executed.");
executed = true;
if (creationFailure != null) {
if (creationFailure instanceof IOException) {
throw (IOException) creationFailure;
} else {
throw (RuntimeException) creationFailure;
}
}
call = rawCall;
if (call == null) {
try {
//創(chuàng)建RealCall實(shí)際網(wǎng)絡(luò)請(qǐng)求對(duì)象
call = rawCall = createRawCall();
} catch (IOException | RuntimeException e) {
creationFailure = e;
throw e;
}
}
}
if (canceled) {
call.cancel();
}
//call.execute()執(zhí)行RealCall.excute（）進(jìn)行網(wǎng)絡(luò)請(qǐng)求
//parseResponse(call.execute())解析服務(wù)器數(shù)據(jù)并返回結(jié)果
return parseResponse(call.execute());
}
可以看出rxRetrofitService.getDataFromInternet().subscribe（）會(huì)調(diào)用OkHttpCall.execute()方法，然后創(chuàng)建實(shí)際的網(wǎng)絡(luò)請(qǐng)求對(duì)象RealCall厅克，然后執(zhí)行RealCall.excute（）進(jìn)行網(wǎng)絡(luò)請(qǐng)求赔退，realCall.excute（）相關(guān)邏輯請(qǐng)參考OkHttp源碼解析。以上就是使用Retrofit+RxJava進(jìn)行網(wǎng)絡(luò)請(qǐng)求的大致流程证舟，
我們發(fā)現(xiàn)無(wú)路是僅使用Retrofit進(jìn)行網(wǎng)絡(luò)請(qǐng)求還是使用Retrofit+RxJava進(jìn)行網(wǎng)絡(luò)請(qǐng)求硕旗，最終進(jìn)行網(wǎng)絡(luò)請(qǐng)求的對(duì)象都是OkHttp，所以網(wǎng)絡(luò)請(qǐng)求工作本質(zhì)上是由OkHttp完成女责。
至此漆枚，Retrofit進(jìn)行網(wǎng)絡(luò)請(qǐng)求代碼執(zhí)行流程已經(jīng)講解完畢。
參考資料：
Android：手把手帶你深入剖析 Retrofit 2.0 源碼
Retrofit源碼學(xué)習(xí)隨筆
最后抵知，感謝本文內(nèi)容所參考文章的作者墙基。
